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Directly accessing octave-spanning dissipative Kerr soliton frequency combs in an AlN microresonator

Haizhong Weng, Jia Liu, Adnan Afridi, Jing Li, Jiangnan Dai, xiang ma, Yi Zhang, Qiaoyin Lu, John Donegan, and Wei-Hua Guo

DOI: 10.1364/PRJ.427567 Received 12 Apr 2021; Accepted 13 May 2021; Posted 13 May 2021  View: PDF

Abstract: Self-referenced dissipative Kerr solitons (DKSs) based on optical microresonators offer prominent characteristics allowing for various applications from precision measurement to astronomical spectrometer calibration. To date, direct octave-spanning DKS generation has been achieved only in ultrahigh-Q silicon nitride microresonators under optimized laser tuning speed or bi-directional tuning. Here we propose a simple method to easily access the octave-spanning DKS in an aluminum nitride (AlN) microresonator. In the design, two modes that belong to different families but with the same polarization are nearly degenerate and act as a pump and an auxiliary resonance, respectively. The presence of the auxiliary resonance balances the thermal dragging effect during dissipative soliton comb formation, crucially simplifying the DKS generation with a single pump and leading to a wide single soliton access window. We experimentally demonstrate the stable DKS operation with a record single soliton step (10 GHz or 80 pm) and an octave-spanning bandwidth (1100- 00 nm) through adiabatic pump tuning. Our scheme also allows for direct creation of the DKS state with high probability and without elaborate wavelength or power schemes being required to stabilize the soliton behavior.

Ultra-broadband microwave absorber based on 3D water microchannel

Yan Chen, Kejian Chen, Dajun Zhang, Shihao Li, Yeli Xu, Xiong Wang, and Songlin Zhuang

DOI: 10.1364/PRJ.422686 Received 18 Feb 2021; Accepted 12 May 2021; Posted 13 May 2021  View: PDF

Abstract: In this paper, an ultra-thin and ultra-broadband metamaterial absorber based on 3D printed water microchannel is proposed. The experimental results show an absorption rate over 90% and a relative bandwidth up to 165% in the frequency band between 9.6 and 98.9 GHz. And this polarization-independent absorber can work at a wide angle of incidence and exhibits good thermal stability. Benefiting from ultra-broadband absorption, thin thickness, low cost and environment-friendly materials, the proposed metamaterial absorber can be used in the fields of electromagnetic wave stealth and electromagnetic radiation protection. Related device design and research methods can be extended to the application researches in THz and optical band.

Biochemical sensing exploiting localized surface plasmon resonance sensors based on gold nanogratings and polymer optical fibers

Francesco Arcadio, Luigi Zeni, Domenico Montemurro, Caterina ERAMO, Stefania DI RONZA, Chiara Perri, Girolamo D Agostino, Guido Chiaretti, Giovanni Porto, and Nunzio Cennamo

DOI: 10.1364/PRJ.424006 Received 03 Mar 2021; Accepted 11 May 2021; Posted 13 May 2021  View: PDF

Abstract: In this work, we present a biochemical sensing approach based on a Localized Surface Plasmon Resonance (LSPR) sensor, combined with a specific receptor, excited, and observed via polymer optical fibers (POFs). The LSPR platform is based on a gold nanograting fabricated by electron beam lithography on a polymethylmethacrylate (PMMA) substrate. The structure parameters of the LSPR sensor have been optimized by performing numerical simulations, in order to achieve the best configuration in terms of performances. Subsequently, the proposed LSPR sensor has been fabricated and then experimentally tested, through a novel and custom 3D-printed holder included in a POFs-based transmission-based experimental setup. Preliminarily, the LSPR sensor has been optically characterized with different water-glycerin mixtures; in a second step, we have deposited upon the LSPR sensor nanograting a biomimetic receptor, specific for Bovine Serum Albumin (BSA), to test its biochemical sensing capabilities. From a comparative analysis with an SPR POF platform, functionalized with the same receptor for BSA, the obtained experimental results have suggested that the developed sensor shows a significant improvement of the performances in terms of ultra-low limit of detection, so standing as a promising candidate for label-free biochemical sensing applications.

Intermittent dynamical state switching in discrete-mode semiconductor lasers subject to optical feedback

Zhuqiang Zhong, Da Chang, Wei Jin, Min Lee, Anbang Wang, Shan Jiang, Jiaxiang He, Jianming TANG, and Yanhua Hong

DOI: 10.1364/PRJ.427458 Received 09 Apr 2021; Accepted 10 May 2021; Posted 10 May 2021  View: PDF

Abstract: Intermittent dynamics switching on the route to chaos in a discrete-mode laser with long time-delayed feedback is experimentally and numerically studied by analyzing the time series, power spectra and phase portraits. The results show two types of dynamics switching: one or multiple times regular intermittent dynamics switching between stable state and square-wave envelope period-one oscillation within one feedback round time, and the irregular intermittent dynamics switching between stable state and quasi-periodic or multi-states or chaos with higher feedback ratio and bias currents. The relationship between the duty cycle of period-one oscillation and the feedback ratio has been analyzed. The map of the dynamics distribution in the parameter space of feedback ratio and bias current is plotted for a better understanding of dynamics evolution in long external cavity discrete-mode lasers.

6 GHz hyperfast rotation of an optically levitated nanosphere in vacuum

Xudong Yu, Jing Zhang, Yuanbin Jin, Jiangwei Yan, Shahjee Khan, and Jie Li

DOI: 10.1364/PRJ.422975 Received 18 Feb 2021; Accepted 09 May 2021; Posted 10 May 2021  View: PDF

Abstract: We report an experimental observation of a record-breaking ultra-high rotation frequency about 6 GHz in an optically levitated nanosphere system. We optically trap a nanosphere in the gravity direction with a high numerical aperture objective lens, which shows significant advantages in compensating the influences of the scattering force and the photophoretic force on the trap, especially at intermediate pressures (about 100 Pa). This allows us to trap a nanoparticle from atmospheric to low pressure ($10^{-3}$ Pa) without using feedback cooling. We measure a highest rotation frequency about 4.3 GHz of the trapped nanosphere without feedback cooling and a 6 GHz rotation with feedback cooling, which is the fastest mechanical rotation ever reported to date. Our work provides useful guides for efficiently observing hyperfast rotation in the optical levitation system, and may find various applications such as in ultrasensitive torque detection, probing vacuum friction, and testing unconventional decoherence theories.

Wave and particle properties can be spatially separated in a quantum entity

Jing-Ling Chen, Pratyusha Chowdhury, and Aran Kumar Pati

DOI: 10.1364/PRJ.425101 Received 16 Mar 2021; Accepted 08 May 2021; Posted 10 May 2021  View: PDF

Abstract: Wave and particle are two fundamental properties of Nature. The wave-particle duality has indicated that a quantum object may exhibit the behaviors of both wave and particle, depending upon the circumstances of the experiment. The major significance of wave-particle duality has led to a fundamental equation in quantum mechanics, the Schrodinger equation. At present, the principle of wave-particle duality has been deeply rooted in people's hearts. This gives raised to a common sense perception that wave property and particle property coexist simultaneously in a quantum entity, and these two physical attributes cannot be completely separated from each other. In classical physics, a similar common sense is that a physical system is inseparable from its physical properties. However, this has been recently challenged and beaten by a quantum phenomenon called the ``quantum Chesire cat", for which a cat and its grin can be separated spatially. In this work, we propose a thought experiment based on the similar technology of quantum Chesire cat. We find that wave and particle attributes of a quantum entity can be completely separated, thus successfully dismantling the wave-particle duality for a quantum entity. Our result is still consistent with the complementarity principle and deepens the understanding of quantum foundations.

Bandpass filter-integrated multiwavelength achromatic Metalens

Hanmeng Li, Xingjian Xiao, Bin Fang, Shenglun Gao, Zhizhang Wang, Chen Chen, Yunwei Zhao, Shining Zhu, and Tao Li

DOI: 10.1364/PRJ.422280 Received 08 Feb 2021; Accepted 06 May 2021; Posted 06 May 2021  View: PDF

Abstract: The design of large scale, high numerical aperture, and broadband achromatism is a big challenge in metalens research. In fact, many colorful imaging systems have RGB color filters, which means the achromatism only for RGB lights would be sufficient. Avoiding broadband achromatism is expected to greatly improve the working efficiency of metalens. Nevertheless, a proper bandpass filter is necessary under a white light illumination in the metalens integrated imaging system. Here, we propose a bandpass filter-integrated multiwavelength achromatic metalens (NA = 0.2), which is designed using a searching optimization algorithm to achieve the achromatism of RGB lights with high efficiencies. The bandpass filter is implemented by composite DBRs and defect layers, by which three desired wavelengths are selected out. The simulations and experiments on the filter integrated-metalens definitely show a good RBG achromatism. Further imaging experiments demonstrate a higher SNR and resolution compared with the one without the filter. Our approach provides not only a RGB achromatic meta-imaging device, but also a new route to access a highly efficient spectrum tailoring meta-system by incorporating bandpass filter designs.

