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Accepted papers to appear in an upcoming issue

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

Private correlated random bit generation based on synchronized wideband physical entropy sources with hybrid electro-optic nonlinear transformation

Zhensen Gao, Sile Wu, Zhitao Deng, Chuyun Huang, Xulin Gao, Songnian Fu, Zhaohui Li, Yuncai Wang, and Yuwen Qin

DOI: 10.1364/OL.465965 Received 06 Jun 2022; Accepted 01 Jul 2022; Posted 01 Jul 2022  View: PDF

Abstract: We propose and experimentally demonstrate a novel private correlated random bit generation scheme based on commonly-driven induced synchronization of two wideband physical entropy sources, which employ an open-loop distributed feedback laser followed by a hybrid electro-optic nonlinear transformation hardware module for effective bandwidth expansion and privacy enhancement. A Mach-Zehnder interferometer followed by an electro-optic self-feedback phase modulation loop as well as a dispersion element are constructed as a private hardware module to perform post-processing and nonlinear transformation of the synchronized signal. A record high rate of 5.2 Gb/s CRBG is successfully achieved between two synchronized wideband physical entropy sources with an enhanced entropy source rate and hardware key space. The demonstrated scheme may provide a new way for CRBG in future high speed secure communication systems.

Lidar backscatter simulation for angular scanning of cirrus clouds with quasi-horizontally oriented ice crystals

Natalia Kustova, Alexander Konoshonkin, Grigorii Kokhanenko, Zhenzhu Wang, Victor Shishko, Dmitry Timofeev, and Anatoli Borovoi

DOI: 10.1364/OL.463282 Received 06 May 2022; Accepted 01 Jul 2022; Posted 01 Jul 2022  View: PDF

Abstract: Backscattering properties of ice crystals are numerically investigated in the case of plate-like quasi-horizontally oriented crystals of cirrus clouds. In this case, a vertically oriented lidar detects the specular reflection from the clouds while a lidar with angular scanning infers the microphysical properties like the transversal shape of the crystals. It is shown the depolarization ratio as a function of the lidar tilts reveals a step at the lidar tilt of about 30° from the vertical. This step has been observed experimentally. Appearance of this step indicates that the transversal shapes of the plate-like crystals are regular.

Performance enhancement of nitrogen-polar GaN-based light-emitting diodes prepared by metalorganic chemical vapor deposition

Yang Wang, Yusen Wang, Lidong Zhang, Yunfei Niu, Jiaqi Yu, Haotian Ma, Chao Lu, Zhifeng Shi, Gaoqiang Deng, Baolin Zhang, and Yuantao Zhang

DOI: 10.1364/OL.463618 Received 13 May 2022; Accepted 01 Jul 2022; Posted 01 Jul 2022  View: PDF

Abstract: Nitrogen-polar (N-polar) III-nitride materials have a great potential application in long-wavelength light-emitting diodes (LEDs). However, the poor quality of N-polar nitride materials hinders the development of N-polar devices. In this work, we report the enhanced performance of N-polar GaN-based LEDs with optimized InGaN/GaN double quantum wells (DQWs) structure grown by metalorganic chemical vapor deposition. Our studies show that N-polar InGaN/GaN DQWs have poor luminesce characteristics due to the zincblende-phase inclusions and rough surface morphology. Further, we improved the quality of N-polar InGaN/GaN DQWs by elevating the growth temperature and introducing hydrogen as the carrier gas during the growth of quantum barrier layers. Photoluminescence measurement results demonstrate that the optimized DQWs exhibits a significantly enhanced luminous intensity due to suppressing zincblende-phase inclusions and improved surface morphology. N-polar LEDs prepared based on optimized InGaN/GaN DQWs show the significantly enhanced external quantum efficiency by over 90% and the weakened droop effect compared to the reference LED. More important is that optimized N-polar DQWs show significantly longer emission wavelength than Ga-polar DQWs under the same QW growth temperature. This work provides a feasible approach to improving the quality of N-polar InGaN/GaN QWs structure, and it will promote the development of N-polar GaN-based long-wavelength light-emitting devices for micro-LED display.

