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Accepted papers to appear in an upcoming issue

Optica Publishing Group posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

Remote erasing and writing of ferroelectric domains by femtosecond laser in lithium niobate

Fengchang Li, Qiang Cao, Xiaoliang Wang, and Ruonan Wang

DOI: 10.1364/OL.519935 Received 25 Jan 2024; Accepted 18 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: We experimentally demonstrate the highly-efficient remote erasing and writing of ferroelectric domains by femtosecond laser in lithium niobate. Based on the induction of a focused infrared femtosecond laser without any relative displacement or additional treatment, the original multiple ferroelectric domains can be either erased (erasing operation) or elongated (writing operation) simultaneously in the crystal, depending on the laser focusing depth and the laser pulse energy. In the erasing operation, the original multiple ferroelectric domains can be cleared completely by just one laser induction, while in the writing operation, the average length of the ferroelectric domains can be elongated up to 5 μm by three laser inductions. A theoretical model has been proposed in which a thermoelectric field and a space charge field are used cooperatively to successfully explain the mechanism of remote erasing and writing. This method greatly improves the efficiency and flexibility of tailoring ferroelectric domain structures, paving the way to large-scale all-optical industrial production for nonlinear photonic crystals and nonvolatile ferroelectric domain wall memories.

Tunable and mode-locked Tm,Ho:GdScO3 laser

Jian Liu, Ning Zhang, Qingsong Song, Heng Ding, Yinyin Wang, Peng Chen, Zebin Wang, Yanyan Xue, Jie Xu, Yongguang Zhao, Xiaodong Xu, kheirreddine Lebbou, and Jun Xu

DOI: 10.1364/OL.514957 Received 05 Dec 2023; Accepted 18 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: A novel Tm,Ho:GdScO3 crystal grown using the Czochralski method was investigated for its polarized spectroscopic properties and laser performance in both the tunable continuous wave (CW) and mode-locked regimes. The crystal's multisite structure (Gd3+/Sc3+ site) and Tm3+/Ho3+ dopants contributed to spectral broadening, enabling tunable laser operation from 1914 nm to 2125 nm (with a broad range of 215 nm). Additionally, a pulse duration of 72 fs was achieved for E ǁ b polarization. These results demonstrate the potential of the Tm,Ho:GdScO3 perovskite crystal as a promising gain material for ultrafast lasers operating around 2 μm.

Quickly tunable ultra-narrow filter via metal film waveguide

Hongrui Shan, Qiheng Wei, Hailang Dai, and Xianfeng Chen

DOI: 10.1364/OL.517815 Received 05 Jan 2024; Accepted 17 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: The development of fast, efficient and cost-effective tunable optical filters is a tireless pursuit of the goal in the field of optical signal processing and communications. However, the traditional filters have been limited by their complex structures, slow tuning speed and high cost. To address this challenge, we present a tunable ultra-narrow bandpass filter which is fabricated by metal layer cladded in a high-parallelism and high-precision piezoelectric ceramic for interlayer. Experimental results show a remarkable full width at half maximum of 51 pm and a fast response time of 800 ns. In addition, by cascading double filters, the wavelength of output light has been fine-tuned from a vernier effect. Then, we realize a tunable filter to select and output several ultra-narrow single peaks with 56% efficiency in the 2nm range. Furthermore, it offers a wide tunable range, exceptional narrowband filtering performance and fast piezoelectric response times. Hence, it is particularly well suited to applications requiring precise wavelength selection and control, opening new possibilities in the field of tunable optical filters.

A reconfigurable origami hologram based on deep neural networks

Kang Wang, dashuang liao, and Hao Gang Wang

DOI: 10.1364/OL.520781 Received 05 Feb 2024; Accepted 17 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: Reconfigurable and multifunctional metasurfaces are becoming indispensable in a variety of applications due to their capability to execute diverse functions acrossvarious states. However, many of these metasurfacesincorporate complex active components, thereby escalating structural complexity and bulk volume. In this research, we propose a reconfigurable passive hologrambased solely on an origami structure, enabling the successful generation of holograms depicting the ‘Z’ and ‘L’ illuminated by a Right-Hand Circular Polarization (RHCP) wave in two distinct states: planar and zigzagconfiguration, respectively. The transformation between the 2D planar metasurface and the 3D zigzag structurewith slant angles of 35 is achieved solely throughmechanically stretching and compressing the origami metasurface. The phases on the origami metasurface are trained through a Deep Neural Network which operates on the NVIDIA Tesla k80 GPU, with the total training process costing 11.88 seconds after 100 epochs. The reconfigurable scheme proposed in this research provides flexibility and ease of implementation in the fields of imaging and data processing.

Vortex ring beams in nonlinear PT-symmetric systems

Cristian Mejía Cortés, Mario Molina, and Jesús Muñoz-Muñoz

DOI: 10.1364/OL.521865 Received 20 Feb 2024; Accepted 17 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: In this paper, we investigate a two-dimensional photonicarray featuring a circular shape and an alternatinggain and loss pattern. Our analysis revolves arounddetermining the presence and resilience of ring modeswith varying vorticity values. This investigation is conductedwith respect to both the array’s length and thestrength of the non-Hermitian parameter. For largervalues of array’s length, we observe a reduction in thestability domain as the non-Hermitian parameter increases.However, a rise up of the vorticity originatesfull stability windows for shorter values of the array’slength.

Low-loss and compact photonic lantern based on step-index double cladding fiber

Cong Zhang, Yue Wang, senyu zhang, Meng Xiang, Songnian Fu, and Yuwen Qin

DOI: 10.1364/OL.516211 Received 15 Jan 2024; Accepted 17 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: The fulfillment of the adiabatic criterion is indispensable for the realization of a low-loss photonic lantern (PL), concurrently imposing a stringent striction on the taper transition length of the PL. Here, by relaxing the adiabatic criterion, a low-loss and compact PL based on step-index double cladding fiber (SI-DCF) is theoretically proposed and experimentally demonstrated. The use of SI-DCF can reduce the mode field diameter (MFD) expansion ratio during the tapering processing, and greatly decrease the taper transition length required for adiabatic tapering. We initially evaluate the variation of both MFD and effective refractive index (RI) along the fiber tapering region based on three types of fiber structures, including the modified standard single mode fiber (SSMF), the graded index fiber (GIF), and the proposed SI-DCF. In comparison with the commonly used fiber geometry, the SI-DCF can reduce the MFD expansion ratio from 77.73% to 38.81%, leading to more than half reduction of tapering length for both 3-mode and 6-mode PLs. Then, two kinds of SI-DCF with different core diameters are fabricated to realize a 3-mode PL. The fabricated PL possesses a 1.5 cm tapering length and less than 0.2 dB insertion loss (IL). After splicing with the commercial few-mode fiber, the PL has an average IL of 0.6 dB and more than 13 dB LP11 mode purity over the C-band. Finally, a back-to-back power matrix measurement indicates that the fabricated PLs have a mode coupling of less than -10 dB at 1550 nm.

Terahertz metalens for generating multi-polarized focal points and images with uniform intensity distributions

Binbin Lu, Yefei Fu, Teng Zhang, Zuanming Jin, XiaoFei Zang, and Yiming Zhu

DOI: 10.1364/OL.519605 Received 23 Jan 2024; Accepted 16 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: Metasurfaces have provided a flexible platform for designing ultracompact metalenses with unusual functionalities. However, traditional multi-foci metalenses are limited to generating circularly-polarized (CP) or linearly-polarized (LP) focal points, and the intensity distributions are always inhomogeneous/chaotical between the multiple focal points. Here, an inverse design approach is proposed to optimize the in-plane orientation of each meta-atom in a terahertz (THz)multi-foci metalens that can generate multi-polarized focal points with nearly uniform intensity distributions. As a proof-of-principle example, we numerically and experimentally demonstrate an inversely designed metalens for simultaneously generating multiple CP- and LP-based focal points with homogeneous intensity distributions, leading to a multi-polarized image (rather than the holography). Furthermore, the multi-channel and multi-polarized images consisting of multiple focal points with homogeneous intensity distributions are also numerically demonstrated. The unique approach for inversely designing multi-foci metalens that can generate multi-polarized focal points and images with uniform intensity distributions will enable potential applications in imaging and sensing.

Large and Tunable Optoelectronic Chromatic Dispersion in PIN-type photodiodes

Ayuushi Dutta, Egor Liokumovitch, Ziv Glasser, and Shmuel Sternklar

DOI: 10.1364/OL.519164 Received 16 Jan 2024; Accepted 15 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: It is known that PN-type photodiodes possess high optoelectronic chromatic dispersion (OED). Here we present a theoretical and experimental study of OED in PIN-type photodiodes. Applying the modulation phase-shift technique, a Ge PIN photodiode exhibits ~0.5 deg/nm phase-shift sensitivity at 10MHz modulation, corresponding to a dispersion of 1.4x〖10〗^9 ps/(nm∙km), many orders of magnitude larger than high-dispersion optical materials. A striking feature of the PIN device is the ability to tune the amount and sign of the OED through the bias voltage. Electronic tuning between -0.8 deg/nm to +0.5 deg/nm is shown. The PIN photodiode is an on-chip device possessing significant tunable dispersion, for applications in optical sensing and spectroscopy.

Pump-power-controlled L-band wavelength-tunable mode-locked fiber laser utilizing all polarization maintaining nonlinear polarization rotation

Guanyu YE, Bowen Liu, Maolin Dai, Yifan Ma, Takuma Shirahata, Shinji Yamashita, and Sze Set

DOI: 10.1364/OL.518882 Received 15 Jan 2024; Accepted 15 Mar 2024; Posted 15 Mar 2024  View: PDF

Abstract: For the first time, we present the pump power-controlled wavelength-tunable mode-locked fiber laser in the L-band (1565 nm to 1625 nm), achieved by all-polarization maintaining (all-PM) nonlinear polarization rotation (NPR). The wavelength of the laser can be tuned over 20 nm, from 1568.2 nm to 1588.9 nm simply by controlling the pump power from 45 mW to 115 mW. In contrast to conventional wavelength tuning mechanisms such as optical bandpass filters, our tuning method is non-mechanical and electrically controllable, featuring simplicity and cost-effectiveness in a superior all-fiber design.

Integrated Segmented IQ-Modulator for Orthogonal Sampling and Multi-Level High-Bandwidth Signal Generation

Younus Mandalawi, Mohamed Hosni, Janosch Meier, Karanveer Singh, Souvaraj De, Ranjan Das, and Thomas Schneider

DOI: 10.1364/OL.519345 Received 18 Jan 2024; Accepted 15 Mar 2024; Posted 15 Mar 2024  View: PDF

Abstract: Photonics-assisted signal processing of high-bandwidth signals emerges as a solution for challenges encountered in electronic-based processing. Here we present a concept for a compact, photonics-assisted digital-to-analog converter (DAC) and optical IQ-modulator in one single integrated device based on two innovative concepts: a segmented Mach-Zehnder modulator and orthogonal sampling. For electrically driving the modulator, only a single radio frequency oscillator and no pulse source or electrical DAC is required. The presented and simulated proof-of-concept device with six segments can generate a multi-level and high-bandwidth signal from low-bandwidth electronic drivers. As an example, we show the generation of a 120 Gbps data rate, 16-quadrature amplitude modulation (16-QAM, 30 Gbaud) signal solely based on low-bandwidth (5 GHz) non-return-to-zero (NRZ) signals. Integrated on a silicon photonics platform, the device provides fixable speed and bandwidth operations, positioning it as a viable solution for diverse communication systems.

Frequency-domain Searching Algorithm in Deflectometry for measuring the surface of transparent planar element

Wanxing Zheng, Dahai Li, Ruiyang Wang, Zekun Zhang, Renhao Ge, and Manwei Chen

DOI: 10.1364/OL.522243 Received 23 Feb 2024; Accepted 15 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: This letter presents the Frequency-domain Searching Algorithm in Deflectometry (FSAD). By encoding specialized multi-frequency fringe patterns and employing a correlation searching algorithm, the limitations of existing frequency-domain methods can be overcome to some extent, thereby separating front and back surface reflections to obtain a complete measurement data. The principles of FSAD are described in detail. In the experiment, a piece of window glass with thickness of 10mm and a square area of 96×96mm is measured to verify the proposed method.

Ultrabroadband Two-Dimensional Electronic Spectroscopy in the Pump–Probe Geometry Using Conventional Optics

Matthew Barclay, Nicholas Wright, Paul Cavanaugh, Ryan Pensack, Eric Martin, and Daniel Turner

DOI: 10.1364/OL.519387 Received 18 Jan 2024; Accepted 14 Mar 2024; Posted 15 Mar 2024  View: PDF

Abstract: We report ultrabroadband two-dimensional electronic spectroscopy (2D ES) measurements obtained in the pump–probe geometry using conventional optics. A phase-stabilized Michelson interferometer provides the pump-pulse delay interval, τ1, necessary to obtain the excitation-frequency dimension. Spectral resolution of the probe beam provides the detection-frequency dimension, ω3 . The interferometer incorporates active phase stabilization via a piezo stage and feedback from interference of a continuous-wave reference laser detected in quadrature. To demonstrate the method, we measured a well-characterized laser dye sample and obtained the known peak structure. The vibronic peaks are modulated as a function of the waiting time, τ2, by vibrational wavepackets. The interferometer simplifies ultrabroadband 2D ES measurements and analysis.

Switchable hybrid-order optical vortex lattice

Xueyun Qin, Hao Zhang, Miaomiao Tang, Yujie Zhou, Yuping Tai, and Xinzhong Li

DOI: 10.1364/OL.515906 Received 14 Dec 2023; Accepted 14 Mar 2024; Posted 14 Mar 2024  View: PDF

Abstract: Optical vortex (OV) modulation is a powerful technique for enhancing the intrinsic degrees-of-freedom in structured light. In particular, the optical vortex lattice (OVL) involving multiple OVs has captured significant interest owing to their exceptional applications in optical tweezers and condensed matter physics. However, all the OVs in the OVL possess the same order, which cannot be modulated individually, and thus, limits its versatile application. Herein, we propose a novel concept, called hot-swap method, to design a switchable hybrid-order OVL (SHO-OVL), where each OV is easily replaced by arbitrary orders. We experimentally generated the SHO-OVL and studied its characteristics, including interferograms, retrieved phase, energy flow and orbital angular momentum. Further, the significant advantages of the SHO-OVL are showcased through the independent manipulation of multiple yeast cells. This study provides a novel scheme for accuracy control and modulation of OVL, which greatly facilitates the diverse applications of optical manipulation and particle trapping and control.

Large optoelectronic chromatic dispersion in PN-type silicon photodiodes and photovoltaic cells

Sapna Mudgal, Pawan Dubey, Ziv Glasser, and Shmuel Sternklar

DOI: 10.1364/OL.514906 Received 01 Dec 2023; Accepted 14 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: Optoelectronic chromatic dispersion (OED) is a significant source of effective chromatic dispersion in photodiodes. We present results of an experimental and theoretical study of OED in PN-type Si photodiodes and photovoltaic cells, which points to a very large effective chromatic dispersion in these devices. As measured with the modulation phase-shift technique at a modulation frequency of 4 kHz for these slow devices, the OED spectral sensitivity for a commercial Si photodiode is approx. 0.02 deg/nm in the 720nm-850nm wavelength band and increases to 0.25 deg/nm at λ=1μm. For a Si photovoltaic cell, the OED is approx. 0.09 deg/nm in this spectral region. These values translate into an effective chromatic dispersion parameter of approx. 10^12 ps/(nm∙km) for these sub-millimeter device lengths, which is over 8 orders of magnitude larger than high-dispersion optical materials such as TiO2. The enormous dispersion in these sub-millimeter sized silicon-based devices can be utilized for on-chip optoelectronic sensors such as wavelength monitoring and spectroscopy. Picometer-range wavelength monitoring is demonstrated. The substantial OED of photovoltaic cells can be utilized for characterization and optimization and opens new applications for optical sensing with these self-powered devices.