Broadband mid-infrared molecular spectroscopy based on passive coherent optical–optical modulated frequency combs

Wenxue Li, Zhong Zuo, CHENGLIN Gu, Daowang Peng, Xing Zou, Yuanfeng Di, Lian Zhou, Daping Luo, and Yang Liu

DOI: 10.1364/PRJ.422397 Received 09 Feb 2021; Accepted 06 May 2021; Posted 06 May 2021  View: PDF

Abstract: Mid-infrared dual-comb spectroscopy is of great interest owing to the strong spectroscopic features of trace gases, biological molecules, and solid matter with higher resolution, accuracy, and acquisition speed. However, the pre-requisite of achieving high coherence of optical sources with the use of bulk sophisticated control systems prevents their widespread use in field applications. Here, we generate a highly mutually coherent dual mid-infrared comb spectrometer based on the optical–optical modulation of a continuous-wave (CW) interband or quantum cascade laser (ICL or QCL). Mutual coherence was passively achieved without post-data processes or active carried envelop phase-locking processes. The center wavelength of the generated mid-infrared frequency combs can be flexibly tuned by adjusting the wavelength of the CW seeds. The parallel detection of multiple molecular species, including C2H2, CH4, H2CO, H2S, COS, and H2O, was achieved. This technique provides a stable and robust dual comb spectrometer that will find non-laboratory applications, including open-path atmospheric gas sensing, industrial process monitoring, and combustion.

Hybrid level anharmonicity and interference induced photon blockade in a two-qubit cavity QED system with dipole-dipole interaction

Chengjie Zhu, Kui Hou, Yaping Yang, and Lu Deng

DOI: 10.1364/PRJ.421234 Received 29 Jan 2021; Accepted 04 May 2021; Posted 04 May 2021  View: PDF

Abstract: We theoretically study a quantum destructive interference (QDI) induced photon blockade in a two-qubit driven cavity QED system with dipole-dipole interaction (DDI). In the absence of dipole-dipole interaction, we show that a QDI-induced photon blockade can be achieved only when the qubit resonance frequency is different from the cavity mode frequency. When DDI is introduced the condition for this photon blockade is strongly dependent upon the pump field frequency, and yet is insensitive to the qubit-cavity coupling strength. Using this tunability feature we show that the conventional energy-level-anharmonicity-induced photon blockade and this DDI-based QDI-induced photon blockade can be combined together, resulting in a hybrid system with substantially improved mean photon number and second order correlation function. Our proposal provides a non-conventional and experimentally feasible platform for generating single photons.

Monolithic and single-functional-unit level integration of electronic and photonic elements: FET-LET hybrid 6T SRAM

Antardipan Pal, Zhang yong, and Dennis Yau

DOI: 10.1364/PRJ.420887 Received 27 Jan 2021; Accepted 04 May 2021; Posted 06 May 2021  View: PDF

Abstract: A broad range of technologies have been developed for the chip and wafer scale connections and integrations of photonic and electronic circuits, although major challenges remain for achieving the single-functional-unit-level integration of electronic and photonic devices. Here we use FET-LET hybrid 6T SRAM as an example to illustrate a novel approach that can alleviate three major challenges to the higher-level integration of the photonic and electronic elements: size mismatch, energy data rate, and cascadability. A hybrid 6T SRAM with two access FETs being replaced by light-effect transistors (LETs) and the electrical word lines replaced by optical waveguides (OWGs) is proposed. This hybrid 6T SRAM is analyzed to reveal its potential in improvement of the switching speed and thus total energy consumption over the conventional 6T SRAM. Numerical analyses, for instance, for a prototype 64 KB hybrid SRAM array, show a factor of 4 and 22 reduction in read delay and read energy consumption, and 3 and 4 in write delay and write energy consumption, respectively, when the access FETs are replaced by LETs. The potential impacts on the peripheral and assist circuits due to this hybrid structure and application of the LETs there are also briefly discussed.

Experimental demonstration of robustness of Gaussian quantum coherence

Haijun Kang, Dongmei Han, Na Wang, Yang Liu, Shuhong Hao, and Xiaolong Su

DOI: 10.1364/PRJ.424198 Received 04 Mar 2021; Accepted 01 May 2021; Posted 04 May 2021  View: PDF

Abstract: Besides quantum entanglement and steering, quantum coherence has also been identified as a useful quantum resource in quantum information. It is important to investigate the evolution of quantum coherence in practical quantum channels. In this paper, we experimentally quantify the quantum coherence of squeezed state and Gaussian Einstein-Podolsky-Rosen (EPR) entangled state transmitted in Gaussian thermal noise channel, respectively. By reconstructing the covariance matrix of the transmitted states, quantum coherence of these Gaussian states is quantified by calculating the relative entropy. We show that quantum coherence of squeezed state and Gaussian EPR entangled state is robust against loss and noise in quantum channel, which is different from the properties of squeezing and Gaussian entanglement. Our experimental results pave the way for application of Gaussian quantum coherence in lossy and noisy environments.

Motional $N$-phonon Bundle States of A Trapped Atom with Clock Transitions

Yuangang Deng, Tao Shi, and Su Yi

DOI: 10.1364/PRJ.427062 Received 08 Apr 2021; Accepted 01 May 2021; Posted 04 May 2021  View: PDF

Abstract: Quantum manipulation of individual phonons could offer new resources for studying fundamental physics and creating an innovative platform in quantum information science. Here, we propose to generate quantum states of strongly correlated phonon bundles associated with the motion of a trapped atom. Our scheme operates in the atom-phonon resonance regime where the energy spectrum exhibits strong anharmonicity such that energy eigenstates with different phonon numbers can be well-resolved in the parameter space. Compared to earlier schemes operating in the far dispersive regime, the bundle states generated here contain a large steady-state phonon number. Therefore, the proposed system can be used as a high quality multiphonon source. Our results open up the possibility of using long-lived motional phonons as quantum resources, which could provide a broad physics community for applications in quantum metrology.

Single-Cavity Bi-Color Laser Enabled by Optical Anti-Parity-Time Symmetry

Xingjie Ni, Yao Duan, Xingwang Zhang, and Yimin Ding

DOI: 10.1364/PRJ.417296 Received 14 Dec 2020; Accepted 30 Apr 2021; Posted 04 May 2021  View: PDF

Abstract: The exploration of quantum-inspired symmetries in optical systems has spawned promising physics and provided fertile ground for developing devices exhibiting exotic functionalities. Founded on the anti-parity-time (APT) symmetry that is enabled by both spatial and temporal interplay between gain and loss, we demonstrate theoretically and numerically bi-color lasing in a single micro-ring resonator with spatiotemporal modulation along its azimuthal direction. In contrast to conventional multi-mode lasers that have mixed-frequency output, our laser exhibits stable, demultiplexed, tunable bi-color emission at different output ports. Our APT-symmetry-based laser may point out a new route for realizing compact on-chip coherent multi-color light sources.

Achieving high responsivity near-infrared detection at room temperature by nano-Schottky junction arrays via a black silicon/platinum contact approach

Fei Hu, Li Wu, Xi-Yuan Dai, Shuai Li, Ming Lu, and Jian Sun

DOI: 10.1364/PRJ.417866 Received 17 Dec 2020; Accepted 30 Apr 2021; Posted 04 May 2021  View: PDF

Abstract: Room temperature sub-bandgap near-infrared (λ>1100 nm) Si photodetector with high responsivity is achieved. The Si photodetector features black Si made by wet etching Si(100), Si/PtSi nano-Schottky junction arrays made from black Si/Pt contacts, and chemical and field-effect passivation of black Si. Responsivities are 147.6, 292.8 and 478.2 mA/W at reverse voltages of 1.0, 1.5 and 2.0 V for 1550 nm light, respectively, with corresponding specific detectivities being 9.79×10⁸, 1.88×10⁹ and 2.97×10⁹ cm×Hz^(½)/W. This work demonstrates a practical room temperature sub-bandgap near-infrared Si photodetector that can be made in a facile and large scale manner.

On-chip Chalcogenide Microresonators with Low Threshold Parametric Oscillation

Bin Zhang, Pingyang Zeng, Zelin Yang, Di Xia, Yaodong Sun, yufei huang, jingcui Song, Jingshun Pan, huanjie cheng, Duk-Yong Choi, and Zhaohui Li

DOI: 10.1364/PRJ.422435 Received 10 Feb 2021; Accepted 27 Apr 2021; Posted 28 Apr 2021  View: PDF

Abstract: Chalcogenide glasses (ChGs) are attractive candidates for broadband nonlinear photonic devices. However, it remains a challenge for on-chip optical parametric processes in a robust ChG microresonators due to the thermal and light induced instabilities and high loss of ChG films. Here, an in-situ light-induced annealing method is demonstrated to overcome the long-standing limitations of ChG film instability. Furthermore, a systematic fabrication process of planar-integrated ChG microring is provided for achieving an intrinsic quality (Q) factor of more than 1 million with anomalous dispersion. Owing to the highly stable and boosted Q-factor, we experimentally demonstrate optical parametric oscillation with a low threshold power of 5.4 mW in the ChG microring for the first time. Our results not only validate that the improved integrated ChG photonic device can be used in low-threshold frequency comb generators, but also establish ChG resonators as the promising parametric converter to realize the mid-infrared frequency combs in previously unattainable bands.