Polarization multiplexed dissipative Kerr solitons in on-chip micro-resonator

Yong Geng, Yanlan Xiao, Xinjie Han, Kun Qiu, Jing Xu, and Heng Zhou

DOI: 10.1364/OL.466368 Received 08 Jun 2022; Accepted 01 Jul 2022; Posted 01 Jul 2022  View: PDF

Abstract: We demonstrate polarization multiplexed dissipative Kerr solitons in an on-chip silicon nitride micro-resonator. In our experiment, TE- and TM-polarized soliton can be individually generated and controlled, thanks to their weak mutual interaction as the result of sufficiently different repetition rates and orthogonal polarization states. Furthermore, we find that TE- and TM-polarized solitons usually exhibit uncorrelated time jitters, therefore the frequency and phase coherence between the polarization multiplexed soliton microcombs change dramatically as a function of pump laser parameters, by optimizing which we achieve narrow dual-microcomb beat note linewidth as small as 4.4 kHz. Potential applications of on-chip polarization multiplexed soliton microcombs include Kerr comb spectral expansion, dual-comb metrology, and measurement of quantum entanglements.

Temporal characterization of broadband femtosecond laser pulses by surface third-harmonic dispersion scan with ptychographic retrieval

Tiago Gomes, Miguel Canhota, and Helder Crespo

DOI: 10.1364/OL.460069 Received 05 Apr 2022; Accepted 30 Jun 2022; Posted 30 Jun 2022  View: PDF

Abstract: We present a new variant of dispersion scan (d-scan) based on surface third-harmonic generation (STHG) and a ptychographic algorithm taylored for full retrieval (amplitude and phase) of broadband laser pulses. We demonstrate the technique by temporally measuring and compressing few-cycle pulses with 7 fs and 2.5 nJ from a Ti:Sapphire oscillator, using a sapphire window as the nonlinear medium. The results are in very good agreement with standard second-harmonic d-scan measurements based on a nonlinear crystal. The intrinsically broadband and phase-matching-independent nature of STHG make this technique very suitable for the characterization of ultrashort laser pulses over a broad wavelength range extending into the mid-infrared.

All-fiber nonvolatile broadband optical switch using an all-optical method

Yu Zhang, Jiming Chen, shuai liu, Wei Jin, siying cheng, Yaxun Zhang, Zhihai Liu, Jianzhong Zhang, and Libo Yuan

DOI: 10.1364/OL.462200 Received 26 Apr 2022; Accepted 30 Jun 2022; Posted 30 Jun 2022  View: PDF

Abstract: Optical switch based on phase change materials has enormous application potential in optical logic circuits and optical communication systems. Integration of all-optical switching devices with optical fibers is a promising approach for realizing practical applications in enabling the optical fiber to transmit and process signals simultaneously. This paper designed an all-fiber nonvolatile broadband optical switch using the all-optical method. We use a single optical pulse to modulate the phase change material deposited on the tapered fiber to achieve logical control of the transmitted light. The response time of our optical switch is 80 ns for SET and 200 ns for RESET. Our optical switches can operate in the C-band (1530 nm-1565 nm). The optical switching contrast is 40%. Our approach paves the way for all-optical nonvolatile fiber optic communication.

Femto-strain resolution fiber-optic sensing with ultra-simple white-light round trip filtering method

Shuangxiang Zhao, Qingwen Liu, Yuanyuan Liu, and Zuyuan He

DOI: 10.1364/OL.463204 Received 10 May 2022; Accepted 30 Jun 2022; Posted 01 Jul 2022  View: PDF

Abstract: In the past decade, laser-driven resonant fiber-optic sensors (RFOSs) have been reported touching their ultimate resolution limit. The practicability of these high-performance sensors is, however, discounted because of high system complexity and dependence on narrow-linewidth lasers. In this paper, a novel white-light-driven RFOS is established based on a round trip filtering (RTF) method. Via measuring the RTF loss of an add-drop fiber ring resonator (FRR) sensor, strain signal can be read out with an ultra-simple open-loop configuration. In the sensing experiment, even several femto-strain resolution around 1 kHz is demonstrated, representing the highest resolution level of RFOS to date. Thanks to the obvious superiority in both resolution, simplicity and cost over traditional laser-driven RFOSs, the proposed white-light-driven RFOS is believed to be a milestone on the development of fiber-optic strain sensors.