Efficient and high-speed coupling modulation of silicon racetrack ring resonators at 2 μm waveband

Xi Wang, Jianing Wang, Yong Yao, Shumin Xiao, Qinghai Song, and Ke Xu

DOI: 10.1364/OL.518729 Received 11 Jan 2024; Accepted 13 Mar 2024; Posted 15 Mar 2024  View: PDF

Abstract: Significantly increased interests have been witnessed for the 2 μm waveband which is considered to be a promising alternative window for fiber and free space optical communications. However, the less mature device technology at this wavelength range is one of the primary obstacles towards practical applications. In this work, we demonstrate an efficient and high-speed silicon modulator based on carrier depletion in a coupling tunable resonator. A benchmark high modulation efficiency of 0.75 V‧cm is achieved. The 3-dB electro-optic bandwidth is measured to be 26 GHz allowing for upto 34 Gbit/s on-off-keying modulation with a low energy consumption of ~0.24 pJ/bit. It provides a solution for silicon modulator with high-speed and low power consumption in 2-μm waveband.

Enhanced Performance of Quantum Dot Light-Emitting Diodes Enabled by Zirconium Doped SnO2 as Electron Transport Layers

Jinxing Zhao, Zhongwei Man, Shuaibing wang, Chaoqi Hao, Zhenzhen Yu, Xu Li, and Aiwei Tang

DOI: 10.1364/OL.521324 Received 12 Feb 2024; Accepted 13 Mar 2024; Posted 13 Mar 2024  View: PDF

Abstract: Next-generation display and lighting based on quantum dot light-emitting diodes (QLEDs) require a balanced electron injection of electron transport layers (ETLs). However, classical ZnO nanoparticles (NPs) as ETL face inherent defects such as excessive electron injection and positive aging effects, urgently requiring the development of new types of ETL materials. Here, we show that high stability SnO2 NPs as ETL can significantly improve the QLED performance to 100567 cd m-2 (luminance), 14.3% (maximum external quantum efficiency), and 13.1 cd A-1 (maximum current efficiency) using traditional device structures after optimizing film thickness and annealing temperature. Furthermore, experimental tests reveal that by doping Zr4+ ions, the size of SnO2 NPs will reduce, dispersion will improve and energy level will shift up. As expected, when using Zr-SnO2 NPs as the ETL, the maximum external quantum efficiency can reach 16.6%, which is close to the state-of-the-art QLEDs based on ZnO ETL. This work opens the door for developing novel type ETL for QLEDs.

Polarization feature fusion and calculation of birefringence dynamics in complex anisotropic media

Rui Hao, Nan Zeng, Zheng Zhang, Honghui He, Chao He, and Hui Ma

DOI: 10.1364/OL.515983 Received 14 Dec 2023; Accepted 13 Mar 2024; Posted 14 Mar 2024  View: PDF

Abstract: As a complex anisotropic medium, the variation in birefringence within biological tissues is closely associated with numerous physiological behaviors and phenomena. In this Letter, we propose a polarization feature fusion method and the corresponding polarimetric parameters, which exhibit excellent performance of capturing the birefringence dynamic variation process in complex anisotropic media. By employing the feature fusion method, we combine and transform polarization basis parameters (PBPs) to derive fused polarization feature parameters (FPPs) with explicit expressions. Subsequently, we conduct Monte Carlo simulation to demonstrate the effectiveness of the proposed FPPs from two variation dimensions of birefringence direction θ and modulus ∆n. Leveraging mathematical modeling and linear transformations, we investigate and abstract their response patterns concerning θ and ∆n. Finally, the experiments confirm that the FPPs show superior adaptability and interpretability in characterizing the birefringence dynamic process of turbid media. The findings presented in this study provide new methodological insights of information extraction for computational polarimetry in biomedical research.

High-power, gigahertz repetition frequency self-mode-locked Ho:GdVO₄ laser resonantly pumped by a Tm-doped fiber laser

Panqiang Kang, Xinlu Zhang, Xiaofan Jing, Changchang Shen, Jinjer Huang, Yulei Wang, and Zhiwei Lv

DOI: 10.1364/OL.519796 Received 24 Jan 2024; Accepted 13 Mar 2024; Posted 14 Mar 2024  View: PDF

Abstract: A self-mode-locked Ho:GdVO₄ laser with the GHz pulse repetition frequency oscillation near 2061.5 nm was demonstrated for the first time, to our best knowledge. The output performances of the self-mode-locked Ho:GdVO₄ laser were investigated for a few of output coupler transmittances at the pulse repetition frequency of 1.89 GHz. At the incident pump power of 8.12 W, the maximum average output power was as high as 2.28 W, corresponding to the slope efficiency and optical-to-optical efficiency of 36.3% and 28.1%, respectively. To the best of our knowledge, this is the maximum average output for the 2 µm self-mode-locked laser with a GHz pulse repetition frequency. This work provides a new way for generating efficient and high-power ultrafast pulse laser with a GHz repetition frequency in the 2 µm waveband.

Nonreciprocal magnon blockade via optical nonlinearity

Han-Qiu Zhang, Shuang-Shuo Chu, Zhang Song, Wenxue Zhong, and Guangling Cheng

DOI: 10.1364/OL.520578 Received 02 Feb 2024; Accepted 13 Mar 2024; Posted 14 Mar 2024  View: PDF

Abstract: We present an alternative scheme to achieve nonreciprocal unconventional magnon blockade (NUMB) in a hybrid system formed by two microwave cavities and one yttrium iron garnet (YIG) sphere, where the pump and signal cavities interact with each other nonlinearly and the signal cavity is coupled to the YIG sphere. Based on the dispersive interactions among three bosonic modes with the large detuning, the second-order nonlinear coupling occurs between the pump cavity and magnon and meanwhile optical Kerr nonlinearity is present in the pump cavity, which leads to the magnon blockade effect with the help of the weak parametric driving of the pump cavity. By analyzing the second-order correlation functions via numerical simulations and analytical calculations, the nonreciprocity of magnon blockade could be achieved by changing the effective Kerr nonlinearity. The responsible mechanism of unconventional magnon blockade (UMB) within the regime of weak coupling strength is the destructive interference of the two excitation pathways. The present work provides an alternative method to achieve nonreciprocal magnon blockade based on optical nonlinearity, which may be helpful for quantum information processing.

Variational Autoencoder-Assisted Unsupervised Hardware Fingerprint Authentication in Fiber Network

Yilin Qiu, Xinyong Peng, Xinran Huang, Zhi Chai, Mingye Li, Weisheng Hu, and Xuelin Yang

DOI: 10.1364/OL.518952 Received 15 Jan 2024; Accepted 12 Mar 2024; Posted 14 Mar 2024  View: PDF

Abstract: Physical-layer authentication (PLA) based on hardware fingerprints can safeguard optical networks against large-scale masquerade or active injection attacks. However, traditional schemes rely on massive labeled close-set data. Here, we propose an unsupervised hardware fingerprint authentication based on a variational autoencoder (VAE). Specifically, the triplets are generated through variational inference on unlabeled optical spectra and then applied to train the feature extractor, which has excellent generalization ability and enables fingerprint feature extraction from previously unknown optical transmitters. The feasibility of the proposed scheme is experimentally verified by the successful classification of 8 optical transmitters after a 20 km standard single-mode fiber transmission, to distinguish efficiently the rogue from legal devices. A recognition accuracy of 99%, and a miss alarm rate of 0% are achieved even under the interference of multiple rogue devices. Moreover, the proposed scheme is verified to have a comparable performance with the results obtained from supervised learning.

Active feedback stabilization of super-efficient microcombs in photonic molecules

Israel Rebolledo, Óskar Helgason, Vicente Duran, Marcello Girardi, Martin Zelan, and Victor Torres Company

DOI: 10.1364/OL.514761 Received 04 Dec 2023; Accepted 12 Mar 2024; Posted 14 Mar 2024  View: PDF

Abstract: Dissipative Kerr soliton frequency combs, when generated within coupled cavities, exhibit exceptional performance concerning controlled initiation and power conversion efficiency. Nevertheless, to fully exploit these enhanced capabilities, it is necessary to maintain the frequency comb in a low-noise state over an extended duration. In this study, we demonstrate the control and stabilization of super-efficient microcombs in a photonicmolecule. Our findings demonstrate that there is a direct relation between the effective detuning and soliton power, allowing the latter to be used as a set point in a feedback control loop. Employing this method, we achieve the stabilization of a highly efficient microcomb indefinitely, paving the way for its practical deployment in optical communications and dual-comb spectroscopy applications.

Intense emission at 605nm from Pr3+-doped fluorotellurite glass fibers

Jinming Yan, Zhixu Jia, Junjie Wang, Chuanze Zhang, Fangning Wang, Fanchao Meng, Yasutake Ohishi, Daming Zhang, Weiping Qin, Fei Wang, and Guanshi Qin

DOI: 10.1364/OL.518023 Received 08 Jan 2024; Accepted 12 Mar 2024; Posted 15 Mar 2024  View: PDF

Abstract: Pr3+-doped fluorotellurite glass fibers (PDFTFs) were fabricated by using a rod-in-tube method. By using a 976/1400 nm dual-wavelength upconversion pump technique, intense emission at 605 nm was obtained from a 6 cm long PDFTF, which was attributed to the transition 1D2→3H4 of Pr3+ ions. With an increase of the power of 976 nm and 1400 nm lasers, the spectral bandwidth of the 605 nm emission decreased and the intensity of the 605 nm emission increased monotonically, indicating the generation of 605 nm amplified spontaneous emission (ASE). To the best of our knowledge, this is the first report of 605 nm ASE in PDFTFs. Our results showed that PDFTFs had the potential for constructing red fiber lasers and amplifiers.

Bidirectional Raman soliton-like combs with unidirectional pump in a spherical microresonator

Alexey Andrianov and Elena Anashkina

DOI: 10.1364/OL.516842 Received 21 Dec 2023; Accepted 12 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: We experimentally demonstrate bidirectional Raman soliton-like combs in a whispering gallery mode microresonator with unidirectional pump, for the first time, to the best of our knowledge. We develop a relatively simple theoretical model and find an analytical solution for forward- and backward-propagating Raman sech2-shaped solitons in an anomalous dispersion region under unidirectional pumping in a normal dispersion region. Raman solitons exist thanks to the balance between losses and Raman gain from a CW wave (which is equal in both directions) as well as between dispersion and Kerr nonlinearity.

Direct Object Detection with Snapshot Multispectral Compressed Imaging in Short-Wave Infrared Band

Naike Wei, Yingying Sun, tingting jiang, and Qiong Gao

DOI: 10.1364/OL.517284 Received 28 Dec 2023; Accepted 12 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: Snapshot multispectral imaging (SMSI) has attracted much attention in recent years for its compact structure and superior performance. High-level image analysis based on SMSI, such as object classification and recognition, usually takes the image reconstruction as the first step, which hinders its application in many important real-time scenarios. Here we demonstrate the first reconstruction-free strategy for object detection with SMSI in the short-wave infrared (SWIR) band. The implementation of our SMSI is based on a modified 4f system which modulates the light with a random phase mask, and the distinctive point spread function (PSF) in each narrow band endows the system with spectrum resolving ability. A deep learning network is trained to detect small object by constructing a dataset with the PSF of our SMSI system and the sky images as background. Our results indicate that a small object with spectral feature can be detected directly with the compressed image output by our SMSI system, and the inferred object category and location information is reliable with moderate noise. This work paves the way towards the use of SMSI to detect multispectral object in practical applications.

Simple few-shot method for spectrally resolving the wavefront of an ultrashort laser pulse

Slava Smartsev, Aaron Liberman, Igor Andriyash, Antoine Cavagna, ALESSANDRO FLACCO, Camilla Giaccaglia, Jaismeen Kaur, Josephine Monzac, Sheroy Tata, Aline Vernier, Victor Malka, Rodrigo Lopez-Martens, and Jerome Faure

DOI: 10.1364/OL.502000 Received 31 Jul 2023; Accepted 12 Mar 2024; Posted 12 Mar 2024  View: PDF

Abstract: We present a novel and straightforward approach for the spatio-spectral characterization of ultrashort pulses. This minimally intrusive method relies on placing a mask with specially arranged pinholes in the beam path before the focusing optic and retrieving the spectrally-resolved laser wavefront from the speckle pattern produced at focus. We test the efficacy of this new method by accurately retrieving chromatic aberrations, such as pulse front tilt, pulse front curvature, and higher-order aberrations introduced by a spherical lens. The simplicity and scalability of this method, combined with its compatibility with single-shot operation, make it a promising candidate to become a new standard diagnostic tool in high-intensity laser facilities.

Collison dynamics between soliton molecules and a single soliton: exploding soliton pair and periodic soliton explosions

Runmin Liu, Defeng Zou, Youjian Song, and Ming-lie Hu

DOI: 10.1364/OL.516363 Received 21 Dec 2023; Accepted 12 Mar 2024; Posted 12 Mar 2024  View: PDF

Abstract: Inherent periodic collisions in dual-wavelength mode-locked fiber lasers (MLFLs) stimulate various intra-cavity collision dynamic phenomena. Analogous to the collision of mater particles, collisions between optical soliton pair (SPs) and single soliton (SSs) have been observed by the real-time spectral measurements. It is demonstrated that the energy accumulation after collision caused by internal motion within bound pulses leads to SP explosions, while the periodic soliton explosions with another cavity parameter setting are almost unaffected by the collision. Additionally, the collision between a SP and a SS is reproduced through numerical simulations, and the collision-induced double Hopf-type bifurcation of SP is predicted. These findings provide novel insights for further understanding the complex collision dynamics in dual-wavelength MLFLs and will help in the design of high-performance dual-comb sources.

Nonlinear errors elimination using the fusion of PGC-DCM, geometric fitting and Atan algorithms

Gang Zhang, Qiang Ge, Linguang Xu, Xuqiang Wu, and Benli Yu

DOI: 10.1364/OL.516756 Received 21 Dec 2023; Accepted 12 Mar 2024; Posted 12 Mar 2024  View: PDF

Abstract: Phase generated carrier (PGC) demodulation scheme are always accompanied by nonlinear errors. We propose a fusion of PGC differential and cross multiplying (PGC-DCM), geometric fitting and arctangent (Atan) algorithms for fiber optic interferometric sensors to eliminate nonlinear errors. The output amplitude of PGC-DCM algorithm is used to judge whether the Lissajous figure of quadrature signals is larger than 1/2 ellipse arc. When the Lissajous figure exceeds 1/2 ellipse arc, the contaminated quadrature signals are corrected by the ellipse correction parameters calculated from the geometric fitting, otherwise the previous fitting parameters are employed for correction. Geometric fitting is realized by minimizing the Sampson error and its failure problem under small signals is solved by using the temporary stability of fitting results. Finally, desired signals are extracted from the corrected quadrature signals by the Atan algorithm. Experimental results show that the fusion combines the merits of the three algorithms and expands the application of the geometric fitting in PGC demodulation schemes.

Magnetically Tunable Brewster Angle in Uniaxial Magneto-Optical Metamaterials for Advanced Integration of High-Resolution Sensing Devices

SULMA Sarmiento, Edwin Moncada, and Jorge Mejía-Salazar

DOI: 10.1364/OL.520552 Received 01 Feb 2024; Accepted 11 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: In this letter, we introduce a concept to produce high-resolution, highly integrable biosensing devices. Our idea exploits the highly absorbing modes in multilayered metamaterials to maximize the transverse magneto-optical Kerr effect (TMOKE). Results are discussed in the context of dielectric uniaxial (ε₁ε₂>0) and hyperbolic metamaterial (ε₁ε₂<0) regimes. For applications in gas sensing, we obtained sensitivities of S=46.02 deg/RIU and S=73.91 deg/RIU when considering the system working in the uniaxial and hyperbolic regimes, respectively, with figures-of-merit (resolution) in the order of 310 or higher. On the contrary, when considering the system for biosensing applications (incidence from an aqueous medium), we observed that the proposed mechanism can only be successfully used in the uniaxial regime, where a sensitivity of 56.87 deg/RIU was obtained.

