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Accepted papers to appear in an upcoming issue

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BGD-based Adam algorithm for time-domain equalizer in PAM-based optical interconnects

Ji Zhou, Haide Wang, Weiping Liu, Jianping Li, xincheng huang, Long Liu, Weixian Liang, Changyuan Yu, Fan Li, and Zhaohui Li

Doc ID: 380550 Received 17 Oct 2019; Accepted 14 Nov 2019; Posted 14 Nov 2019  View: PDF

Abstract: To the best of our knowledge, for the first time, we propose adaptive moment estimation (Adam) algorithm based on batch gradient descent (BGD) to design a time-domain equalizer (TDE) for PAM-based optical interconnects. Adam algorithm has been widely applied in the fields of artificial intelligence. For TDE, BGD-based Adam algorithm can obtain globally optimal tap coefficients without being trapped in locally optimal tap coefficients. Therefore, fast and stable convergence can be achieved by BGD-based Adam algorithm with low mean square error. Meanwhile, BGD-based Adam algorithm is implemented by parallel processing, which is more efficient than conventional serial algorithms, such as least mean square and recursive least square algorithms. The experimental results demonstrate that BGD-based Adam feed-forward equalizer works well in 120-Gbit/s PAM8 optical interconnects. In conclusion, BGD-based Adam algorithm shows great potential for converging the tap coefficients of TDE in future optical interconnects.

Development of high luminous efficacy red-emitting phosphor in glass (PiG) for high-power LED lighting system using our original low Tg and Ts glass

Sun Woog Kim, Young Ji Park, Gyu Jin Jeong, Jin-Ho Kim, Young Jin Lee, Cheol Jin Kim, and Jonghee Hwang

Doc ID: 378364 Received 20 Sep 2019; Accepted 14 Nov 2019; Posted 15 Nov 2019  View: PDF

Abstract: Red-emitting PiG materials with a high luminescence efficiency were developed by co-firing commercial red-emitting (Sr,Ca)AlSiN3:Eu2+ (SCASN) phosphor and our original glass frits with composition of Li2O-Na2O-ZnO-Al2O3-B2O3-P2O5, which has a low Tg (271 °C) and Ts (380 °C) temperatures. By optimizing the sintering temperature and the content of the phosphor, the highest luminous efficacy was obtained for the 3 wt% SCASN-based PiG sintered at 400 °C, which showed a luminous efficacy of 25 lm/Wrad by combining the PiG materials with a blue LED chip-on-board (COB; incident power = 100 mA). The internal quantum efficiency of this sample under excitation at 450 nm was 53%. The PiG-based LED maintained a high luminous efficacy when incident power of the blue COB increased up to 5.5W (47 lm).

Optical damage thresholds of microstructures made by laser 3D nanolithography

Agnė Butkutė, Laurynas Čekanavičius, Gabrielius Rimšelis, Darius Gaulevičius, Vygantas Mizeikis, Andrius Melninkaitis, Tommaso Baldacchini, Linas Jonusauskas, and Mangirdas Malinauskas

Doc ID: 378915 Received 26 Sep 2019; Accepted 14 Nov 2019; Posted 15 Nov 2019  View: PDF

Abstract: Direct laser writing based on non-linear 3D nanolithography (also known as 3D laser lithography, 3DLL) is a powerful technology to manufacture polymeric micro-optical components. However, practical applications of these elements are limited due to the lack of knowledge of their optical resilience and durability. In this work, we employ 3DLL for the fabrication of bulk (i.e. fully filled) and woodpile structures out of different photopolymers. We then characterize them using S-on-1 laser induced damage threshold (LIDT) measurements. In this way, quantitative data of LIDT values can be collected. Furthermore, this method permits to gather damage morphologies. The results presented in this work demonstrate that LIDT values depend on the material and the geometry of the structure. Bulk non-photosensitized hybrid organic-inorganic photopolymer SZ2080 structures are found to be the most resilient with a damage threshold being of 169±15 mJ/cm2.

Engineering colors in all-dielectric metasurfaces: metamodeling approach

Alma González-Alcalde, Rafael Salas-Montiel, Victor Kalt, Sylvain Blaize, and Demetrio Macias

Doc ID: 379704 Received 07 Oct 2019; Accepted 14 Nov 2019; Posted 15 Nov 2019  View: PDF

Abstract: In this letter, we engineer the colors of all-dielectric metasurfaces by means of a meta-model based optimization approach. This algorithm combines heuristic optimization and neural networks to retrieve the metasurface's optimal geometrical parameters that serve to reproduce a prescribed color. The metasurfaces were fabricated and experimentally validated through dark field optical microscope images. We present typical results for periodic arrays of nanoparticles with arbitrary cross section. The approach is well-suited for color reproduction and computationally inexpensive.

1030-nm passively Q-switched Yb-doped fiber laser using excited-state absorption of thulium fiber

Tzong-Yow Tsai and Zhi-Cheng Lee

Doc ID: 381946 Received 29 Oct 2019; Accepted 14 Nov 2019; Posted 15 Nov 2019  View: PDF

Abstract: We demonstrated a pulsed ytterbium all-fiber laser passively Q-switched using excited-state absorption of thulium fiber and mode-field-area mismatch. The absorption cross section of the excited state 3F4 was measured and determined to be the key factor inducing pulsing, and it was much higher than that of the ground state 3H6 over 0.95 to 1.15 μm. By successfully realizing the pulsed laser at 1030 nm, which is the most critical wavelength for Q-switching, we verified that the excite state 3F4 of Tm3+ could be a full-range saturable-absorber Q-switch for a Yb fiber laser over 1.0 to 1.15 μm.

In-band crosstalk-induced power penalties in various signal modulation formats

Chul Han Kim

Doc ID: 379089 Received 03 Oct 2019; Accepted 13 Nov 2019; Posted 13 Nov 2019  View: PDF

Abstract: A simple equation for the estimation of in-band crosstalk-induced power penalty has been derived by considering the symbol peak power as well as the impact of average inter-symbol distance in various modulation formats of optical signals. The derived equation can easily estimate the in-band crosstalk-induced penalty by considering the level of crosstalk and Q-value. Among various formats of signals, the in-band crosstalk-induced penalties in on-off keying (OOK), differential quadrature phase shift keying, and pulse amplitude modulation-4 (PAM-4) signals have been estimated for comparison. From the results, we reconfirmed that the OOK non-return-to-zero signal would be 9 dB more tolerant to in-band crosstalk than the PAM-4 signal. The estimated results agreed well with the measured results.

Sub-50 fs, µJ-level pulses from a Mamyshev regenerator-amplifier system

Paul Repgen, Dieter Wandt, Uwe Morgner, Joerg Neumann, and Dietmar Kracht

Doc ID: 381674 Received 28 Oct 2019; Accepted 12 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We present a Mamyshev regenerator with an output power of 332 mW and a pulse energy of 31 nJ which is directly amplified in an additional fiber section. By balancing the gain narrowing effect with self-phase modulation during the amplification, we achieved an average output power of 11 W, corresponding to a pulse energy of more than 1 µJ. The pulse duration can be compressed to sub-50 fs behind the amplification stage.

Cross-sectional refractive-index variations in fiber Bragg gratings measured by quantitative phase imaging

Grayson Noah, Yijun Bao, and Thomas Gaylord

Doc ID: 377794 Received 13 Sep 2019; Accepted 12 Nov 2019; Posted 13 Nov 2019  View: PDF

Abstract: Unexpected micron-scale patterns in the induced refractive index of various commercial fiber Bragg gratings (FBGs) are observed in the cross-sectional fiber directions which are in addition to the expected periodic variations along the fiber axis. These measurements were made using 3D tomographic deconvolution phase microscopy (TDPM), a type of quantitative phase imaging (QPI). The cross-sectional patterns observed are shown to exhibit a variety of appearances including fringes normal to the fiber axis and radial blades, the details apparently depending on the FBG writing method. Such patterns appear to be due to the interaction of the locally inhomogeneous structure of the Ge-doped glass with the high-intensity exposure light.

Interconversion of orbital and spin angular momentum of light beams in sum-frequency generation process from the surface of isotropic chiral medium

Kirill Grigoriev, Vladislav Diukov, and Vladimir Makarov

Doc ID: 379023 Received 02 Oct 2019; Accepted 12 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We study the interaction between spin and orbital components of the angular momentum of the electromagnetic waves in the sum-frequency generation process at reflection from a surface of the nonlinear isotopic chiral medium. Both bulk and near-surface response of the medium are taken into account. Classical and quantum explanation of particular features of three-wave mixing on the surface of nonlinear medium are presented.

32-Gb/s chaotic optical communications by deep learning-based chaos synchronization

junxiang ke, Lilin Yi, Zhao Yang, yunpeng yang, Qunbi Zhuge, Yaping Chen, and Weisheng Hu

Doc ID: 380030 Received 09 Oct 2019; Accepted 12 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: Chaotic optical communications were originally proposed to provide high-level physical layer security for optical communications. Limited by the difficulty of chaos synchronization, experimental demonstration of high-speed chaotic optical communications is only a few and point to multi-point chaotic optical networking is hard to be implemented. Here, we propose a method to overcome the current limitations. By using a deep-learning-based scheme to learn the complex nonlinear model of the chaotic transmitter, wideband chaos synchronization can be realized in the digital domain. Therefore, the chaotic receiver can be significantly simplified while still guaranteeing security. A successful transmission of 32-Gb/s messages hidden in a wideband chaotic optical carrier was experimentally demonstrated over a 20-km fiber link. We believe the proposed deep-learning-based chaos synchronization method will enable a new direction for further development of high-speed chaotic optical communication systems and network.

Time-resolved investigation of the optical phase change as a potential diagnostics tool for XUV FEL pump - optical probe experiments

Victor Tkachenko, Sven Toleikis, Vladimir Lipp, Beata Ziaja, and Ulrich Teubner

Doc ID: 380271 Received 23 Oct 2019; Accepted 12 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: Measurement of transient optical properties (reflectivity and transmissivity) is widely performed in extreme ultraviolet (XUV) pump - optical probe experiments to study the transient state of irradiated materials. In order to extend the material diagnostics, here we propose an additional measurement of the transient phase change of the optical probe pulse. It can be recorded in parallel to other transient optical properties, enabling access to the full information on the refractive index and the thickness of the radiation-modified material layer. The latter is essential for investigations of phase transitions progressing in XUV (and X-ray) irradiated materials. We perform a computational study that clearly shows that the measurement of the optical phase from a probe pulse at correctly tuned pulse parameters can provide a signal strong enough to extract information on transient material properties. The calculations suggest that in some cases it is even more preferable to measure the transient phase change than other optical parameters. Such phase measurement, feasible with modern experimental setups, can then be a basis for an improved diagnostic tool for the temporal characteristics of an ultrashort XUV pulse.

Kink-based mirrorless quasi-bistability in resonantly absorbing media

Denis Novitsky and Alexander Shalin

Doc ID: 378802 Received 25 Sep 2019; Accepted 12 Nov 2019; Posted 13 Nov 2019  View: PDF

Abstract: Optical bistability, the basic nonlinear phenomenon mediating the control of light by light, paves the way to the all-optical logic being of ultimate demand for a plethora of applications in laser information technologies. The desirable features of the optically bistable elements are low power consumption, speed of switching and small size. The two most general designs are driven by the presence or absence of an external feedback giving rise to a variety of possible setups. Among them, mirrorless architecture seems promising being free of bulky mirrors, resonant cavities, photonic crystals, etc. In this paper, we propose a novel method to achieve optical quasi-bistability governed by the formation of specific nonlinear waveforms called ``kinks'. We show that a thin layer of the relatively dilute resonant medium specially designed to support kinks could serve as a platform for compact, ultra-fast, low power optical switching. This new physical mechanism do not require high densities of resonant particles specific for other feedback-free devices driven by local field corrections and dipole-dipole interactions, and enhance the overall practical relevance of such devices for optical computing.

Iterative reconstruction for general linear imaging polarimetry without polarimetric calibration

Feng Han, Tingkui Mu, Donghao Bao, Abudusalamu Tuniyazi, Qiuxia Li, Hang Gong, Zeyu Chen, and Chunmin Zhang

Doc ID: 378633 Received 25 Sep 2019; Accepted 12 Nov 2019; Posted 14 Nov 2019  View: PDF

Abstract: Usually, the practical analysis states of an imaging polarimeter must be calibrated, with a set of standard polarization states, for the accurate reconstruction of Stokes parameters. However, it is challenged to get the standard elements for the polarimetric calibration. In this letter, an iterative reconstruction method is presented at the first time to recover the polarization parameters from the data acquired by linear-Stokes polarimeters without polarimetric calibrations. Inspired from phase shifting interferometry, the method employs two least-squares iterative procedure and requires no any extra element for assistant. Experimental results show that the iterative method is more robust to noise perturbation and gets higher reconstruction accuracy compared to the traditional calibration method with reference polarization states.

Compact terahertz spectrometer based on sequential modulation of disordered rough surfaces

Tao Yang, Yue Zhang, Jiacheng Ge, Lei Wang, Yi-qiang QIN, Y Zhu, Wei Huang, and Ho-Pui Ho

Doc ID: 377509 Received 23 Sep 2019; Accepted 12 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We present herein a compact THz spectrometer in which transmission intensity distribution associated with dispersive interference effects in disordered random surfaces are used for reconstructing the frequency contents of an incoming THz beam. The device sweeps the frequency-dependent parameter of a roughened transmission plate through lateral displacement or electro-optic modulation. 2-D transmission intensities are sequentially captured by a single detector for a range of modulation depths. With a calibration data set as the reference, one can reconstruct the spectra of the probe terahertz beam by solving a system of simultaneous linear equations. A smoothing Tikhonov regularization approach has been implemented to improve the accuracy of the spectral reconstruction. The reported compact, broadband, high-resolution terahertz spectrometer is well suited for portable terahertz spectroscopy applications.

High spectral purity photons generation from a dual-interferometer coupled silicon microring

Yingwen Liu, Chao Wu, Xiaowen Gu, yuechan kong, xinxin yu, Renyou Ge, Xinlun Cai, Xiaogang Qiang, Junjie Wu, xuejun yang, and Ping Xu

Doc ID: 376986 Received 26 Sep 2019; Accepted 11 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We experimentally demonstrate a high spectral purity photon source by designing a dual-Mach-Zehnder-interferometer coupled silicon ring resonator wherein the linewidths of pump and signal (idler) resonances can be engineered independently. A high spectral purity of 95%±1.5% is obtained via g² correlation measurement which exceeds the theoretical 93% bound of traditional ring's spontaneous four-wave mixing photon source. This source also possesses high performance in other metrics including a measured coincidence of 9599 pairs/s and a preparation heralding efficiency of 52.4% at a relatively low pump lower of 61 μW as well as a high drop-to-through suppression of 20.2 dB. By overcoming the trade-off between the spectral purity and brightness in the post-filtering way, such method guarantees the bright pure photons and will pave the development of on-chip quantum information processing with improved operation fidelity and efficiency.

Strain-induced tunable dual-bottle shaped optical microresonator

Haoye Qin, Yiheng Yin, and Ming Ding

Doc ID: 379633 Received 11 Oct 2019; Accepted 11 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: We present a novel dual-bottle microresonator with a high Q-factor exceeding 10⁷. Such a resonator consists of two lateral resonators and one central resonator. The maximum diameter of the lateral resonator is ~ 180 µm and the central diameter is 124.91 µm. Characteristics of the WGM spectra are investigated and explained by the microbottle resonance, modes interference and scattering effects. Strain tuning sensitivity varies from 0.126 to 1.7 pm/µε when tapered fiber is placed at the resonator’s different positions. With coupled area at the middle of the central resonator, the highest strain sensitivity of 1.7 pm/µε is achieved, which is higher than previously reported solid microresonator strain sensors.