High-resolution ghost imaging through complex scattering media via temporal correction

Yin Xiao, Lina Zhou, and Wen Chen

DOI: 10.1364/OL.463897 Received 12 May 2022; Accepted 30 Jun 2022; Posted 01 Jul 2022  View: PDF

Abstract: Ghost imaging (GI) derives from quantum entanglement, and a ghost image can be retrieved based on spatially correlated beams. In this Letter, we propose high-resolution GI through complex scattering media using temporal correction. We provide evidence that theoretical description about the GI based on spatially correlated beams is still incomplete and cannot work in complex scenarios. We complete the description of temporal correction of beam correlations in the GI. The optical experiments demonstrate that high-resolution ghost images can always be retrieved by using the rectified temporally-corrected beam correlation algorithm even in complex, dynamic and highly strong scattering environments where conventional GI totally cannot work. The established general framework provides optical insights beyond the current understanding of GI, and the rectified theory and experimental results would represent a key step towards applications of the GI over a wide range of free-space wave propagation environments.

Clarification for the fields of a radially-polarized Laguerre-Gaussian light beam

Spencer Jolly and Miguel Porras

DOI: 10.1364/OL.464118 Received 23 May 2022; Accepted 30 Jun 2022; Posted 01 Jul 2022  View: PDF

Abstract: Radially-polarized light beams have found many applications in particle manipulation, laser processing, and microscopy. Just as with linear polarization, radially-polarized light beams can have higher-order transverse modes that involve Laguerre polynomials. Fields of a radially-polarized Laguerre-Gaussian light beam have been calculated before, even beyond the paraxial approximation. However, there are in fact multiple solutions to the paraxial wave equation that involve Laguerre polynomials with different properties and propagation characteristics. We therefore clarify the discrepancies between three valid radially-polarized solutions to the paraxial wave equation that involve Laguerre polynomials.

Non-Planar Illumination Deflectometry for Axicon Metrology

Henry Quach, Hyukmo Kang, Byeongjoon Jeong, Heejoo Choi, and Daewook Kim

DOI: 10.1364/OL.465046 Received 26 May 2022; Accepted 30 Jun 2022; Posted 01 Jul 2022  View: PDF

Abstract: We introduce an on-axis deflectometry test configuration for axicon metrology. Axicons are challenging to measure due to their characteristically steep, convex geometry. However, if an axicon is coaxially aligned with a camera and a surrounding cylindrical illumination source, high-resolution surface measurements can be obtained via the principle of deflectometry. Emitted from the temporally-modulated source, light deflects at the conical surface and into the entrance pupil of camera, illuminating the full axicon aperture except the 0.5 mm rounded tip. Deflectometry measurements of a 100º and 140º axicon show holistic cone angle agreement within 0.035º against touch probe data and up to 7.93 μm RMS difference from a best-fit cone. We discuss the non-planar illumination architecture, sensitivity, and experimental results of arbitrary apex angle axicons.

On-chip ultrafast all-optical MoSe₂ modulator

Mohammed AlAloul, Jacob Khurgin, Ibrahim Abdulrahman Mahmood Alani, Khalil Ahmed As'ham, Lujun Huang, Haroldo Hattori, and Andrey Miroshnichenko

DOI: 10.1364/OL.465171 Received 26 May 2022; Accepted 30 Jun 2022; Posted 01 Jul 2022  View: PDF