On-chip optical wavefront shaping by transverse spin induced Pancharatanam-Berry phase

Wanyue Xiao and Shubo Wang

DOI: 10.1364/OL.521060 Received 06 Feb 2024; Accepted 11 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: Pancharatnam-Berry (PB) metasurfaces can be applied to manipulate the phase and polarization of light within subwavelength thickness. The underlying mechanism is attributed to the geometric phase originating from the longitudinal spin of light. Here, we demonstrate a new type of PB geometric phase derived from the intrinsic transverse spin of guided light. Using full-wave numerical simulations, we show that the rotation of a metallic nano bar sitting on a metal substrate can induce a geometric phase covering 2π full range for the surface plasmons carrying intrinsic transverse spin. Specially, the geometric phase is different for the surface plasmons propagating in opposite directions due to spin-momentum locking. We apply the geometric phase to design metasurfaces to manipulate the wavefront of surface plasmons to achieve steering and focusing. Our work provides a new mechanism for on-chip light manipulations with potential applications in designing ultra-compact optical devices for imaging and sensing.

Echelon grating refractive index sensor

Haotian Zhang, Xiaoping Li, Yue Pan, Hongzhong Cao, Yunjie Xia, and Rende Ma

DOI: 10.1364/OL.520742 Received 02 Feb 2024; Accepted 11 Mar 2024; Posted 15 Mar 2024  View: PDF

Abstract: There are few reports on optical refractive index sensors that have both high resonant-wavelength resolution (RWR) and high refractive index sensitivity (RIS). Herein, based on an echelon grating, we design a refractive index sensor that combines the two advantages together. The principal fringe of echelon grating has a small full width at half maximum and a good signal-to-noise ratio, leading to a high RWR. The wavefront splitting interference makes the sensor have high RIS. The large free spectral range (FSR) of the principal fringes expands the dynamic range of the sensor. The experimentally realized RWR, RIS, and FSR are 3.76 × 10¯³ nm, 1.14 × 10⁴ nm/RIU (RIU: Refractive Index Unit), and 130 nm, respectively. The detection limit of refractive index is 3.3 × 10¯⁷ RIU. The dynamic range of the sensor is 1.14 × 10¯² RIU. Moreover, the theoretically predicted detection limit of refractive index is around the order of 10¯⁸ RIU. The echelon grating refractive index sensor features low detection limit, low cost, high stability, and good robustness.

Nonlinear-Tolerant Two-Dimensional Distribution Matcher Scheme for Probabilistic Shaping

yanan luo, Bin Chen, and Qin Huang

DOI: 10.1364/OL.519549 Received 22 Jan 2024; Accepted 11 Mar 2024; Posted 12 Mar 2024  View: PDF

Abstract: This letter proposes a nonlinear-tolerant two-dimensional distribution matcher (2D-DM) scheme. It removes the corner points of probabilistically shaped quadrature amplitude modulation (QAM) to obtain better nonlinear tolerance. Because the remaining number of points is not a power of two, we propose to divide constellation points into different layers and symbols. Then, the proposed 2D-DM performs matching using one-dimensional shapers, which generates the in-phase and quadrature components of QAM together. In fact, it realizes two-dimensional shapers from one-dimensional shapers. Simulation results show that two-dimensional shapers generated by the proposed 2D-DM have higher tolerance to power amplifier nonlinearity and fiber nonlinearity compared to one-dimensional shapers.

Optical Snake States in Photonic Graphene

Olha Bahrova, Sergei Koniakhin, Anton Nalitov, and Evgenia Cherotchenko

DOI: 10.1364/OL.519717 Received 25 Jan 2024; Accepted 11 Mar 2024; Posted 12 Mar 2024  View: PDF

Abstract: We propose an optical analogue of electron snake states based on artificial gauge magnetic field in photonic graphene implemented by varying distance between cavity pillars.We develop an intuitive and exhaustive continuous model based on tight-binding approximation and compare it with numerical simulations of a realistic photonic structure.The allowed lateral propagation direction is shown to be strongly coupled to the valley degree of freedom and the proposed photonic structure may be used a valley filter.

2.05-μm Tm,Ho:YLF waveguide lasers

Zichen Bai, Zhixiang Chen, yujie xiong, Hongliang Liu, Siying Gao, Yingying Ren, Xingjuan Zhao, Fengqin Liu, Yuechen Jia, and Feng Chen

DOI: 10.1364/OL.520576 Received 05 Feb 2024; Accepted 10 Mar 2024; Posted 12 Mar 2024  View: PDF

Abstract: In this work, we report on the first 2.05-μm laser based on femtosecond-laser direct written (FsLDW) Tm,Ho:YLF cladding waveguides. A channel waveguide with a 90-μm diameter “fiber-like” low-index cladding is fabricated in a 6 at.% Tm3+, 0.4 at.% Ho3+:LiYF4 crystal by FsLDW. Pumped by Ti:sapphire laser at 795.1 nm, the fabricated waveguide supports efficient lasing oscillation at 2050 nm with a maximum output power of 47.5 mW, a minimum lasing threshold of 181 mW, and a slope efficiency of 20.1%. The impacts of cavity conditions and polarizations of the pump light on the obtained lasing performance are well studied. The experimental results obtained in this study demonstrate the great potential of utilizing Tm,Ho:YLF and FsLDW for the development of durable mid-infrared lasers featuring compact designs.

Nanoprinted microstructure-assisted light incoupling into high numerical aperture multimode fibers

Matthias Zeisberger, Henrik Schneidewind, Torsten Wieduwilt, Oleh Yermakov, and Markus Schmidt

DOI: 10.1364/OL.521471 Received 13 Feb 2024; Accepted 10 Mar 2024; Posted 12 Mar 2024  View: PDF

Abstract: The coupling of light into optical fibers is limited by the numerical aperture. Here, we show that large-area polymer axial-symmetric microstructures printed on silica multimode fibers improve their in-coupling performance by 2-3 orders of magnitude beyond the numerical aperture limit. A ray-optical mathematical model describing the impact of the grating-assisted light coupling complements the experimental investigation. This study clearly demonstrates the improvement in-coupling performance by nanoprinting microstructures on fibers, opening new horizons for multimode fibers applications in life sciences, quantum technologies and ‘lab-on-fiber’ devices.

Hybrid Graphene Anti-resonant Fiber with Tunable Light Absorption

Kang She, Guo Sheng, Zhengping Shan, Piaorong Xu, and Exian Liu

DOI: 10.1364/OL.520824 Received 07 Feb 2024; Accepted 10 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: Controlling the output light-intensity and realizing the light-switch function in hollow-core anti-resonant fibers (HC-ARFs) is crucial for their applications in polarizers, lasers, sensors systems. Here we theoretically propose a hybrid light-intensity-tunable HC-ARF deposited with the sandwiched graphene/hBN/graphene based on the typical six-circular-tube and the nested structures. Changing the external drive voltage from 12.3V to 31.8V, the hybrid HC-ARF experiences a high-low alterative attenuation coefficient with a modulation depth 3.87 dB/cm and 1.91 dB/cm for the six-circular-tube and nested structures respectively, serving as a well-performance light-switch at the optical communication wavelength of 1.55 μm. This response is attributed to the variation of the Fermi level of graphene and is obviously influenced by the core size, fiber length, and the number of graphene and hBN layers. Moreover, one weak attenuation peak originating from the surface plasmon resonance is also found simultaneously and shifts with the incident wavelength. Our design provides a feasible paradigm for integrating graphene with anti-resonant fibers and high-performance electro-optic modulators.

Efficient photorefractive effect triggered bypyroelectricity in magnesium doped LiNbO3 films

Anton Perin, Ludovic gauthier-Manuel, Florent Bassignot, and Mathieu Chauvet

DOI: 10.1364/OL.516930 Received 22 Dec 2023; Accepted 10 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: An attractive photorefractive effect triggered by pyroelectricity is displayed in slab waveguides constituted of magnesium oxide (MgO) doped LiNbO3 film on insulator. Microwatts CW 532 nm guided mode can remarkably self-trapped to form 10 µm FWHM beam triggered by a few degrees temperature increase of the sample. Fast self-focusing response time on the order of milliseconds is measured for milliwatts of injected beam, which is more than two orders of magnitude faster than in undoped LiNbO3 film. Long living 2-D induced waveguides are found to be memorized in the films.

Generation of high-energy, sub-20 fs deep-UV pulses in a twin-crystal third harmonic generation scheme

Peter Susnjar, Gabor Kurdi, Paolo Cinquegrana, Alexander Demidovich, Ivaylo Nikolov, Paolo Sigalotti, and M Danailov

DOI: 10.1364/OL.519486 Received 23 Jan 2024; Accepted 10 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: Ultrashort deep ultraviolet (DUV) pulses serve as indispensable tools for investigating molecular dynamics on the femtosecond scale. Nonlinear frequency up-conversion of near-infrared (NIR) light sources in a sequence of nonlinear crystals is a common method for their generation. However, preserving the temporal duration of the starting source encounters challenges owing to phase-matching bandwidth limitations within the harmonic generation process. Here we propose an approach for circumventing this limitation and demonstrate it for the case of generation of the third harmonic of 800 nm pulses in a two-stage scheme (second harmonic generation succeeded by sum-frequency mixing of the fundamental and second harmonic pulses). Expanding the bandwidth of the DUV pulse involves the utilization for the last mixing process of two nonlinear crystals, detuned to convert opposite sides of the spectrum. The implementation of this approach yields 20 µJ, 263 nm DUV pulses as short as 19 fs after compression. The setup is very compact and extremely stable due to the common-path scheme which makes it very interesting for a variety of advanced ultrafast spectroscopy applications.

Dual high-order QAM-modulated mm-wave signal transmission in the Q-band enabled by simple IM/DD architecture and bandpass delta-sigma modulation

Hengxin Yan, Xinying Li, Xiaolong Pan, tangyao Xie, Liye Fang, Jiahao Bi, Han Jiang, and Xiangjun Xin

DOI: 10.1364/OL.521343 Received 08 Feb 2024; Accepted 09 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: The intensity-modulation (IM)/direct-detection (DD) systems have been proven effective and low-cost due to their simple system architecture. However, the Mach‒Zehnder modulator (MZM) of the IM/DD systems only reserves its driving signal intensity. Therefore, the IM/DD systems are generally unable to transmit vector signals and have a restricted spectrum efficiency and channel capacity. Similarly, the radio-over-fiber (RoF) transmission systems based on IM/DD are limited by their simple architecture and generally cannot transmit high-order quadrature amplitude modulation (QAM) signals, which hinders the improvement of their spectrum efficiency. To address the challenges, we propose a novel scheme to simultaneously transmit the dual independent high-order QAM-modulated millimeter-wave (mm-wave) signals in the RoF system with a simple IM/DD architecture, enabled by precoding-based optical carrier suppression (OCS) modulation and bandpass delta-sigma modulation (BP-DSM). The dual independent signals can carry different information, which increases channel capacity and improves spectrum efficiency and system flexibility. Based on our proposed scheme, we experimentally demonstrate the dual 512-QAM mm-wave signal transmission in the Q-band (33-50GHz) under three different scenarios: 1) dual single-carrier (SC) signal transmission, 2) dual orthogonal-frequency-division-multiplexing (OFDM) signal transmission, and 3) hybrid SC and OFDM signal transmission. We achieve high-fidelity transmission of dual 512-QAM vector signals over a 5 km single-mode fiber-28 (SMF-28) and a 1-m single-input single-output (SISO) wireless link operating in the Q-band, with the bit error rates (BERs) of all three scenarios below the hard decision forward error correction (HD-FEC) threshold of 3.8 10-3. To the best of our knowledge, this is the first time to achieve dual high-order QAM-modulated mm-wave signal transmission in a RoF system with a simple IM/DD architecture.

A liquid crystal waveplate operating close to 18 THz

Fabio Novelli, Patrick Friebel, Marta Murillo-Sanchez, J. Michael Klopf, and Laura Cattaneo

DOI: 10.1364/OL.519177 Received 23 Jan 2024; Accepted 09 Mar 2024; Posted 12 Mar 2024  View: PDF

Abstract: Controlling the properties of mid and far-infrared radiation can provide a means to transiently alter the properties of materials for novel applications. However, a limited amount of optical elements are available to control its polarization state. Here we show that a 15-micron thick liquid crystal cell containing 8CB (4-Octyl-4'-cyanobiphenyl) in the ordered, smectic A phase can be used as a phase retarder or waveplate. This was tested using the bright, short-pulsed (~1 ps) radiation centered at 16.5 μm (18.15 THz) that is emitted by a free electron laser at high repetition rate (13 MHz). These results demonstrate a possible tool for the exploration of the mid and far-infrared range and could be used to develop novel metamaterials or extend multidimensional spectroscopy to this portion of the electromagnetic spectrum.

Tunable liquid crystal lens with symmetric bipolar operation

Zhanna Zemska and Tigran Galstian

DOI: 10.1364/OL.519493 Received 19 Jan 2024; Accepted 09 Mar 2024; Posted 14 Mar 2024  View: PDF

Abstract: We describe an electrically tunable liquid crystal lens that can dynamically generate symmetric wavefront profiles. The curvature of these profiles may be inversed enabling thus a bipolar response (focusing and defocusing). Different wavefronts, including non-monotonic, are predicted theoretically and demonstrated experimentally. The optical performance of the devices is characterized experimentally in an imaging scheme.

Learning-enabled data transmission with up to 32 multiplexed orbital angular momentum channels through a commercial multi-mode fiber

Jihong Tang, Yaling Yin, Jingwen Zhou, Yong Xia, and Jianping Yin

DOI: 10.1364/OL.518681 Received 15 Jan 2024; Accepted 09 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: Multiplexing orbital angular momentum (OAM) modes enables high-capacity optical communication. However, the highly similar speckle patterns of adjacent OAM modes produced by strong mode coupling in common fibers prevents the utility of OAM channel demultiplexing. In this paper, we propose a machine learning-supported fractional OAM-multiplxed data transmission system to sort highly scattered data from up to 32 multiplexed OAM channels propagating through a commercial multi-mode fiber parallelly with an accuracy of >99.92%, which is the largest bit number of OAM superstates reported to date. Here, by learning limited samples, unseen OAM superstates during the training process can be predicted precisely, which reduces the explosive quantity of dataset. To verify its application, both gray and colored images, encoded by the given system, have been successfully transmitted with error rates of <0.26%. Our work might provide a promising avenue for high-capacity OAM optical communication in scattering environments.

Untrained neural network enables fast structured illumination microscopy

zitong ye, Xiaoyan Li, Yile Sun, YURAN HUANG, Xu Liu, Yubing Han, and Cuifang Kuang

DOI: 10.1364/OL.511983 Received 21 Nov 2023; Accepted 08 Mar 2024; Posted 14 Mar 2024  View: PDF

Abstract: Structured illumination microscopy (SIM) offers a two-fold resolution enhancement beyond the optical diffraction limit. At present, SIM requires several raw structured illuminated image frames to reconstruct a super-resolution (SR) image, which limits its imaging speed. Considering this, we herein propose an untrained structured-illumination reconstruction neural network (USRNN), that applies the untrained convolutional neural network (CNN) to reduce the amount of raw data required for SIM reconstruction and thus improve the temporal resolution of SIM. Benefiting from the unsupervised optimizing strategy and CNNs structure priors, the high-frequency information is obtained from the network without a requirement of a large dataset and thus a high-fidelity SR image can be reconstructed using fewer image frames, which allows for SIM imaging with higher speed and greatly reduced photo-bleaching. Experiments on reconstructing non-biological and biological samples demonstrate the high-speed and high-universality capabilities of our method.

Fabrication of elliptical-silica microfiber for ultrasound detection

Haokun Yang, GERARD TATEL, Yuan Wang, Liang Chen, and Xiaoyi Bao

DOI: 10.1364/OL.513749 Received 20 Nov 2023; Accepted 08 Mar 2024; Posted 18 Mar 2024  View: PDF

Abstract: Photons can excite many high order modes in asymmetric fiber which form in-fiber Mach-Zehnder (MZI) interferometers for time dependent displacement sensing without the need of average, due to high contrast. In this paper, we present the design and fabrication of an ultra-compact elliptical-silica microfiber utilizing off-axis flame-drawing for ultrasound detection. This microfiber is engineered with the purpose to excite multiple high-order modes and multi-mode interference. Consequently, this design results in a transmission spectrum with a remarkably sharp slope and high contrast, it gives the high level of detection sensitivity. With a major-axis diameter of 6.25 μm, the elliptical-silica microfiber sensor exhibits a broadband ultrasound frequency response spanning from 20 kHz to 38.5 MHz. Furthermore, it achieves a signal-to-noise ratio (SNR) of up to 80 dB at 1 MHz which is resonance frequency of the microfiber and the linear response for different driving voltages of the PZT ultrasound generator. This low-cost microfiber sensor offers exceptional sensitivity across a broad ultrasonic bandwidth response, making it an ideal choice for non-destructive testing (NDT) and medical imaging applications. Its compact size and immunity to electric and magnetic fields further enhance its utility in various environments.