Ghost imaging normalized by second-order coherence

Shuai Sun, WeiTao Liu, Jun-Hao Gu, Huizu Lin, Liang Jiang, Yao-Kun Xu, and Ping-Xing Chen

Doc ID: 382082 Received 30 Oct 2019; Accepted 11 Nov 2019; Posted 14 Nov 2019  View: PDF

Abstract: Towards improvements on the quality of reconstructed image, the errors in the point spread function of ghost imaging system caused by limited number of samplings and imperfect illumination is discussed. We propose an algorithm by normalizing with the second- order coherence of the illumination field, with which the errors caused by imperfect illumination can be reduced, such as non-uniform spatial distribution of the average intensity, spatial varying profile of the second- order degree of coherence, or power fluctuation.

100 µJ, 100 kHz, CEP-Stable High-Power Few-Cycle Fiber Laser

Evgeny Shestaev, D Hoff, A SAYLER, Arno Klenke, Steffen Hadrich, Florian Just, Tino Eidam, Péter Jójárt, Zoltan Várallyay, Karoly Osvay, Gerhard Paulus, Andreas Tünnermann, and Jens Limpert

Doc ID: 377169 Received 06 Sep 2019; Accepted 11 Nov 2019; Posted 14 Nov 2019  View: PDF

Abstract: We present a CEP-stable Yb-doped fiber laser system delivering 100 µJ few-cycle pulses at a repetition rate of 100 kHz. The CEP stability of the system when seeded by a CEO-locked oscillator is 360 mrad, as measured pulse-to-pulse with a Stereo-ATI phase meter. Slow CEP fluctuations have been suppressed by implementing a feedback loop from the phase meter to the pulse picking AOM. To the best of our knowledge, this is the highest CEP stability achieved to date with a fiber-based, high-power few-cycle laser.

Expansion of the FOV in speckle autocorrelation imaging by spatial filtering

Meijun Chen, Honglin Liu, Zhentao Liu, Puxiang Lai, and Shensheng Han

Doc ID: 379750 Received 07 Oct 2019; Accepted 10 Nov 2019; Posted 15 Nov 2019  View: PDF

Abstract: Optical imaging through inhomogeneous media based on correlations suffers from a limited field of view (FOV) since the optical memory effect of a scattering medium has its inherent angular extent. Here we successfully expand the angle memory effect range (AMER) by exploiting a spatial filtering technique to select low frequency components, mainly ballistic light and less-scattered light, thereby increasing the FOV of the speckle autocorrelation imaging. Both simulation and experimental verifications are presented. This technique, not limited to the discussed 4f structure, can provide a guideline for the design of an optical system to image through scattering media.

Real-time transition dynamics between multi-pulsing states in a mode-locked fiber laser

Junjie Zeng and Michelle Sander

Doc ID: 377895 Received 02 Oct 2019; Accepted 10 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: We experimentally studied the transition dynamics between multi-pulsing states, specifically, the build-up and annihilation of soliton pulses between a double pulsing and a three-pulse state, utilizing the dispersive Fourier transform technique. The birth of an additional pulse in a mode-locked soliton fiber laser in a multi-pulsing regime arises from a dispersive wave that experiences strong intensity fluctuations while the other pulses maintain their shapes. During the decaying process to a double pulsing state, it is observed that all the pulses undergo a unique breathing behavior before settling into steady-state.

Dense parallax images acquisition method using single-pixel imaging for integral photography

Tetsuhiko Muroi, Ren Usami, Teruyoshi Nobukawa, Masato Miura, Norihiko Ishii, and Eriko Watanabe

Doc ID: 377299 Received 09 Sep 2019; Accepted 09 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: In Integral photography, it is difficult to obtain three-dimensional photographs with high spatial resolution, high angular resolution, and a wide viewing angle, simultaneously. Thus, we proposed a dense parallax images acquisition method using single-pixel imaging. We confirmed that parallax images can be obtained depending on the position of the photo detector. By replacing the detector to each pixel of an image sensor, a two-dimensional image with different parallax in each pixel can be acquired. We demonstrated the reconstruction of dense parallax images according to the pixel position of the image sensor. This method is effective in addressing the trade-off among spatial resolution, angular resolution, and viewing angle. It can also improve the image quality in integral photography.

Dither-free stabilization of a femtosecond doubly-resonant OPO using parasitic sum-frequency mixing

Yuk Shan Cheng, Richard McCracken, and Derryck Reid

Doc ID: 378020 Received 13 Sep 2019; Accepted 09 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: Stable operation of a doubly-resonant femtosecond optical parametric oscillator (OPO) requires sub-micron matching of the OPO and pump-laser cavity lengths, which is normally implemented using a dither-locking feedback scheme. Here we show that parasitic sum-frequency-mixing between the pump and resonant pulses of a degenerate femtosecond OPO provides an error signal suitable for actuating the cavity length with the precision needed to maintain oscillation on a single fringe and at maximum output power. Unlike commonly used dither-locking approaches, the method introduces no modulation noise and requires no additional optical components, except for one narrowband filter. The scheme is demonstrated on a Ti:sapphire-pumped sub-40-fs PPKTP OPO, from which data are presented showing a tenfold reduction in relative intensity noise compared with dither locking.

Efficient Electro-optical Tuning of Optical Frequency Microcomb on a Monolithically Integrated High-Q Lithium Niobate Microdisk

Zhiwei Fang, Haipeng Luo, Jintian Lin, Min Wang, Rongbo Wu, Jianhao Zhang, Junxia Zhou, Wei Chu, Tao Lu, and Ya Cheng

Doc ID: 378433 Received 20 Sep 2019; Accepted 09 Nov 2019; Posted 13 Nov 2019  View: PDF

Abstract: We demonstrate efficient tuning of a monolithically integrated lithium niobate microdisk (LN) optical frequency microcomb. Utilizing the high optical quality (Q) factor (i.e., Q~7.1×10^6) of the microdisk, the microcomb spans over a spectral bandwidth of ~200 nm at a pump power as low as 20.4 mW. Combining the large eletro-optic coefficient of LN and optimum design of the geometry of microelectrodes, we demonstrate electro-optical tuning of the comb with a spectral range of 400 pm and a tuning efficiency of ~38 pm/100V.

Reconstructing 3D point clouds in real time with look-up tables for structured light scanning still objects along both horizontal and vertical directions

Kai Liu, Jianwen Song, Daniel Lau, Xiujuan Zheng, Ce Zhu, and Xiaomei Yang

Doc ID: 376275 Received 26 Aug 2019; Accepted 08 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: By scanning still, not moving, objects along both the horizontal and vertical axes instead of one, structured light illumination achieves more accurate and robust 3D surface reconstructions but with greater latency on computing 3D point clouds. If scanning is performed along only one axis, it has been reported look-up tables, manually derived from the calibration matrices of a camera and a projector, can significantly help to speed up computation; however, it has been nearly impossible to manually derive similar look-up tables for phases scanned along two axes. In this Letter, we bridge this divide by introducing the constraint of epipolar geometry to automatically compute look-up tables and, thus, significantly speed up computing 3D point clouds only with basic arithmetic operations rather than time-consuming matrix computations. Experimental results show that the proposed method, only using single-thread CPU computing, reduces process latency by an order of magnitude.

High power 2 GHz fs-pulsed all-fiber laser at 2.0 micrometer

tian qiao, Huihui Cheng, Xiaoxiao Wen, Wenlong Wang, Wei Lin, yi zhou, Yuankai Guo, Yicai Liu, and Zhongmin Yang

Doc ID: 380127 Received 11 Oct 2019; Accepted 08 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: High power fs-pulsed all-fiber lasers operating at high repetition rates are highly demanded for various applications, including laser micromachining, nonlinear optical imaging, high-speed optical sampling, arbitrary waveform generation and frequency metrology. However, their performance has long been limited by either the average power, repetition rate, pulsewidth or compactness, which prevents practical applications. In this work, we report a high repetition rate fs-pulsed all-fiber laser at 2.0 micrometer that so far provides the best performance metrics, to the best of our knowledge, i.e., ~2 GHz fundamental repetition rate, 126 fs pulsewidth, ~8 W average power and all-fiber configuration. We anticipate that this laser can be a promising fs-pulsed fiber laser source for applications requiring a GHz repetition rate.

Frequency-agile injection-seeded terahertz-wave parametric generation

Yoshikiyo Moriguchi, Yu Tokizane, Yuma Takida, Kouji Nawata, Shigenori Nagano, Manabu Sato, Taiichi Otsuji, and Hiroaki Minamide

Doc ID: 376683 Received 30 Aug 2019; Accepted 08 Nov 2019; Posted 08 Nov 2019  View: PDF

Abstract: An injection-seeded terahertz (THz)-wave parametric generator (is-TPG) enables access to low-frequency fingerprints of molecules in the THz frequency region. However, its conventional scan-rate is limited below 1 Hz. Thus, we propose an electrically controlled tuning system for the is-TPG, which provides high-speed scanning and random hopping agility. We achieved rapid THz frequency sweeping on a pulse-by-pulse basis by employing a gain-switched laser diode and a micro-electro-mechanical system tunable vertical-cavity surface-emitting laser as the pump and seed lasers. A THz spectrum was acquired with a ten times higher scan rate of 10 Hz for the 1–3 THz range with a frequency resolution of 4.6 GHz.

High performance sub-wavelength grating-based resonator sensors with substrate overetch

Enxiao Luan, Kashif Awan, Karen Cheung, and Lukas Chrostowski

Doc ID: 380097 Received 14 Oct 2019; Accepted 07 Nov 2019; Posted 08 Nov 2019  View: PDF

Abstract: We propose a strategy to improve sensing performance of sub-wavelength grating (SWG) waveguide-based sensors by introducing a substrate-overetch (SOE) geometry. The proposed SOE-SWG waveguide shows enhanced analyte interaction and a reduced group index, which improves the sensitivity of resonator-based sensors. The SiO2 overetch process was realized in Ar/C4F8/O2 plasma for 40 sec with a SiO2/Si selectivity of 10:1, obtaining a 285-nm anisotropic overetch in the SiO2 layer. Sensor performance of the SOE-SWG architecture is characterized by using isopropyl alcohol solutions, indicating an enhanced bulk sensitivity up to 575 nm/RIU (479 nm/RIU before the SOE), and a maximum waveguide mode sensitivity larger than 1.

Phase shifted modal interferometers for high accuracy optical fiber sensing

Joel Villatoro

Doc ID: 377351 Received 09 Sep 2019; Accepted 07 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: The use of two separated, compact modal interferometers with an adequate phase shift is proposed for precision optical fiber sensing. The output spectrum of interferometers with such features is a well-defined peak. Changes in wavelength position or amplitude of said peak caused by a measurand can be detected with high precision. The advantages of phase-shifted interferometers for sensing include sensitivity enhancement, easy implementation, simple interrogation, and compactness, among others. The concept is demonstrated by placing two supermode interferometers in series that were built with multicore fiber to sense vibrations with low frequencies and low amplitudes. However, many other parameters can be sensed. The sensing architecture here proposed can also be implemented with other type of optical fiber interferometers and the advantages mentioned above can be achieved.

Artificial compound eye tipped optical fiber for wide field illumination

Feng Chen, Feng Liu, Qing Yang, Hao Bian, Fan Zhang, Xun Hou, and Depeng Kong

Doc ID: 378866 Received 26 Sep 2019; Accepted 07 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: In this letter, we present a novel component with beam delivering and wide field beam homogenizing functions by grafting of artificial compound eye (ACE) micro-structure onto the polymer optical fiber (POF) end face. The three dimensional (3D) ACE mold is fabricated by femtosecond laser-assisted micro machining, and the ACE micro-structure is transferred onto the end face through high accuracy nano-imprinting. The resultant POF end integrates over 400 spherical micro-lenses, enabling a 40% enhancement in both acceptance angle and effective numerical aperture. Meanwhile, the integrated ommatidia array serves as an outstanding beam homogenizer, shaping the output beam into quasi flat-top distribution, which is demonstrated promising in wide field homogeneous illumination, by reflection and transmission imaging experiments in both visible and near infrared bands.

Laser speckle auto-inverse covariance imaging for mean-invariant estimation of blood flow

Pengcheng Li, jiachi hong, liang shi, Xuan Zhu, and Jinling Lu

Doc ID: 380428 Received 15 Oct 2019; Accepted 07 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: Laser speckle contrast imaging maps the changes in blood flow by estimating the decorrelation time of scattered light field through speckle contrast. However, the speckle contrast is a biased statistic estimator which results in a theoretic bias between its expected value and the true value. Moreover, the average of speckle contrast depends on the statistical sampling size, which further hinders the estimation of decorrelation time from speckle contrast. Here, we present a new unbiased statistics based on auto-inverse covariance to improve the estimation of decorrelation time using laser speckle. Theoretical and experimental results demonstrated that the speckle auto-inverse covariance analysis is mean-invariant so that the average of the estimation is not dependent on the sampling size. Furthermore, it can produce less statistical fluctuation and consume less computation time than that speckle contrast analysis did.

Constant intensity conical diffraction in discrete one-dimensional lattices with charge-conjugation symmetry

Mojgan Dehghani, Cem Yuce, Tsampikos Kottos, and Hamidreza Ramezani

Doc ID: 375589 Received 21 Aug 2019; Accepted 07 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We engineer anomalous conical diffraction (CD), occurring in discrete one-dimensional lattices with charge-conjugation symmetry when an exceptional point (EP) is in the proximity of the modes that compose the initial excitation. The evolving waveform propagates ballistically, acquiring a constant intensity profile within the boundaries of the spreading cone. The linear increase in the total intensity along the propagation direction is responsible for the generation of the constant intensity CD.

All-optical control of pattern dynamics generated by Airy beams

Lamyae Drouzi, Jordan Maufay, Marc Sciamanna, D Wolfersberger, and Nicolas Marsal

Doc ID: 379137 Received 30 Sep 2019; Accepted 07 Nov 2019; Posted 07 Nov 2019  View: PDF

Abstract: We study a pattern forming system driven by two counter propagating 2D Airy beams in a nonlinear single feedback configuration. When increasing the Airy beam power, modulation instability takes place but with several successive instability thresholds that correspond to destabilization of the different Airy beam satellite lobes. Most importantly, the self-organization is accompanied by a natural drifting dynamics related to the intrinsic acceleration of the Airy beam. The drifting dynamics is controlled by the Airy beam parameters. Numerical simulations reproduce the experimental findings.

Asymmetric near-zero edge mode in a topological photonic lattice

Kaiwen Ji, Zhengjuan Liu, Yanan Dai, Zengrun Wen, Yishan Wang, Guoquan Zhang, Jintao Bai, and Xinyuan Qi

Doc ID: 371790 Received 10 Jul 2019; Accepted 07 Nov 2019; Posted 08 Nov 2019  View: PDF

Abstract: Generally speaking, a system will degenerate into a topological trivial one and the edge state will also disappear once the topological condition is violated, e.g., the values of the coupling constants in a waveguide array are exchanged. In this Letter, we study both theoretically and numerically the light dynamics in a photonic system without chiral or particle-hole symmetry. The results indicate that the system can restore its original Zak phase by removing an edge waveguide. Further study shows that the system can support an asymmetric near-zero mode on the right edge even if the Hamiltonian of the system is not chiral or particle-hole symmetric. Our work provides a new way to realize photonic near-zero mode which may have important applications in the future quantum computation.