Topological scattering singularities and embedded eigenstates for polarization control and sensing applications

Zarko Sakotic, Aleksandr Krasnok, Andrea Alu, and Nikolina Jankovic

DOI: 10.1364/PRJ.424247 Received 08 Mar 2021; Accepted 27 Apr 2021; Posted 28 Apr 2021  View: PDF

Abstract: Epsilon-near-zero and epsilon near-pole materials enable reflective systems supporting a class of symmetry-protected and accidental embedded eigenstates (EE) characterized by a diverging phase-resonance. Here we show that pairs of topologically protected scattering singularities necessarily emerge from EEs when a non-Hermitian parameter is introduced, lifting the degeneracy between oppositely charged singularities. The underlying topological charges are characterized by an integer winding number and appear as phase vortices of the complex reflection coefficient. By creating and annihilating them, we show that these singularities obey charge conservation, and provide versatile control of amplitude, phase and polarization in reflection, with potential applications for polarization control and sensing.

PIC-integrable, uniformly 0.56%-tensile strained Ge-on-insulator photodiodes enabled by recessed SiNx stressor

Yiding Lin, Danhao Ma, Kwang Hong Lee, Rui-Tao Wen, Govindo Syaranamual, Lionel Kimerling, Chuan Seng Tan, and Jurgen Michel

DOI: 10.1364/PRJ.419776 Received 15 Jan 2021; Accepted 26 Apr 2021; Posted 26 Apr 2021  View: PDF

Abstract: Mechanical strain engineering has been promising for many integrated photonic applications. However, for the engineering of material electronic bandgap, a trade-off exists between the strain uniformity and the integration compatibility with photonic-integrated circuits (PICs). Herein, we adopted a straightforward recess-type design of silicon nitride (SiNx) stressor to achieve a uniform strain with enhanced magnitude in the material of interest on PICs. Normal-incidence, uniformly 0.56%-tensile strained germanium (Ge)-on-insulator (GOI) metal-semiconductor-metal photodiodes were demonstrated, using the recessed stressor with 750-MPa tensile stress. The device exhibits a responsivity of 1.59 A/W at 1,550 nm. The extracted Ge absorption coefficient is enhanced by ~3.2× to 8,340 cm-1 at 1,612 nm and is superior to that of In₀.₅₃Ga₀.₄₇As up to 1,630 nm limited by measurement spectrum. Compared to the non-recess strained device, additional absorption coefficient improvement of 10‒20% in the C-band and 40‒60% in the L-band were observed. This work facilitates the recess-strained GOI photodiodes for free-space PIC applications and paves the way for various (e.g. Ge, GeSn or III-V based) uniformly strained photonic devices on PICs.

Tunable Photon blockade with single atom in a cavity under electromagnetically induced transparency

Jing Tang, Yuangang Deng, and Chaohong Lee

DOI: 10.1364/PRJ.419275 Received 07 Jan 2021; Accepted 23 Apr 2021; Posted 26 Apr 2021  View: PDF

Abstract: We present an experimental proposal to achieve strong photon blockade by employing electromagnetically induced transparency (EIT) with single alkaline-earth-metal atom trapped in an optical cavity. In the presence of optical Stark shift, both second-order correlation function and cavity transmission exhibit asymmetric structures between the red and blue sidebands of the cavity. For weak control field, the photon quantum statistics for the coherent transparency window (i.e. atomic quasi-dark state resonance) are insensitive to the Stark shift, which should also immune to the spontaneous emission of the excited state by taking advantages of the intrinsic dark-state polariton of EIT. Interestingly, by exploiting the interplay between Stark shift and control field, the strong photon blockade at atomic quasi-dark state resonance has an optimal second-order correlation function $g^{(2)}(0)\sim10^{-4}$ and a high cavity transmission simultaneously. The underlying physical mechanism is ascribed to the Stark shift enhanced spectrum anharmonicity and the EIT hosted strong nonlinearity with loss-insensitive atomic quasi-dark state resonance, which is essentially different from the conventional proposal with emerging Kerr nonlinearity in cavity-EIT. Our results reveal a new strategy to realize high-quality single photon sources, which could open up a new avenue for engineering nonclassical quantum states in cavity QED.

Mimicking gravitational effect with graded index lens in geometrical optics

Wen Xiao, Sicen Tao, and Huanyang Chen

DOI: 10.1364/PRJ.418787 Received 05 Jan 2021; Accepted 19 Apr 2021; Posted 19 Apr 2021  View: PDF

Abstract: General Relativity establishes the equality between matter–energy density and the Riemann curvature of spacetime. Therefore, light or matter will be bent or trapped when passing near the massive celestial objects and the Newton’s second law fails to explain it. The gravitational effects have not only been extensively studied in astronomy, but also attracts a great interestin the field of optics. In the past decades, people in optics have mimicked the black holes, Einstein’s ring, deSitter Space and other fascinating effects. Lots of optical applications emerged inspired by the these mimicking including wave-front shaping waveguide, light absorbers. Most of them are presented in wave optics, rarely in geometrical optics. Here, based on opticalmechanical analogy, in geometrical optics regime, with a graded index lens, we mimic the Schwarzschild precession in the orbit of the star S2 near the Galactic Centre massive black hole, which was first detected by European Southern Observatory recently. We also find that another series of graded index lenses can be used to mimic the possible Reissner-Nordström metric of Einstein’s field equation and the dark matter particles motions, where light or matter paths in the graded lenses will be closed in some cases while in others will be trapped by the center or keep travelling around the center. Our work provides an efficient way to investigate the complex celestial behaviors which is difficult to directly detect using astronomical tools and enriches the family of absolute optical instruments due to the closed trajectories as well.

Nanohole Array Structured GaN-based White-LEDs with improved Modulation Bandwidth via Plasmon Resonance and Non-Radiative Energy Transfer

Rongqiao Wan, Guoqiang Li, Xiang Gao, Zhiqiang Liu, Junhui Li, Xiaoyan Yi, Nan Chi, and Liancheng Wang

DOI: 10.1364/PRJ.421366 Received 09 Feb 2021; Accepted 18 Apr 2021; Posted 19 Apr 2021  View: PDF

Abstract: Commercial white LEDs (WLEDs) are generally limited in modulation bandwidth due to slow stokes process, long lifetime of phosphors and quantum-confined Stark effect (QCSE). Here we report a novel plasmonic WLED by infiltrating nanohole LED (H-LED) with quantum dots (QDs) and Ag nanoparticles (NPs) together (M-LED). This decreased QW-QD distance would open extra non-radiative energy transfer (NRET) channel and thus enhance stokes transfer efficiency. The presence of Ag NPs enhances the spontaneous emission rate significantly. Compared with the H-LED filled with QDs (QD-LED), the optimized M-LED demonstrates a maximum CRI of 91.2, a 43% increase in optical power at 60mA, and a lowered CCT. Simultaneously, M-LED exhibits a date rate of 2.21Gbps at low current density of 96A/cm2 (60mA), which is 77% higher than QD-LED. This is mainly due to the higher optical power and modulation bandwidth of M-LED under the influence of plasmon, resulting to a higher date rate and higher signal-to-noise ratio (SNR) under the forward error correction (FEC). We believe the approach reported in this work should contribute to WLED light source with increased modulation bandwidth for higher speed VLC (Visible Light Communication) application.

Broad-intensity-range optical nonreciprocity based on feedback-induced Kerr nonlinearity

Lei Tang, Jiangshan Tang, Haodong Wu, Jing Zhang, Min Xiao, and Keyu Xia

DOI: 10.1364/PRJ.413286 Received 23 Oct 2020; Accepted 16 Apr 2021; Posted 19 Apr 2021  View: PDF

Abstract: Nonreciprocal light propagation plays an important role in modern optical systems, from photonic networks to integrated photonics. We propose a nonreciprocal system based on a resonance-frequency-tunable cavity and intensity-adaptive feedback control. Because the feedback-induced Kerr nonlinearity in the cavity is dependent on the incident direction of light, the system exhibits nonreciprocal transmission with a high isolation contrast of 0.90 and a very low insertion loss of 0.09 dB. By utilizing the intensity-adaptive feedback control, the operating intensity range of the nonreciprocal system is broadened to 20.0 dB, which relaxes the limitation of the operating intensity range for nonlinear nonreciprocal systems. Our protocol paves the way to realize high-performance nonreciprocal propagation in optical systems and can also be extended to microwave systems.