Abstract: Monolayer transition metal dichalcogenides (TMDCs), like MoS₂, MoSe₂, WS₂, and WSe₂, feature direct bandgaps, strong spin-orbit coupling, and exciton-polariton interactions at the atomic scale, which could be harnessed for efficient light emission, valleytronics, and polaritonic lasing, respectively. Nevertheless, to build next-generation photonic devices that make use of these features, it is first essential to model the all-optical control mechanisms in TMDCs. Herein, a simple model is proposed to quantify the performance of a 35μm long Si₃N₄ waveguide-integrated all-optical MoSe₂ modulator. Using this model, switching energies of 55.1pJ and 55.7pJ are obtained for a transverse-magnetic (TM) and transverse-electric (TE) polarised blue light pump signal at λ=450nm, respectively. Moreover, extinction ratios of 20.7dB and 20.2dB are achieved for a TM and TE polarised cyan probe signal at λ=500nm, respectively, with an ultra-low insertion loss of <0.3dB and an ultrafast recovery time of 1.4ps. These findings facilitate modeling and designing novel TMDC-based photonic devices.

Simultaneous measurement of displacement and temperature using balloon-like hybrid fiber sensor

João Santos, Joerg Bierlich, Jens Kobelke, and Marta Ferreira

DOI: 10.1364/OL.465403 Received 30 May 2022; Accepted 30 Jun 2022; Posted 01 Jul 2022  View: PDF

Abstract: A fiber sensor based on a silica capillary in a balloon-like shape for simultaneous measurement of displacement and temperature is proposed and experimentally demonstrated. The sensor is fabricated by splicing a segment of a hollow core fiber between two single mode fibers (SMF) and by creating a balloon shape with the capillary at the top-center position. The SMF-capillary-SMF configuration excites an antiresonant (AR) guidance and the balloon shape enhances a Mach-Zehnder interferometer (MZI). Experimental results show that, for a balloon length of 4 cm and a capillary length of 1.2 cm, AR is insensitive to displacement and its sensitivity to temperature is 14.3 pm/°C, while MZI has a sensitivity to displacement of 1.68 nm/mm and of 28.6 pm/°C to temperature, twice the value of AR. The proposed fiber sensor has only one sensing element in one configuration which makes it of simple fabrication as well as low cost.

Optical responses of Fano resonators in non-spectral parametric domains

Ankit Singh and Jer-Shing Huang

DOI: 10.1364/OL.465901 Received 06 Jun 2022; Accepted 30 Jun 2022; Posted 01 Jul 2022  View: PDF

Abstract: Fano resonance observed in various classical and quantum systems features an asymmetric spectral line shape. For designing nanoresonators for monochromatic applications, it is beneficial to describe Fano resonance in non-spectral parametric domains of critical structural parameters. We develop the analytical model of the parametric Fano profile based on a coupled harmonic oscillator (CHO) model and theoretically demonstrate its application in describing the optical response of a chirped waveguided plasmonic crystal (CWPC). The developed parametric Fano model may find applications in the design of monochromatic and spectrometer-free nanodevices.

Multi-channel parallel ultrasound detection based on a photothermal tunable fiber optic sensor array

Liuyang Yang, Chenhao Dai, Anqi Wang, Geng Chen, Dongchen Xu, Yanpeng Li, Zhijun Yan, and Qizhen Sun

DOI: 10.1364/OL.464148 Received 17 May 2022; Accepted 29 Jun 2022; Posted 29 Jun 2022  View: PDF

Abstract: A multi-channel parallel ultrasound detection system based on a photothermal tunable fiber optic sensor array is proposed. The resonant wavelength of ultrasound sensor has a quadratic relationship with the power of 980 nm heating laser. The maximum tuning range is larger than 15 nm. Through photothermal tuning, the inconsistent operating wavelengths of the FP sensor array can be solved, and then a multiplexing capacity up to 53 can be theoretically realized, which could greatly reduce the time required for data acquisition. Then, a fixed wavelength laser with ultra-narrow linewidth is used to interrogate the sensor array. The interrogation system demonstrates a NEP as low as 0.12 kPa, which is 5.5 times lower than the commercial hydrophone. Furthermore, a multi-channel ultrasound detection system is built to demonstrate the parallel detection capability. Compared with the independent detection, the SNR of parallel detection does not deteriorate, proving that the parallel detection system and the sensor array own very low crosstalk characteristics. The parallel detection technique paves a way for real time photoacoustic/ultrasound imaging.