Nearest Neighbor Bit Assisted Decision Scheme for ISI Mitigation in Optical Camera Communications

Jin Shi and Jing He

DOI: 10.1364/OL.520900 Received 05 Feb 2024; Accepted 08 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: To enable higher transmission rate in optical camera communication (OCC) systems, severe ISI occurs owing to the reduction of the number of pixel-row-per-bit (PPB). Therefore, those pixels representing logic bit 0 or 1 may have same grayscale values, significantly deteriorating the bit decision when using conventional thresholding scheme. In this letter, a simple yet efficient scheme, referred to as nearest neighbor bit assisted decision (NNBAD) scheme, is proposed and experimentally demonstrated for signal decision in optical camera communication (OCC) systems. NNBAD leverages the nearest neighbor bit to jointly assist bit decision for pixels with severe ISI. Experimental results show that, for OCC systems with OOK modulation, those pixels with severe ISI cannot be distinguished by conventional thresholding scheme. Yet, NNBAD scheme exhibits strong robustness against ISI, remarkably improving the BER performance. The proposed scheme can achieve a throughput of 8.2 kbps with OOK modulation under an illuminace of 600 lx.

Deep Learning Empowers Photothermal Microscopy with Super-Resolution capabilities

Yonghui Wang, zhuoyan yue, Fei Wang, Peng Song, and Junyan Liu

DOI: 10.1364/OL.517164 Received 28 Dec 2023; Accepted 08 Mar 2024; Posted 12 Mar 2024  View: PDF

Abstract: In the past two decades, Photothermal microscopy (PTM) has reached the sensitivity of single particle or molecule, and it has been used in the fields of material science and biology. PTM is a far-field imaging method, its resolution is restricted by the diffraction limits. In our previous work, the modulated difference PTM (MDPTM) was proposed to improve the lateral resolution, but, its resolution improvement was seriously constrained by the information loss and the artifacts. In this letter, a deep learning approach of the cycle generative adversarial network (Cycle GAN) is employed for further improving the resolution of PTM, called DMDPTM. The point spread functions (PSF) of both PTM and MDPTM are optimized and act as the second generator of Cycle GAN. Besides, the relationship between the sample’s volume and the photothermal signal is taken into account during dataset construction. The images of both PTM and MDPTM are used as the input of the Cycle GAN, as well as bring more information to the network. In the simulation, the distance of 80nm between two nanoparticles (diameter of 60nm) can be quantitively determined by DMDPTM, and this replies that the DMDPTM has a 3.3fold resolution enhancement over the conventional PTM. Consequently, the super-resolution of DMDPTM is experimentally verified by restored images of Au nanoparticles, achieving the resolution of 114nm. Finally, the DMDPTM is successfully applied for the imaging of carbon nanotubes with diameters of 10-30nm. Therefore, the DMDPTM will serve as a powerful tool to improve the lateral resolution of PTM.

A Visible Light Positioning System Using Smartphone’s Built-in Ambient Light Sensor and Inertial Measurement Unit

Yuan Zhuang, Yaxin Wang, xiansheng yang, and Tianbing Ma

DOI: 10.1364/OL.519674 Received 25 Jan 2024; Accepted 08 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: In recent years, the visible light positioning field has experienced remarkable advancements. However, smartphones find it difficult to identify LED and extract each LEDs light signal intensity due to the low-frequency and uneven sampling of built-in Ambient Light Sensors (ALS, which is a photodiode that measures ambient light in lux units). Thus, traditional visible light positioning systems cannot be directly applied to smartphones. In this paper, we propose a single-light visible light positioning system using a non-modulated LED as an emitter, the built-in ALS as the receiver, and the inertial measurement unit of the smartphone to assist in measuring the smartphones attitude. It only requires the user to turn the smartphone by a few angles in a stationary position to estimate its current 3D spatial position. This method does not require modification of the existing lighting system and consumes less power than the camera-based VLP systems. We have built an experimental site measuring 5m × 5m × 2.2m to evaluate the performance of the positioning system, and the preliminary results show that the proposed system achieves sub-meter level positioning accuracy.

Free spectral range measurement based on multi-longitudinal mode laser self-mixing ellipse fitting degree detection technique

Zhen Huang, HAOZHONG XU, and Dongyu Li

DOI: 10.1364/OL.519913 Received 25 Jan 2024; Accepted 08 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: A method by detecting the ellipse fitting degree of the trajectory equation formed by two self-mixing (SM) signals in the multi-longitudinal mode laser self-mixing system with a Wollaston prism is presented to test the free spectral range (FSR) of the laser. By utilizing the orthogonal vector and phase-shift characteristics between adjacent longitudinal modes, the variations in multi-mode self-mixing effects caused by changes in the external cavity length are converted to changes in the trajectory consisting of two orthogonal SM signals. The FSR is calculated by detecting the difference in external cavity lengths between the two positions, where the trajectory of the two SM signals has the best fit to an ellipse. To achieve automatic FSR measurement, the ellipse fitting degree is proposed as the criterion for positioning external cavity mode. Experimental results indicate that the FSR of the laser diode is measured to be 85. GHz with a resolution of 0.48 GHz while the corresponding external cavity resolution is 10 μm and the resolution of the ellipse fitting degree is less than 1. The compact and straightforward design, coupled with high sensitivity, automated measurements, and immunity to optical feedback, holds significant promise as a robust tool for measuring FSR and assessing laser performance.

Tunable and highly sensitive fluorescent thermometers from La2CaZrO6:Cr3+ with time-resolved technology

Ganggang Guo, QIONG XI, Cong Li, Tao Yin, Zheng Ren, Yayuan Zhang, Jianju Nie, Li Guan, Zhenyang Liu, Fenghe Wang, and Xu Li

DOI: 10.1364/OL.518384 Received 16 Jan 2024; Accepted 08 Mar 2024; Posted 08 Mar 2024  View: PDF

Abstract: The non-contact optical temperature measurement can effectively avoid the disadvantages of traditional contact thermometry, and thus become a hot research topic. Herein, a fluorescence intensity ratio (FIR) thermometry using a time-resolved technique based on La2CaZrO6: Cr3+ (LCZO) is proposed, with a maximum relative sensitivity (Sr-FIR) of 6.17% K-1 and a minimum temperature resolution of 0.155 K. Moreover, the relative sensitivity and temperature resolution can be effectively controlled by adjusting the width of the time gate based on the time-resolved technique. Our work provides new viewpoints into the development of novel optical thermometers with adjustable relative sensitivity and temperature resolution on an as-needed basis.

Integrated photon pair source based on a silicon nitride micro-ring resonator for quantum memories

Juan Durán-Gómez, Roberto Ramirez Alarcón, Mauricio Gómez Robles, Patricia Tavares Ramírez, Gerardo Rodríguez Becerra, Erasto Ortíz-Ricardo, and Rafael Salas-Montiel

DOI: 10.1364/OL.519784 Received 24 Jan 2024; Accepted 07 Mar 2024; Posted 08 Mar 2024  View: PDF

Abstract: We report the design of an integrated photon pair source based on spontaneous four wave mixing (SFWM), implemented in an integrated micro-ring resonator in the silicon nitride platform (Si₃N₄). The signal photon is generated with emission at 606 nm and bandwidth of 3.98 MHz, matching the spectral properties of Praseodymium ions (Pr), while the idler photon is generated at 1430.5 nm matching the wavelength of a CWDM channel in the E-band. This novel device is designed to interact with a quantum memory based on a Y₂SiO₅ crystal doped with Pr³+ ions, in which, we used cavity-enhanced SFWM along with dispersion engineering to reach the required wavelength and the few megahertz signal photon spectral bandwidth.

Thermal-tagging Photoacoustic Remote Sensing Flowmetry

Yun Lu, Yunxu Sun, Zhousheng Shen, Xiaochuan Xu, Ting Ma, Chang Peng, Fenfang Li, Chengqing Ning, Jiawei Wang, Shutian Liu, Wei Liu, Lingji Xu, and Zhengjun Liu

DOI: 10.1364/OL.521564 Received 13 Feb 2024; Accepted 07 Mar 2024; Posted 08 Mar 2024  View: PDF

Abstract: Ultrasound coupling is one of the critical challenges for the traditional photoacoustic (or optoacoustic) microscopy (PAM) technique transferred to the clinical examinations of chronic wounds and open tissues. A promising alternative potential solution for breaking the limitation of ultrasound coupling in PAM is photoacoustic remote sensing (PARS), which implements all-optical non-interferometric photoacoustic measurements. Functional imaging of PARS microscopy was demonstrated from the aspects of histopathology and oxygen metabolism, while its performance in hemodynamic quantification remains unexplored. In this Letter, we present an all-optical thermal-tagging flowmetry approach for PARS microscopy and demonstrate it with comprehensive mathematical modelling and ex vivo and in vivo experimental validations. Experimental results demonstrated that the detectable range of blood flow rate was from 0 to 12 mm/s with a high accuracy (measurement error: ±1.2%) at 10-kHz laser pulse repetition rate. The proposed all-optical thermal-tagging flowmetry offers an effective alternative approach for PARS microscopy realizing non-contact dye-free hemodynamic imaging.

Coherent beam combining of femtosecond third-harmonic generators: Towards high-power, high-beam-quality UV light generation

Genyu Bi, Chenming Yu, Bowen Liu, Jintao Fan, Yuxi Chu, Xiaohui Zhang, and Ming-lie Hu

DOI: 10.1364/OL.520637 Received 02 Feb 2024; Accepted 07 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: Coherent beam combining (CBC) of two femtosecond third-harmonic (TH) generators is proposed and demonstrated. By applying phase modulation to one of the fundamental laser pulses, the feedback loop effectively eliminates both phase and pointing errors between the two TH femtosecond laser beams. The system delivers 345-nm femtosecond laser pulses with 22-W average power at 1-MHz repetition rate. The average combining efficiency is 91.5% over approximately one hour of testing. The beam quality of the combined ultraviolet (UV) laser beam is near-diffraction-limited with M² factors of M²x=1.36, M²y=1.24, which are similar to those of the individual channels. This scheme exhibits promising potential for increasing high-beam-quality UV laser power.

Pulse pattern manipulation of dichromatic soliton complexes by a twistable tapered fiber filter

Bowen Liu, Shinji Yamashita, and Sze Set

DOI: 10.1364/OL.517054 Received 15 Jan 2024; Accepted 06 Mar 2024; Posted 14 Mar 2024  View: PDF

Abstract: Soliton complexes highlight the particle-like dynamics of dissipative pulse motions. Whereas simple and reliable manipulation of bound solitons remains challenging. Here, we report controllable pulse patterns of robustly coexisting dichromatic soliton complexes in an all-polarization-maintaining fiber laser based on a twistable tapered fiber filter. According to the twist angle, dichromatic pulses are switched between different patterns. Components at each wavelength can also be independently manipulated depending on the twist direction, enabling extended encoding formats from the time to frequency domain. To the best of our knowledge, it is the first experimental demonstration of dual-wavelength soliton complexes that different bound pulse patterns coexist at separated wavebands.

Decoding of compressive data pages for optical data storage utilizing FFDNet

Zehao He, Yan Zhang, Daping Chu, and Liangcai Cao

DOI: 10.1364/OL.516785 Received 08 Jan 2024; Accepted 06 Mar 2024; Posted 15 Mar 2024  View: PDF

Abstract: Coded aperture-based compression has proven to be an effective approach for high-density cold data storage. Nevertheless, its limited decoding speed represents a significant challenge for its broader application. We introduce a novel decoding method leveraging the fast and flexible denoising network (FFDNet), capable of decoding a coded aperture-based compressive data page within 30.64 s. The practicality of the method has been confirmed in the decoding of monochromatic photo arrays, full-color photos, and dynamic videos. In experimental trials, the variance between decoded results obtained via the FFDNet-based method and the FFDNet-absent method in terms of average PSNR is less than 1 dB, while realizing a decoding speed enhancement of over 100-fold when employing the FFDNet-based method.

Ultrafast Laser Bursts Welding of Glass and Metal with an Ultra-Large Molten Pool

Haodong Ren, Chenyun Tian, and Hong Shen

DOI: 10.1364/OL.520150 Received 31 Jan 2024; Accepted 06 Mar 2024; Posted 08 Mar 2024  View: PDF

Abstract: A novel method is proposed for the welding of glass and metal with a large gap filled with solder paste using ultrafast laser bursts. The addition of solder paste enables a reliable glass-metal connection even at gaps of hundreds of microns, while the position of the glass can be flexibly adjusted. By ultrafast laser bursts, the volume of the molten pool increases significantly, and the height of the molten pool reaches approximately 350 μm, which is more than an order of magnitude higher than that of conventional ultrafast lasers (10-20 μm). Cross-sectional analysis of the welded region shows that extensive material mixing and element diffusion occur, and stable connections are achieved at multiple interfaces. Analysis of the interaction between the ultrafast laser bursts and the material, as well as the mixing of multiple materials during the welding process, leads to a clear welding mechanism.

Terahertz-triggered ultrafast nonlinear optical activities in two-dimensional centrosymmetric PtSe₂

Xin Chen, Jianhua Sang, kang wang, zhuorui zheng, Yifei Fang, Jun Wang, Xiaojun Wu, Liwei Song, Ye Tian, Yuxin Leng, and Ruxin Li

DOI: 10.1364/OL.520416 Received 01 Feb 2024; Accepted 06 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: The nonlinear mechanisms of polarization and optical fields can induce extensive responses in materials. In this study, we report on two kinds of nonlinear mechanisms in the topological semimetal PtSe₂ crystal under the excitation of intense terahertz pulses, which are manipulated by the real and imaginary parts of the nonlinear susceptibility of PtSe₂. Regarding the real part, the broken inversion symmetry of PtSe₂ is achieved through terahertz electric field polarization approach, which is characterized by second harmonic generation (SHG) measurements. The transient terahertz-laser-induced SHG signal occurs within 100 fs and recombines to the equilibrium state within 1 ps, along with a high signal-to-noise ratio (~51 dB) and a high on/off ratio (~10²). Regarding the imaginary part, a nonlinear absorption change can be generated in the media. We reveal a terahertz-induced absorption enhancement in PtSe₂ via nonlinear transmittance measurements, and the sheet conductivity can be modulated up to 42% by terahertz electric fields in our experiment. Therefore, the terahertz-induced ultrafast nonlinear photoresponse reveals the application potential of PtSe₂ in photonic and optoelectronic devices in terahertz technology.

Tracking bandwidth limitations in strong optical-turbulence conditions

Matthew Kalensky, Darren Getts, and Mark Spencer

DOI: 10.1364/OL.521092 Received 06 Feb 2024; Accepted 06 Mar 2024; Posted 07 Mar 2024  View: PDF

Abstract: We derive a modified fundamental tracking frequency, which is applicable for beam-control systems that do not employ adaptive-optics compensation. Specifically, we show that when higher-order phase aberrations are appreciably present (when D/r0>4, where D is the aperture diameter and r0 is the Fried parameter), there are diminishing returns on tracking faster than the modified fundamental tracking frequency. This conclusion results from beam spreading being the dominate driver for decreased system performance, as opposed to beam jitter.

17.5 Gb/s physical layer key distribution over 100 km fiber link based on channel physical intrinsic property and polarization reciprocity

Taihang Qiu, Lei Deng, Qi Yang, Xiaoxiao Dai, Deming Liu, and Mengfan Cheng

DOI: 10.1364/OL.517847 Received 05 Jan 2024; Accepted 06 Mar 2024; Posted 08 Mar 2024  View: PDF

Abstract: Secure key distribution (SKD) schemes based on fiber channel reciprocity provide information-theoretic security as well as a simple symmetric structure. However, the nonlinear effects and backscattering effects introduced during the bidirectional transmission process degrade the channel reciprocity. Recent unidirectional SKD schemes avoid non-reciprocal factors but require additional negotiation mechanisms to aggregate the transmitter and receiver data. Here, we propose a unidirectional SKD scheme based on channel physical intrinsic property and polarization reciprocity. The designed loopback structure constructs asymmetry between legitimate and illegitimate parties while aggregating data. The deployment of a broadband chaotic entropy source significantly improves the key generation rate (KGR). In the experiment, the KGR reaches 17.5 Gb/s and the distribution distance reaches 100km.