Creation of complex nano-interferometric field structures

Zhongsheng Man, Peiwen Meng, and Shenggui Fu

Doc ID: 374530 Received 05 Aug 2019; Accepted 07 Nov 2019; Posted 08 Nov 2019  View: PDF

Abstract: With dual two-dimensional Airy-like waveforms, we demonstrate the creation of highly-confined electromagnetic fields in the transverse plane and circular or elliptical propagation trajectories in the longitudinal plane by using specially designed Pancharactnam–Berry (PB) phases. Applying the Richards and Wolf vectorial diffraction methods, the explicit expressions are obtained to calculate the strength vectors and energy flux of the three-dimensional electromagnetic fields. Calculations reveal that the nano-interferometric structures of such highly-confined fields highly depend on the indexes γ1 and γ2 determining the PB phase, thereby enabling the engineering of highly-confined fields with tunable size, spacing and propagation trajectories.

Bismuth plasmonics for extraordinary light absorption in deep sub-wavelength geometries

Imre Ozbay, Amir Ghobadi, Bayram Butun, and GONUL TURHAN-SAYAN

Doc ID: 379670 Received 15 Oct 2019; Accepted 06 Nov 2019; Posted 07 Nov 2019  View: PDF

Abstract: In this letter, we demonstrate an ultra-broadband metamaterial absorber of unrivaled bandwidth (BW) using extraordinary optical response of Bismuth (Bi) metal; a material selected through our analysis methodology. Based on our theoretical model, we investigate the maximum metal-insulator-metal (MIM) cavity BW achievable by any metal with a known n-k data. We show that an ideal metal in such structures should have positive real permittivity part in the near-infrared (NIR) regime. Contrary to noble and lossy metals utilized by most research groups within the field, this requirement is satisfied only by Bi, whose data greatly adheres to the ideal material properties predicted by our analysis. A Bi nano disc based MIM resonator with an absorption above 0.9 in an ultra-broadband range of 800 nm- 90 nm is designed, fabricated, and characterized. To the best of our knowledge, this is the broadest absorption BW reported for a MIM cavity in the near infrared with its upper to lower absorption edge ratio exceeding best contenders by more than 150%. According to the findings of this paper, the use of proper materials and dimensions will lead to realization of deep sub-wavelength efficient optical devices.

Quasi-distributed fiber-optic acoustic sensing system with an ultra-low noise level based on pulse compression technique and phase-noise compensation configuration

Mengshi Wu, Xinyu Fan, Qingwen Liu, and Zuyuan He

Doc ID: 379833 Received 08 Oct 2019; Accepted 06 Nov 2019; Posted 07 Nov 2019  View: PDF

Abstract: In this letter, an ultra-low noise level is achieved for a quasi-distributed acoustic sensing system. This system is based on pulse compression technique and phase noise compensation configuration. In this system, a prototype of weak reflector array is designed and fabricated to have a ∼-40 dB reflectivity with a 20-m interval, and used for improving the system signal-to-noise ratio (SNR). The two techniques reduce the noise level by 18 dB, among which 11.56 dB is obtained with the assist of the phase noise compensation configuration. In the experiment to simulate the scenario with a link loss of 20 km and 20 m array interval, the system noise level is demonstrated to be -93.16 dB re rad/√Hz @500-2500Hz, which equals to a strain resolution of 92.84 fε/√Hz@500-2500 Hz.

Origin of continuous curves and dotted spots in laser transverse modes with geometric structures

Yung-Fu Chen, Jung-Chen Tung, M. X. Hsieh, Y. H. Hsieh, Hsing-Chih Liang, and K. F. Huang

Doc ID: 381875 Received 30 Oct 2019; Accepted 06 Nov 2019; Posted 08 Nov 2019  View: PDF

Abstract: The transverse structures of geometric modes in degenerate laser resonators with large astigmatism are systematically investigated by starting from the Gaussian wave-packet formulation with ray-wave connections. The overlapping degree D between Gaussian wave packets is derived as an analytic expression that manifests the critical overlapping with D=1. The transverse patterns are confirmed to display a structure of continuous curves or dotted spots, depending on D>1 or D<1, respectively. A thorough comparison between experimental results and numerical calculations is performed to validate the theoretical analysis. The present exploration provides useful insights not only into exploring the Lissajous geometric modes but also into designing the multiple-pass resonators.

Frequency-Doubled FDML-MOPA Laser in the Visible

Sebastian Karpf and Bahram Jalali

Doc ID: 378919 Received 26 Sep 2019; Accepted 05 Nov 2019; Posted 08 Nov 2019  View: PDF

Abstract: Wavelength-swept lasers enable high-speed measurements in absorption spectroscopy [1], Raman spectroscopy [2], nonlinear Raman hyperspectral microscopy [3, 4], rapid confocal microscopy [5], short impulse generation [6] and most importantly for high speed optical coherence tomography (OCT) [7-11] with speeds up to video-rate volumetric imaging [12]. Recently, we introduced a pulsed wavelength-swept laser based on the Fourier Domain Mode-Locked (FDML) Laser principle [8] combined with a Master-Oscillator Power Amplifier (MOPA) architecture [13]. The high peak powers reached with this laser enabled rapid two-photon microscopy and two-photon fluorescence lifetime microscopy (FLIM) [14] and high-speed LIDAR measurements [15]. Here we present the extension of this laser into the visible wavelength range by frequency doubling the output from 1064nm to 532nm via second harmonic generation (SHG) in a DKDP crystal. The result is a wavelength-swept laser source around 532nm that outputs a pulse train of distinct, almost monochromatic wavelengths at 88MHz pulse repetition rate and 342kHz sweep repetition rate. This swept-source laser in the visible can open up new research applications in spectroscopy, metrology, sensing, and high-speed imaging.

Optical modulation characteristics of Zeolitic Imidazolate Framework-67 (ZIF-67) in the near infrared regime

Hongwei Chu, Han Pan, Xiao Wang, Ying Li, Shengzhi Zhao, Guiqiu Li, and Dechun Li

Doc ID: 380948 Received 18 Oct 2019; Accepted 05 Nov 2019; Posted 06 Nov 2019  View: PDF

Abstract: We reported the passively Q-switched (PQS) operation in the near infrared (NIR) regime with as-prepared Zeolitic Imidazolate Framework-67 (ZIF-67) as saturable absorbers (SAs) for the first time, to the best of our knowledge. Based on the excellent saturable absorption properties of the as-prepared ZIF-67, passively Q-switched Nd:GdVO4 lasers were achieved operating at 4F3/2 → 2I11/2 and 4F3/2 → 2I13/2 transitions. The stable Q-switched lasers pulses with a pulse duration of 120 ns at a repetition rate of 566 kHz and a pulse duration of 108 ns at a repetition rate of 415 kHz were obtained, corresponding to the transition 4F3/2 → 2I11/2 at 1 μm and transition 4F3/2 → 2I13/2 at 1.3 μm respectively. The results indicate that the ZIF-67 saturable absorber with advantages of large modulation depth and high thermal stability is a promising saturable absorber candidate for the NIR pulse generation.

Amorphous Ga-Sb-Se thin films fabricated by co-sputtering

Tomáš Halenkovič, JAN GUTWIRTH, Marek Bouska, laurent calvez, Petr Nemec, and Virginie Nazabal

Doc ID: 378913 Received 02 Oct 2019; Accepted 05 Nov 2019; Posted 05 Nov 2019  View: PDF

Abstract: Ternary chalcogenides of Ga-Sb-Se system are prospective materials for potential applications in the field of infrared optics. This letter deals with the optical properties and photosensitivity and of Ga-Sb-Se thin films deposited by co-sputtering, enabling to fabricate amorphous thin films outside the glass-forming region. The optical bandgap range 1.92-1.35 eV with corresponding refractive index at 1.55 μm ranging from 2.47-3.33 can be reliably covered using Ga2Se3 and Sb2Se3 targets. Furthermore, the prolonged irradiation by the near-bandgap light under the pure argon atmosphere leads to the irreversible photo-bleaching effect in fabricated films. The magnitude of this effect decreases monotonically with an increasing antimony content.

Optical properties of spherulite opals

Yallapragada Jayasurya and Dan Oron

Doc ID: 372660 Received 24 Jul 2019; Accepted 05 Nov 2019; Posted 05 Nov 2019  View: PDF

Abstract: Spherulites are birefringent sturctures with spherical symmetry, which are typically observed in crystallized polymers. We compute the band structure of opals made of close-packed assemblies of highly birefringent spherulites. We demonstrate that spherulitic birefringence of constituent spheres does not affect the symmetries of an opal, and yet significantly affects the dispersion of eigenmodes, leading to new pseudogaps in sections of the band structure, and consequently enhanced reflectivity.

High-efficiency Raman conversion in SF6 and CF4-filled hollow-core photonic bandgap fibers

Shahar Edelstein and Amiel Ishaaya

Doc ID: 374509 Received 06 Aug 2019; Accepted 04 Nov 2019; Posted 05 Nov 2019  View: PDF

Abstract: We present a comparative experimental investigation of vibrational stimulated Raman scattering in hollow-core photonic bandgap fibers pressurized with Sulfur hexafluoride (SF6) and Tetrafluoromethane (CF4) gases. Ns-duration pulses at a wavelength of 1030 nm are coupled into the gas-filled fiber, and the first and second Stokes orders are measured at the fiber output. We characterize the conversion process as a function of gas, fiber length and input power. With a 15 m fiber filled with SF6, we obtain conversion efficiency to the first Stokes of 55.7% at an input peak power of 0.63 kW. In comparison, with CF4 we obtained a higher conversion threshold and maximum conversion efficiency of 45.4%. To the best of our knowledge, this is the first reported conversion experiment with hollow-core fibers filled with SF6 gas.

Cell-specific three-photon-fluorescence brain imaging: neurons, astrocytes, and gliovascular interfaces

Alexandr Lanin, Matvey Pochechuev, artem chebotarev, ilya kelmanson, Dmitry Bilan, Darya Kotova, Victor Tarabykin, Anatoly Ivanov, Andrey Fedotov, Vsevolod Belousov, and Aleksei Zheltikov

Doc ID: 377494 Received 11 Sep 2019; Accepted 04 Nov 2019; Posted 05 Nov 2019  View: PDF

Abstract: We present brain imaging experiments on rat cortical areas, demonstrating that, when combined with a suitable high-brightness, cell-specific genetically encoded fluorescent marker, three-photon-excited fluorescence (3PEF) enables subcellular-resolution, cell-specific 3D brain imaging modality that is fully compatible and readily integrable with other nonlinear-optical imaging modalities, including two-photon-fluorescence and harmonic-generation microscopy. With laser excitation provided by sub-100-fs, 1.25-μm laser pulses, cell-specific 3PEF from astrocytes and their processes detected in parallel with a three-photon-resonance-enhanced third harmonic from blood vessels is shown to enable a high-contrast 3D imaging of gliovascular interfaces.

Incident angle dependence-reduced-polarization grating performance by using optically biaxial polymer liquid crystal

Ryusei Momosaki, Kazunari Ashikawa, Moritsugu Sakamoto, Kohei Noda, Tomoyuki Sasaki, Nobuhiro Kawatsuki, and Hiroshi Ono

Doc ID: 378009 Received 27 Sep 2019; Accepted 04 Nov 2019; Posted 05 Nov 2019  View: PDF

Abstract: We have succeeded in forming the polarization grating whose polarization diffraction properties are extremely independent of the incident angle by using the polymer liquid crystal exhibiting biaxial optical anisotropy. It is considered that the extension of the optical path length and the decrease in the effective amplitude of optical anisotropy due to oblique incidences are offset by the biaxial optical anisotropy, and as a result, the retardation is compensated. The properties of this developed device have been experimentally demonstrated and also theoretically explained.

Prism lens for beam collimation in silicon photonic crystal beam-steering device

Jun Maeda, Daichi Akiyama, Hiroyuki Ito, Hiroshi Abe, and Toshihiko Baba

Doc ID: 379187 Received 30 Sep 2019; Accepted 04 Nov 2019; Posted 05 Nov 2019  View: PDF

Abstract: The doubly-periodic Si photonic crystal waveguide operates as a nonmechanical beam-steering device that can be applied to light detection and ranging. This study develops a prism lens that collimates a fan-shaped beam emitted from the waveguide independent of the steering angle. Its fundamental profile is investigated using theoretical analysis for thick lenses and then its detailed aspherical design is obtained. In ray tracing, this prism lens suppresses beam divergence to less than the diffraction limit in most of the targeted beam-steering range. The prism lens is fabricated by acrylic cutting and its expected characteristics are observed.

Nanosecond pulsed 620 nm source by frequency-doubling a phosphosilicate Raman fiber amplifier

Anita Chandran, Timothy Runcorn, Robert T. Murray, and J. Taylor

Doc ID: 381243 Received 25 Oct 2019; Accepted 04 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We demonstrate a nanosecond pulsed source at 620 nm with watt-level average power by frequency-doubling a 1240 nm phosphosilicate Raman fiber amplifier. A gain-switched laser diode operating at 1064 nm is amplified in an ytterbium fiber master oscillator power amplifier system, and then converted to 1240 nm using a phosphosilicate Raman fiber amplifier with a conversion efficiency of up to 66%. The Raman fiber amplifier is seeded with a continuous-wave 1240 nm laser diode to obtain narrow-linewidth radiation, which is subsequently frequency-doubled in a periodically poled lithium tantalate crystal. A maximum average power of 1.5 W is generated at 620 nm, corresponding to a pulse energy of 300 nJ at a repetition rate of 5 MHz. The source has excellent beam quality (M² ≤ 1.16) and an optical efficiency (1064 nm to 620 nm) of 20%, demonstrating an effective architecture for generating red pulsed light for biomedical imaging applications.

On-chip Fourier-transform spectrometers and machine learning: a new route to smart photonic sensors

alaine herrero, Jiangfeng Li, Mohammad Khazaei, Yuri Grinberg, Aitor Velasco, Martin Vachon, Pavel Cheben, Lina Stankovic, Vladimir Stankovic, Dan-Xia Xu, Jens Schmid, and Carlos Alonso-Ramos

Doc ID: 371219 Received 27 Jun 2019; Accepted 04 Nov 2019; Posted 04 Nov 2019  View: PDF

Abstract: Miniaturized silicon photonics spectrometers capable of detecting specific absorption features have great potential for mass market applications in medicine, environmental monitoring, and hazard detection. However, state-of-the-art silicon spectrometers are limited by fabrication imperfections and environmental conditions, especially temperature variations, since uncontrolled temperature drifts of only 0.1 °C distort the retrieved spectrum precluding the detection and classification of the absorption features. Here, we present a new strategy that exploits the robustness of machine learning algorithms to signal imperfections, enabling recognition of specific absorption features in a wide range of environmental conditions. We combine on-chip spatial heterodyne Fourier-transform spectrometers and supervised learning to classify different input spectra in the presence of fabrication errors, without temperature stabilization or monitoring. We experimentally show differentiation of four different input spectra under an uncontrolled 10 °C range of temperatures, about 100x increase in operational range, with a success rate up to 82.5% using state-of-the-art support vector machines and artificial neural networks.

Dynamics of Strongly Coupled Two-Component Plasma via Ultrafast Spectroscopy

Alexander Bataller, Alexandra Latshaw, John Koulakis, and Seth Putterman

Doc ID: 377988 Received 17 Sep 2019; Accepted 04 Nov 2019; Posted 04 Nov 2019  View: PDF

Abstract: A combination of ultrafast emission and transmission spectroscopy is presented that provides a model-independent temperature measurement and tracking of the expansion dynamics for a dense, strongly coupled plasma. For femtosecond laser breakdown of hydrogen gas at 10 bar, we observe a 30,000K two-component plasma for hundreds of picoseconds where both electrons and protons have a strong coupling parameter value of Γ~0.5. Furthermore, the plasma’s degree of ionization (45%) results in a condition where the Debye screening length (6 Å) is less than the interatomic spacing (13 Å). Plasma formation occurs under an isochoric initial condition which simplifies hydrodynamic modeling of the plasma channel expansion. The channel radius is found to accelerate at a constant rate until the front is moving with the speed of sound. Comparing hydrogen and deuterium for the same breakdown conditions grants unique insight into the hydrodynamics of strongly coupled plasma due to their nearly identical electronic structure yet large mass difference. The ultimate goal of these experiments is to access and measure a region of strongly coupled plasma parameter space where continuum mechanics becomes non-local, as compared to, for instance, the hydrodynamic motion described by the Navier-Stokes equations.