High-energy, mid-IR, picosecond fiber-feedback optical parametric oscillator

Yudi Wu, Sijing Liang, Qiang Fu, Tom Bradley, Francesco Poletti, David Richardson, and Lin Xu

DOI: 10.1364/OL.461118 Received 18 Apr 2022; Accepted 28 Jun 2022; Posted 29 Jun 2022  View: PDF

Abstract: A compact, mid-infrared (MIR), synchronously pumped, fiber-feedback optical parametric oscillator (OPO) based on periodically poled lithium niobate is developed with tunable signal and idler wavelength ranges of 1472.0 - 1758.2 nm and 2559.1 - 3562.7 nm, respectively. A solid-core SMF-28 fiber and a hollow-core fiber were used as the feedback-fibers in order to compare the effect of their substantially different levels of nonlinearity. The OPO generates 1-MHz, 120-ps, MIR pulses with up to 1.50-μJ pulse energy and 11.7-kW peak power.

Elliptical Gold Nanowires: Controlled Fabrication and Plasmonic Fabry-Pérot Resonances

Kejing Huang, Wentao Wang, Jiaming Zhang, Cong Zhao, Ran Huang, Liping Zhen, Hongang Luo, Jie Liu, Yongliang Zhang, and jinglai duan

DOI: 10.1364/OL.464600 Received 23 May 2022; Accepted 28 Jun 2022; Posted 29 Jun 2022  View: PDF

Abstract: Nanowires (NWs) are essential building blocks of photonic devices for guiding light waves. However, the controlled synthesis of non-circular NWs remains challenging. Herein we develop a bottom-up approach for the fabrication of high-quality elliptical gold NWs with finely tuned geometry engineering by using an advanced ion track template technology. Compared to ordinary NWs, the rotational symmetry breaking leads to highly polarization-dependent plasmonic responses. Modal analysis shows that the lowest dipolar HE1 mode splits into two branches where the attenuation of the long-range branch decreases by 40%, while the short-range branch has a stronger enhanced near-field. Novel plasmonic Fabry-Pérot resonances on finite NWs are measured. Our method can be extended to fabricate non-circular NWs with other materials, holding potential for novel applications from quantum to collective scales.

Experimental evidence of pump-wavefront induced Stern-Gerlach-like splitting in optical parametric generators

Abhishek Mondal and Ritwick Das

DOI: 10.1364/OL.460995 Received 12 Apr 2022; Accepted 28 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: A quantum mechnaical Stern-Gerlach (SG)-like effect have been usually excluded from domain of optics due to the absence of any interaction of photons with conventional magnetic field. A few recent investigations point towards the possibility of observing SG-like effect in nonlinear optics via wedge-shaped poling in long lithium niobate (LN) crystal so as to generate a spatially-varying equivalent magnetic-field (B₀). This leads to two discreet propagation direction by mutually orthogonal pseudo-spin states formed by equal superposition of signal and idler modes but with opposite phases. In this work, we present theoretical formalism to show an equivalent SG-like splitting in a frequency downconversion process and experimentally validate the assertion by producing an optimum transverse gradient in B₀ through an inhomogeneous pump wavefront. The experimental results show SG-like splitting in an optical parametric generation (OPG) process using a widely-used periodically-poled LN (PPLN) crystal and an optimally-tailored Gaussian pump laser beam. The experimentally measured deviation angle for the mutual beam closely matches with the prediction from theoretical formalism using a Gaussian pump wavefront

Laser cooling experiments to measure the quantum efficiency of Yb doped silica fibers

Brian Topper, Alexander Neumann, Alexander Albrecht, Angel Flores, Stefan Kuhn, Denny Haessner, Sigrun Hein, Christian Hupel, Johannes Nold, Nicoletta Haarlammert, Thomas Schreiber, Mansoor Sheik-Bahae, and Arash Mafi