A generalized framework for non-sinusoidal fringe analysis using deep learning

Shijie Feng, Chao Zuo, Liang Zhang, Wei Yin, and Qian Chen

DOI: 10.1364/PRJ.420944 Received 02 Feb 2021; Accepted 13 Apr 2021; Posted 13 Apr 2021  View: PDF

Abstract: Phase retrieval from fringe images is essential to many optical metrology applications. In the field of fringe projection profilometry, the phase is often obtained with systematic errors if the fringe pattern is not perfect sinusoidal. Several factors can account for non-sinusoidal fringe patterns, such as the nonlinear input-output response (e.g., the gamma effect) of digital projectors, the residual harmonics in binary defocusing projection, and the image saturation due to intense reflection. Traditionally, these problems are handled separately with different well-designed methods, which can be seen as “one-to-one” strategies. Inspired by recent successful artificial intelligence-based optical imaging applications, we propose a “one-to-many” deep learning technique that can analyze non-sinusoidal fringe images resulting from different non-sinusoidal factors and even the coupling of these factors. We show for the first time, to the best of our knowledge, a trained deep neural network can effectively suppress the phase errors due to various kinds of non-sinusoidal patterns. Our work paves the way to robust and powerful learning based fringe analysis approaches.

Efficient and Wideband Acousto-Optic Modulation on Thin-Film Lithium Niobate for Microwave to Photonic Conversion

Ahmed Hassanien, Steffen Link, Yansong Yang, Edmond Chow, Lynford Goddard, and Songbin Gong

DOI: 10.1364/PRJ.421612 Received 02 Feb 2021; Accepted 13 Apr 2021; Posted 13 Apr 2021  View: PDF

Abstract: Microwave photonics, a field that crosscuts microwave/millimeter-wave engineering with optoelectronics, has sparked great interest from research and commercial sectors. This multidisciplinary fusion can achieve ultrawide bandwidth and ultrafast speed that were considered impossible in conventional chip-scale microwave/mm-wave systems. Conventional microwave-to-photonic converters, based on the resonant acousto-optic modulation produce highly efficient modulation but sacrifice bandwidth and limit their applicability for most real-world microwave signal processing applications. In this article, we build highly efficient and wideband microwave-to-photonic modulators using the acousto-optic effect on suspended lithium niobate thin films. A wideband microwave signal is first piezoelectrically transduced using interdigitated electrodes into Lamb acoustic waves, which directly propagates across an optical waveguide and causes refractive index perturbation through the photo-elastic effect. This approach is power efficient, with phase shifts up to 0.0166 rad/√mW over a 45 µm modulation length and with bandwidth up to 140 MHz at a center frequency of 1.9 GHz. Compared to the state-of-the-art, a 9× more efficient modulation has been achieved by optimizing the acoustic and optical modes and their interactions.

Ultrafast all-optical terahertz modulation based on inverse-designed metasurface

Weibao He, Tong mingyu, Zhongjie Xu, Yuze Hu, Xiang'ai Cheng, and Tian Jiang

DOI: 10.1364/PRJ.423119 Received 18 Feb 2021; Accepted 10 Apr 2021; Posted 13 Apr 2021  View: PDF

Abstract: Metasurface plays a key role in various terahertz metadevices, while the designed terahertz metasurface still lacks flexibility and variety. On the other hand, inverse design has drawn a plenty of attentions due to its flexibility and robustness in the application of photonics. This provides an excellent opportunity for metasurface design as well as the development of multifunctional, high-performance terahertz devices. In this work, we demonstrate that, for the first time, a terahertz metasurface supported by electromagnetically induced transparency (EIT) effect can be constructed by inverse design, which combines particle swam optimization (PSO) algorithm with finite-difference time-domain (FDTD) method. Incorporating germanium (Ge) film with inverse-designed metasurface, an ultrafast EIT modulation on the picosecond scale has been experimentally verified. The experimental results suggest a feasibility to build terahertz EIT effect in the metasurface through optimization algorithm of inverse design. Furthermore, this method can be further utilized to design multifunctional and high-performance terahertz devices, which is hard to accomplish in traditional metamaterial structure. In a word, our method not only provides a novel way to design ultrafast all-optical terahertz modulator based on artificial metamaterials, but also shows the potential applications of inverse design on the terahertz devices.

Superior performances of 2 kHz Nd:YAG pulse laser with a gradient dopant crystal

Haihe Jiang, Mengen Wei, Tingqing Cheng, Renqin Dou, and Qing-li Zhang

DOI: 10.1364/PRJ.424989 Received 12 Mar 2021; Accepted 10 Apr 2021; Posted 13 Apr 2021  View: PDF

Abstract: The improvement of high-repetition-rate Nd:YAG laser performances is still long-standing challenge, although many novel architectures of the laser have been developed. The key difficulty is that the uniform Nd3+-doped YAG crystals adsorb pumping light with a remarkable decrease of pumping strength along axis direction, leading to an uneven pumping distribution with unsatisfactory laser performance. Herein, we report a home-made new Nd:YAG crystal rod that contains a gradient dopant of 0.39-0.80 at.% Nd3+ from end to end, achieving superior performances of 2 kHz Nd:YAG pulse laser. The optical-optical conversion efficiency reached 53.8 %, and the maximal output power of laser was 24.2 W, enhanced by 35.9 % comparing with a uniform crystal rod with the same total concentration of Nd3+. Significantly, our experiments revealed that the gradient concentration crystal produced a relatively even pumping distribution along the rod axis, greatly reducing the temperature gradient as well as the smaller thermal effect. The smoothing pump and thermal distribution obviously improved the features of laser oscillation and output.

Effect of dispersion on indistinguishability between single-photon wave-packets

Yunru Fan, Chenzhi yuan, Ruiming Zhang, Si Shen, Peng Wu, Heqing Wang, Hao Li, Guangwei Deng, Hai-Zhi Song, Lixing YOU, Zhen Wang, You WANG, Guang-can Guo, and Qiang Zhou

DOI: 10.1364/PRJ.421180 Received 02 Feb 2021; Accepted 09 Apr 2021; Posted 13 Apr 2021  View: PDF

Abstract: With propagating through a dispersive medium, the temporal-spectral profile of laser pulses should be inevitably modified. Although such dispersion effect has been well studied in classical optics, its effect on a single-photon wave-packet, i.e., the matter wave of a single-photon, has not yet been entirely revealed. In this paper, we investigate the effect of dispersion on indistinguishability between single-photon wave-packets through the Hong-Ou-Mandel (HOM) interference. By dispersively manipulating two indistinguishable single-photon wave-packets before interfering with each other, we observe that the difference of the second-order dispersion between two optical paths of the HOM interferometer can be mapped to the interference curve, indicating that (1) with the same amount of dispersion effect in both paths, the HOM interference curve must be only determined by the intrinsic indistinguishability between the wave-packets, i.e., dispersion cancellation due to the indistinguishability between Feynman paths; (2) unbalanced dispersion effect in two paths cannot be cancelled and will broaden the interference curve thus providing a way to measure the second-order dispersion coefficient. Our results suggest a more comprehensive understanding of the single-photon wave-packet and pave ways to explore further applications of the HOM interference.

Band dynamics accompanied by bound states in the continuum at the third-order Γ point in leaky-mode photonic lattices

Sun-Goo Lee, seong-han kim, and Chul-Sik Kee

DOI: 10.1364/PRJ.417150 Received 09 Dec 2020; Accepted 08 Apr 2021; Posted 13 Apr 2021  View: PDF

Abstract: Bound states in the continuum (BICs) and Fano resonances in planar photonic lattices, including metasurfaces and photonic crystal slabs, have been studied extensively in recent years. Typically, the BICs and Fano resonances are associated with the second stop bands open at the second-order Γ point. This paper address the fundamental properties of the fourth stop band accompanied by BICs at the third-order Γ point in one-dimensional leaky-mode photonic lattices. At the fourth stop band, one band edge mode suffers radiation loss, thereby generating a Fano resonance, while the other band edge mode becomes a nonleaky BIC. The fourth stop band is controlled primarily by the Bragg processes associated with the first, second, and fourth Fourier harmonic components of the periodic dielectric constant modulation. The interplay between these three major processes closes the fourth band gap and induces a band flip whereby the leaky and BIC edges transit across the fourth band gap. At the fourth stop band, a new type of BIC is formed owing to the destructive interplay between the first and second Fourier harmonics. When the fourth band gap closes with strongly enhanced Q factors, Dirac cone dispersions can appear at the third-order Γ point.

Covert wireless communication using massive optical comb channels for deep denoising

Xianglei Yan, Xihua Zou, Peixuan Li, Wei Pan, and Lianshan Yan

DOI: 10.1364/PRJ.419605 Received 13 Jan 2021; Accepted 08 Apr 2021; Posted 13 Apr 2021  View: PDF

Abstract: Covert wireless communications are unprecedentedly vital for security and privacy of individuals, government and military bodies. Besides encryption, hiding signal transmission deeply under noise background highly proliferates the covertness in physical layer. A deep signal hiding leads to a low interception probability at interceptor but a poor data recovery at receiver. To ensure both high covertness and high-fidelity recovery, massive and dense optical comb channels are utilized for deep denoising. The available optical comb channels can scale up without physical bottlenecks on immense hardware and spectrum requirements. Thus a striking signal-to-noise ratio (SNR) rise can be achieved for deep denoising. Combination of massive comb channels (a record high of 1024) through analog spectrum convolution enables a 29-dB SNR enhancement, even with in-band noises by 18dB in both frequency and time domains. This method opens a new avenue for covert communications.