A Stretchable and Upconversion-Luminescent Polymeric Optical Sensor for Wearable Multifunctional Sensing

Jingjing Guo, Bingqian Zhou, Changxi Yang, Qionghai Dai, and Lingjie Kong

Doc ID: 380015 Received 09 Oct 2019; Accepted 04 Nov 2019; Posted 04 Nov 2019  View: PDF

Abstract: Stretchable sensors with multiple sensory functions are highly demanded for healthcare monitoring and artificial intelligence. Despite recent advances in wearable electronic sensors, it remains a significant challenge to achieve simultaneous sensing of both thermal and mechanical stimuli with a single sensor while integrating high stretchability. Herein, a stretchable and multifunctional optical sensor (SMOS) with simultaneous readout of temperature and strain is developed for wearable physiological monitoring of human body. The SMOS primarily consists of a stretchable optical sensing fiber made from polymer nanocomposites containing Lanthanide-based upconversion nanoparticles (Ln-UCNPs). Temperature measurements are achieved by ratiometric intensity measurements of the dual-emission UCNPs upon near-infrared (NIR) excitation. By virtue of the ratiometric detection, the temperature readout of the SMOS is independent of strain deformations, enabling stable and continuous measurements of skin temperature during body motions. Furthermore, deformation of the SMOS by stretching leads to detectable and reversible changes in its light transmission, allowing tensile strains to be simultaneously measured. As a proof of concept, we demonstrate the capabilities of the SMOS in real-time and simultaneous detection of both skin temperature and motion activities of the human body.

Enhanced multiple-plane phase retrieval using adaptive support

Christian Ray Buco and Percival Almoro

Doc ID: 377252 Received 09 Sep 2019; Accepted 03 Nov 2019; Posted 04 Nov 2019  View: PDF

Abstract: In the single-plane phase retrieval method, the use of a fixed object support is not efficient and could lead to inaccurate reconstructions. While there have been adaptive support strategies for the single-plane method, numerical processing is slow because such strategies are based in the space domain. Here a novel adaptive support strategy based in the Fourier domain in conjunction with the multiple-plane phase retrieval method is presented and demonstrated through simulations and experiments. Optimisations of Fourier filter size and mask threshold parameters resulted in 3x faster convergence compared to the conventional multiple-plane method for the test object waves used. The proposed strategy offers fast and automated determination of the object support, affords the use of fewer intensity patterns, and can be adopted in other multiple intensity-based phase retrieval methods.

Intensity noise suppression of a high-power single-frequency CW laser by controlling the stimulated emission rate

Yongrui Guo, Huadong Lu, Weina Peng, Jing Su, and Kunchi Peng

Doc ID: 379744 Received 10 Oct 2019; Accepted 03 Nov 2019; Posted 06 Nov 2019  View: PDF

Abstract: The intensity noise of a high-power single-frequency continuous-wave laser is very harmful for applications in precise measurements and quantum communication. By simply lengthening the length of a laser resonator to decrease the stimulated emission rate of laser, the coupling strength of all noise sources into the resonant laser field will be reduced and thus the intensity noise of the output laser will be prominently suppressed. Based on theoretical analyses of the laser noise spectra, we experimentally implement a low noise high-power single-frequency laser with 1050 mm-long resonator. With the assistance of an intracavity imaging system and nonlinear second-harmonic-generation, the amplitude of resonant relaxation oscillation peak and the shot noise level (SNL) cutoff frequency are successfully reduced to 8.6 dB/Hz above the SNL and 1.0 MHz, respectively, under the output power of 16 W. The work provides an effective way to develop a high-quality laser with high output power and low intensity noise.

Fast diffraction-limited image recovery through turbulence via subsampled bispectrum analysis

Byungjae Hwang, Taeseong Woo, and Jung-Hoon Park

Doc ID: 378420 Received 19 Sep 2019; Accepted 03 Nov 2019; Posted 05 Nov 2019  View: PDF

Abstract: Imaging through temporally changing aberrations is a common challenge that can be found in many different fields such as astronomy, long-range surveillance, and deep tissue bio-imaging. Based on the notions originally developed in speckle interferometry, time varying aberrations can be used to our advantage to obtain diffraction limited resolution images through turbulence via bispectrum analysis. However, due to the heavy computational load brought on by the triple correlation and the phase extraction process, widespread use has been limited. Here, we demonstrate a novel Fourier domain subsampling scheme that can accelerate the speed of bispectrum analysis by more than two orders of magnitude. In contrast to other approaches for parallelization such as those based on Radon transform or image segmentation, our proposed method enables diffraction-limited imaging without suffering from resolution loss or image artifacts.

Femtosecond laser micro-machining enabled all-fiber mode selective converter

Zhang Cong, Li Zhuoying, Songnian Fu, Ming Tang, and Deming Liu

Doc ID: 378208 Received 18 Sep 2019; Accepted 03 Nov 2019; Posted 05 Nov 2019  View: PDF

Abstract: We demonstrate a compact all-fiber mode selective converter enabled by femtosecond laser micro-machining on the few-mode fiber (FMF) facet. By introducing micro-structure into the FMF core, we can achieve a π spatial phase difference to the fundamental mode of light to be converted. Theoretical optimization reveals that various high-order modes, including LP11, LP02, and LP21 modes, can be selectively converted by various femtosecond laser inscribed micro-structures on the FMF facet, with mode extinction ratio of more than 25dB and mode coupling efficiency of better than 45% over the C-band. Finally, a proof-of-concept experiment is conducted by inscribing a micro-slot on the two-mode fiber (TMF) facet for the LP01 to LP11 mode conversion. A micro-slot with a width of 6.7μm and a depth of 5.4μm is fabricated under the optimal femtosecond laser parameters. A LP01 to LP11 mode conversion with an average insertion loss of 2.7dB is realized over the C-band, together with a mode intensity profile correlation efficient of more than 65%. Efficient higher-order mode conversion is feasible with a precise femtosecond laser micro-machining.

Measurement of effective nonlinear coefficients in few-mode fiber

Liang Cui, Xiaodong Liu, Cheng Guo, Zhenzhen Zhang, Ningbo Zhao, Michael Vasilyev, and Xiaoying Li

Doc ID: 378864 Received 26 Sep 2019; Accepted 01 Nov 2019; Posted 04 Nov 2019  View: PDF

Abstract: Because of the random mode coupling, the nonlinear coefficient in few-mode fibers (FMFs) is averaged to an effective value, which can be theoretically modeled and calculated by using the multi-mode Manakov equations. In this Letter, we experimentally measure the effective nonlinear coefficients in a 530-m-long FMF supporting two mode groups, namely, the LP₀₁ and LP₁₁ mode groups, by exploiting the self-phase and cross-phase modulations of pulsed fields. By using the nonlinear coefficient of the LP₀₁ mode as a reference and comparing the spectral broadening of the pulsed fields, we obtain the intra-modal effective nonlinear coefficient of the LP₁₁ mode and the inter-modal effective nonlinear coefficient between the LP₀₁ and LP₁₁ modes. The experimental results are in good agreement with the theoretical predictions of the multi-mode Manakov equations.

Carbon dioxide absorption spectroscopy with a mid-infrared silicon photonic waveguide

Floria Ottonello-Briano, Carlos Errando-Herranz, Henrik Rödjegård, Hans Martin, Hans Sohlström, and Kristinn Gylfason

Doc ID: 370397 Received 25 Jun 2019; Accepted 01 Nov 2019; Posted 06 Nov 2019  View: PDF

Abstract: Carbon dioxide is a vital gas for life on Earth, a waste product of human activities, and widely used in agriculture and industry. Its accurate sensing is therefore of great interest. Optical sensors exploiting the mid-infrared light absorption of CO₂ provide high selectivity, but their large size and high cost limit their use. Here, we demonstrate CO₂ gas sensing at 4.2 μm wavelength using an integrated silicon waveguide, featuring a sensitivity to CO₂ of 44 % that of free-space sensing. The suspended waveguide is fabricated on a silicon-on-insulator substrate by a single-lithography step process, and we route it into a mid-infrared photonic circuit for on-chip-referenced gas measurements. Its demonstrated performance and its simple and scalable fabrication make our waveguide ideal for integration in miniaturized CO₂ sensors for distributed environmental monitoring, personal safety, medical, and high-volume consumer applications.

Kapitza Light Guiding in Photonic Mesh Lattice

Andre Luiz Muniz, Alessandro Alberucci, Jisha Pannian, Monika Monika, Stefan Nolte, Roberto Morandotti, and Ulf Peschel

Doc ID: 378043 Received 17 Sep 2019; Accepted 01 Nov 2019; Posted 04 Nov 2019  View: PDF

Abstract: We experimentally demonstrate the transverse confinement of light in the presence of a longitudinally periodic photonic potential with vanishing average. In agreement with Kapitza’s original findings in classical mechanics, we confirm that light undergoes a transverse localization due to the action of an effective potential proportional to the square of the first derivative of the potential. Experiments are performed based on (1+1)D synthetic dimensions realized in a fiber loop system, allowing for complete control of the transverse and longitudinal distribution of the potential.

Polarization-Based Truncated SU(1,1) Interferometer based on Four-wave Mixing in Rb vapor

Nikunj Prajapati and Irina Novikova

Doc ID: 377485 Received 11 Sep 2019; Accepted 31 Oct 2019; Posted 04 Nov 2019  View: PDF

Abstract: We propose and demonstrate a polarization-based truncated SU(1,1) interferometer that outputs the desired optical joint-quadrature of a two-mode squeezed vacuum field and allows its measurements using a single balanced homodyne detector. Using such setup we demonstrated up to 1.8 dB of quantum noise suppression below the shot-noise limit in intensity-difference and phase-sum joint quadratures, and confirmed entanglement between the two quantum fields. Our proposed technique results in a better balance between the two ports of the detector and, consequently, in better common noise suppression for differential measurements. As a result, we were able to observe flat joint-quadrature squeezing and entanglement at wide range of detection frequencies: from several MHz (limited by the photodiode gain bandwidth) down to a few hundred Hz (limited by electronic noises).

Measurement of bending-induced birefringence in a hollow-core photonic crystal fiber

Dongyun Chung, Hee Su Park, Fabian Rotermund, and Byoung Kim

Doc ID: 375331 Received 29 Aug 2019; Accepted 31 Oct 2019; Posted 31 Oct 2019  View: PDF

Abstract: We report the measurement of bending-induced birefringence in the presence of large intrinsic birefringence in a hollow-core photonic crystal fiber. The fast axis of bending-induced birefringence was found to be normal to the bending plane, contrary to the conventional fiber case. The dependence of the induced birefringence on the bending radius was also different from the typical inverse square law. Possibilities and design criteria for polarization controllers using bending-induced birefringence in hollow-core photonic crystal fibers are presented.

Ionization-assisted refocusing of femtosecond Gaussian beams

Xiaohui Gao, Gauri Patwardhan, Bonggu Shim, and Alexander Gaeta

Doc ID: 378372 Received 20 Sep 2019; Accepted 31 Oct 2019; Posted 31 Oct 2019  View: PDF

Abstract: Ionization occurs ubiquitously in intense laser-matter interaction and often leads to rapid decrease in laser intensity via plasma defocusing, shortening the effective interaction length of desired high-field processes. Refocusing of pulses may compensate for this adverse effect. However, it typically relies on Kerr-induced self-focusing and requires a sufficiently high power. Here we present simulations showing the refocusing of intense pulses with an initial Gaussian beam profile in atmospheric pressure gases at a relatively low power. We attribute this refocusing to the formation of ring-structure plasmas. We find that, a tighter focusing leads to a stronger refocusing, and the initial chirp of the pulse greatly affects its dynamics due to spatio-temporal coupling of focused broadband pulses. Our results highlight a novel aspect of complex pulse dynamics, and can be relevant to applications involving tightly focused ultrafast Gaussian beams.

Fiber optic-based Laser Interferometry Array for Three Dimensional Ultrasound Sensing

Xiangdong Ma, Yiqi Cai, Bo Fu, Lijun Xu, and jianguo ma

Doc ID: 378504 Received 02 Oct 2019; Accepted 31 Oct 2019; Posted 31 Oct 2019  View: PDF

Abstract: Ultrasound imaging is promising in medicine due to the non-invasive, radiation-free, and real-time features. In recent years, optic resonance-based ultrasound sensors performed higher sensitivity and broader bandwidth than piezoelectric ultrasound transducers. However, they worked at specific laser wavelengths or angles only, which was unavailable for array sensing. On the contrary, non-resonance based optical sensing arrays did not perform sufficient bandwidth or frame rate. Optical ultrasound sensing arrays for medical imaging is still in demand. In this research, we propose a fiber optic-based ultrasound sensing array at medical frequency with high sensitivity, broad bandwidth, and three dimensional (3D) sensing capabilities. In the experiment, the optical ultrasound sensor exhibited a noise equivalent pressure of <200 Pa, a signal-to-noise ratio of 46.8 dB, a -6 dB bandwidth from almost 0 to at least 27. 2 MHz, a pressure linearity of <5%, and a -3 dB angular uniformity up to ±71°. For the 3D sensing capability in spherical coordinates, the radial distance error was <5%, the polar angle error was <4°, and the azimuthal angle error was <2°. In brief, this research demonstrated the viability and high performance of the optical fiber array for 3D ultrasound sensing.

Avalanche-like behavior of up-conversion luminescence by nonlinear coupling of pumping rates

Mikhael Korolkov, Inna Khodasevich, Alexander Grabtchikov, Dmitri Mogilevtsev, and Elena Kolobkova

Doc ID: 376708 Received 30 Aug 2019; Accepted 30 Oct 2019; Posted 04 Nov 2019  View: PDF

Abstract: Here we report and discuss the avalanche-like up-conversion behavior in absence of the avalanche. We experimentally observed significant changes in the slope of the curve for the intensity dependence of up-conversion luminescence of erbium ions in green band (520–560 nm) on the pump intensity of the diode laser. Such changes are typical for the photon avalanche. However, the concentration of erbium ions is insufficient for an efficient exchange of energy between them, and excitation of a photon avalanche is not possible. Using a simple three-level approximation of the up-conversion process model, we have shown that the observed avalanche-like luminescence process can also occur in the absence of a photon avalanche due to the non-linear relation between the efficiency of two pumping channels of erbium ion caused by intensity dependence of the absorption.

High-magnification shadowgraphy for the study of drop breakup in a high-speed gas flow

Hazem El-Rabii and Luc Biasiori-Poulanges

Doc ID: 377180 Received 05 Sep 2019; Accepted 30 Oct 2019; Posted 30 Oct 2019  View: PDF

Abstract: Direct observation of the droplet breakup process in high-speed gas flows is a critical challenge that needs to be addressed to elucidate the physical mechanisms underlying the fragmentation phenomenon. Here, we present a high-magnification and high-speed shadowdograph technique that allows the visualization of this process over its whole evolution and resolves detailed features of the breakup zone. The developed experimental method uses a high-speed camera equipped with a long-distance microscope. The backlight illumination source is provided by the laser-induced fluorescence of a dye solution that delivers short pulses at a high-repetition rate. Artefacts resulting from the laser coherence are therefore reduced.