DOI: 10.1364/OL.463157 Received 09 May 2022; Accepted 28 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: A detailed investigation into the wavelength-dependent cooling efficiencies of two ultra-pure large core diameter ytterbium doped silica fibers is carried out by means of the Laser-Induced Thermal Modulation Spectroscopy (LITMoS) method. From these measurements, a quantum efficiency of 0.99 is obtained for both fibers. Optimal cooling is seen for pump wavelengths between 1032-1035nm. The crossover wavelength from heating to cooling is identified to be between 1018-1021nm. The fiber with higher Yb3+ ion density exhibits better cooling, seen by the input power normalized temperature differential.

Silicon mode-insensitive modulator for TE₀ mode and TE₁ mode

Gangqiang Zhou, Ran Huan, Liangjun Lu, Jianping Chen, and Linjie Zhou

DOI: 10.1364/OL.465973 Received 07 Jun 2022; Accepted 28 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: Mode-division multiplexing, which could further increase the capacity and flexibility of the communication systems, has drawn lots of attention. In this letter, we demonstrate a proof-of-principle silicon mode-insensitive modulator based on the balanced Mach-Zehnder interferometer that could realize modulation of both TE₀ and TE₁ modes using a horizontal PN junction. The PN junction is offset from the center of the waveguide to the n-type doped region to modulate both TE₀ and TE₁ modes effectively. An adiabatic directional coupler is used as a mode-insensitive 3-dB power splitter for both modes. A mode-insensitive thermal phase shifter is used to change the operation point of the modulator. 32 Gb/s on-off keying modulation is successfully demonstrated for both TE₀ and TE₁ modes. This modulator can be potentially used in MDM-assisted optical sampling systems.

Realizing transmissive and reflective focusing with an on-chip metalens

Xiang Xiong, wei wen, Wenjie Tang, Ruwen Peng, and Mu Wang

DOI: 10.1364/OL.463934 Received 13 May 2022; Accepted 28 Jun 2022; Posted 29 Jun 2022  View: PDF

Abstract: Metalens made of compact planar metastructure exhibits a magnificent capability of focusing. The high-quality transmissive and reflective focusing simultaneously provides Fourier transformation (FT) operation for optical information processing. Here we show a transflective on-chip metalens (TOM) made of orthogonal nano-grooves (ONGs). The TOM simultaneously converges the transmitted and reflected (T&R) waves to the designed focal points. By adjusting the phase gradient profiles provided by the ONGs, the focal lengths of the T&R in-plane waves can be independently tuned. Our simulations show that the TOM possesses the advantages of broadband (>400 nm bandwidth) and high focusing efficiency (~60%) dual-focusing capability. Further, we utilize the TOM to build a one-to-two 4-f optical system. Two different spatial filtering operations based on FT can be simultaneously implemented in axial transmission and off-axis reflection channels for one input signal. We expect the dual-focusing metalens approach can realize parallel optical processing in on-chip optical computing, spatial filtering, and beyond.

Polarization-Insensitive Local-Oscillator-Carrier Loopback Modulation for Cost-effective and High-port-count Wavelength Routing Optical Switch

Ryosuke Matsumoto, Ryotaro Konoike, Hiroyuki Matsuura, Keijiro Suzuki, Takashi Inoue, Kazuhiro Ikeda, Shu Namiki, and Ken-ichi Sato

DOI: 10.1364/OL.461951 Received 11 May 2022; Accepted 27 Jun 2022; Posted 30 Jun 2022  View: PDF

Abstract: The wavelength routing optical switch uses a wavelength tunable laser at each input-port, and this transmitter implements output port selection by tuning the wavelength that is associated with each output port. With coherent transmission, loopback modulation of a local oscillator (LO) carrier generated at the output port can eliminate the wavelength tunable laser. However, loopback modulation can be unstable since the power fluctuates as fiber traversal creates polarization rotation. We propose here a simple polarization-stabilization circuit and verify its effectiveness in creating a high-port-count optical switch system. The proposed circuit consists of passive components and aligns the polarization state of the supplied LO carrier to be linearly polarized along the x-direction of a TE-input DP-IQ modulator. The circuit is shown to yield stable modulation with Q-variation less than 0.8 dB regardless of any birefringence on the transmission path. The proposal’s effectiveness is verified in optical switch system experiments on DP-QPSK signals; 1,856 x 1,856 switch scale is achieved with loopback modulation.