Preconditioned deconvolution method for high-resolution ghost imaging

Zhishen Tong, Zhentao Liu, Chenyu Hu, Jian Wang, and Shensheng Han

DOI: 10.1364/PRJ.420326 Received 19 Jan 2021; Accepted 05 Apr 2021; Posted 05 Apr 2021  View: PDF

Abstract: Ghost imaging (GI) can nonlocally image objects by exploiting the fluctuation characteristics of light fields, where the spatial resolution is determined by the normalized second-order correlation function $g^{(2)}$. However, the spatial shift-invariant property of $g^{(2)}$ is distorted when the number of samples is limited, which hinders the deconvolution methods from improving the spatial resolution of GI. In this paper, based on the prior of transfer functions of GI, we propose a preconditioned deconvolution method to improve the imaging resolution of GI by refining the mutual coherence of sampling matrix in GI. Our theoretical analysis shows that the preconditioned deconvolution method actually extends the deconvolution technique to GI, and it regresses into the classical deconvolution technique for the conventional imaging system. The imaging resolution of GI after preconditioning is restricted to the detection noise. Both simulated and experimental results exhibit that the spatial resolution of the reconstructed image is obviously enhanced by using the preconditioned deconvolution method. In the experiment, $1.4$-fold resolution enhancement over the Rayleigh's criterion is achieved via the preconditioned deconvolution method. Our results extend the deconvolution technique that is only applicable to spatial shift-invariant imaging systems to all linear imaging systems, and will promote their applications in biological imaging and remote sensing for high-resolution imaging demands.

Focus-tunable microscope for imaging small neuronal processes in freely moving animals

Arutyun Bagramyan, Loïc Tabourin, Ali Rastqarfarajzadeh, Narges Karimi, Frédéric Bretzner, and Tigran Galstian

DOI: 10.1364/PRJ.418154 Received 21 Dec 2020; Accepted 04 Apr 2021; Posted 05 Apr 2021  View: PDF

Abstract: Miniature 1-photon microscopes have been widely used to image neuronal assemblies in the brain of freely moving animals over the last decade. However, these systems have important limitations for imaging in-depth fine neuronal structures. We present a novel subcellular imaging 1-photon device that uses an electrically tunable liquid crystal lens to enable a motion-free depth scan in the search of such structures. Our miniaturized microscope is compact (10 mm x 17 mm x 12 mm), lightweight (≈ 1.4 g), provides fast acquisition rate (30-50 frames/second), high magnification (8.7x) and high resolution (1.4 µm) that allow imaging of calcium activity of fine neuronal processes in deep brain regions during a wide range of behavioural tasks of freely moving mice.

Harmonic injection locking of high-power mid-infrared quantum cascade lasers

Feihu Wang, Steven Slivken, and Manijeh Razeghi

DOI: 10.1364/PRJ.423573 Received 24 Feb 2021; Accepted 03 Apr 2021; Posted 05 Apr 2021  View: PDF

Abstract: High-power, high-speed quantum cascade lasers (QCLs) with stable emission in the mid-infrared regime are of great importance for applications in metrology, telecommunication, and fundamental tests of physics. Owing to the inter-sub-band transition, the unique ultrafast gain recovery time of the QCL with picosecond dynamics is expected to overcome the modulation limit of classical semiconductor lasers and bring a revolution for the next generation of ultrahigh-speed optical communication. Therefore, harmonic injection locking, offering the possibility to fast modulate and greatly stabilize the laser emission beyond the rate limited by cavity length, is inherently adapted to QCLs. In this work, we demonstrate for the first time the harmonic injection locking of a mid-infrared QCL with an output power over 1 watt in continuous-wave operation at 288 K. Compared with an unlocked laser, the inter-mode spacing fluctuation of an injection locked QCL can be considerably reduced by a factor of 10^3, which permits the realization of an ultra-stable mid-infrared semiconductor laser with high phase coherence and frequency purity. Despite temperature change, this fluctuation can be still stabilized to hertz level by a microwave modulation up to 18 GHz. These results open up the prospect of the applications of mid-infrared QCL technology for frequency comb engineering, metrology and the next generation ultrahigh-speed telecommunication. It may also stimulate new schemes for exploring ultrafast mid-infrared pulse generation in QCLs.

Integrating the optical tweezers and spanner onto individual single-layer metasurfaces

Tianyue Li, Boyan Fu, Xiaohao Xu, Shuming Wang, Baojun Li, Zhenlin Wang, and Shining Zhu

DOI: 10.1364/PRJ.421121 Received 28 Jan 2021; Accepted 01 Apr 2021; Posted 02 Apr 2021  View: PDF

Abstract: Optical tweezers (OT) and optical spanner (OS) are powerful tools of optical manipulation, which are responsible for particle trapping and rotation, respectively. Conventionally, the OT and OS are built using bulky three-dimensional devices, such as microscope objectives and spatial light modulators. Recently, metasurfaces are proposed for setting up them on a microscale platform, which greatly miniaturizing the systems. However, the realization of both OT and OS with one identical metasurface is posing a challenge. Here, we offer a metasurface-based solution to integrating the OT and OS. We show that, by utilizing the interplay between the geometric and dynamic phases, it is possible to construct an output field, which promises a high-numerical-aperture focal spot, accompanied with a coaxial vortex. Optical trapping and rotation are numerically demonstrated by estimating the mechanical effects on a particle probe. Moreover, we demonstrate an on-demand control of the OT-to-OS distance and the topological charge possessed by the OS. By revealing the OT-OS metasurfaces, our results may empower advanced applications in on-chip particle manipulation.

Complex Swift Hohenberg equation dissipative solitonfiber laser

Ankita Khanolkar, Yimin Zang, and Andy Chong

DOI: 10.1364/PRJ.419686 Received 12 Jan 2021; Accepted 30 Mar 2021; Posted 30 Mar 2021  View: PDF

Abstract: Complex Swift Hohenberg Equation (CSHE) has attracted intensive research interest over the years as it enables modeling of mode-locked lasers with saturable absorber more realistic by adding a fourth order term to the spectral response. Multiple researchers have reported a variety of numerical solutions of the CSHE model which reveal interesting pulse patterns and structures. In this work, we have demonstrated a CSHE dissipative soliton fiber laser experimentally using a unique spectral filter with a complicatedtransmission profile. The behavior and performance of the laser agree qualitatively with the numerical simulations. Our findings bring insight into dissipative soliton dynamics and make our mode-locked laser a powerful testbed for observing dissipative solitons of CSHE, which may open a new course in ultrafast fiber lasers research.

Modeling of a SiGeSn Quantum Well Laser

Bahareh Marzban, Daniela Stange, Denis Rainko, Zoran Ikonic, Dan Buca, and Jeremy Witzens

DOI: 10.1364/PRJ.416505 Received 02 Dec 2020; Accepted 30 Mar 2021; Posted 31 Mar 2021  View: PDF

Abstract: We present comprehensive modeling of a SiGeSn multi-quantum-well laser that has been previously experimentally shown to feature an order of magnitude reduction in optical pump threshold compared with bulk lasers. We combine experimental material data obtained over the last few years with k·p theory in order to adapt transport, optical gain and optical loss models to this material system (drift-diffusion, thermionic emission, gain calculations, free carrier absorption and intervalence band absorption). Good consistency is obtained with experimental data and the main mechanisms limiting the laser performance are discussed. In particular, modeling results indicate a low non-radiative lifetime, in the 100 ps range for the investigated material stack, and lower than expected Γ-L energy separation to play a dominant role in the device properties. Moreover, they further indicate that these lasers emit in the transverse magnetic polarization at higher temperatures due to lower intervalence band absorption losses. To the best of our knowledge, this is the first comprehensive modeling of experimentally realized SiGeSn lasers taking the wealth of experimental material data accumulated over the past years into account. The methods described in this paper pave the way to predictive modeling of new SiGeSn laser device concepts.

Arbitrary cylindrical vector beam generation enabled by polarization-selective Gouy phase shifter

Junliang Jia, Kepeng Zhang, Guangwei Hu, Maping Hu, Tong Tong, Quanquan Mu, Hong Gao, fuli li, Chengwei Qiu, and Pei Zhang

DOI: 10.1364/PRJ.419368 Received 12 Jan 2021; Accepted 29 Mar 2021; Posted 30 Mar 2021  View: PDF

Abstract: Cylindrical vector beams (CVBs), which possesses polarization distribution of rotational symmetry on the transverse plane, can be developed in many optical technologies. Conventional methods to generate CVBs contain redundant interferometers or need to switch among diverse elements, thus being inconvenient in applications containing multiple CVBs. Here we provide a passive polarization-selective device to substitute interferometers and simplify generation setup. It is accomplished by reversing topological charges of orbital angular momentum based on polarization-selective Gouy phase. In the process, tunable input light is the only condition to generate CVB with arbitrary topological charges. To cover both azimuthal and radial parameters of CVBs, we express the mapping between scalar Laguerre-Gaussian light on basic Poincaré sphere and CVB on high-order Poincaré sphere. The proposed device simplifies the generation of CVBs enormously, and thus has potentials in integrated devices for both quantum and classic optical experiments.