Co-LSTM based fiber link modeling with ASE noise tracking for long-haul coherent optical transmission

Jiayu Zheng, tianhong zhang, and Fan Zhang

DOI: 10.1364/OL.517041 Received 03 Jan 2024; Accepted 05 Mar 2024; Posted 07 Mar 2024  View: PDF

Abstract: In this letter, a novel channel modeling scheme based on cascading chromatic dispersion-nonlinearity feature decoupling modules is proposed with the center-oriented long-short term memory (Co-LSTM) network structure adopted for modeling nonlinearity of each optical fiber span. By tracking amplified spontaneous emission (ASE) noise at the output of each fiber span, the Co-LSTM based channel modeling scheme achieves a high waveform accuracy for long-haul coherent optical transmission compared with the conventional split-step Fourier transform method (SSFM), while saving calculation time by one order of magnitude.

New Fast Nonlinear Fourier Transform Algorithms forOptical Data Processing

Sergey Medvedev, Irina Vaseva, Dmitry Kachulin, Igor Chekhovskoy, and Mikhail Fedoruk

DOI: 10.1364/OL.515200 Received 06 Dec 2023; Accepted 05 Mar 2024; Posted 05 Mar 2024  View: PDF

Abstract: The nonlinear Fourier transform (NFT) is an approach that is similar to a conventional Fourier transform. In particular, NFT allows to analyze the structure of a signal governed by the nonlinear Schrödinger equation(NLSE). Recently, NFT applied to NLSE has attracted special attention in applications of fiber-optic communication. Improving the speed and accuracy of the NFT algorithms remains an urgent problem in optics. We present an approach that allows to find all variants of symmetric exponential splitting schemes suitable for the fast NFT (FNFT) algorithms with low complexity. One of the obtained schemes showed good numerical results comparing with other fast fourth order NFT schemes.

Joule-Class THz Pulses from Microchannel Targets

Gerrit Bruhaug, Hans Rinderknecht, Kale Weichman, Matthew VanDusen-Gross, John Palastro, Mingsheng Wei, Sean Regan, Yiwen E, Kareem Garriga Francis, Xi-Cheng Zhang, Gilbert Collins, and James Rygg

DOI: 10.1364/OL.518981 Received 15 Jan 2024; Accepted 05 Mar 2024; Posted 06 Mar 2024  View: PDF

Abstract: Inference of joule class THz radiation sources from microchannel targets driven with 100’s of joule, picosecond lasers is reported. THz sources of this magnitude are useful for non-linear pumping of matter and for charged particle acceleration and manipulation. Microchannel targets demonstrate increased conversion efficiency compared to planar foil targets, with laser energy to THz energy conversion up to ~0.9% in the best cases.

Instantaneous frequency measurement based on photonic compressive sensing with sub-Nyquist pseudo-random binary sequences

Runcheng Li, shuna yang, Bo Yang, Yiran Gao, Hongxia He, and Hao Chi

DOI: 10.1364/OL.520471 Received 01 Feb 2024; Accepted 05 Mar 2024; Posted 06 Mar 2024  View: PDF

Abstract: We propose a novel approach to realizing instantaneous frequency measurement with ultra-high measurement bandwidth, which utilizes three-channel photonic compressive sensing (CS) with sub-Nyquist pseudo-random binary sequences (PRBSs). In each CS channel, an alias frequency is recovered due to the sub-Nyquist property of the applied PRBS. A frequency identification algorithm is employed to determine the frequency of the signal under measurement according to the three alias frequencies. The proposed approach significantly reduces the bit rate of the applied PRBSs and the sampling rate required by the digitizers in CS. A proof-of-concept experiment for measuring frequency in the Ku band is demonstrated using PRBSs at 1 Gb/s and digitizers with a sampling rate of 250 MS/s.

Architecture for Low-cost and Highly Flexible Metro-access Networks using SOA-based OADM Nodes and Digital Subcarrier Multiplexing with Power Loading

Zhouyi Hu, Shiyi Xia, Henrique Freire Santana, Marijn Rombouts, Bin Shi, and Nicola Calabretta

DOI: 10.1364/OL.514171 Received 23 Nov 2023; Accepted 05 Mar 2024; Posted 05 Mar 2024  View: PDF

Abstract: Metro-access networks exploiting wavelength division multiplexing (WDM) to cope with the ever-growing bandwidth demands are sensitive to cost and need to be fast-configurable to meet the requirements of many new network services. Optical add-drop multiplexers (OADMs) are a key component in enabling fast dynamic wavelength allocation and optimization. In this Letter, we propose and demonstrate a novel architecture for high-performance metro-access networks that utilizes semiconductor optical amplifier (SOA) -based OADM nodes, digital subcarrier multiplexing (DSCM), low-cost direct detection receivers, and power loading techniques, which makes the designed metro-access network cost-effective, fast reconfigurable, and flexible for bandwidth allocation on demand. Through a proof-of-concept experiment, we have successfully demonstrated a prototype horseshoe optical network consisting of up to 4 SOA-based OADM nodes at 40 Gb/s per wavelength channel by leveraging the proposed scheme. Flexible bandwidth allocation and dynamic add and drop operations have also been achieved in an emulated WDM optical network. All results indicate the great scalability and flexibility of the proposed architecture.

Compact and broadband silicon polarization splitter-rotator using adiabaticity engineering

Yung-Jr Hung, Chih-Hsien Chen, Hung-Ching Chung, Jun-Zhu Lai, and Shuo-Yen Tseng

DOI: 10.1364/OL.518607 Received 12 Jan 2024; Accepted 05 Mar 2024; Posted 05 Mar 2024  View: PDF

Abstract: We propose and demonstrate a short and broadband silicon mode-conversion polarization splitter-rotator (PSR) consisting of a mode-conversion taper and an adiabatic coupler-based mode sorter both optimized by adiabaticity engineering (AE). AE is used to optimize the distribution of adiabaticity parameter over the length of the PSR, providing shortcut to adiabaticity at a shorter device length. The total length of the PSR is 85 μm. The design is compatible with standard silicon photonicsplatforms and requires only one patterning step. Fabricated PSR has a polarization crosstalk of less than -20 dB over the entire O-band for the TE polarization, and a polarization crosstalk of less than -15 dB from 1267 to 1348 nm for the TM polarization. Overall, the PSR shows low polarization crosstalk (-15 dB) over a bandwidth of 81 nm in the O-band. Cross-wafer measurements show that the PSR has good fabrication tolerance.

Bound states in the continuum in circular waveguides: toward the on-chip integration of nanofiber on silicon platform

Haitao Zhou, Zhiyuan Gu, Sen Jiang, Ping Zhong, and Ying Yu

DOI: 10.1364/OL.519298 Received 18 Jan 2024; Accepted 05 Mar 2024; Posted 08 Mar 2024  View: PDF

Abstract: In previously reported researches on bound state in the continuum (BIC) waveguides, almost all of them are demonstrated with top-down fabrication procedures, leading to the inconvenience for post-manipulation and size tunning. Nanofiber with circular cross-section is the fundamental component to transport energy due to their intrinsic advantages of high flexibility and adjustability, which is replaceable and can be readily manipulated over size and position on substrate. In this work, we explore the possibility of achieving on-chip integration of silica nanofiber onto silicon-on-insulator platform. By constructing additional leakage channels in coupled nanofiber waveguides, coherently destructive interferences are successfully achieved. The heavy leakage losses from low-index nanofiber to high-index silicon substrate are completely eliminated with BIC and the propagation length of the nanofiber waveguide is significantly improved.

Design and demonstration of high efficiency perfectly vertical grating couplers with random structure

Xin Jin, Jinbin Xu, Cuiwei Xue, chenxing guo, Liucheng Fu, Min Liu, Yunliang Shen, Xueling Quan, and Xiu-Lan Cheng

DOI: 10.1364/OL.519489 Received 22 Jan 2024; Accepted 04 Mar 2024; Posted 08 Mar 2024  View: PDF

Abstract: Utilizing an automated optimization method, we propose a perfectly vertical grating coupler (PVGC) characterized by random structure, superior performance, simplified fabrication process, and increased minimum feature size (MFS). Within the range of MFS from 60 nm to 180 nm, the optimized PVGC exhibited a simulated coupling efficiency of approximately -2.0 dB at 1550 nm with a 34 nm 1-dB bandwidth. Experimental results for the corresponding structure demonstrated coupling efficiencies ranging from -2.5 dB to -2.8 dB with a 32 nm 1-dB bandwidth, while maintaining high manufacturing tolerances. This represents the most outstanding experimental outcome to date regarding the coupling performance of a PVGC fabricated on 220nm silicon on insulator (SOI), without requiring any complex processes as reported in existing literature.

High-Sensitivity Fiber Optic Graphene Resonant Accelerometer

Liu Yujian, Cheng Li, Jing Li, Zhen Wan, and Chun Fan

DOI: 10.1364/OL.521357 Received 14 Feb 2024; Accepted 04 Mar 2024; Posted 11 Mar 2024  View: PDF

Abstract: This study proposes a high-sensitivity resonant graphene accelerometer based on a pressure-induced sensing mechanism. The accelerometer design encompasses an optical fiber and a vacuum-sealed graphene resonator affixed to a silicon sensitive film, incorporating a proof mass. This indirect sensing mechanism effectively mitigates the vibration mode aliasing of graphene and the proof mass, while ensuring a minimal energy loss in the operating resonator. The mechanical vibration of graphene is excited and detected through an all-fiber optical system. Notably, the proposed sensor demonstrates a sensitivity of 34.3 kHz/g within the range of 0~3.5g, which is eight times higher than comparable accelerometers utilizing a proof mass on a graphene membrane. This work exhibits a novel approach to acceleration measurement using 2D resonators, exhibiting distinct advantages in terms of compact size and heightened sensitivity.

Polarized vortex Smith–Purcell radiation with cascaded metasurfaces

Wen-xia Xu, Wenjia Li, Yehan Wang, Chunhua Qin, Botian Sun, Chunying Guan, Jianlong Liu, and Jin-hui Shi

DOI: 10.1364/OL.503537 Received 17 Aug 2023; Accepted 04 Mar 2024; Posted 06 Mar 2024  View: PDF

Abstract: We introduce the concept of polarized vortex Smith–Purcell radiation by the interaction of electron beam and cascaded metasurfaces. The spin and orbital angular momenta of Smith–Purcell radiation are determined by the cascaded metasurface that consists of a grating and a phase gradient metasurface. The grating converts the electron beam radiation into the desired polarized light, while the phase gradient metasurface generates vortex light. Furthermore, the vortex Smith–Purcell radiation with linear and circular polarizations can be achieved by the various cascaded metasurfaces. In particular, the conversion of chirality in Smith–Purcell radiation carrying circular polarization is accompanied by the alteration of positive and negative topological charges. This work paves the way for generating polarized vortex electron radiation and is beneficial to promote the development of free electron-driven devices.

Near-perfect absorption of honeycomb metasurface through QBIC

Haosen Zhang, Kedi Wu, and Guo Ping Wang

DOI: 10.1364/OL.517673 Received 02 Jan 2024; Accepted 04 Mar 2024; Posted 06 Mar 2024  View: PDF

Abstract: All-dielectric high-Q metasurface absorbers based on quasi-bound states in the continuum (QBIC) are essential for optical and photonic devices. However, achieving perfect absorption requires adding back reflectors at the bottom or placing at least four asymmetric elements in each unit of monolayer metasurfaces, which will increase the design complexity. This work proposes a honeycomb structure with units periodically arranged as a hexagonal lattice. Each unit cell is made of two nanopost elements. By only tuning the radius difference of two elements to break the in-plane symmetry, two orthogonal QBIC modes corresponding to toroidal dipole (TD) and electric dipole (ED) modes are excited, respectively. The maximum absorption reaches 92.3% at 955 nm with a Q factor 1501, breaking the monolayer limit of 50% by the degenerate critical coupling. Our work may provide a promising route for designing high-Q all-dielectric metasurface absorbers applied in ultrafast optoelectronic devices.

Subwavelength resolution using the near field of quantum emitters

Aziz Kolkiran

DOI: 10.1364/OL.514768 Received 30 Nov 2023; Accepted 04 Mar 2024; Posted 05 Mar 2024  View: PDF

Abstract: We propose a novel approach to super-resolution optical imaging by combining quantum optics and near-field optics. Our concept involves the utilization of single-photon quantum emitters to generate a stand-alone evanescent wave. We demonstrate that the quantum interference effects of point dipoles as single-photon emitters, in conjunction with their near-field, result in a higher resolution of sub-wavelength structures than systems that are only quantum-enhanced or only near-field-enhanced. We believe that nano-sized emitters could be employed to accomplish the goals of this research, taking into account the current progress in nanophotonics and quantum optics technology.

Sub-Doppler spectroscopy of the near-UV Cs atom 6S$_{1/2}$ - 7P$_{1/2}$ transition in a microfabricated vapor cell

Emmanuel Klinger, Andrei Mursa, Carlos Rivera-Aguilar, Remy Vicarini, Nicolas Passilly, and Rodolphe Boudot

DOI: 10.1364/OL.514866 Received 01 Dec 2023; Accepted 04 Mar 2024; Posted 05 Mar 2024  View: PDF

Abstract: We report on the characterization of sub-Doppler resonances detected by probing the 6S$_{1/2}$ - 7P$_{1/2}$ transition of Cs atom at 459 nm in a microfabricated vapor cell. The dependence of the sub-Doppler resonance (linewidth, amplitude) on some key experimental parameters, including the laser intensity and the cell temperature, is investigated. These narrow atomic resonances are of interest for high-resolution spectroscopy, instrumentation, and may constitute the basis of a near-UV microcell optical standard.

Extending the Reach of Multi-core Fiber via Voronoi Constellations with Concatenated Multi-level Coding

Can zhao, Bin Chen, Yi Lei, Shen Li, Jiaqi Cai, Daohui Hu, Wenkai fang, and Lin Sun

DOI: 10.1364/OL.517409 Received 12 Jan 2024; Accepted 04 Mar 2024; Posted 05 Mar 2024  View: PDF

Abstract: This paper proposes a novel coded modulation scheme for randomly-coupled multi-core fiber (RC-MCF) via multi-dimensional constellation with concatenated two-level multi-level coding (MLC). In the proposed system, the 16-dimensional (16D) Voronoi constellation (VC), naturally fitting with the sixteen degrees of freedom of a four-core fiber (two quadratures, two polarizations, and four cores), is generated by a latticed-based shaping method to provide higher shaping gains. Moreover, combining it with the concatenated two-level MLC can further achieve better performance-complexity tradeoff. It is demonstrated by simulation results of long-haul multi-channel RC-MCF transmission that, the proposed coded modulation scheme for four-core fiber transmission offers 77% reduction in the number of decoding operations, and up to 21% (585km) reach increase over the conventional bit-interleaved coded modulation scheme for quadrature amplitude modulation.

Optical phase encoding in pulsed approach to reservoircomputing

Johan Henaff, Matthieu Ansquer, Miguel Cornelles Soriano, Roberta Zambrini, Nicolas Treps, and Valentina Parigi

DOI: 10.1364/OL.518505 Received 23 Jan 2024; Accepted 04 Mar 2024; Posted 05 Mar 2024  View: PDF

Abstract: The exploitation of the full structure of multimode light fields enables compelling capabilities in many fields including classical and quantum information science. We exploit data-encoding on the optical phase of the pulses of a femtosecond laser source for a photonic implementation of a reservoir computing protocol. Rather than intensity detection, data-reading is done via homodyne detection that accesses combinations of amplitude and phase of the field. Numerical and experimental results on NARMA tasks and laser dynamic predictions are shown. We discuss perspectives for quantum enhanced protocols.