Generation of high-repetition-rate few-cycle mid-infrared pulses by optical modulation of CW QCLs and ICLs

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

Doc ID: 378485 Received 24 Sep 2019; Accepted 30 Oct 2019; Posted 30 Oct 2019  View: PDF

Abstract: We demonstrate an effective method to obtain high-repetition-rate few-cycle mid-infrared (mid-IR) pulses by modulating mid-IR continuous-wave (CW) quantum and interband cascade lasers (ICLs and QCLs). In the experiment, a high-repetition-rate femtosecond ytterbium-doped fiber laser with nJ-level pulse energy was used as the pump source of optical parametric amplifiers (OPA) to modulate and amplify the mid-IR CW laser. Near transform-limited (TL) 84-fs duration (7.3 cycles) mid-IR pulses were generated with above 200 mW average power and a repetition rate of 160 MHz. Moreover, the spectral tunability was demonstrated using mid-IR CW lasers at different wavelengths. The scheme offered a simple method to produce high-repetition-rate ultrafast pulses and that can be flexibly adopt in other mid-IR region.

Highly efficient tunable picosecond deep ultraviolet laser system for Raman spectroscopy

Anton Shutov, Georgi Petrov, Da-Wei Wang, Marlan Scully, and Vladislav Yakovlev

Doc ID: 379495 Received 02 Oct 2019; Accepted 30 Oct 2019; Posted 30 Oct 2019  View: PDF

Abstract: We present a narrowband laser system tunable from 219 to 246 nm for the deep ultraviolet Raman spectroscopy. The demonstrated laser system produces 6.7 ps transform-limited pulses with the peak power more than 50 kW. The system consists of a two-staged optical parametric amplifier of a narrow-band CW diode laser and subsequent frequency conversion to the DUV radiation. We achieve more than 300 mW in the signal wave using LBO (LiB₃O₅) and BBO (BaB₂O₄) crystals, with the total 2.7 W pump after two staged OPA. We reach 12% conversion efficiency of the OPA signal wave into the deep ultraviolet radiation using type-I phasematching in BBO crystal. Finally, we demonstrate the applicability of the system for DUV Raman spectroscopy by collecting a high-dynamic range, high spectral resolution spontaneous Raman spectrum of air.

Coherent propulsion with negative-mass fields in a photonic lattice

Yumiao Pei, Yi Hu, Ping Zhang, Chunmei Zhang, Cibo Lou, Christian Haunhorst, Detlef Kip, Demetrios Christodoulides, Zhigang Chen, and Jingjun Xu

Doc ID: 370069 Received 14 Jun 2019; Accepted 29 Oct 2019; Posted 31 Oct 2019  View: PDF

Abstract: We demonstrate the first coherent propulsion with negative-mass fields in an optical analog. We observe a self-accelerating state driven by nonlinear coherent interaction of its two components with opposite “mass” signs in a photonic lattice. Surprisingly, the coherent propulsion is highly immune to the initial phase of the two components, in sharp contrast with the behavior encountered in traditional coherent wave interactions. Comparing to its incoherent counterpart, the coherent propulsion exhibits an enhanced acceleration. Our study may herald new possibilities in a variety of physical systems involving negative-mass dynamics for both fundamental interests and potential applications.

Non-Bloch PT symmetry breaking in non-Hermitian Photonic Quantum Walks

Stefano Longhi

Doc ID: 378042 Received 17 Sep 2019; Accepted 29 Oct 2019; Posted 30 Oct 2019  View: PDF

Abstract: A hallmark of topological band theory in periodic media is that bulk properties are not affected by boundary conditions. Remarkably, in certain non-Hermitian lattices the bulk properties are largely affected by boundaries, leading to such major effects as the non-Hermitian skin effect and violation of the bulk-boundary correspondence. Here we unveil that non-unitary discrete-time quantum walks of photons in systems involving gain and loss show rather generally non-Bloch parity-time (PT) symmetry breaking phase transitions, and suggest a bulk probing method to detect such boundary-driven phase transitions.

Chirp-controlled high-harmonic and attosecond-pulse generation via coherent-wake plasma emission driven by mid-infrared laser pulses

Alexander Mitrofanov, Dmitry Sidorov-Biryukov, Pavel Borisovich, Mikhail Rozhko, Evgeny Stepanov, Anton Shutov, Sergey Ryabchuk, Aleksandr Voronin, Andrey Fedotov, and Aleksei Zheltikov

Doc ID: 374617 Received 05 Aug 2019; Accepted 29 Oct 2019; Posted 29 Oct 2019  View: PDF

Abstract: Coherent-wake plasma emission induced by ultrashort mid-infrared laser pulses on a solid target is shown to give rise to high-brightness, high-order harmonic radiation, offering a promising source of attosecond pulses and a probe for ultrafast subrelativistic plasma dynamics. With 80-fs, 0.2-TW pulses of 3.9-micrometer radiation used as a driver, optical harmonics up to the 34th order are detected, with their spectrum stretching from the mid-infrared to the extreme ultraviolet. The harmonic spectrum is found to be highly sensitive to the chirp of the driver. Particle-in-cell analysis of this effect suggests, in agreement with the generic scenario of coherent-wake emission, that optical harmonics are radiated as trains of extremely short, attosecond ultraviolet pulses with a pulse-to-pulse interval varying over the pulse train. A positive chirp of the driver pulse can partially compensate for this variation in the interpulse separation, allowing harmonics of highest orders to be generated in the plasma emission spectrum.

Angle-adjustment based tunable chirped mirrors with continuous dispersion compensation

Ruiyi Chen, yanzhi wang, Kesheng Guo, Yuhui Zhang, Zhihao Wang, Meiping Zhu, Kui Yi, Yuxin Leng, and Jianda Shao

Doc ID: 380701 Received 16 Oct 2019; Accepted 29 Oct 2019; Posted 04 Nov 2019  View: PDF

Abstract: We report the feasibility of continuously tunable dispersion control with chirped mirrors (CMs). The concept of tunable second-order and higher-order dispersion is also proposed. Our prototype dispersion-tunable CM makes it possible to provide continuous dispersion support, advancing CM technique to a new level by overcoming the drawback of discrete dispersion compensation nature of traditional CMs. This brings extremely convenience and flexibility to the compensation of the dispersion and ensures the tailored dispersion compensation in ultrafast laser systems. In our proof of concept study, continuously tunable group delay dispersion (GDD) is achieved by altering the angles of incidence (AOI) on the mirrors. Moreover, continuous duration tunable laser pulses are demonstrated by applying our GDD-tunable CMs in ultrafast laser system.

Optimal tradeoff between precision and spatial resolution in DoFP imaging polarimeters

Li Xiaobo, Haofeng Hu, Matthieu Boffety, stephane roussel, T. Liu, and Francois Goudail

Doc ID: 375743 Received 19 Aug 2019; Accepted 29 Oct 2019; Posted 31 Oct 2019  View: PDF

Abstract: Linear division-of-focal-plane camera combined with controllable polarization modulator constitute a versatile full-Stokes imager with four possible spatial resolution modes depending on the number of acquisitions. Considering several polarization modulator architectures, we determine the parameter settings that minimize estimation variance in each resolution mode, so that precision, resolution and acquisition time can be optimally and dynamically balanced to implement the imaging solution best adapted to a given application.

Constellation Size for Probabilistic Shaping Under the Constraint of Limited ADC Resolution

Qiulin Zhang and Chester C.T. Shu

Doc ID: 376311 Received 26 Aug 2019; Accepted 29 Oct 2019; Posted 31 Oct 2019  View: PDF

Abstract: We investigate the optimal constellation size for probabilistic shaping (PS) under the constraint of different effective number of bits (ENOB) of the analog-to-digital converter (ADC) at the receiver. For a fixed entropy, increasing the constellation size will bring a larger shaping gain while it also leads to a higher peak to average power ratio (PAPR), which makes the signal more sensitive to the ENOB and the fiber nonlinearity. Our experimental results show that PS-44 QAM outperforms both PS-64 QAM and uniformly-shaped 32 QAM (U-32 QAM) when the ENOB of ADC is lower than 4.5. The optimal launched power and the maximum achievable distance for U-32 QAM, PS-44 QAM and PS-64 QAM are analyzed by simulation.

A compressed Raman classification method with upper bounded error probability

Frederic Galland, Philippe Réfrégier, and Emmanuel Chevallier

Doc ID: 376588 Received 28 Aug 2019; Accepted 29 Oct 2019; Posted 31 Oct 2019  View: PDF

Abstract: Classification of different species with Raman measurements is analyzed when a total of exactly N photons are detected with binary filtered Raman spectra. This approach leads to classification error probabilities upper bounded by the Bhattacharyya bound and that are invariant to the multiplication of the spectrum intensities by an unknown factor. Furthermore, it is shown that this approach can be implemented with a number of binary filters smaller than the number of species to discriminate.

Collective lattice resonances in arrays of dielectric nanoparticles: a matter of size

Vadim Zakomirnyi, Alexander Ershov, Valeriy Gerasimov, Sergei Karpov, Hans Agren, and Ilia Rasskazov

Doc ID: 379884 Received 09 Oct 2019; Accepted 28 Oct 2019; Posted 31 Oct 2019  View: PDF

Abstract: Collective lattice resonances (CLRs) in finite-size 2D arrays of dielectric nanospheres have been studied via the coupled dipole approximation. We show that even for sufficiently large arrays, up to 100x100 nanoparticles (NPs), electric or magnetic dipole CLRs may significantly differ from the ones calculated for infinite arrays with the same NP sizes and interparticle distances. The discrepancy is explained with the existence of a sufficiently strong cross-interaction between electric and magnetic dipoles induced at NPs in finite-size lattices, which is ignored for infinite arrays. We support this claim numerically, and propose an analytic model to estimate a spectral width of CLRs for finite-size arrays. Provided that most of the current theoretical and numerical researches on collective effects in arrays of dielectric NPs rely on modeling infinite structures, the reported findings may contribute to thoughtful and optimal design of inherently finite-size photonic devices.

Ho:Y₂O₃ ceramic laser generate over 113W of output power at 2117 nm

Fei Wang, jinwen tang, Enhao Li, Chongfeng Shen, Jun Wang, Dingyuan Tang, and Deyuan SHEN

Doc ID: 378174 Received 18 Sep 2019; Accepted 28 Oct 2019; Posted 04 Nov 2019  View: PDF

Abstract: We demonstrate efficient laser operation using a Ho:Y₂O₃ ceramic with low scattering loss and excellent optical quality fabricated in-house through improved technique in support of high power laser operation. The Ho:Y₂O₃ ceramic laser was in-band pumped by a Tm fiber laser of 1931 nm at room temperature. With an optically polished but uncoated sample of 0.5 at.% Ho3+ doping, up to 113.6 W continuous wave (CW) output power at 2117 nm has been generated with a slope efficiency of 55.6% with respect to the absorbed pump power. To the best of our knowledge, this is the highest output power achieved with a Ho-doped ceramic.

Wide Field-of-View Optical Broadcasting for Bi-directional Indoor Optical Wireless Communications Employing PAM-4 Modulation

Feng Feng, Paramin Sangwongngam, Grahame Faulkner, and Dominic O'Brien

Doc ID: 374598 Received 05 Aug 2019; Accepted 28 Oct 2019; Posted 29 Oct 2019  View: PDF

Abstract: We present a wide field-of-view bi-directional point-to-multipoint indoor optical wireless communications operating over a range of 4 metres. The system is designed to integrate with fibre-to-the-home/building networks realized by a passive optical network. A Phase-only spatial light modulator based beam steering base station with ±30º field-of-view broadcasts downstream transmissions to two nomadic user terminals that use mirror-based beam steering to provide a ±50º field-of-view. At the base station, a composite phase mask is constructed on the spatial light modulator to not only perform optical broadcasting but also steer upstream optical transmissions from user terminals at a different wavelength. Successful upstream and downstream data transmission of 25 Gbit/s PAM4 is achieved.

An Artificial Modulation-free Pound-Drever-Hall Method for Laser Frequency Stabilization

H. M. Wang, Zi-Shan Xu, Sai-Qun Ma, Ming-Hao Cai, Shu-Hang You, and H. P. Liu

Doc ID: 378212 Received 20 Sep 2019; Accepted 28 Oct 2019; Posted 29 Oct 2019  View: PDF

Abstract: We have proposed an artificial modulation-free PoundDrever-Hall (PDH) method for laser frequency stabilization and demonstrated it via the two-color polarization spectroscopy of Rydberg electromagnetically induced transparency (EIT) resonance in a roomtemperature rubidium vapor. Due to the unique error signal profile, PDH method owns a large capture rangewithout losing high stability in laser frequency locking. Instead of modulating the laser frequency and using a super-stable optical cavity as the frequency reference, we manually construct the PDH error signal viaa linear combination of polarization spectroscopies of the Rydberg EIT resonances without and with magnetic field applied. The artificial modulation-free PDH error signal owns a sub-natural linewidth dispersion curve as well as a large capture range with which we successfully stabilize the laser to an absolute atomic frequency reference in a long running time, immune to environmental fluctuation and even man-made impulseperturbation. Our extended PDH technique abandons the laser frequency modulation module and optical cavity, providing a cheap but robust laser stabilization approach.

Endocardial irrigated catheter for volumetric optoacoustic mapping of radio-frequency ablation lesion progression

Cagla Özsoy, XOSÉ DEÁN-BEN, and Daniel Razansky

Doc ID: 378425 Received 25 Sep 2019; Accepted 28 Oct 2019; Posted 29 Oct 2019  View: PDF

Abstract: Radiofrequency (RF) catheter ablation is widely employed for various minimally invasive procedures, including treatment of tumors, cardiac arrhythmias and varicose veins. Accurate real-time monitoring of the ablation treatments remains challenging with the existing clinical imaging modalities due to the lack of spatial or temporal resolution or insufficient tissue contrast for differentiating thermal lesions. Optoacoustic (OA) imaging has been recently suggested for monitoring temperature field and lesion progression during RF interventions. However, strong light absorption by standard metallic catheters hindered practical implementations of this approach. Herein, we introduce a new RF ablation catheter concept for combined RF ablation and OA lesion monitoring. The catheter tip encapsulates a multimode fiber bundle for optoacoustic excitation with near-infrared light whereas the electric current is conducted through the irrigation solution, thus avoiding direct exposure of the metallic parts to the excitation light. We optimized the catheter diameter and the saline flow rate in order to attain uniform and deep lesions. The newly introduced hybrid catheter design was successfully tested by real-time monitoring of the ablation process in smooth ventricle and rough atrium walls of a blood-filled ex-vivo porcine heart, mimicking in vivo conditions in the clinical setting.

Emission of orbital angular momentum based on spoof localized surface plasmons

Youfei Zhang, Qingle Zhang, Chi Chan, Erping Li, Jianming Jin, and Hao Gang Wang

Doc ID: 378969 Received 26 Sep 2019; Accepted 28 Oct 2019; Posted 29 Oct 2019  View: PDF

Abstract: An approach to producing thee orbital angular momentum (OAM) based on spoof localized surface plasmons (spoof LSPs) in microwave frequencies is demonstrated both theoretically and experimentally. The fundamental and high-order modes of spoof LSPs occur when a textured metallic surface is excited with a microstrip line. Two orthogonal modes of spoof LSPs with +90° or -90° phase retardation are superimposed, resulting in a OAM-vortex mode. In the proposed design, two separate feeding ports are employed to excite the orthogonal resonant modes simultaneously, and a hybrid coupler is used to provide the required ±90° phase retardation. By loading a circularly arranged dipole array on the spoof LSPs, the confined surface waves of the spoof LSPs can be converted into radiated vortex waves. To verify this idea, an OAM-mode emitter with indices of ±3 is fabricated and measured. Experimental near-field distributions and far-field radiation patterns show excellent agreement with the simulated results.