Femtosecond-laser-enabled simultaneous figuring and finishing of glass with subnanometer optical surface

Jie Qiao and Gong Chen

DOI: 10.1364/OL.467413 Received 10 Jun 2022; Accepted 27 Jun 2022; Posted 01 Jul 2022  View: PDF

Abstract: We demonstrate simultaneous figuring and surface finishing of glass using a femtosecond laser. For the first time to our knowledge, we have achieved deterministic material removal with nanometer precision, and maintained sub-nanometer surface roughness, without inducing any mid-spatial frequency errors to the initial surface. A dynamic pulse propagation model is established to predict the interaction process, including plasma generation and surface temperature. The interactive modeling and the experiments enable the selection of a set of laser parameters to achieve controllable optical figuring and finishing. This demonstration shows the potential for using femtosecond lasers for advanced freeform optic forming, finishing, and reduction of detrimental mid-spatial-frequency errors, and laser-ablation-based patterning used for fabrication of integrated photonics and lasers.

Photonic Time-Frequency Filter Based on Software-Defined Time-Frequency Prism

Guanyu Han, Shangyuan Li, Xiaoxiao Xue, and Xiaoping Zheng

DOI: 10.1364/OL.457157 Received 02 Mar 2022; Accepted 27 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: In this letter, for the first time, we propose a microwave photonic 2D time-frequency filter. A novel concept named photonic time-frequency prism is introduced, with which a time-varying frequency response is produced by deviating the transfer function of an ordinary frequency filter in the 2D time-frequency plane. Moreover, the angle of deviation can be defined by software, allowing the filter to illuminate the 2D time-frequency plane at any rotated angle. Experimentally, we depict the time-varying passband in the time-frequency plane. Besides, as a demonstration, two chirp signals with overlapped spectra are separately extracted with the proposed technique.

2.8 μm erbium-doped ZBLAN fiber laser pumped at 1.7 μm

junxiang zhang, Rui Wang, Shijie Fu, Quan Sheng, Wenxin Xia, lu Zhang, Wei Shi, and Jian-Quan Yao

DOI: 10.1364/OL.463186 Received 06 May 2022; Accepted 27 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: In this paper, a novel efficient pump scheme for erbium-doped fluoride fiber laser at 2.8 μm mid-infrared region is proposed and demonstrated. Singular pump source at 1.7 μm is used to excite Er3+ ions from ground state 4I15/2 to lower laser level 4I13/2, and further boost the ions to 4I9/2, where non-radiation transition occurs for the Er3+ ions to reach upper laser level 4I11/2. This scheme can efficiently recycle ions on the lower laser level 4I13/2 by excited state absorption, therefore realizing population inversion and enhancing laser efficiency. In our demonstration, 660 mW laser output at 2.8 μm was achieved from a 1.7-μm core-pumped erbium-doped fluoride fiber laser, where the laser threshold and slope efficiency were 147 mW and 30.9%, respectively. The proposed innovative pump scheme is of great potential to realize high-power, high-efficiency erbium-doped fiber lasers at 2.8 μm.