Unsupervised Spectral Reconstruction from RGB images under Two Lighting Conditions

Xuheng Cao, Yusheng Lian, Zilong Liu, Jin Li, and Kaixuan Wang

DOI: 10.1364/OL.517007 Received 27 Dec 2023; Accepted 04 Mar 2024; Posted 07 Mar 2024  View: PDF

Abstract: Unsupervised spectral reconstruction (SR) aims to recover the hyperspectral image (HSI) from corresponding RGB images without annotations. Existing SR methods achieve SR from single RGB image, hindered by the significant spectral distortion. Although several deep learning-based methods increase the SR accuracy by adding RGB image, their network are always designed for other image recovery task, leaving a huge room for improvement. To overcome this problem, we propose a novel approach that reconstructs the HSI from a pair of RGB images captured under two illuminations, significantly improving reconstruction accuracy. Specifically, an SR iterative model based on two illuminations is constructed at first. By unfolding the proximal gradient algorithm solving this SR model, an interpretable unsupervised deep network is proposed. All the modules in the proposed network have precise physical meanings, which enables our network have both superior performance and good generalization capability. Experimental results on two public datasets and our real-world images show the proposed method significantly improves both visually and quantitatively as compared with state-of-the-art methods.

Fast-beam-switching optical phased array for moving objects in wireless optical communication networks

Shichong Yang, Guihan Wu, Kaifei Tang, Fuhao Yu, Xiang Ji, Yu Xin, and Wei Jiang

DOI: 10.1364/OL.517454 Received 23 Jan 2024; Accepted 04 Mar 2024; Posted 04 Mar 2024  View: PDF

Abstract: For optical wireless communication systems, mechanical beam steering struggles to timely switch between multiple users or search for moving users. Here we demonstrate a fast-beam-switching optical phased array (OPA) for agile wireless communications networks. For point-to-multi-point (P2MP) scenarios, a setup of OPA-based fast beam switching between two aligned receivers was developed. A loss-free image transmission experiment was used to demonstrate the stability of switching. Furthermore, we have developed an approach to using the fast-switching OPA to follow the trajectory of moving objects so as to help enable agile random-access switching between moving objects. These results could help offer fast switching and reconfiguration for indoor wireless optical communications.

Optimized LNS-FAID of LDPC Codes: A Hybrid Precision Decoding Approach for 50G-PON

Yanchen Lyu, Ming Jiang, Mingyang Zhu, Xinyu Zhong, and Chunming Zhao

DOI: 10.1364/OL.520880 Received 16 Feb 2024; Accepted 03 Mar 2024; Posted 04 Mar 2024  View: PDF

Abstract: Efficient error correction in high-speed communication networks, such as the 50G passive optical network (50G-PON), is paramount. This letter focuses on optimizing a layered non-surjective finite alphabet iterative decoder (LNS-FAID) for 50G-PON, with an emphasis on high-throughput and low-power consumption. We propose using a distinct look-up table (LUT) for each iteration to enhance decoding performance and lower error floors. Additionally, we improve the 2-bit LNS-FAID architecture by adding operational states and a sign backtracking (SBT) strategy. This paper also introduces a hybrid precision model that merges 3-bit and 2-bit LNS-FAIDs, which balances error correction with computational efficiency. Our simulation results show that these approaches significantly improve performance of the LDPC code in 50G-PON.

Tailored fabrication of self-rolled-up AlGaN/GaN tubular structure with photoelectrochemical etching

Hyunsu Hwang, Seonghun Ahn, Hyun Gyu Song, Kie Young Woo, and Yong-Hoon Cho

DOI: 10.1364/OL.518076 Received 09 Jan 2024; Accepted 03 Mar 2024; Posted 06 Mar 2024  View: PDF

Abstract: Group III-nitride semiconductors with tubular structure have been considered to be applicable to various fields, such as optics, electronics, and chemical sensors. Thereafter, the method of tailored fabrication of the tubular structure is needed. In this research article, micro-sized tubular structures were fabricated through the rolling of a planar heterostructure composed of group III-nitride alloys, employing the photoelectrochemical (PEC) etching method. The rolling direction was precisely controlled using a triangular-shaped pattern with a stem structure created through photolithography. To customize the geometry of the tubular structure, an analytical calculation of strain and deformation was conducted for the AlGaN/GaN heterostructure. Subsequent to the calculation, an AlGaN/GaN/InGaN/n-GaN/sapphire structure was designed and fabricated using metal-organic chemical vapor deposition (MOCVD). Photolithography and PEC etching were employed to selectively etch the sacrificial layer, which in this study was a 5-nm thick InGaN layer. Micro-photoluminescence (μ-PL) and micro Raman spectroscopy were employed to examine the position-dependent strain in the tubular structure. The polarization-resolved PL measurement revealed strain anisotropy in the rolled-up microtube structure, emphasizing the importance of appropriate pattern design for achieving strain uniformity across the entire tubular structure.

Research on Phase Error of Sagnac Interferometer Induced by Modulation of Multifunctional Integrated Optical Modulator

Qiaohan Wang, xiaowu shu, and Ran Bi

DOI: 10.1364/OL.520702 Received 08 Feb 2024; Accepted 02 Mar 2024; Posted 06 Mar 2024  View: PDF

Abstract: The high-precision IFOG requires an optical sensitivity of up to 〖10〗^(-8) 〖rads〗^(-1) for interferometers, and noise and error are one of the main reasons limiting its accuracy improvement. Any possible source of signal error source is worth to be studied. This article describes the relevant research work on the modulation signal error caused by the energy loss of MIOC crystal mechanical vibration on the modulation signal. This article theoretically derives and simulates the frequency spectrum of energy loss from the perspective of electromechanical coupling, and verifies it through experiments. This article also verified the influence of MIOC mechanical loss on the output of SAGNAC interferometer through experiments. This study is an indispensable part of the bottleneck for improving the accuracy of ultra high precision closed-loop IFOG, and has potential engineering application value.

A data-driven method of super-resolution image recovery for speckle-illumination photoacoustic computed tomography

Tianhua Zhou, Boyi Li, Xin liu, and Dean Ta

DOI: 10.1364/OL.509788 Received 16 Nov 2023; Accepted 01 Mar 2024; Posted 05 Mar 2024  View: PDF

Abstract: Methods have been proposed in recent years aimed at pushing photoacoustic imaging resolution beyond the acoustic diffraction limit, among which those based on random speckle illumination show particular promise. In this Letter, we propose a data-driven deep learning approach to processing the added spatiotemporal information resulting from speckle illumination, where the neural network learns the distribution of absorbers from a series of different samplings of the imaged area. In ex-vivo experiments based on the tomography configuration with prominent artifacts, our method successfully breaks the acoustic diffraction limit, and delivers better results in identifying individual targets when compared against a selection of other leading methods.

Flexible GaN based ultraviolet VCSELs

Yang Mei, peng gu, shuai yang, Leiying Ying, and Baoping Zhang

DOI: 10.1364/OL.517756 Received 08 Jan 2024; Accepted 01 Mar 2024; Posted 04 Mar 2024  View: PDF

Abstract: Flexible opto-electronic platforms which integrate optoelectronic devices on a flexible substrate are promising in more complex working environments benefiting from the mechanical flexibility. Herein, for the first time to the best of our knowledge, a flexible GaN based vertical cavity surface-emitting laser (VCSEL) in the ultraviolet A (UVA) range was demonstrated by using a thin film transfer process based on laser lift-off (LLO) and spin-coating of a flexible substrate. The lasing wavelength is 376.5 nm with a linewidth of 0.6 nm and a threshold energy of 98.4 nJ/pulse, corresponding to a threshold energy density of 13.9 mJ/cm2. The flexible substrate in this study is directly formed by spin-coating of photosensitive epoxy resin, which is much more simplified and cost-effective, and a 2-inch wafer scale GaN based membrane can be successfully transferred to flexible substrate through this method. Such flexible UVA VCSELs are promising for the development of next-generation flexible and wearable technologies.

Cladding-pumped laser and amplifier for E- and S-bands based on multimode bismuth-doped GRIN fibers: toward “watt-level” output power

Alexander Vakhrushev, Andrey Umnikov, Alexandr Dostovalov, Konstantin Riumkin, Sergey Alyshev, Elena Firstova, Aleksandr Khegai, Mikhail Melkumov, Sergey Babin, and Sergey Firstov

DOI: 10.1364/OL.514236 Received 23 Nov 2023; Accepted 01 Mar 2024; Posted 01 Mar 2024  View: PDF

Abstract: In this paper, we investigated the potential scalability of output power of a cladding-pumped laser and a power amplifier (booster) based on multimode Bi-doped fiber (BDF) using mode-selection approach. We fabricated the multimode double-clad graded-index (GRIN) fiber with a confined Bi-doped germanosilicate glass core having a diameter of ≈30 and ≈60 μm. Using femtosecond (fs) inscription technology with high spatial resolution, Bragg gratings of a special transverse structure allowing the selection of low-order modes were written into the core of BDFs. The operation features of the cladding-pumped multimode bismuth-doped GRIN fiber lasers with the inscribed Bragg gratings having various reflection coefficients were investigated. In addition, the behaviorof the output power and beam quality (M² parameter) of the optical radiation of the developed devices was studied. The CW laser and booster operating at near 1.45 µm with a maximum output power of ≈0.8 W and ≈1 W, correspondingly, based on the 60-µm-core BDF under pumping by multimode laser diodes at 808 nm were developed, which are to the best of our knowledge the most powerful cladding-pumped BDF devices to date. Near single-mode lasing (M²<1.3) is demonstrated for 30-µm-core fiber. The experimental data open new possibilities to achieve higher powers in cladding-pumped BDF sources, which are more cost-effective compared to core-pumped counterparts.

Dual wavelength channel GHz repetition rate mode-locked VECSEL cavities sourced from a common gain medium

Simon Tsaoussis, Sadhvikas Addamane, R. Jason Jones, and Jerome Moloney

DOI: 10.1364/OL.516721 Received 22 Dec 2023; Accepted 01 Mar 2024; Posted 01 Mar 2024  View: PDF

Abstract: Mode-locked vertical external cavity semiconductor lasers are a unique class of nonlinear dynamical systems driven far from equilibrium. We present a novel experimental result, supported by rigorous microscopic simulations, of two coexisting mode-locked V-cavity configurations sourced by a common gain medium and operating as independent channels at angle controlled separated wavelengths. Microscopic simulations support pulses coincident on the common gain chip extracting photons from a nearby pair of coexisting kinetic holes burned in the carrier distributions.

Dissipative three-dimensional topological optical solitons with crossed localization of polarization components

Nikolay Veretenov, Sergey Fedorov, and Nikolay Rosanov

DOI: 10.1364/OL.520839 Received 06 Feb 2024; Accepted 29 Feb 2024; Posted 04 Mar 2024  View: PDF

Abstract: We present a new type of vector three-dimensional dissipative optical solitons with more extended degrees of freedom in a laser or laser medium with saturable absorption. These solitons are reconfigurable, includes polarization singularities and have various mutual orientation of nearly toroidal localization domains of polarization components. Numerical modeling confirm the stability of these solitons and breathers, and revealtheir symmetry and even "supersymmetry", as well as transformations when parameters leave the stability region. These solitons, which have no scalar analogues, are capable of carrying more than one bit of information. Our results expand the “alphabet” of solitons, and can provide a route to breakthroughs in larger-capacity communication and information applications.

A novel integrated approach for simultaneously measuring thermophysical parameters of semi-transparent materials

Yanfen Xu, Kaihua Zhang, Kun Yu, and Yufang Liu

DOI: 10.1364/OL.519601 Received 23 Jan 2024; Accepted 28 Feb 2024; Posted 01 Mar 2024  View: PDF

Abstract: To concurrently determine the thermophysical parameters of semi-transparent materials, a novel integrated approach for concurrent measurement is proposed. In the measurement setup, a high-temperature radiation source and a beam reducer are employed to minimize the influence of background radiation. In order to differentiate between transmitted and emitted radiation in the detection signal, the radiation signals from the radiation source are measured under four different conditions, enabling the calculation of transmissivity, emissivity, and reflectivity. The reliability and accuracy of the measurement method are validated by the thermophysical parameters of sapphire, an infrared window material. The results demonstrate a strong agreement between the measured data and previous findings, highlighting the novel contribution of this method in investigating the thermophysical parameters of semi-transparent materials.

Topological Corner State Localized Bound States in Continuum in Photonic Crystals

Zhenbin Zhang, Banxian Ruan, Enduo Gao, Chao Liu, and Hongjian Li

DOI: 10.1364/OL.517816 Received 05 Jan 2024; Accepted 28 Feb 2024; Posted 28 Feb 2024  View: PDF

Abstract: In the field of optics, bound states in the continuum (BICs) are of significant practical importance as they can trap electromagnetic waves spatially, even though their frequency lies within the continuous spectrum. Previous research, however, has shown that BICs localized in optical cavities are highly sensitive to geometric and environmental changes. This sensitivity implies that slight variations can lead to the loss of BICs, necessitating extreme precision in manufacturing, which poses a challenge for practical implementation. To overcome this issue, this study employs topological photonic crystals (PhCs) to engineer topological corner states (TCS) within PhCs. By doing so, it establishes a method for creating topological BICs that are inherently robust against disturbances, thereby enhancing their suitability for real-world applications.

Highly efficient upconversion luminescence in narrow-bandgap Y2Mo4O15

wen You, xiaomin Zhang, Ruoxi Yu, Chao Chen, mingxing li, Gencai Pan, and Yanli Mao

DOI: 10.1364/OL.519702 Received 25 Jan 2024; Accepted 28 Feb 2024; Posted 28 Feb 2024  View: PDF

Abstract: Lanthanide-ion-doped upconversion materials have been extensively investigated for their unique capability to convert low-energy excitation into high-energy emission. Contrary to previous reports suggesting that efficient upconversion luminescence is exclusively observed in materials with a wide bandgap, we have discovered in this study that Y2Mo4O15:Yb3+/Tm3+ microcrystals, a narrowband material, exhibit highly efficient upconversion emission. Remarkably, these microcrystals do not display any four or five-photon upconversion emission bands. This particular optical phenomenon is independent of the variation in doping ion concentration, temperature, phonon energy and excitation power density. Combining theoretical calculations and experimental results, we attribute the vanishing emission bands to the strong interaction between the bandgap of the Y2Mo4O15 host matrix (3.37 eV) and the high energy levels (1I6 and 1D2) of Tm3+ ions. This interaction can effectively catalyze the upconversion emission process of Tm3+ ions, which leads to Y2Mo4O15:Yb3+/Tm3+ microcrystals possessing very strong upconversion luminescence intensity. The brightness of these microcrystals outshines commercial upconversion NaYF4:Yb3+,Er3+ green phosphors by a factor of 10 and is 1.4 times greater than that of upconversion NaYF4:Yb3+,Tm3+ blue phosphors. Ultimately, Y2Mo4O15:Yb3+/Tm3+ microcrystals, with their distinctive optical characteristics, are being tailored for sophisticated anti-counterfeiting and information encryption applications.

All-solid-state 3-μm single-frequency Er:CaF₂ laser with stable and switchable wavelength

mengyu zong, Zhen Zhang, jingjing Liu, Jie Liu, and Liangbi Su

DOI: 10.1364/OL.519873 Received 25 Jan 2024; Accepted 28 Feb 2024; Posted 28 Feb 2024  View: PDF

Abstract: We have demonstrated a 3-μm all-solid-state single-frequency laser with a stable center frequency and switchable wavelength us-ing the intra-cavity Fabry-Pérot etalons method. Experimentally, the central wavelengths of the laser for single longitudinal mode are 2728 nm and 2794 nm, with maximum output powers of 268 mW and 440 mW, respectively. The corresponding sin-gle-longitudinal mode linewidths are 25 MHz and 11 MHz. In particular, the central wavelengths of the single-longitudinal mode laser remain almost constant as the incident pump power increases. In the 3 μm region, this study represents the first instance of using a laser diode to directly pump Er:CaF₂ block single crystals for single-frequency lasers. Additionally, it achieves the highest output power of 3 μm all-solid-state single-longitudinal mode, to the best of our knowledge.