High-resolution real-time 360° 3D model reconstruction of handheld object with fringe projection profilometry

Jia Ming Qian, Shijie Feng, Tianyang Tao, Yan Hu, Kai Liu, Shuaijie Wu, Qian Chen, and Chao Zuo

Doc ID: 379889 Received 10 Oct 2019; Accepted 28 Oct 2019; Posted 29 Oct 2019  View: PDF

Abstract: The digitization of the complete shape of real objects have essential applications in fields of intelligent manufacturing, industrial detection, and reverse modeling. In order to build the full geometric models of rigid objects, the object must be moved relative to the measurement system (or the scanner moved relative to the object) to obtain and integrate views of the object from all sides, which not only complicates the system configuration, but makes the whole process time-consuming. In this Letter, we present a high-resolution real-time 360° 3D model reconstruction method that allows one to rotate an object manually and see a continuously-updated 3D model during the scanning process. A multi-view fringe projection profilometry system acquires high-precision depth information about a hand-held object from different perspectives, and meanwhile the multiple views are aligned and merged together in real time. To increase the efficiency of 3D measurement for each side view, our system employs stereo phase unwrapping and adaptive depth constraint which can unwrap the phase of dense fringe images robustly without increasing the number of captured patterns. Then, to match the 3D surface segments rapidly we develop an efficient coarse-to-fine registration strategy. It separately creates two processing threads to carry out the initial coarse matching by improved simultaneous localization and mapping techniques and refine the global registrations with the iterative closest point algorithm. Our experiments demonstrate that our method can reconstruct the high-precision complete 3D model of complex objects under arbitrary rotation without any instrument assist and expensive pre/post-processing.

First-order perturbation theory for material changes in the surrounding of open optical resonators

Steffen Both and Thomas Weiss

Doc ID: 378831 Received 14 Oct 2019; Accepted 28 Oct 2019; Posted 30 Oct 2019  View: PDF

Abstract: The single-mode approximation of the resonant state expansion has proven to give accurate first-order approximations of resonance shifts and linewidth changes when modifying the material properties inside open optical resonators. Here, we extend this first-order perturbation theory to modifications of the material properties in the surrounding medium. As a side product of our derivations, we retrieve the already known analytical normalization condition for resonant states. We apply our theory to two example systems: A metallic nanosphere and a periodic array of metallic nanoslits.

Machine-learning based spectral classification for spectroscopic single-molecule localization microscopy

Zheyuan Zhang, Yang Zhang, Leslie Ying, Cheng Sun, and Hao Zhang

Doc ID: 374670 Received 07 Aug 2019; Accepted 28 Oct 2019; Posted 31 Oct 2019  View: PDF

Abstract: Spectroscopic single-molecule localization microscopy (sSMLM) simultaneously captures the spatial locations and emission spectra of single molecular emission and enables simultaneous multi-color super-resolution imaging. Existing sSMLM relies on extracting spectral signatures, such as weighted spectral centroids, to distinguish different molecular labels. However, the rich information carried by the complete spectral profiles are not fully utilized; thus, the misclassification rate between molecular labels can be high at low spectral analysis photon budget. We developed a deep artificial neural network-based method to analyze the full spectral profiles of each molecular emission and reduce the misclassification rate. We experimentally validated our method by imaging immunofluorescently labeled COS-7 cells using two far-red dyes typical used in sSMLM (AF647 and CF660) to resolve mitochondria and microtubules, respectively. We showed that the machine-learning method achieved 10-fold reduction in misclassification and 2-fold improvement in spectral data utilization comparing to the existing spectral centroid method.

Tornado waves

Apostolos Brimis, Konstantinos Makris, and Dimitris Papazoglou

Doc ID: 374464 Received 01 Aug 2019; Accepted 28 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: We show that light spiraling like a tornado can be generated by superimposing abruptly auto-focusing ring-Airy beams that carry orbital angular momentum of opposite handedness. The superimposing ring-Airy beams are tailored so that they abruptly auto-focus at overlapping focal regions although following distinct parabolic trajectories. This results to a complex wave with intense lobes that twist and shrink in an accelerating fashion along propagation. By achieving angular acceleration that exceeds 295 rad/mm², these Tornado waves can find broad application in laser trapping, direct laser writing and high harmonic generation.

Fully tunable and switchable coupler for photonic routing in quantum detection and modulation

Vojtěch Švarc, Martina Nováková, Glib Mazin, and Miroslav Jezek

Doc ID: 374506 Received 26 Aug 2019; Accepted 28 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: Photonic routing is a key building block of many opticalapplications challenging its development. We reporta 2×2 photonic coupler with splitting ratio switchableby a low-voltage electronic signal with 10 GHzbandwidth and tens of nanoseconds latency. The couplercan operate at any splitting ratio ranging from 0:100to 100:0 with the extinction ratio of 26 dB in opticalbandwidth of 1.3 THz. We show 100 ps switching betweenarbitrary coupling regimes including balanced50:50 beam splitter, 0:100 switch, and a photonic tap.The core of the device is based on Mach-Zehnder interferometerin a dual-wavelength configuration allowingreal-time phase lock with long-term sub-degree stabilityat single-photon level. Using the reported coupler,we demonstrate for the first time the perfectly balancedtime-multiplexed device for photon-number-resolvingdetectors and also the active preparation of a photonictemporal qudit state up to four time bins. Verified long-termstable operation of the coupler at the single photonlevel makes it suitable for wide application rangein quantum information processing and quantum opticsin general.

Speckle-field digital polarization holographic microscopy

VINU RV, Ziyang Chen, Jixiong Pu, Yukitoshi Otani, and Rakesh Singh

Doc ID: 374591 Received 02 Aug 2019; Accepted 28 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: We present a new polarization holographic microscopy technique based on speckle-field illumination with enhanced spatial resolution and controlled coherent noise reduction. The proposed technique employs a spatial light modulator for the generation of sequential speckle pattern for the illumination of the sample. The developed microscope is capable of simultaneous extraction of orthogonal polarization components of the field emanating from the sample. We demonstrate the potential features of the technique by presenting spatially resolved images of the known samples and the inhomogeneous anisotropic samples. The technique has substantial significance in biomedical imaging with digital auto-focusing and complex field imaging.

4H-SiC microring resonators for integrated nonlinear photonics

Yi Zheng, Minhao Pu, Ailun Yi, Xin Ou, and Haiyan Ou

Doc ID: 376266 Received 26 Aug 2019; Accepted 28 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: We demonstrate enhanced four-wave mixing (FWM) in high-quality factor, high-confinement 4H-SiC microring resonators via continuous-wave FWM. With the large power buildup effect of the microring resonator, -21.7 dB FWM conversion efficiency is achieved with 79 mW pump power. Thanks to the strong light confinement in SiC-on-insulator (SiCOI) waveguides with sub-micron cross-sectional dimensions, a high nonlinear parameter γ of 7.4 ± 0.9 W-1m-1 is obtained, from which the nonlinear refractive index (n2) of 4H-SiC is estimated to be (6.0 ± 0.6)×10-19 m2/W at the telecom wavelengths. Besides, we are able to engineer the dispersion of a SiCOI waveguide to achieve 3-dB FWM conversion bandwidth of more than 130 nm. This work represents a step towards enabling all-optical signal processing functionalities using highly nonlinear SiCOI waveguides.

Experimental quantum key distribution with uncharacterized sources and projective measurements

Jian-Rong Zhu, Wen-Zhe Wu, Liang Ji, Chunmei Zhang, and Qin Wang

Doc ID: 377117 Received 09 Sep 2019; Accepted 28 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: In theory, quantum key distribution (QKD) can offer information-theoretic secure communication based on the laws of quantum mechanics. However, the vast majority of practical QKD implementations assume the perfect state preparation to ensure the security, which is a demanding requirement with current technology. Here, by incorporating the mismatched-basis data, we report an experimental decoy-state QKD demonstration with uncharacterized encoding sources, which only requires the encoding states are two-dimensional. Furthermore, the measurement operation of the receiver is loosened to be projective measurements. With a rigorous statistical fluctuation analysis, we can distribute secret keys when the transmission distances of the standard fiber link are 101 km and 202 km. Our experimental demonstration represents a significant step toward realizing long-distance quantum communication even with uncharacterized sources and projective measurements.

Tunable dual-color terahertz wave parametric oscillator based on KTP crystal

Longhuang Tang, Degang Xu, Yuye Wang, Chao Yan, Yixin He, Jining Li, Kai Zhong, and Jian-Quan Yao

Doc ID: 378834 Received 25 Sep 2019; Accepted 28 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: A tunable dual-color KTP terahertz wave parametric oscillator (TPO) pumped by dual-wavelength laser was proposed in this letter. Theoretical analysis denotes that the emission of tunable dual-color THz wave can be achieved by the simultaneous stimulated polariton scattering processes from multiple A1-symmetry phonon modes of the KTP crystal. The tunable dual-color THz wave emitted from KTP TPO was demonstrated in our experiment, where the THz frequencies simultaneously tuned from 3.15 THz to 11.63 THz and from 1.47 THz to 6.03 THz with some gaps. The maximum dual-color THz output energy of 1.31μJ was obtained under the THz frequencies of 5.94 THz and 4.42 THz. Moreover, at a certain phase matching angle, the THz output energies for the two frequencies were independent, which means that the dual-color THz wave emission with any energy ratio can be achieved by adjusting the pump energy ratio between dual-wavelength laser.

Generating electromagnetic nonuniformly correlated beams

Milo Hyde, Xifeng Xiao, and David Voelz

Doc ID: 378851 Received 26 Sep 2019; Accepted 28 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: We develop a method to generate electromagnetic nonuniformly correlated (ENUC) sources from vector Gaussian Schell-model (GSM) beams. Having spatially varying correlation properties, ENUC sources are more difficult to synthesize than their Schell-model counterparts [which can be generated by filtering circular complex Gaussian random numbers], and, in past work, have only been realized using Cholesky decomposition---a computationally intensive procedure. Here, we transform electromagnetic GSM field instances directly into ENUC instances, thereby avoiding computing Cholesky factors resulting in significant savings in time and computing resources. We validate our method by generating (via simulation) an ENUC beam with desired parameters. We find the simulated results to be in excellent agreement with the theoretical predictions. This new method for generating ENUC sources can be directly implemented on existing spatial-light-modulator-based vector-beam generators and will be useful in applications where nonuniformly correlated beams have shown promise, e.g., free-space/underwater optical communications.

Broadband high quantum efficiency InGaAs/InP focal plane arrays via high precision plasma thinning

Wei He, Shao Xiumei, Yingjie Ma, Gaoqi Cao, Yu Chen, Xue Li, and Haimei Gong

Doc ID: 376305 Received 27 Aug 2019; Accepted 28 Oct 2019; Posted 06 Nov 2019  View: PDF

Abstract: We report on the fabrication of a 160×120 visible-extended (Vis-) InGaAs/InP focal plane array (FPA) by means of the inductive-coupled plasma etching. Compared to the conventional Vis-InGaAs FPAs, a higher quantum efficiency in visible spectrum has been achieved. High precision thinning of the n-type InP contact layer down to 10 nm has led to quantum efficiencies higher than 60% over a broad wavelength range of 500-1700 nm. Benefiting from the textured surface after the plasma etching, 17% lower reflectance over the entire response range was also found. Enhanced visible/near infrared laboratory imaging capability has also been demonstrated, which has proved the feasibility of such processes for fabrication of future higher definition VIS/NIR InGaAs imagers.

Second-harmonic generation in multilayer hexagonal boron nitride flakes

Sejeong KIM, Johannes Froech, Augustine Gardner, Chi Li, Igor Aharonovich, and Alexander Solntsev

Doc ID: 378995 Received 03 Oct 2019; Accepted 28 Oct 2019; Posted 05 Nov 2019  View: PDF

Abstract: We report second-harmonic generation (SHG) from thick hexagonal boron nitride (hBN) flakes with approximately 109-111 layers. The resulting effective second-order susceptibility is similar to previously reported few-layer experiments. This confirms that thick hBN flakes can serve as a platform for nonlinear optics, which is useful because thick flakes are easy to exfoliate while retaining a large flake size. We also show spatial second-harmonic maps revealing that SHG remains a useful tool for the characterization of the layer structure even in the case of a large number of layers.

Frequency comb dynamics of a 1.3-μm hybrid-silicon quantum dot semiconductor laser with optical injection

Bozhang Dong, Heming Huang, Jianan Duan, Geza Kurczveil, Di Liang, Raymond Beausoleil, and Frederic Grillot

Doc ID: 378002 Received 23 Sep 2019; Accepted 27 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: This work reports on the influence of bias voltage applied on saturable absorber (SA) on sub-threshold linewidth enhancement factor (LEF) in hybrid-silicon quantum dot optical frequency comb lasers (QD-OFCLs). Results show that the reverse bias voltage on SA contributes to enlarge the LEF and improve the comb dynamics. The optical injection is also found to be able to improve the comb spectrum in term of 3-dB bandwidth and its flatness. Such novel findings are promising for the development of high-speed dense wavelength division multiplexing (DWDM) photonic integrated circuits (PICs) in optical interconnects and datacom applications.

Ultrahigh-Q toroidal dipole resonance in all-dielectric metamaterials for terahertz sensing

Xu Chen and Wen-Hui Fan

Doc ID: 375777 Received 20 Aug 2019; Accepted 26 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: By arranging two pairs of high-index dielectric disks into a unit cell, a novel terahertz metamaterials sensor integrated with microfluidic channel is proposed. With introducing a new way of symmetry breaking (out-of-plane symmetry breaking) in the unit cell, the strong toroidal dipole response with ultrahigh-Q is excited and investigated, which is related to the existence of the trapped mode. Simulation results show the calculated Q-factor and the corresponding FoM of this sensor can reach 3189 and 515, respectively. These advantages make the proposed structure has potential applications in high performance gases, liquids and biological materials sensing.

Characteristics of resonance-induced optical vortices and spatial reshaping

Wei Zhang, Aaron Charous, Masaya Nagai, Daniel Mittleman, and Rajind Mendis

Doc ID: 379027 Received 26 Sep 2019; Accepted 26 Oct 2019; Posted 31 Oct 2019  View: PDF

Abstract: The spatial profile of a beam can experience complicated reshaping after interacting with a planar resonator near the resonant conditions. Previously, this phenomenon was recognized as the Goos-Hänchen effect, which only partially explains the experimental observations. In this letter, we introduce a 2D model that can fully describe the resonance-induced spatial reshaping. The model predicts several general features of the output beam profile, and suggests that optical phase or polarization vortices can be generated and manipulated by an arbitrary planar resonator. We validate our theoretical results with experimental measurements using terahertz spectroscopy.

Coupling of a whispering gallery mode to a silicon chip with photonic crystal

Yuyang Zhuang, Hajime Kumazaki, Shun Fujii, Riku Imamura, Nurul Ashikin Daud, Ishida Rammaru, He-ming Chen, and Takasumi Tanabe

Doc ID: 375068 Received 12 Aug 2019; Accepted 25 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: We demonstrate the efficient coupling (99.5%) of a silica whispering gallery mode microresonator directly with a silicon chip by using a silicon photonic crystal waveguide as a coupler. The efficient coupling is attributed to the small effective refractive index difference between the two devices. The large group index of the photonic crystal waveguide mode also contributes to the efficient coupling. A coupling Q of 2.68×10⁶ is obtained, which allows us to achieve the critical coupling of a silica whispering gallery mode with an intrinsic Q of close to 107 with a Si chip.

Thulium-Doped Tellurium Oxide Waveguide Amplifier with 7.6 dB Net Gain on a Silicon Nitride Chip

Khadijeh Miarabbas Kiani, Henry Frankis, Hamidu M. Mbonde, Richard Mateman, Arne Leinse, Andy Knights, and Jonathan Bradley

Doc ID: 374323 Received 31 Jul 2019; Accepted 25 Oct 2019; Posted 25 Oct 2019  View: PDF

Abstract: We report on thulium-doped waveguide amplifiers integrated on a low-loss silicon nitride platform. The amplifier structure consists of a thulium-doped tellurium oxide thin film coated on a silicon nitride strip waveguide on silicon. We determine a waveguide background loss of 0.7 dB/cm at 1479 nm based on the quality factor measured in microring resonators. Gain measurements were carried out in straight and 6.7-cm-long s-bend waveguides realized on a 2.2-cm-long chip. We measure internal net gain over the wavelength range 1860–2000 nm under 1620 nm pumping and up to 7.6 dB total gain at 1870 nm, corresponding to 1.1 dB/cm. These results are promising for the realization of highly compact thulium-doped amplifiers in the emerging 2-µm band for silicon-based photonic microsystems.