Experimental demonstration of pyramidal neuron-like dynamics dominated by dendritic action potentials based on a VCSEL for all-optical XOR classification task

Shuiying Xiang, Yahui Zhang, xing cao, ShiHao Zhao, Xingxing Guo, Aijun Wen, and Yue Hao

DOI: 10.1364/PRJ.422628 Received 15 Feb 2021; Accepted 29 Mar 2021; Posted 30 Mar 2021  View: PDF

Abstract: We experimentally and numerically demonstrate an approach to optically reproduce a pyramidal neuron-like dynamics dominated by dendritic Ca2+ action potentials (dCaAPs) based on a vertical-cavity surface-emitting laser(VCSEL) for the first time. The biological pyramidal neural dynamics dominated by dCaAPs indicate that the dendritic electrode evoked somatic spikes with current near threshold but failed to evoke (or evoked less) somatic spikes for higher current intensity. The emulating neuron-like dynamics are performed optically based on the injection locking, spiking dynamics, and damped oscillations in the optically injected VCSEL. Besides, the exclusive OR (XOR) classification task is examined in the VCSEL neuron equipped with the pyramidal neuron-like dynamics dominated by dCaAPs. Furthermore, a single spike or multiple periodic spikes are suggested to express the result of the XOR classification task for enhancing the processing rate or accuracy. The experimental and numerical results show that the XOR classification task is achieved successfully in the VCSEL neuron enabled to mimic the pyramidal neuron-like dynamics dominated by dCaAPs. This work reveals valuable pyramidal neuron-like dynamics in a VCSEL and offers a novel approach to solve XOR classification task with a fast and simple all-optical spiking neural network, hence shows great potentials for future photonic spiking neural networks and photonic neuromorphic computing.

Solving the century-old problem of incoherent imaging systems with synthetic aperture using a single opening instead of two

Angika Bulbul and Joseph Rosen

DOI: 10.1364/PRJ.422381 Received 09 Feb 2021; Accepted 25 Mar 2021; Posted 30 Mar 2021  View: PDF

Abstract: Imaging with an optical incoherent synthetic aperture (SA) means that the incoherent light from observed objects is processed over time from various points of view to obtain a resolution equivalent to single-shot imaging by the SA larger than the actual physical aperture. The operation of such systems has always been based on two-wave interference where the beams propagate through two separate channels. This limitation of two channels at a time is removed in the present study with the proposed SA where the two beams pass through the same single channel at any given time. The system is based on a newly developed self-interference technique named coded aperture correlation holography. At any given time, the recorded intensity is obtained from interference between two waves co-propagating through the same physical channel. One wave oriented in a particular polarization is modulated by a pseudorandom coded phase mask and the other one oriented orthogonally passes through an open subaperture. Both subapertures are multiplexed at the same physical window. The system is calibrated by a point spread hologram synthesized from the responses of a guidestar. All the measurements are digitally processed to achieve a final image with a resolution higher than obtained by the limited physical aperture. This unique configuration can eliminate the dependency of current cumbersome systems composed of far apart optical channels in the large optical astronomical interferometers and paves the way to a SA system with a single less-expensive compact light collector in an incoherent optical regime that may be utilized for the future ground-based or space telescopes.

Inflection point: a new perspective on photonic nanojets

Guoqiang Gu, Pengcheng Zhang, SiHai Chen, Yi Zhang, and Hui Yang

DOI: 10.1364/PRJ.419106 Received 06 Jan 2021; Accepted 25 Mar 2021; Posted 30 Mar 2021  View: PDF

Abstract: When light propagates through the edge or middle part of microparticle’s incoming interface, there is a basic rule that light converges and diverges rapidly or slowly at the output port. These two parts are referred to as region of rapid change (RRC) and region of slow change (RSC), respectively. Finding the boundary point between RRC and RSC is the key to reveal and expound this rule scientifically. Based on the correlation between light convergence-divergence and the slope of emergent light, combined with the relationship between natural logarithm and growth in physical reality and the second derivative of a function in practical significance, we determine the boundary point between RRC and RSC, namely the inflection point. From such perspective, photonic nanojet (PNJ) and near-field focusing by light irradiation on RSC and RRC, as well as the position of the inflection point under different refractive index contrast and the field distribution of light-focusing, are studied with finite-element-method-based numerical simulation and ray-optics-based theoretical analysis. By illuminating light of different field intensity ratios to the regions divided by the inflection point, we demonstrate the generation of photonic hook (PH) and the modulation of PNJ/PH in a new manner.

Genetic Algorithm based Deep Neural Networks for High-efficient photonic devices design

Yangming Ren, Lingxuan Zhang, Weiqiang Wang, Xinyu Wang, Yufang Lei, Yulong Xue, xiaochen sun, and Wenfu Zhang

DOI: 10.1364/PRJ.416294 Received 01 Dec 2020; Accepted 25 Mar 2021; Posted 30 Mar 2021  View: PDF

Abstract: Deep-learning have already demonstrated their tremendous potential for photonic structure design. Neural networks often need to prepare a large amount of labeled data to complete the training of thousands to millions of learning parameters. However, generating data requires physical simulations or experimental measurements. Collecting a massive dataset is time consuming, expensive and even not always practical. In order to reduce the burden of data collection, a highly efficient inverse design method of photonic devices using a deep learning approach is presented. The method combines neural networks with genetic algorithm, and optimizes the geometry of a photonic device in the polar coordinate system. The method requires significantly less training data compared with previous deep neural network inverse design methods. It presents great flexibility and high efficiency in designing ultra-compact photonic devices with challenging properties. We apply this method for designing several silicon photonics devices including power splitters with specific splitting ratios, a TE mode converter, and a broadband power splitter. These devices present good performance at micrometers footprint in full compliance with fabrication design rules.

Towards simple, generalizable neural networks with universal training for low SWaP hybrid vision

Baurzhan Muminov, Altai Perry, Rakib Hyder, Salman Asif, Luat Vuong, and Gavin OMalley

DOI: 10.1364/PRJ.416614 Received 07 Dec 2020; Accepted 25 Mar 2021; Posted 19 Apr 2021  View: PDF

Abstract: We demonstrate generalizable image reconstruction with the simplest of hybridmachine vision systems: fixed, linear optical preprocessors combined with no-hidden-layer,"small-brain" neural networks. Such neural network are capable of learning the reconstruction ofa "universal data training set" composed of Fourier, random, and vortex singularities. Modelsthat are trained with sinusoidal or random patterns uniformly distribute errors around the image,whereas models trained with datasets with vortices detect edges and corners more sharply.Although the spectral methods shown here are intuitive, the outcomes are not obvious from theneural network architectures. Reconstructed images carry a background behind objects thatlimit accuracy, which can be seen in the reconstruction of CIFAR images. With thresholdingand objects, we achieve consistent accuracy of<5%with the reconstruction of various disjointdatasets, including MNIST and Fashion MNIST. Our work is favorable for future real-timemachine vision systems: we reconstruct images on a 15W laptop CPU with 15k fps: faster by afactor of 3 than previously reported results and 3 orders of magnitude faster than convolutional neural networks.

FSR-free filters with ultra-wide tunability across S+C+L band

Lan Li, Chunlei Sun, Chuyu Zhong, Maoliang Wei, Hui Ma, Ye Luo, Zequn Chen, Renjie Tang, Jialing Jian, and Hongtao Lin

DOI: 10.1364/PRJ.420005 Received 15 Jan 2021; Accepted 24 Mar 2021; Posted 25 Mar 2021  View: PDF

Abstract: Optical filters are essential parts of advanced optical communication and sensing systems. Among them, the ones with an ultra-wide free-spectral range (FSR) are especially critical. They are promising to provide access to numerous wavelength channels highly desired for large-capacity optical transmission and multi-point multi-parameter sensing. Present schemes for wide-FSR filters either suffer from limited cavity length or poor fabrication tolerance or impose an additional active-tuning control requirement. We theoretically and experimentally demonstrate a filter that features FSR-free operation capability, sub-nanometer optical bandwidth, and acceptable fabrication tolerance. Only one single deep dip within a record-large waveband (S+C+L band) is observed by appropriately designing a side-coupled Bragg grating assisted Fabry-Perot (F-P) filter, which has been applied as the basic sensing unit for both the refractive index and temperature measurement. Five such basic units are also cascaded in series to demonstrate a multi-channel filter. This work provides a new insight to design FSR-free filters and opens up a possibility of flexible large-capacity integration using more wavelength channels, which will greatly advance integrated photonics in optical communication and sensing.