Broadband chaos generation in a distributed-feedback laser by selecting residual side modes

Luan Zhang and Sze-Chun Chan

DOI: 10.1364/OL.518915 Received 15 Jan 2024; Accepted 27 Feb 2024; Posted 28 Feb 2024  View: PDF

Abstract: Chaotic dynamics with spectral broadening is experimentally obtained by selective excitation of residual side modes in a distributed-feedback (DFB) laser. For the single-mode laser that emits only at the main mode when free-running, feedback to a residual side mode is introduced via a fiber Bragg grating (FBG). The FBG feedback suppresses the main mode, selectively excites the residual side mode, and generates a broadband chaotic dynamics. Such a chaos of the residual side mode has a broad electrical bandwidth reaching at least 26 GHz, which corresponds to a significant broadening by over 50% when compared with the main mode. The dynamics is attributed entirely to the one selected mode without invoking multimode interactions. The wavelength is tunable beyond 10 nm by using different FBGs. Through avoiding multimode interactions, this approach of broadband chaos generation is potentially simple to model and thus promising for applications.

The microscopic behavior of time-reversed electromagnetic fields in anisotropic media

Elias Le Boudec, Nicolas Mora, Farhad Rachidi-Haeri, Marcos Rubinstein, and Felix Vega

DOI: 10.1364/OL.510604 Received 16 Nov 2023; Accepted 27 Feb 2024; Posted 28 Feb 2024  View: PDF

Abstract: Electromagnetic time reversal is commonly used for field imaging and focusing. This method relies on the time-reversal invariance of the wave equation in most media and has been shown to reliably leverage medium inhomogeneities such as scatterers to achieve high spatial resolution and temporal compression. This paper builds upon the main theoretical framework, the time reversal cavity. We study the microscopic behavior of the fields using modern methods of mathematical physics involving Colombeau generalized functions and Schwartz distributions. This approach allows for a direct expression of time-reversed fields valid for the electric and magnetic fields in time-reversal invariant (and possibly nonreciprocal) media. Moreover, the results hold for any arbitrary localized source and can readily be applied beyond the dipole approximation. Finally, a general result allows the prediction of the quality of focusing of the time-reversed fields as a function of the electrical permittivity and the magnetic permeability tensors in homogeneous anisotropic media, which contributes to the understanding of time reversal in complex media such as super-resolution enabling metamaterials.

EO nonlinear function generator

Zhangqi Dang, Zeyu Deng, Tao Chen, Zhenming Ding, and Ziyang Zhang

DOI: 10.1364/OL.514381 Received 27 Nov 2023; Accepted 27 Feb 2024; Posted 28 Feb 2024  View: PDF

Abstract: An electro-optical programmable nonlinear function generator (PNFG) is developed on a multimode waveguide with four parallel thermal electrodes. The current on one electrode is chosen as the input, while the rest serve as function-defining units to modulate the multimode interference. The electro-thermo-optical effects are analyzed step by step and the impact on the eigenmode properties is derived. It shows that the optical output power variation by altered interference, in response to the input current, manifests as a complex ensemble of functions in general. The PNFG aims to find the special setting under which such relation can be simplified into some basic function. Through an optimization program, a variety of such functions are found, including Sigmoid, SiLU, and Gaussian. Furthermore, the shape of these functions can be adjusted by finetuning the defining units. This device may be integrated in a large-scale photonic computing network that can tackle complex problems with nonlinear function adaptability.

Scan-less 3D microscopy based on spatiotemporal encoding on a single-cavity dual-comb laser

Wanping Lu, Zhiwei Zhu, Benjamin Willenberg, Justinas Pupeikis, Christopher Phillips, Ursula Keller, and Shih-Chi CHEN

DOI: 10.1364/OL.507661 Received 06 Oct 2023; Accepted 27 Feb 2024; Posted 29 Feb 2024  View: PDF

Abstract: Dual-comb microscopy enables high-speed and high-precision optical sampling by simultaneously extracting both amplitude and phase information from the interference signals with frequency division multiplexing. In this letter, we introduce a spatiotemporal encoding approach for dual-comb microscopy that overcomes previous limitations such as mechanical scanning, low sampling efficiency, and system complexity. By employing free-space angular-chirp-enhanced delay (FACED) and a low-noise single-cavity dual-comb laser, we achieve scan-less 3D imaging with nanometer precision and a 3D distance-imaging rate of 330 Hz, restricted only by the repetition rate difference of the dual-comb laser. Specifically, the FACED unit linearly arranges the laser beam into an array. A grating subsequently disperses this array transversely into lines, facilitating ultrafast spectroscopic applications that are 1-2 orders of magnitude quicker than traditional dual-comb methods. This spatiotemporal encoding also eases the stringent conditions on various dual-comb laser parameters, such as repetition rates, coherence, and stability. Through carefully designed experiments, we demonstrate that our scan-less system can measure 3D profiles of microfabricated structures at a rate of 7 million pixels per second. Our method significantly enhances measurement speed while maintaining high precision, using a compact light source.

Octave soliton microcombs in the lithium niobate microresonators

Pi-Yu Wang, Shuai Wan, Rui Ma, Wei Li, Fang Bo, Guang-can Guo, and Chunhua Dong

DOI: 10.1364/OL.514893 Received 01 Dec 2023; Accepted 27 Feb 2024; Posted 27 Feb 2024  View: PDF

Abstract: Soliton microcombs are regarded as an ideal platform for the applications such as optical communications, optical sensing, low-noise microwave sources, optical atomic clocks, and frequency synthesizers. Many of these applications require a broad comb spectrum that covers an octave, essential for implementing the f − 2 f self-referencing techniques. In this work, we have successfully generated an octave-spanning soliton microcomb based on a z-cut Thin-film lithium niobate (TFLN) microresonator. This achievement is realized under on-chip optical pumping at 340 mW, and through extensive research into the broadening of dual dispersion waves. Furthermore, the repetition rate of the octave soliton microcomb is accurately measured using an electro-optic comb generated by an x-cut TFLN racetrack microresonator. Our results represent a crucial step towards the realization of practical, integrated and fully stabilized soliton microcomb systems based on TFLN.

Vectorial holography over a multimode fiber

Haotian Liu, jianwei Ye, Pengbai Xu, LEIMING WU, Yi Xu, and Yuwen Qin

DOI: 10.1364/OL.513636 Received 16 Nov 2023; Accepted 26 Feb 2024; Posted 27 Feb 2024  View: PDF

Abstract: Vectorial holography through a strongly scattering medium can facilitate various applications in optics and photonics. However, the realization of vectorial holography with arbitrary distribution of optical intensity is still limited because of experimental noise during the calibration of vectorial transmission matrix (TM) and reconstruction noise during the retrieval of input wavefront for a given holographic target. Herein, we propose and experimentally demonstrate the vectorial holography with arbitrary distribution of optical intensity over a multimode fiber (MMF) using the Tikhonov regularization. By optimizing the noise factor, the performance of vectorial holography over an MMF is improved compared with the conjugate transpose and inverse TM methods. Our results might shed new light on the optical communication and detection mediated by MMFs.

NANOSCALE SURFACE METROLOGY WITH LIQUID CRYSTAL BASED PHASE SHIFTING ANGULAR SHEARING INTERFEROMETER

Debasish Bag, Susanta Chakraborty, and Aloka Sinha

DOI: 10.1364/OL.514441 Received 30 Nov 2023; Accepted 26 Feb 2024; Posted 28 Feb 2024  View: PDF

Abstract: In this letter, a phase-shifting angular shearing interferometer has been proposed for the application in optical surface metrology by using a combination of wedge-shaped liquid crystal (LC) cell and a polarization phase shifter. The demonstration of this angular shearing interferometer for step-height measurement is accomplished with the help of phase shifting technique. Four phase-shifted interferograms produced by a geometrical phase shifter are subjected to a simplified Weiner deconvolution method, which resembles a simple analysis technique for shearing interferograms in comparison to alternative approaches. A simulation study has been conducted to validate the proposed technique. The experimental results show an accuracy of 5.56% for determining the step height, which also agrees with the results obtained through Atomic Force Microscopy. Owing to the tunability of birefringence, the proposed LC based angular shearing interferometry technique will be useful to control the spatial resolution in optical metrology.

Longitudinal imaging of vitreal hyperreflective foci in mice with acute optic nerve damage using visible-light optical coherence tomography

Weijia Fan, David Miller, Shichu Chang, JUNGHUN KWON, Wei-Hong Yeo, Marta Grannonico, Xiaorong Liu, and Hao Zhang

DOI: 10.1364/OL.512029 Received 14 Dec 2023; Accepted 25 Feb 2024; Posted 04 Mar 2024  View: PDF

Abstract: Hyperreflective foci (HRF) appear in optical coherence tomography (OCT) images of the retina and vitreous of patients with various ocular diseases, including uveitis, diabetic retinopathy, age-related macular degeneration, and glaucoma. HRF are hypothesized to be immune cells that appear in response to ischemia or tissue damage. To accurately identify HRF and establish their clinical significance, it is necessary to replicate the detection of similar patterns in vivo in a small animal model. We combined visible-light OCT with temporal speckle averaging (TSA) to visualize and track vitreal HRF (VHRF) densities for three days after optic nerve crush (ONC) injury. Resulting vis-OCT images revealed that VHRF density significantly increased approximately 10-fold at 12 hours after ONC and returned to baseline three days after ONC.

Bifocal photon-sieve imaging in hard X-ray region

Xiaojun Bai, Junyong Zhang, Huiya Liu, and Cheng Liu

DOI: 10.1364/OL.519852 Received 25 Jan 2024; Accepted 25 Feb 2024; Posted 27 Feb 2024  View: PDF

Abstract: Hard X-rays are widely used for plasma diagnosis, non-destructive inspection, and high-resolution X-ray imaging. A typical X-ray source is a table-top micro-focus X-ray source. Here, a bifocal photon sieve (PS) with the smallest diameter of 59.6 nm was designed and fabricated by electron-beam lithography to focus hard X-rays on variable-resolution array images. An imaging experiment at 8.39 keV demonstrates that PS can provide considerably more functionality than a Fresnel zone plate (FZP) in that the first has large amounts of pinholes to be optimized, while the latter has a finite number of transparent rings to be used directly. A multi-focal PS provides the possibility of splitting X-rays and further extends interferometry from visible light to hard X-rays.

Spectrally resolved nonlinearities within a laser pulse in a single-scan and spectrometer-based nonlinear optical probing

Jitendra Acharyya, Albin KURIAKOSE, and G. Vijaya Prakash

DOI: 10.1364/OL.520803 Received 05 Feb 2024; Accepted 25 Feb 2024; Posted 27 Feb 2024  View: PDF

Abstract: The intricate spectrally resolved optical nonlinearities from spectrally broad femtosecond Gaussian laser pulse have been unraveled using a single-scan and spectrometer-based nonlinear optical probing technique. The interaction of the broad femtosecond laser pulse with a strongly absorbing porphyrin dye has unveiled a remarkably distinct nonlinear absorption behavior across the broad spectral window. The nonlinear absorption behavior reveals an unusual transition from the reverse saturation absorption (RSA) to the saturation absorption (SA) as we sweep the wavelength at both sides of the central wavelength. A competition between band-filling and excited-state absorption results in such a dramatic switch over from RSA to SA due to the variation of the intensity distribution across the Gaussian pulse spectrum. On the other hand, the nonlinear refraction studies dictate more over constant positive nonlinear refractive indices across the entire laser pulse, with a pronounced contribution from nonlinear absorption phase dominating at the center of the pulse. The presented technique establishes a robust and simple spectrometer-based technique which offers new avenues for the estimation of optical nonlinearities for rapid nonlinear optical measurements.

A Multi-Harmonic NIR-UV Dual-Comb Spectrometer

Kristina Chang, Daniel Lesko, Carter Mashburn, Peter Chang, Eugene Tsao, Alexander Lind, and Scott Diddams

DOI: 10.1364/OL.515776 Received 15 Dec 2023; Accepted 25 Feb 2024; Posted 26 Feb 2024  View: PDF

Abstract: Dual-comb spectroscopy in the ultraviolet (UV) and visible would enable broad bandwidth electronic spectroscopy with unprecedented frequency resolution. However, there are significant challenges in generation, detection and processing of dual-comb data that have restricted its progress in this spectral region. In this work, we leverage robust 1550 nm few-cycle pulses to generate frequency combs in the UV-visible. We couple this source to a wavelength multiplexed dual-comb spectrometer and simultaneously retrieve 100 MHz comb-mode-resolved spectra over three distinct harmonics spanning 380-800 nm. The experiments highlight the path to continuous dual-comb coverage spanning 200-750 nm, offering extensive access to electronic transitions in atoms, molecules, and solids

Optical wireless communication using flexible and waterproof perovskite color converter

Feifei Qin, Feng Chen, Yue Cao, Linning Wang, Chenwei Wang, Yanan Liao, Yuhang Dai, Junfeng Lu, Xinru Lan, Xu Wang, xianwu tang, Xiaoyan Liu, Gangyi Zhu, and yongjin wang

DOI: 10.1364/OL.518687 Received 12 Jan 2024; Accepted 25 Feb 2024; Posted 15 Mar 2024  View: PDF

Abstract: In this paper, the CH3NH3PbBr3 nanocrystals are embedded into the interstices of the fluorine (polyvinyl fluoride/polyvinylidene fluoride, PVF/PVDF) matrix on polyethylene terephthalate (PET) substrate to introduce a new advantage, such as flexible and waterproof, while maintaining the high optical performance of perovskites. The sample's photoluminescence (PL) spectra under 325 nm laser is green emission peaked at 537 nm with full width at half maximum (FWHM) of about 21.5 nm and a fast PL decay time. As a color converter, it shows high optical absorption and can transform light from solar-blind ultraviolet to blue region into green region in air, water, and bending conditions. While excited by 270 nm ultraviolet light emitting diode (LED), the system's observed -3dB bandwidth with the color converter is near 4.4 MHz in air and water condition with well-eye diagrams at a data rate of 30 Mbps. Finally, we demonstrate an audio transmission application with an ultraviolet light source, color conversion layer, and low-cost silicon-based photodetector.

Towards high-energy few-cycle optical vortices with minimized topological charge dispersion

Federico Furch and Gunnar Arisholm

DOI: 10.1364/OL.509316 Received 17 Oct 2023; Accepted 23 Feb 2024; Posted 23 Feb 2024  View: PDF

Abstract: A simple approach to generate high energy few-cycle optical vortices with minimized topological charge dispersion is introduced. By means of numerical simulations it is shown that, by leveraging the intrinsic properties of optical parametric chirped pulse amplification (OPCPA), clean transfer of topological charge from a high energy narrowband pump pulse to a broadband idler is feasible under certain particular conditions, enabling the generation of high energy few-cycle vortex pulses with extremely low topological charge dispersion.

Vortex retarder-based Stokes polarimeters: optimal data processing and autocalibration capability

Xiaobo Li and Francois Goudail

DOI: 10.1364/OL.519554 Received 23 Jan 2024; Accepted 23 Feb 2024; Posted 23 Feb 2024  View: PDF

Abstract: We present a full Stokes polarimeter that utilizes a vortex retarder (VR) in conjunction with a polarization camera. We demonstrate its capability to estimate the full Stokes vector in a single shot with optimal precision and to autocalibrate the VR retardance, ensuring precise measurements even in dynamic environments where retardance is variable.

Dual-comb spectroscopy at a fast rate in the water-transparent 8-12 μm region

Luca Moretti, Mathieu Walsh, Nawaf Abualsaud, Davide Gatti, Marco Lamperti, Jérôme Genest, Aamir Farooq, and Marco Marangoni

DOI: 10.1364/OL.515199 Received 07 Dec 2023; Accepted 23 Feb 2024; Posted 28 Feb 2024  View: PDF

Abstract: We introduce a dual-comb spectrometer based on Erbium-fiber oscillators at 250 MHz that operates in the 8-12 μm spectral range over optical bandwidths up to 9 THz with a multi-kHz acquisition rate. Over an observation bandwidth of 0.8 THz, the signal-to-noise ratio per spectral point reaches 168 Hz⁰·⁵ at an acquisition rate of 26 kHz, which allows investigation of transient processes in the gas phase at high temporal resolution. The system also represents an attractive solution for multispecies atmospheric gas detection in open paths due to the water transparency of the spectral window, the use of thermo-electrically cooled detectors and the out-of-loop phase correction of the interferograms.