Ultra high Q Microring Resonators Using Single Crystal Aluminum Nitride on Sapphire Platform

Yi Sun, Walter Shin, David Laleyan, Ping Wang, Ayush Pandey, Xianhe Liu, yuanpeng wu, Mohammad Soltani, and Zetian Mi

Doc ID: 376514 Received 29 Aug 2019; Accepted 25 Oct 2019; Posted 25 Oct 2019  View: PDF

Abstract: Aluminum nitride on sapphire has recently emerged as a novel low-loss photonics platform for a variety of on-chip electro-optic as well as linear and nonlinear optics applications. In this letter, we demonstrate ultra-high microring resonators using single crystal aluminum nitride grown on sapphire substrate with optimized design and fabrication process. A record high intrinsic quality factor (Qint) up to 2.8 ×10⁶ at the wavelength of 1550 nm is achieved with fully etched structure, indicating a low propagation loss less than 0.13 dB/cm. Such high Qint aluminum nitride on sapphire resonators with their wide bandgap and electro-optical and nonlinear optical properties are promising for a wide range of low power and high power compact on-chip applications over a broad spectral range.

Narrow-band PPLN non-resonant optical parametric oscillator

Li Wang, Andrey Boyko, Andre Schirrmacher, Edlef Büttner, Weidong Chen, Ning Ye, and Valentin Petrov

Doc ID: 376872 Received 03 Sep 2019; Accepted 24 Oct 2019; Posted 25 Oct 2019  View: PDF

Abstract: We report on a narrowband, non-resonant PPLN optical parametric oscillator using a VBG as the spectral narrowing element. Pumping by a Nd:YVO4 laser at 1.06 μm, a maximum output power of 4.75 W is achieved at a repetition rate of 20 kHz for a conversion efficiency of 47.5%. Both signal and idler spectra are narrowed to less than 2 nm, at good beam quality and stability.

Al₂O₃:Yb³+ integrated microdisk laser label-free biosensor

Michiel de Goede, Lantian Chang, Jinfeng Mu, Meindert Dijkstra, Raquel Obregón, Elena Martínez, Laura Padilla, Francesc Mitjans, and Sonia Garcia-Blanco

Doc ID: 376128 Received 23 Aug 2019; Accepted 24 Oct 2019; Posted 24 Oct 2019  View: PDF

Abstract: Whispering gallery mode resonator lasers hold the promise of an ultra-low intrinsic limit of detection. However, the widespread use of these devices for biosensing applications has been hindered by the complexity and lack of robustness of the proposed configurations. In this work we demonstrate biosensing with an integrated microdisk laser. Al₂O₃ doped with Yb³+ was utilized because of its low optical losses as well as its emission in the range 1020—1050 nm, outside the absorption band of water. Single-mode laser emission was obtained at a wavelength of 1024 nm with a linewidth of 250 kHz while the microdisk cavity was submerged in water. A limit-of-detection of 300 pM (3.6 ng/ml) of the protein rhS100A4 in urine was experimentally demonstrated, showing the potential of the proposed devices for biosensing.

100km Single-ended Distributed Vibration Sensor based on Remotely Pumped EDFA

Lieke van Putten, Ali Masoudi, and Gilberto Brambilla

Doc ID: 376707 Received 30 Aug 2019; Accepted 24 Oct 2019; Posted 24 Oct 2019  View: PDF

Abstract: In this study, a single-ended distributed vibration sensor with 100km sensing range is reported. This sensing range is achieved by remotely pumping two pieces of Er-doped fibers incorporated along the sensing fiber with a 1480nm Raman fiber laser at the front-end of the fiber. A strain resolution of 100nε combined with a spatial resolution of 2m is achieved at the far end of the fiber.

Design of a new optical system to generate narrowband guided waves with an application to evaluating health status of rail material

Kim Ming NG, Faeez Masurkar, Peter W. Tse, and Nitesh Yelve

Doc ID: 371456 Received 05 Jul 2019; Accepted 24 Oct 2019; Posted 25 Oct 2019  View: PDF

Abstract: The letter presents a new design of Sagnac interferometer-based optical system (SIOS) that emits a line-arrayed pattern generating narrowband high energy waves in a specimen. The SIOS is further used to excite Rayleigh waves in a pristine rail specimen to evaluate its intrinsic nonlinearity resulting from the lattice anharmonicity and dissolved impurities. Such a nonlinearity appears in the response in the form of a second harmonic that is sensed in the present study using a scanning laser Doppler Vibrometer. In addition to this noncontact measurement, a contact measurement of the nonlinearity of rails steel using wedge-transducers is also carried out to compare the performance of the SIOS. Both the experimentally evaluated nonlinearities are compared with that obtained using the nonlinear elasticity equations. The close agreement with the theoretically estimated nonlinearity and higher repeatability show that the SIOS is effective in measuring intrinsic nonlinearity of the rail steel and, thereby, predicting health status of the rail specimens before fixing them on the track.

Simultaneous functional imaging of neuronal and photoreceptor layers in living human retina

Clara Pfäffle, Hendrik Spahr, Lisa Kutzner, Sazan Burhan, Felix Hilge, Yoko Miura, Gereon Huttman, and Dierck Hillmann

Doc ID: 372504 Received 19 Jul 2019; Accepted 24 Oct 2019; Posted 24 Oct 2019  View: PDF

Abstract: Functional retinal imaging, especially of neuronal activity non-invasively in humans, is of tremendous interest. Although the activation of photoreceptor cells (PRC) could be detected in humans, imaging the function of other retinal neurons was so far hardly possible. Here, using phase-sensitive full-field swept-source OCT (FF-SS-OCT) we show simultaneous imaging of theactivation in the photoreceptor and ganglion/inner plexiform layer. The signals from the ganglion cell layer are ten-fold smaller than those from the PRC and were only detectable using algorithms for suppression of motion artifacts and pulsatile blood flow in the retinal vessels. FF-SS-OCT with improved phase evaluation algorithms, therefore, allowed us to map functional connections between PRC and GCL confirming previous ex vivo results. The demonstrated functional imaging of retinal neuronal layers can be a valuable tool in diagnostics and basic research.

Far-Field Raman Color Superlensing Based on Disordered Plasmonics

Sergey Kharintsev

Doc ID: 376719 Received 30 Aug 2019; Accepted 23 Oct 2019; Posted 29 Oct 2019  View: PDF

Abstract: Plasmon multiple scattering within a disordered metal-dielectric medium allows one drastically to enhance a cubic susceptibility and thus stimulated Raman scattering (SRS) can occur in highly confined media exposed to the continuous-wave low-powered pump. In this study, a percolated 50 nm titanium oxynitride thin film is used as a disordered nonlinear metalens that meets ENZ wavelengths in the visible region. We experimentally demonstrate a far-field Raman superlensing effect by showing a sub-wavelength resolution of λ/6NA at different SRS overtones using multi-walled carbon nanotubes directly dispersed on the metalens.

Control of spin-selective absorption with two-dimensional chiral plasmonic gratings

Wenxing Liu, Liren Mei, Yunhui Li, LongKun Yu, Zhenquan Lai, Hong Chen, and Tian Yu

Doc ID: 377767 Received 13 Sep 2019; Accepted 22 Oct 2019; Posted 01 Nov 2019  View: PDF

Abstract: We report that the spin-selective absorption is observed in a two-dimensional (2D) chiral plasmonic grating. For the proposed structure, the right-handed circularly polarized light is absorbed with nearly 100% efficiency, while the left-handed circularly polarized light is reflected without reversing its handedness. The functionality arises from the chiral-dependent plasmonic cavity resonance. We show that the location of spin-selective absorption can be controlled flexibility by tuning the plasmonic cavity dimension. Moreover, we demonstrate that the intensity of spin-selective absorption can be enhanced as well as suppressed based on Fabry-Perot interference phase relation. Such the 2D chiral plasmonic gratings could find many potential applications in novel photon-spin selective devices, such as circularly polarized light detectors/emitters, chiral sensors, chiral cavities and spin lasers.

Ultrasmall broadband wavelength and polarization router based on hybrid waveguide of monolithic-LiNbO3

Cuicui Lu, Zhouhui Liu, Yuxuan Zhang, Weixuan Guo, Yong-Chun Liu, and Xiaoyong Hu

Doc ID: 377644 Received 13 Sep 2019; Accepted 22 Oct 2019; Posted 24 Oct 2019  View: PDF

Abstract: Nanoscale wavelength and polarization router, which can simultaneously separate wavelength and polarization modes, is an essential component of on-chip nanophotonic devices. Here, an on-chip wavelength and polarization router is realized experimentally based on a three-layer hybrid waveguide of Au-SiO2-LiNbO3 with asymmetric nano-cavities etched on. The footprint is only 1.60 × 1.96 µm2, which is the smallest one ever demonstrated. A broad operation band covers from 500 nm to 1150 nm with low crosstalk of under 10 dB. The monolithic-LiNbO3 is introduced for the first time to on-chip multi-channel wavelength and polarization routers. This work plays a key role for dense chip integration, visible light displays and communications, and can inspire LiNbO3-based nanophotonic devices.

Color Conversion Efficiency Enhancement of Colloidal Quantum Dot through Its Linkage with Synthesized Metal Nanoparticle on a Blue Light-emitting Diode

Yao-Tseng Wang, Chi-Wu Liu, Po-Yu Chen, Ruei-Nan Wu, Chia-Chun Ni, Cheng-Jin Cai, Yean-woei Kiang, and Chih-Chung Yang

Doc ID: 377319 Received 09 Sep 2019; Accepted 21 Oct 2019; Posted 24 Oct 2019  View: PDF

Abstract: Four surface-modified and hence positively-charged metal nanoparticles (NPs) of different localized surface plasmon (LSP) resonance wavelengths are synthesized for linking with negatively-charged, red-emitting colloidal CdZnSeS/ZnS quantum dots (QDs) on the top surface of a blue-emitting InGaN/GaN quantum well (QW) light-emitting diode (LED) through electro-static force. The metal NP-QD linkage leads to a short distance between them for producing their strong surface plasmon (SP) coupling such that QD absorption and emission can be enhanced. Meanwhile, the small p-GaN thickness in the LED results in strong SP coupling between the LSP resonance of metal NP and the QWs of the LED, leading to enhanced QW emission and hence stronger QD excitation. All those factors together result in the increase of the color conversion efficiency of QD.

Detecting the single nanoparticle by imaging the localized enhancement and interference of surface plasmon polaritons

xu Sun, Hongyao Liu, Liwen Jiang, Ruxue Wei, Xue Wang, Chang Wang, Xinchao Lu, and Chengjun Huang

Doc ID: 379520 Received 03 Oct 2019; Accepted 21 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: Label-free single nanoparticle detection is crucial for fast detection to nanoparticles and viruses in environmental monitoring and biological sciences. In this article, benefitting from the leakage radiation that transforms the near-field SPP distribution along interface to far field, we demonstrated the plasmonic imaging to single polystyrene nanoparticles with particle size down to 39nm. The imaging is composed of the localized enhancement and interference of SPPs. The localized enhancement is due to the charges accumulation around the nanoparticle, and connects to the size and refractive index of nanoparticles. The interference is induced by the coupling between the incident SPPs and the scattered SPPs, which is verified by extracting the interference fringe periodicity to be half of the SPP wavelength. Our study provides an in-depth physical understanding for plasmonic imaging to single nanoparticles, which paves the way for fast identification to the nanomaterials.

Optimization of Brillouin instantaneous frequency measurement using convolutional neural networks

Xiuting Zou, Shaofu Xu, Shujing LI, Jianping Chen, and Weiwen Zou

Doc ID: 375257 Received 12 Aug 2019; Accepted 21 Oct 2019; Posted 24 Oct 2019  View: PDF

Abstract: Brillouin instantaneous frequency measurement (B-IFM) is used to measure instantaneous frequencies of an arbitrary signal with high frequency and broad bandwidth. However, the instantaneous frequencies measured using the B-IFM system always suffer from errors due to system defects. To address this, we adopt a convolutional neural network (CNN), which establishes a function mapping between the measured and nominal instantaneous frequencies to obtain the accurate frequency of a signal and improve B-IFM accuracy. Using the proposed CNN-optimized B-IFM system, the average maximum and root mean square (RMS) errors between the optimized and nominal instantaneous frequencies are reduced from up to 105.8 MHz and 57.0 MHz to less than 26.3 MHz and 15.5 MHz, respectively compared with the existing B-IFM system.

Unidirectional invisibility and enhanced reflection ofshort pulses in quasi-PT-symmetric layered media

Boris Mantsyzov, Vladimir Bushuev, Vladimir Konotop, and Dmitri M. Tsvetkov

Doc ID: 378663 Received 24 Sep 2019; Accepted 21 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: We consider interaction of a short optical pulse withlayer with periodically modulated permittivity and periodic gain-and-loss landscape. It is found that if themedium is quasi-PT-symmetric, in the vicinity ofthe exceptional point, the propagation manifests strongunidirectional reflection and invisibility. Due to strongfrequency selectivity, quasi-PT-symmetric periodiclayers manifest efficient filtering of back radiation.

Three-photon-excited laser-induced fluorescence (3pLIF) detection of atomic hydrogen in flames

Waruna Kulatilaka, Ayush Jain, and Yejun Wang

Doc ID: 377069 Received 20 Sep 2019; Accepted 21 Oct 2019; Posted 30 Oct 2019  View: PDF

Abstract: In many recent studies, ultrashort, femtosecond 2-photon (2p) laser-induced fluorescence (LIF) of H has been demonstrated using 205-nm excitation. However, 205-nm- deep UV pulses can be problematic in practical devices containing thick transmissive optics and also susceptible to photolytic production at high laser energies. In the present study, we investigate the 3-photon (3p) excitation scheme of H by using red-shifted 307.7-nm fs laser pulses. Efficient 3p excitation resulting from intense fs laser pulses enable 3pLIF detection of H, which was previously unattainable in most flame conditions using ns or ps excitation. Measurements are reported in atmospheric pressure CH4/O2/N2 Bunsen jet flames and premixed CH4/air calibration flames and compared similar 2pLIF schemes with fs pulses. Saturation effects, photolytic interferences, and stimulated emissions effects are studied, as well as benefits of 3pLIF in diagnostic hardware with thick optical windows. To the best of our knowledge, the present work is the first successful demonstration of 3pLIF of H using 307.7-nm.

Electric Field Vector Measurements Via Nanosecond Electric Field Induced Second Harmonic Generation

Tat Loon Chng, Maya Naphade, Benjamin Goldberg, Igor Adamovich, and Svetlana Starikovskaya

Doc ID: 374833 Received 15 Aug 2019; Accepted 19 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: Electric field induced second harmonic generation, or E-FISH, has received renewed interest as a non-intrusive tool for probing electric fields in gas discharges and plasmas using ultrashort laser pulses. An important contribution of this work lies in establishing that the E-FISH method works effectively in the nanosecond regime, yielding field sensitivities of about a kV/cm at atmospheric pressure from a 16 ns pulse. This is expected to broaden its applicability within the plasma community, given the wider access to conventional nanosecond laser sources. A Pockels-cell-based pulse-slicing scheme, which may be readily integrated with such nanosecond laser systems, is shown to be a complementary and cost-effective option for improving the time resolution of the electric field measurement. Using this scheme, a time resolution of ~3 ns is achieved, without any detriment to the signal sensitivity. This could prove invaluable for non-equilibrium plasma applications, where time resolution of a few nanoseconds or less is often critical. Finally, we take advantage of the field vector sensitivity of the E-FISH signal to demonstrate simultaneous measurements of both the horizontal and vertical components of the electric field.