Spin-decoupled metalens with intensity-tunable multiple focal points

Bingshuang Yao, XiaoFei Zang, Yang Zhu, dahai yu, Jingya Xie, Lin Chen, Sen Han, Yiming Zhu, and Songlin Zhuang

DOI: 10.1364/PRJ.420665 Received 22 Jan 2021; Accepted 23 Mar 2021; Posted 25 Mar 2021  View: PDF

Abstract: The control of spin electromagnetic (EM) waves is of great significance in optical communications. Although geometric metasurfaces have shown unprecedented capability to manipulate the wavefronts of spin EM waves, they are still challenging to independently manipulate each spin state and intensity distributions, which inevitably degrades metasurface-based devices for further applications. Here, we propose and experimentally demonstrate an approach to designing spin-decoupled metalenses based on pure geometric phase, i.e. geometric metasurfaces with predesigned phase modulation possessing functionalities of both convex lenses and concave lenses. Under the illumination of left/right-handed circularly polarized (LCP (or RCP)) terahertz waves, these metalenses can generate transversely/longitudinally distributed RCP/LCP multiple focal points. Since the helicity-dependent multiple focal points are locked to the polarization state of incident THz waves, the relative intensity can be controlled with different weights of LCP and RCP THz waves, leading to the intensity-tunable functionality. This robust approach for simultaneously manipulating orthogonal spin states and energy distributions of spin EM waves will open a new avenue for designing multifunctional devices and integrated communication systems.

Superconducting microstrip single-photon detector with system detection efficiency over 90% at 1550 nm

Guangzhao Xu, Weijun Zhang, Lixing YOU, Jiamin Xiong, xingqu sun, HAO HUANG, Xin Ou, Yiming Pan, chaolin lv, Hao Li, Zhen Wang, and Xiaoming Xie

DOI: 10.1364/PRJ.419514 Received 11 Jan 2021; Accepted 23 Mar 2021; Posted 23 Mar 2021  View: PDF

Abstract: Generally, a superconducting nanowire single-photon detector (SNSPD) is composed of wires with a typical width of ~100 nm. Recent studies have found that superconducting stripes with a micrometer-scale width can also detect single photons. Compared with the SNSPD, the superconducting microstrip single-photon detector (SMSPD) have smaller kinetic inductance, higher working current, and lower requirement in fabrication accuracy, providing potential applications in the development of ultra-large active area detectors. However, the study on SMSPD is still in its infancy, and the realization of its high-performance and practical use remains an opening question. This study demonstrates a NbN SMSPD with a saturated system detection efficiency (SDE) of ~92.2% at a dark count rate of ~200 cps, a polarization sensitivity of ~1.03, and a timing jitter of ~48 ps, at the telecom wavelength of 1550 nm when coupled with a single mode fiber and operated at 0.84 K. Furthermore, the detector’s SDE is over 70% when operated at a 2.1-K closed-cycle cryocooler.

Non-iterative complex wave-field reconstruction based on Kramers-Kronig relations

Cheng Shen, Mingshu Liang, An Pan, and Changhuei Yang

DOI: 10.1364/PRJ.419886 Received 19 Jan 2021; Accepted 23 Mar 2021; Posted 25 Mar 2021  View: PDF

Abstract: A non-iterative and non-interferometric computational imaging method, synthetic aperture imaging based on Kramers-Kronig relations (KKSAI), to reconstruct complex wave-field is reported. By collecting images through a modified microscope system with pupil modulation capability, we show that the phase and amplitude profile of the sample at pupil limited resolution can be extracted from as few as two intensity images by using Kramers-Kronig (KK) relations. It is established that as long as each sub-aperture’s edge crosses the pupil center, the collected raw images are mathematically analogous to off-axis holograms. This in turn allows us to adapt a recently reported KK relations based phase recovery framework in off-axis holography for use in KKSAI. Since KKSAI is non-iterative, free of parameter tuning and is applicable to a wide range of samples, simulation and experiment results have proved that it has much lower computational burden and achieves the best reconstruction quality when compared with two existing phase imaging methods.

Lead-halide perovskites for next-generation self-powered photodetectors: A comprehensive review

Chandrasekar veeramalai, shuai feng, XIAOMING ZHANG, S.V.N Pammi, Vincenzo Pecunia, and Chuanbo li

DOI: 10.1364/PRJ.418450 Received 05 Feb 2021; Accepted 22 Mar 2021; Posted 22 Mar 2021  View: PDF

Abstract: Metal halide perovskites have aroused tremendous interest in optoelectronics due to their attractive properties, encouraging the development of high-performance devices for emerging application domains such as wearable electronics and Internet of Things. Specifically, the development of high-performance perovskite-based photodetectors, as an ultimate substitute for conventional photodetectors made up of inorganic semiconductors such as silicon, InGaAs, GaN and germanium based-commercial photodetectors, attracts great attention by virtue of its solution processing, film deposition technique and tunable optical properties. Importantly, perovskite photodetectors can also deliver high performance without external power source, so called self-powered perovskite photodetectors (SPPDs), and have found eminent application in next generation nanodevices operate independently, wirelessly and remotely. Earlier research reports clearly indicate that perovskite-based SPPDs have excellent photo responsive behavior and wide band spectral response ranges. This review aims to give a comprehensive summary of the research results on self-powered, lead-halide perovskite photodetectors. In spite of the high-performance perovskite photodetectors, their commercialization is hindered by long-term material stability under ambient conditions. So, commercial viability of perovskite photodetectors among the existing conventional photodetectors is highlighted. In addition, a brief introduction has been given on flexible, self-powered perovskite photodetectors. Finally, we put forward some perspective on the further development of perovskite based self-powered photodetector. We believe that this review can provide the state-of-the-art current research on self-powered perovskite photodetector and guide to the improvising path for enhancing the performance to meet the versatility of practical device application.

Fully transparent MOVPE-grown AlGaN-based tunnel heterojunction LEDs emitting at 2 nm

Frank Mehnke, Christian Kuhn, Martin Guttmann, Luca Sulmoni, Verena Montag, Johannes Glaab, Tim Wernicke, and M Kneissl

DOI: 10.1364/PRJ.414315 Received 09 Nov 2020; Accepted 21 Mar 2021; Posted 22 Mar 2021  View: PDF

Abstract: We present the growth and electro-optical characteristics of fully transparent AlGaN-based tunnel heterojunction light emitting diodes (LEDs) emitting at 2 nm entirely grown by metalorganic vapor phase epitaxy. A GaN:Si interlayer was embedded into a highly Mg- and Si-doped Al₀.₈₇Ga₀.₁₃N tunnel junction to enable polarization field enhanced tunneling. The LEDs exhibit an on-wafer integrated emission power of 77 μW at 5 mA which correlates to an external quantum efficiency (EQE) of 0.29% with 45 μW emitted through the bottom sapphire substrate and 32 μW emitted through the transparent top surface. After depositing a highly reflective aluminum reflector, a maximum emission power of 1.73 mW was achieved at 100 mA under pulsed mode operation with a maximum EQE of 0.35% as collected through the bottom substrate.

Lamellar hafnium ditelluride as an ultrasensitive surface-enhanced Raman scattering platform for label-free detection of uric acid

Yang Li, Haolin Chen, Yanxian Guo, Kangkang Wang, Yue Zhang, Peilin Lan, Jinhao Guo, Wen Zhang, Huiqing Zhong, Zhou Guo, Zhengfei Zhuang, and ZhinMing Liu

DOI: 10.1364/PRJ.421415 Received 04 Feb 2021; Accepted 20 Mar 2021; Posted 23 Mar 2021  View: PDF

Abstract: The development of two-dimensional (2D) transition metal dichalcogenides has been in rapid growth phase for the utilization in surface-enhanced Raman scattering (SERS) analysis. Herein, we report a promising 2D transition metal tellurides (TMTs) material, hafnium ditelluride (HfTe₂), as ultrasensitive platform for Raman identification of trace molecules, which demonstrates extraordinary SERS activity in sensitivity, uniformity and reproducibility. The highest Raman enhancement factor of 2.32 × 10⁶ is attained for rhodamine 6G molecule through the highly efficient charge transfer process at the interface between the HfTe₂ layered structure and the adsorbed molecules. At the same time, we provide an effective route for large-scale preparation of SERS substrates in practical applications via a facile stripping strategy. Further application of the nanosheets for reliable, rapid and label-free SERS fingerprint analysis of uric acid molecules, one of the biomarker associated with gout disease, is performed, which indicates arresting SERS signals with the limits of detection as low as 0.1 mM. The study based on this type of 2D SERS substrate not only reveals the great feasibility of applying TMTs to SERS analysis, also paves the way for nanodiagnostics, especially early marker detection.

Free-space Realization of Tunable Pin-like Optical Vortex Beams

domenico bongiovanni, Denghui Li, Michail Goutsoulas, Hao Wu, Yi Hu, Daohong song, Roberto Morandotti, Nikolaos Efremidis, and Zhigang Chen

DOI: 10.1364/PRJ.420872 Received 27 Jan 2021; Accepted 19 Mar 2021; Posted 19 Mar 2021  View: PDF

Abstract: We demonstrate, both analytically and experimentally, free-space ultra-long pin-like optical vortex beams. Such angular-momentum-carrying beams feature tunable peak intensity and undergo robust anti-diffracting propagation, realized by judiciously modulating both the amplitude and the phase profile of a standard laser beam. Specifically, they are generated by impressing a radially-symmetric power-law phase that adds an orbital angular momentum term carrying the intrinsic topological charge. During propagation, these vortex beams initially exhibit autofocusing dynamics in free-space. Subsequently, their amplitude patterns morph into a high-order Bessel-like profile, characterized by a hollow-core and an annular main-lobe with a constant or tunable width during propagation. In contrast with numerous previous endeavors on Bessel beams, our work represents the first demonstration of long-distance free-space generation of optical vortex “pins”, with their peak intensity evolution controlled by the impressed amplitude structure. Both the Poynting vectors and the optical radiation forces associated with these beams are also numerically analyzed, revealing fascinating properties that may be useful for a wide range of applications.