Vibration-insensitive polarimetric fiber optic current sensor based on orbital angular momentum modes in air-core optical fiber

Lina Xiang, Fufei Pang, zhongyin Xiao, Liang Zhang, Heming Wei, mengshi zhu, Siddharth Ramachandran, and Tingyun Wang

DOI: 10.1364/OL.519974 Received 26 Jan 2024; Accepted 23 Feb 2024; Posted 28 Feb 2024  View: PDF

Abstract: Current or magnetic field sensing is usually achieved by exploiting the Faraday effect of an optical material combined with an interferometric probe that provides the sensitivity. Being interferometric in nature, such sensors are typically sensitive to several other environmental parameters such as vibrations and mechanical disturbances, which however inevitably impose the inaccuracy and instability of the detection. Here we demonstrate a polarimetric fiber optic current sensor based on orbital angular momentum modes of an air-core optical fiber. In the fiber, spin-orbit interactions imply that the circular birefringence, that is sensitive to applied currents or resultant magnetic fields, is naturally resilient to mechanical vibrations. The sensor, which effectively measures polarization rotation at the output of a fiber in a magnetic field, exhibits high linearity in the measured signal versus applied current that induces the magnetic field, with a sensitivity of 0.00128 rad/A and a noise limit of 1×10^(-5)/√Hz. The measured polarization varies within only ±0.1% under mechanical vibrations with the frequency of up to 800 Hz, validating the robust environmental performance of the sensor.

Ultra-broadband TM-pass polarizer based on anisotropic metamaterials in lithium niobate on insulator

Xu Han, Rui Cheng, liang huang, Panpan Yu, Lantian Feng, Guanghui Ren, Arnan Mitchell, Yonghui Tian, Xifeng Ren, and haojie xia

DOI: 10.1364/OL.517103 Received 27 Dec 2023; Accepted 22 Feb 2024; Posted 28 Feb 2024  View: PDF

Abstract: An ultra-broadband TM-pass polarizer is designed, fabricated and experimentally demonstrated based on subwavelength grating (SWG) metamaterials in a lithium niobate on insulator (LNOI) platform. According to our simulation, the designed device is predicted to work at a 220 nm wavelength range from 1460 to 1680 nm, covering the S-, C-, L-, U- bands of optical fiber communication. By depositing and subsequently etching a silicon nitride thin film atop the LNOI chip, SWG structures are successfully formed by using complementary metal-oxide semiconductor (CMOS)-compatible fabrication processes. The measured results show a high polarization extinction ratio larger than 20 dB and relatively low insertion loss below 2.5 dB over a 130 nm wavelength range from 1500 to 1630 nm, mainly limited by the operation bandwidth of our laser source.

Dalton’s law of partial optical thermodynamic pressures in highly multimoded nonlinear photonic systems

Huizhong Ren, Georgios Pyrialakos, Fan Wu, Nikolaos Efremidis, Mercedeh Khajavikhan, and Demetrios Christodoulides

DOI: 10.1364/OL.517715 Received 03 Jan 2024; Accepted 22 Feb 2024; Posted 01 Mar 2024  View: PDF

Abstract: We show that in highly multimoded nonlinear photonic systems, the optical thermodynamic pressures emerging from different species of the optical field obey Dalton’s law of partial pressures. Under thermal equilibrium conditions, we formally derive an equation that establishes a direct link between the partial thermodynamic pressures and the electrodynamic radiation pressures exerted by each polarization species. Our theoretical framework provides a straightforward approach for quantifying the total radiation pressure through the system’s thermodynamics variables without invoking the Maxwell stress tensor formalism. In essence, we show that the total electrodynamic pressure in such arrangements can be obtained in an effortless manner from initial excitation conditions, thus avoiding time-consuming simulations of the utterly complex multimode dynamics. To illustrate the validity of our results, we carry out numerical simulations in multimoded nonlinear optical structures supporting two polarization species and demonstrate excellent agreement with the Maxwell stress tensor method.

Integrated Visible-Light Polarization Rotators and Splitters for Atomic Quantum Systems

Ashton Hattori, Tal Sneh, Milica Notaros, Sabrina Corsetti, Patrick Callahan, Dave Kharas, Thomas Mahony, Robert McConnell, John Chiaverini, and Jelena Notaros

DOI: 10.1364/OL.509747 Received 18 Oct 2023; Accepted 22 Feb 2024; Posted 23 Feb 2024  View: PDF

Abstract: In this work, we design and experimentally demonstrate the first integrated polarization splitters and rotators at blue wavelengths. We develop compact and efficient designs for both a polarization splitter and rotator at a 422-nm wavelength, an important laser-cooling transition for 88Sr+ ions. These devices are fabricated in a 200-mm wafer-scale process and experimentally demonstrated, resulting in a measured polarization-splitter TE thru-port coupling of 98.0% and TM tap-port coupling of 77.6% for a compact 16-µm-long device, and a polarization-rotator conversion efficiency of 92.2% for a separate compact 111-µm-long device. This work paves the way for more sophisticated integrated control of trapped-ion and neutral-atom quantum systems.

Widefield Functional Speckle-correlation Optical Scattering Mesoscope Towards Hemodynamic Imaging

Ruifeng Zhang, Liang Fei, Xiangru Liu, Yunxu Sun, Xiaochuan Xu, Shutian Liu, Zhengjun Liu, Lingji Xu, and Wei Liu

DOI: 10.1364/OL.519610 Received 24 Jan 2024; Accepted 22 Feb 2024; Posted 26 Feb 2024  View: PDF

Abstract: Speckle-correlation optical scattering imaging (SCOSI) has shown the potential for noninvasive biomedical diagnostics applications, which directly utilizes the scattering patterns to reconstruct the deep and non-line-of-sight objects. However, the course of the translation of this technique to preclinical biomedical imaging applications has been postponed by the following two facts: 1) the field of view of SCOSI was significantly limited by the optical memory effect, and 2) the molecular-targeted functional imaging of the biological tissues remains largely unexplored. In this work, a proof-of-concept design of the widefield functional SCOSI (WF-SCOSI) was presented for achieving mesoscopic mapping of fluid structure and speed, which was realized by simultaneously implementing the concepts of scanning synthesis and fluorescence scattering flowmetry. The ex vivo imaging results of the fluorescence-labelled large-scale vessel network phantom underneath the scatters demonstrated the effectiveness of WF-SCOSI towards non-invasive hemodynamic imaging applications.

Enhanced Evanescent Field via Integration of Graphene Oxide/PMMA Hybrid Film on Coreless D-shaped Fibers

Bing Sun, Kai Wan, Kaiming Zhou, Zhendong Huang, and Zuxing Zhang

DOI: 10.1364/OL.507194 Received 02 Oct 2023; Accepted 22 Feb 2024; Posted 27 Feb 2024  View: PDF

Abstract: We present the first-ever demonstration of an evanescent field-based sensing structure utilizing a graphene oxide/poly(methyl methacrylate) (PMMA) hybrid film integrated on coreless D-shaped fibers (cDsFs). Theoretical and experimental analyses were conducted to elucidate the internal working mechanism of the hybrid film-coated cDsF (GoP-cDsF). Additionally, the performance of the cDsF with the PMMA film alone was employed as a reference for comparison. Our findings underscore the significant role played by the graphene oxide in enhancing the evanescent field, leading to a synergistic effect that contributes to the overall enhancement of the device's evanescent field. Consequently, the as-fabricated GoP-cDsF sensor demonstrates a remarkable sensitivity of -4.936 nm/°C, making it highly suitable for high-sensitivity temperature sensing applications. Furthermore, these attributes position the GoP-cDsF as a promising candidate for measuring both magnetic and electric fields, thereby offering a viable strategy for multifunctional sensing applications.

Regulation of laser-induced nanogratings by tuning Marangoni-SPPs coupling effect

Kang Xu, Lingyu Huang, Xuanzheng Zhou, Mandong Zheng, Min Wang, and Shaolin Xu

DOI: 10.1364/OL.517787 Received 10 Jan 2024; Accepted 21 Feb 2024; Posted 22 Feb 2024  View: PDF

Abstract: Laser-induced subwavelength nanogratings on films find widespread applications in enhancing spectrum detection or creating metasurfaces through surface plasmon excitation. It is still challenging to achieve a high degree of uniformity, diversity, and controllability due to the intricate interplay between two basic mechanisms in laser nanostructuring: the Marangoni effect and surface plasmon polaritons (SPPs). Here, we tune the coupling effect on Ge2Sb2Te5 films by adjusting the laser polarization, whose components control the two effects’ strength ratio, where the Marangoni effect dominates when the direction of SPPs mismatches with the growing direction of nanogratings. Tuning this competition relationship helps to create large-area regulated nanogratings with tunability in duty cycle and distribution, which are significant for light modulation applications. A highly efficient direct writing method with a line-shaped laser beam is employed to create large-area nanogratings at the same time to enhance the effect tuning. We further demonstrate diverse Au nanogratings with the aid of a liftoff operation, and apply them in surface plasmon-coupled emission (SPCE), showcasing exceptional enhancement and narrowing performance.

Observation of quantum correlated twin beams in cascaded nonlinear interactions

Salvatore Castrignano, Iolanda Ricciardi, Pasquale Maddaloni, Paolo De Natale, Stefan Wabnitz, and Maurizio De Rosa

DOI: 10.1364/OL.514976 Received 11 Dec 2023; Accepted 20 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: We report on the generation of twin beams through a cascaded process of optical parametric oscillation in a doubly resonant second-harmonic generation system. These bright beams exhibit strong quantum correlation, enabling the observation of up to 5 dB of noise reduction in their intensity difference below the standard quantum limit.

Interplay of gain and loss in arrays of nonlinear plasmonic nanoparticles: toward parametric downconversion and amplification

Syed Shah, Michael Clark, Joseph Zyss, Maxim Sukharev, and Andrei Piryatinski

DOI: 10.1364/OL.515621 Received 11 Dec 2023; Accepted 20 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: With the help of a theoretical model and finite-difference-time-domain simulations based on the hydrodynamic-Maxwell model, we examine the effect of difference frequency generation in an array of L-shaped metal nano-particles characterized by intrinsic plasmonic nonlinearity. The outcomes of the calculations reveal the spectral interplay of the gain and loss in the vicinity of the fundamental frequency of the localized surface-plasmon resonances. Subsequently, we identify different array depths and pumping regimes facilitating parametric amplification and parametric down-conversion. Our results suggest that the parametric amplificationregime becomes feasible on a scale of hundreds of nanometers and parametric downconversion on the scale of tens of nanometers, opening up new exciting opportunities for developing building blocks of photonic metasurfaces.

High-Efficiency Radiation-Balanced Yb-Doped Silica Fiber Laser With 200-mW Output

Enkeleda Balliu, Bailey Meehan, Mary Ann Cahoon, Thomas Hawkins, John Ballato, Peter Dragic, Tommy Boilard, Lauris Talbot, Martin Bernier, and Michel Digonnet

DOI: 10.1364/OL.517568 Received 02 Jan 2024; Accepted 18 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: The focus of this study was the development of a second generation of fiber lasers internally cooled by anti-Stokes fluorescence. The laser consisted of a length of single-mode fiber spliced to fiber Bragg gratings to form the optical resonator. The fiber was single-moded at the pump (1040 nm) and signal (1064 nm) wavelengths. Its core was heavily doped with Yb, in the initial form of CaF2 nanoparticles, and co-doped with Al to reduce quenching and improve the cooling efficiency. After optimizing the fiber length (4.1 m) and output-coupler reflectivity (3.3%), the fiber laser exhibited a threshold of 160 mW, an optical efficiency of 56.8%, and a radiation-balanced output power (no net heat generation) of 192 mW. On all three metrics, this performance is significantly better than the only previously reported radiation-balanced fiber laser, which is even more meaningful given that the small size of the single-mode fiber core (7.8-µm diameter). At the maximum output power (~2 W), the average fiber temperature was still barely above room temperature (470 mK). This work demonstrates that with anti-Stokes pumping, it is possible to induce significant gain and energy storage in a small-core Yb-doped fiber while keeping the fiber cool.

Computer-generated holography with ordinary display

Otoya Shigematsu, Makoto Naruse, and Ryoichi Horisaki

DOI: 10.1364/OL.516005 Received 19 Dec 2023; Accepted 18 Feb 2024; Posted 20 Feb 2024  View: PDF

Abstract: We propose a method of computer-generated holography (CGH) using incoherent light emitted from a mobile phone screen. In this method, we suppose a cascade of holograms in which the first hologram is a color image displayed on the mobile phone screen. The hologram cascade is synthesized by solving an inverse problem with respect to the propagation of incoherent light. We demonstrate three-dimensional color image reproduction using a two-layered hologram cascade composed of an iPhone and a spatial light modulator.

Dynamic beam steering for wireless optical power transfer in IoT applications

NGOC-LUU NGUYEN, Khanh-Hung Nguyen, Nadeem Javed, and Jinyong Ha

DOI: 10.1364/OL.518243 Received 12 Jan 2024; Accepted 13 Feb 2024; Posted 21 Feb 2024  View: PDF

Abstract: The alignment of a receiver with pencil beam in a wireless optical power transfer (WOPT) system employing resonance beam charging (RBC) technology limits the establishment of a resonance cavity. Accurate tracking necessitates precise and dependable monitoring, which requires the exact placement of transmitting and receiving devices. Herein, we present a concept of a two-dimensional (2D) beam steering mechanism for RBC-based WOPT systems utilizing dispersed laser beams. The proposed approach allows significant improvement, including reduction of scanning times and minimization of errors, in relation to conventional pencil-beam-based systems. Experimental results reveal an improvement of 121.01% in the efficiency of acquisition time, a reduction of 81.09% in pointing errors, and 75.4% increase in tracking performance. These results establish the prerequisites for the implementation of dispersed beam steering in the RBC-based WOPT system. This capability empowers the system to charge movable devices and Internet of Things devices consistently in smart factories.

Off-plane quartz-enhanced photoacoustic spectroscopy

Huijian Luo, Junming Li, Haohua Lv, Jiabao Xie, Chenglong Wang, Haoyang Lin, Ruobin Zhuang, Wenguo Zhu, Yongchun Zhong, Ruifeng Kan, JianHui Yu, and Huadan Zheng

DOI: 10.1364/OL.506650 Received 25 Sep 2023; Accepted 01 Jan 2024; Posted 31 Jan 2024  View: PDF

Abstract: In this work, we developed off-plane quartz-enhanced photoacoustic spectroscopy (OP-QEPAS). In the OP-QEPAS the light beam neither went through the prong spacing of the quartz tuning fork (QTF), nor in the QTF plane. The light beam is in parallel with the QTF with an optimal distance, resulting in low background noise. A radial-cavity (RC) resonator was coupled with the QTF to enhance the photoacoustic signal by radial resonance mode. By offsetting both the QTF and the laser position from the central axis, we enhance the effect of acoustic radial resonance and prevent the noise generated by direct laser irradiation of the QTF. Compared to IP-QEPAS based on a bare QTF, the developed OP-QEPAS with a RC resonator showed a >10× signal-to-noise ratio (SNR) enhancement. The OP-QEPAS system has great advantages in the use of light emitting devices (LEDs), long-wavelength laser sources such as mid-infrared quantum cascade lasers, and terahertz sources. When employing a LED as excitation source, the noise level was suppressed by ~2 orders of magnitude. Furthermore, the radial and longitudinal resonance modes can be combined to further improve the sensor performance.

Extreme-value statistics in nonlinear optics

Aleksei Zheltikov

DOI: 10.1364/OL.510419 Received 26 Oct 2023; Accepted 27 Dec 2023; Posted 13 Feb 2024  View: PDF

Abstract: We show that, although nonlinear optics may give rise to a vast multitude of statistics, all these statistics converge, in their extreme-value limit, to one of a few universal extreme-value statistics. Specifically, in the class of polynomial nonlinearities, such as those found in the Kerr effect, weak-field harmonic generation, and multiphoton ionization, the statistics of the nonlinear-optical output converges, in the extreme-value limit, to the exponentially tailed, Gumbel distribution. Exponentially growing nonlinear signals, on the other hand, such as those induced by parametric instabilities and stimulated scattering, are shown to reach their extreme-value limits in the class of the Fréchet statistics, giving rise to extreme-value distributions with heavy, manifestly nonexponential tails, thus favoring extreme-event outcomes and rogue-wave buildup.