Green-pumped optical parametric oscillator based on fan-out grating periodically-poled MgO-doped congruent LiTaO3

Sukeert ., Chaitanya Kumar Suddapalli, and Majid Ebrahim-Zadeh

Doc ID: 378029 Received 18 Sep 2019; Accepted 18 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: We report a green-pumped optical parametric oscillator (OPO) based on periodically-poled MgO-doped congruent lithium tantalate (MgO:cPPLT). Pumped at 532 nm by a frequency-doubled Q-switched Nd:YAG laser, and using a fanned grating structure, the singly-resonant OPO provides continuous tuning across 689-1025 nm in the signal and 1106- 36 nm in the idler at room temperature by simple mechanical translation of the crystal. The tuning range can be further extended to 677 nm and 2479 nm in the signal and idler, respectively, by temperature tuning the crystal to 200 °C. With 29-mm-long crystal, the OPO generates 131 mW of average idler power at 1476.5 nm for an input pump power of 1.8 W at 25 kHz repetition rate, with a slope efficiency of 11.3%. Bulk damage in the MgO:cPPLT crystal has been observed for pump powers above ~1.8 W, and at pump powers beyond ~1.4 W under long-term operation. The passive power stability of the generated idler at 1357 nm is 3.9% over 30 minutes, with output in Gaussian spatial profile.

Reflection suppression via elastomeric films

David Miller, Marvin Alim, and Robert McLeod

Doc ID: 368888 Received 31 May 2019; Accepted 18 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: Transparent substrates introduce challenges in optical metrology, recording, and microscopy. Backside reflections reduce signal to noise, are recorded as artifacts, or introduce spurious signals. These reflections often need to be suppressed, but large angular and spectral bandwidths preclude the use of anti-reflection coatings. Using elastomeric materials doped with optical absorbers, we detail a method and a materials set for temporary suppression of Fresnel reflections for multiple substrates spanning wide spectral and angular bandwidth. Tuning the refractive index of the elastomer to match a substrate minimizes reflection, and the addition of different absorptive dopants allows for either broadband or wavelength-selective reflection suppression. As performance is limited only by index mismatch, both spectral and angular performance significantly exceed that of anti-reflection coatings. We demonstrate reflection suppression in excess of 30 dB spanning over 500 nm bandwidth. After use, these light traps may be removed and reused without damaging the substrate.

Study on the temperature dependent characteristics of O-band bismuth-doped fiber amplifier

Yu Wang, Naresh Kumar Thipparapu, Siyi Wang, Pranabesh Barua, David Richardson, and Jayanta Sahu

Doc ID: 375387 Received 20 Aug 2019; Accepted 18 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: We report the temperature dependent performance of an O-band bismuth (Bi)-doped fiber amplifier (BDFA) in both single and double pass configurations in the temperature range from -60 to +80 ºC. At room temperature, maximum gains of 27 and 40 dB with NFs of 4.3 and 4.8 dB are measured for - dBm signal power in the single and double pass BDFA, respectively. An increment in gain and reduction in NF is observed as the ambient temperature of the BDFA is reduced. In the double pass BDFA, the temperature-dependent-gain coefficient from -60 to +80 ºC is found to be around -0.02 and -0.03 dB/ ºC across the wavelength band of 1300-1360 nm for -10 and - dBm signal powers, respectively. We also study the gain and NF characteristics with pump power and signal power at different temperatures, and a maximum gain of 45 dB is obtained at -60 ºC for -30 dBm signal power. Moreover, we compare the temperature dependent gain and NF of different BDFAs, and correlate this with the Bi-doped fiber unsaturable loss and OH concentration.

Arbitrary decomposition of a Mueller matrix

Jose Gil and Ignacio San José

Doc ID: 378692 Received 24 Sep 2019; Accepted 18 Oct 2019; Posted 23 Oct 2019  View: PDF

Abstract: Mueller polarimetry involves a variety of instruments and technologies whose importance and scope of applications are rapidly increasing. The exploitation of these powerful resources depends strongly on the mathematical models that underlie the analysis and interpretation of the measured Mueller matrices and, very particularly, on the theorems for their serial and parallel decompositions. In this letter, the most general formulation for the parallel decomposition of a Mueller matrix is presented, which overcomes certain critical limitations of the previous approaches. In addition, the results obtained lead to a generalization of the polarimetric subtraction procedure and allow for a formulation of the arbitrary decomposition that integrates, in a natural way, the passivity criterion.

A silicon dual-series Mach-Zehnder modulator with high linearity

qiang zhang, hui Yu, Linghua Wang, Penghui Xia, Qiman Cheng, Zhilei Fu, Xiaofei Wang, and Jianyi Yang

Doc ID: 376569 Received 29 Aug 2019; Accepted 17 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: In this paper, we demonstrate a highly linear silicon modulator based on the dual-series Mach-Zehnder modulator (MZM) architecture. The two sub-MZMs are biased at quadrature points of opposite polarities. A proper power splitting ratio of the driving RF signal on the two sub-MZMs enables the suppression of the 3rd order intermodulation distortion (IMD3). The spurious-free dynamic ranges (SFDR) for IMD3 are 109.5/100.5 dB·Hz2/3 at 1/10 GHz. In contrast, the reference single MZM on the same chip exhibits SFDRs of 95.2/86.8 dB·Hz2/3 at 1/10 GHz at its optimal reverse bias voltage.

A Versatile and Scalable Fabrication Method for Laser Generated Focused Ultrasound Transducers

Esra Aytac Kipergil, Erwin Alles, Janvi Karia, Hendrik Pauw, Sacha Noimark, and Adrien Desjardins

Doc ID: 380611 Received 16 Oct 2019; Accepted 17 Oct 2019; Posted 25 Oct 2019  View: PDF

Abstract: A versatile and scalable fabrication method for laser-generated focused ultrasound transducers is proposed to address existing technical challenges for minimally invasive clinical applications. The method is based on stamping a coated negative mould onto polydimethylsiloxane (PDMS); it can be adapted to include different optical absorbers that are directly transferred or synthesized in situ. Transducers with a range of sizes down to 3 mm in diameter are presented, incorporating two carbonaceous (multiwalled carbon nanoparticles and candle soot nanoparticles) and one plasmonic (gold nanoparticles) optically absorbing components. The fabricated transducers operate at central frequencies in the vicinity of 10 MHz with bandwidths in the range of 15-20 MHz. A transducer with a diameter of 5 mm was found to generate a positive peak pressure greater than 35 MPa in the focal zone with a tight focal spot of 150 µm in lateral width. Ultrasound cavitation on the tip of an optical fibre was demonstrated in water for a transducer with a diameter as small as 3 mm. The transducers fabricated with carbonaceous components that have broad optical absorption spectra can accommodate many laser sources for ultrasound generation, whereas wavelength-selective absorbers are promising for multimodal applications.

Graphene-based metasufaces for switching polarization states of anomalous reflection and focusing

Hua Zhu, Shuqi Chen, jing wen, Jian Wang, and Lin Chen

Doc ID: 375839 Received 20 Aug 2019; Accepted 11 Oct 2019; Posted 11 Oct 2019  View: PDF

Abstract: Metasurfaces have shown great potential to manipulate electromagnetic waves, and hence have found numerous applications in photonics. However, the functionalities of most of the reported metasurfaces are polarization-unfriendly after the fabrication process and can not be reconfigured dynamically with switchable polarization. Here, graphene-based metasurfaces are proposed to exhibit polarization-switchable electromagnetic response before and after switch of the chemical potential of graphene. The phase shifts covering 0-to-2π range can be switched from x polarization to y polarization by tuning the chemical potential of graphene from one value to another one. High-performance polarization-switchable anomalous reflection and focusing have been demonstrated with the designed metasurfaces. The presented design strategy can be applied to make other polarization-switchable meta-devices in different frequency domains, and impact numerous photonic applications.

Near-infrared frequency comb generation in mid-infrared interband cascade lasers

Lukasz Sterczewski, Mahmood Bagheri, Clifford Frez, Chadwick Canedy, Igor Vurgaftman, Mijin Kim, Chul Soo Kim, Charles Merritt, William Bewley, and Jerry Meyer

Doc ID: 374791 Received 06 Aug 2019; Accepted 11 Oct 2019; Posted 31 Oct 2019  View: PDF

Abstract: The interband cascade laser (ICL) is an ideal candidate for low-power mid-infrared frequency comb spectroscopy. In this work, we demonstrate that its intracavity second order optical nonlinearity induces a coherent up-conversion of the generated mid-infrared light to the near-infrared through second-harmonic and sum-frequency generation. 10 milliwatts of light at 3.6 μm convert into sub-nanowatt levels of optical power at 1.8 μm, spread across 30 nm of spectral coverage. The observed linear-to-nonlinear conversion efficiency exceeds 3 μW/W^2 in continuous wave operation. We use a dual-band ICL frequency comb source to characterize water vapor absorption in both spectral bands.

Buffered polarization diverse detection for single camera polarization-sensitive optical coherence tomography

Tae Joong Eom, Kwan Seob Park, and Jun Geun Shin

Doc ID: 375436 Received 21 Aug 2019; Accepted 08 Oct 2019; Posted 08 Oct 2019  View: PDF

Abstract: Herein we propose a method to mitigate a position mismatch problem for a spectral-domain polarization-sensitive optical coherence tomography (SD-PS-OCT) system that uses a single line-scan detection scheme. A single detector-based PS-OCT detects two orthogonal polarization components as two adjacent A-scan signals in turns. Thus two adjacent A-scan signals are not scattered at a fix point in time (position mismatch problem), resulting in uncorrelated signals between them. To achieve sequential detection of simultaneously scattered light, a buffering single mode fiber was connected to one of the two ports coming out of the optical switch, provided a proper time delay. A single-mode optical fiber of 2.69 km in length was used to buffer and its length was determined by a frame rate of the spectrometer used as a detector. With the proposed SD-PS-OCT scheme, the PS-OCT system with a simple configuration and the minimized position mismatch problem between two polarization components can be set.

Optomechanical response with nanometer resolution in the self-mixing signal of a terahertz quantum cascade laser

Andrea Ottomaniello, James Keeley, Pierluigi Rubino, Lian He Li, Marco Cecchini, Giles Davies, Edmund Linfield, Paul Dean, Alessandro Pitanti, and Alessandro Tredicucci

Doc ID: 374949 Received 13 Aug 2019; Accepted 02 Oct 2019; Posted 08 Oct 2019  View: PDF

Abstract: Owing to their intrinsic stability against optical feedback, quantum cascade lasers (QCLs) represent a uniquely versatile source to further improve self-mixing interferometry at mid-infrared and terahertz (THz) frequencies. Here, we show the feasibility of detecting with nanometer precision the deeply subwalength (< λ/6000) mechanical vibrations of a suspended silicon-nitride membrane used as external element of a THz QCL feedback interferometer. Besides representing an extension of the applicability of vibrometric characterization to THz frequencies, our system can be exploited for the realization of optomechanical applications, such as dynamical switching between different optical feedback regimes and a still-lacking THz master-slave configuration.

Direction-resolved homodyne laser-Doppler vibrometry by analyzing space-time fringes created by the successive 1D intensity profiles of the interference fringes

Mohammad Hossein Daemi and Saifollah Rasouli

Doc ID: 375558 Received 29 Aug 2019; Accepted 30 Sep 2019; Posted 04 Oct 2019  View: PDF

Abstract: In this Letter, we introduce a simple direction-resolved homodyne Laser-Doppler Vibrometry method, by sewing successive one-dimensional images of the interference pattern recorded by a linear array detector, and creating a two-dimensional space-time fringes pattern. A space-time fringes pattern visualizes the vibration form and it can be used for characterizing vibration of the object. We measure the vibration of a harmonically driven loudspeaker as a known source to demonstrate the capability of the method. We also employ the method to characterize the vibrational properties of the resonator elements of a thin-disk laser. The method reveals the environmental and instrumental sources of the vibration. The use of an array detector in the detection system simplifies the fringe chasing procedure and optical setup, and by the aid of space-time image, the vibration waveform is directly determined with no requirement to a time consuming SPS algorithm.

Orbital angular momentum and informational entropy in perturbed vortex beams

Alexander Volyar, Mikhail Bretsko, Akimova Yana, and Egorov Yuriy

Doc ID: 371437 Received 01 Jul 2019; Accepted 27 Sep 2019; Posted 04 Oct 2019  View: PDF

Abstract: We theoretically and experimentally investigated transformations of vortex beams subjected to sector perturbations in the form of hard-edged aperture. The transformations of the vortex spectra, the orbital angular momentum, and the informational entropy of the perturbed beam were measured. We found that relatively small angular sector perturbations have almost no effect on the OAM, although the informational entropy is rapidly increasing due to the birth of new optical vortices caused by diffraction at the diaphragm edges. At large perturbation angles, the uncertainty principle between the angle and OAM involves vortices, with both positive and negative topological charges, so that the OAM decreases to almost zero, and the entropy increases sharply.

Bi-functional polarization conversion in hybrid graphene-dielectric metasurfaces

Shengnan Guan, Jie -Rong Cheng, Tiehong Chen, and Shengjiang Chang

Doc ID: 373792 Received 29 Jul 2019; Accepted 24 Sep 2019; Posted 24 Sep 2019  View: PDF

Abstract: In this paper, we propose a hybrid graphene-dielectric metasurface as a bi-functional polarization converter. It can switch between a reflective half-wave plate and a quarter-wave plate around 1 THz by merely applying external biasing voltage, without reoptimizing the dielectric structure. Switching of the two wave plates originates from distinct dispersion of the orthogonal eigenmodes with the chemical potential, which is further explained by the overlapping of graphene and the dielectric resonance modes. Compared with graphene-metallic metasurfaces, combination of graphene with dielectric microstructures offers an alternative solution for active terahertz devices with high efficiency and large flexibility.

Phase critical angle scattering for measurement of transient nanoscale growth rate of micron-sized bubble

Yingchun Wu, Lin Shi, Xuecheng Wu, Jianqi Shen, Linghong Chen, and Kefa Cen

Doc ID: 374413 Received 02 Aug 2019; Accepted 20 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: We developed phase critical angle scattering (PCAS) to simultaneously measure the spherical and transparent bubble size at the micron scale and transient bubble growth at the nanoscale. The theoretical derivation of PCAS reveals that the phase of the fine structure of critical angle scattering caused by reflection and first-order refraction is highly sensitive to and linearly shifts with bubble diameter growth. Experiments on a single growing bubble are implemented with a Fourier imaging system. The results show that the PCAS technique can measure the tiny bubble growth down to tens of nanometers, providing a promising tool for accurate characterization of bubble dynamics.

Optimizing energy transfer for highly efficient single-emissive-layer white thermally activated delayer fluorescence organic light-emitting diodes

Hui Xu, Feifei Gao, Ruiming Du, and Ying Wei

Doc ID: 370151 Received 24 Jul 2019; Accepted 06 Sep 2019; Posted 09 Sep 2019  View: PDF

Abstract: Thermally activated delayed fluorescence (TADF) white light-emitting diodes (WOLED) with simplified structures have great potential for daily lighting applications. However, the complicated energy and charge transfer processes between TADF emitters limit the development of single-layer white TADF systems. Here, we demonstrate high-efficiency WOLEDs with single emissive layers composed of blue and yellow TADF emitters with approporiate steric hindrances and energy gaps, which optimize the energy transfer from blue to yellow dopants for rational exicton allocation. As consequence, the single-emissive-layer WOLEDs achieve the maximum external quantum efficiency beyond 20% and small roll-offs.

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