A Steering Paradox for Einstein-Podolsky-Rosen Argument and its Extended Inequality

Xiaoqi Zhou, Tianfeng Feng, Qin Feng, Changliang Ren, Maolin Luo, Xiaogang Qiang, and Jing-Ling Chen

DOI: 10.1364/PRJ.411033 Received 06 Oct 2020; Accepted 17 Mar 2021; Posted 19 Mar 2021  View: PDF

Abstract: The Einstein-Podolsky-Rosen (EPR) paradox is one of the milestones in quantum foundations, arising from the lack of local realistic description of quantum mechanics. The EPR paradox has stimulated an important concept of "quantum nonlocality", which manifests itself by three different types: quantum entanglement, quantum steering, and Bell nonlocality. Although Bell nonlocality is more often used to show the ``quantum nonlocality', the original EPR paradox is essentially a steering paradox. In this work, we formulate the original EPR steering paradox into a contradiction equality "k=1", thus making it amenable to an experimental verification. We perform an experimental test of the steering paradox "2=1" in a two-qubit scenario. Furthermore, by starting from the steering paradox "k=1', we generate a generalized linear steering inequality and transform this inequality into a mathematically equivalent form, which is more friendly for experimental implementation, i.e., one may only measure the observables in x-, y-, or z-axis, rather than other arbitrary directions. We also perform experiments to demonstrate this scheme. Within the experimental errors, the experimental results coincide with the theoretical predictions. Our results deepen the understanding of quantum foundations and provide an efficient way to detect the steerability of quantum states.

High-resolution two-photon transcranial imaging of brain using direct wavefront sensing

Congping Chen, Zhongya Qin, Sicong He, Shaojun Liu, Shun-Fat Lau, Wanjie Wu, Dan Zhu, Nancy Ip, and Jianan Qu

DOI: 10.1364/PRJ.420220 Received 20 Jan 2021; Accepted 14 Mar 2021; Posted 16 Mar 2021  View: PDF

Abstract: Imaging of the brain in its native state at high resolution poses major challenges to visualization techniques. Two-photon microscopy integrated with the thinned-skull or optical clearing skull technique provides a minimally invasive tool for in vivo imaging of the cortex of mice without activating immune response and inducing brain injury. However, the imaging contrast and resolution are severely compromised by the optical heterogeneity of the skull, limiting the imaging depth to the superficial layer. In this work, an optimized configuration of adaptive optics two-photon microscope system and new wavefront sensing algorithm are proposed for accurate correction for the aberrations induced by the skull window and brain tissue. Using this system, we achieved high-resolution transcranial imaging of layer 5 pyramidal neurons up to 700 µm below pia in living mice. In addition, we investigated microglia-plaque interaction in living brain of Alzheimer’s disease and demonstrated high-precision laser dendrotomy and single-spine ablation.

Cylindrical vector beam revealing multipolar nonlinear scattering for super-localization of silicon nanostructures

Bin Wang, Ying Che, Xiangchao Zhong, Wen Yan, Tianyue Zhang, Kai Chen, Yi Xu, Xiaoxuan Xu, and Xiangping Li

DOI: 10.1364/PRJ.419300 Received 08 Jan 2021; Accepted 10 Mar 2021; Posted 25 Mar 2021  View: PDF

Abstract: The resonant optical excitation of dielectric nanostructures offers unique opportunities for developing remarkable nanophotonic devices. Light that is structured by tailoring the vectoral characteristics of the light beam provides an additional degree of freedom in achieving flexible control of multipolar resonances at the nanoscale. Here, we investigate the nonlinear scattering of subwavelength silicon nanostructures with radially and azimuthally polarized cylindrical vector beams to show a strong dependence of the photothermal nonlinearity on the polarization state of the applied light. The resonant magnetic dipole, selectively excited by an azimuthally polarized beam, enables enhanced photothermal nonlinearity, thereby inducing large scattering saturation. In contrast, radially polarized beam illumination shows no observable nonlinearity owing to off-resonance excitation. Numerical analysis reveals a difference of more than two orders of magnitude in photothermal nonlinearity under two types of polarization excitations. Nonlinear scattering and the unique doughnut-shaped focal spot generated by the azimuthally polarized beam are demonstrated as enabling far-field high-resolution localization of nanostructured Si with an accuracy approaching 50 nm. Our study extends the horizons of active silicon photonics and holds great potential for label-free super-resolution imaging of silicon nanostructures.

Polarization-robust mid-infrared carpet cloak with minimized lateral shift

Yao Huang, Jingjing Zhang, Jinhui Zhou, Bo Qiang, Zhengji XU, Lin Liu, Jifang Tao, Nicolas Kossowski, Qijie Wang, and Yu Luo

DOI: 10.1364/PRJ.414437 Received 12 Nov 2020; Accepted 04 Mar 2021; Posted 25 Mar 2021  View: PDF

Abstract: With the advent and rapid development of the transformation optics and metamaterials, invisibility cloaks have captivated much attention in recent years. While most cloaking schemes suffer from limited bandwidth, the carpet cloak which can hide an object on a reflecting plane can operate over a broadband frequency range. However, carpet cloaks experimentally realized thus far still have several limitations. For example, the quasi-conformal mapping carpet cloak leads to a lateral shift of the reflected light ray, while the birefringent carpet cloak only works for a specific polarization. In this work, we propose a conformal transformation scheme to tackle these two problems, simultaneously. As an example, we design a mid-infrared carpet cloak in a silicon platform and demonstrate its polarization-insensitive property as well as the minimized lateral shift over a broad frequency band from 24 THz to 28.3 THz.

Phonon laser sensing in a hetero optomechanical crystal cavity

Kaiyu Cui, Zhilei Huang, Qiancheng Xu, Fei Pan, Jian Xiong, Xue Feng, Fang Liu, Wei Zhang, Yidong Huang, and ning wu

DOI: 10.1364/PRJ.403833 Received 30 Jul 2020; Accepted 01 Mar 2021; Posted 23 Mar 2021  View: PDF

Abstract: Micro- and nanomechanical resonators have emerged as promising platforms for sensing a broad range of physical properties, such as mass, force, torque, magnetic field, and acceleration. The sensing performance relies critically on the motional mass, the mechanical frequency, and the linewidth of the mechanical resonator. Herein, we demonstrate a hetero optomechanical crystal (OMC) cavity based on a silicon nanobeam structure. The cavity supports phonon lasing in a fundamental mechanical mode with a frequency of 5.91 GHz, an effective mass of 116 fg, and a mechanical linewidth narrowing in the range from 3.3 MHz to 5.2 kHz, while the optomechanical coupling rate is as high as 1.9 MHz. With this phonon laser, on-chip sensing can be attained with a resolution of δλ/λ = 1.0×10⁻⁸, which is at least two orders of magnitude larger than that obtained with conventional silicon-based sensors. The use of a silicon-based hetero OMC cavity that harnesses phonon lasing could pave the way toward high-precision sensors that allow silicon monolithic integration and offer unprecedented sensitivity for a broad range of physical sensing applications.

Towards smart optical focusing: Deep learning-empowered dynamic wavefront shaping in nonstationary scattering media

yunqi luo, Suxia Yan, Huanhao Li, Puxiang Lai, and Yuanjin Zheng

DOI: 10.1364/PRJ.415590 Received 20 Nov 2020; Accepted 21 Jan 2021; Posted 22 Jan 2021  View: PDF

Abstract: Optical focusing through scattering media is of great significance yet challenging in lots of scenarios, including biomedical imaging, optical communication, cybersecurity, and 3D displays etc. Wavefront shaping is a promising approach to solve this problem, but most implementations thus far have only dealt with static media which, however, deviates from realistic applications. Herein, we put forward a deep learning-empowered adaptive framework which is specifically implemented by a proposed Timely-Focusing-Optical-Transformation-Net (TFOTNet), and it effectively tackles the grand challenge of real-time light focusing and refocusing through time-variant media without complicated computation. The introduction of recursive fine-tuning allows timely focusing recovery, and the adaptive adjustment of hyperparameters of TFOTNet on the basis of medium changing speed efficiently handles the spatiotemporal non-stationarity of the medium. Simulation and experimental results demonstrate that the adaptive recursive algorithm with the proposed network significantly improves light focusing and tracking performance over traditional methods, permitting rapid recovery of an optical focus from degradation. It is believed that the proposed deep learning-empowered framework delivers a promising platform towards smart optical focusing implementations requiring dynamic wavefront control.

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