On-axis polarization of beams radiated by electromagnetic circularly coherent sources

Juan Carlos de Sande, Olga Korotkova, Massimo Santarsiero, Rosario Martinez-Herrero, Gemma Piquero, and Franco Gori

DOI: 10.1364/OL.465816 Received 02 Jun 2022; Accepted 27 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: On-axis spectral density and degree of polarization of beams radiated by electromagnetic (EM) sources with circular correlations are shown to be finely controlled by changing the source parameters. We reveal, in particular, that in this beam class, unlike for all previously known stationary beams, it is possible to control independently the dynamics of the on-axis spectral density and the degree of polarization. This was enabled by the obtained analytical expression for the on-axis polarization matrix, derived for general EM sources with circular coherence and Gaussian spectral density across the source plane. A simple experimental scheme for generating a broad class of EM circularly coherent sources is devised involving only a line source, a lens and a transparency, possibly anisotropic.

Few-cycle Yb laser source at 20 kHz using multidimensional solitary states in hollow-core fibers

Loïc Arias, Adrien Longa, François Légaré, Philippe Lassonde, Reza Safaei, Guangyu Fan, Heide Ibrahim, Fabio boschini, Gaetan Jargot, Antoine Pommerleau, and Paul Corkum

DOI: 10.1364/OL.464428 Received 31 May 2022; Accepted 27 Jun 2022; Posted 29 Jun 2022  View: PDF

Abstract: We demonstrate ultrashort pulse compression from 300 fs down to 17 fs at a repetition rate of 20 kHz and 160 µJ output pulse energy (3.2 W of average power) using multidimensional solitary states (MDSS) in a 1-meter hollow-core fiber (HCF) filled with N2O. Under static pressure, thermal limitations at this repetition rate annihilate the MDSS with suppression of spectral broadening. The results obtained in differential pressure configuration mitigate thermal effects and significantly increase the range of repetition rate over which MDSS can be used to compress sub-picosecond laser pulses.

Air-gap Fabry–Pérot cavity filtered 30 nm broadband electro-optic frequency combs for high-order coherent communications

Chenbo Zhang, Yixiao Zhu, Bibo He, Rongwei Liu, Zhangyuan Chen, Weiwei Hu, and Xiaopeng Xie

DOI: 10.1364/OL.467447 Received 09 Jun 2022; Accepted 27 Jun 2022; Posted 27 Jun 2022  View: PDF

Abstract: Broadband electro-optic (EO) frequency combs, which have flexible and high repetition frequencies, are prospective light sources for dense-wavelength-division-multiplexed coherent optical communications. In most cases, nonlinear spectral broadening and amplification procedures are demanded to achieve broadband and high-power EO frequency combs. It leads to a low optical carrier-to-noise ratio (OCNR) for comb lines, limiting the transmission capacity. Here, we propose to use an air-gap Fabry-Pérot (FP) cavity to simultaneously improve the OCNR for all the comb lines covering a 30 nm broadband spectrum. A 12 dB OCNR (0.1 nm bandwidth) improvement is obtained experimentally via using an FP cavity with ~790 MHz bandwidth. We apply a 150-channel filtered EO comb with 25 GHz channel spacing and load 20 GBaud signals on each comb line to demonstrate the effect of OCNR improvement. 137/150 channels have a bit error rate below the threshold of soft-decision forward error correction when using the 128 QAM format. While none of these channels can support this modulation format without cavity filtering. We also investigate the long-term stability and channel consistency, highlighting the advantages of using an air-gap FP cavity. Our results show a practical solution to boost the transmission capacity when applying broadband EO combs in optical communications.

Characterization of pixelated nanogratings in 3D holographic display by imaging Mueller matrix ellipsometry

Chao Chen, Xiuguo Chen, Zhongwen Xia, Jiacheng Shi, Sheng Sheng, Wen Qiao, and Shiyuan Liu

DOI: 10.1364/OL.459522 Received 30 Mar 2022; Accepted 27 Jun 2022; Posted 27 Jun 2022  View: PDF

Abstract: Diffraction grating, as an element that can control the direction of the emitted light, is the key component used in holographic sampling three-dimensional (3D) displays. The structural accuracy of nanogratings greatly affects the precision of light modulation, thus influence crosstalk and resolution in 3D display. It is of great significance for nondestructive measurement of the nanogratings. However, existing measurement methods have certain limitations such as destructiveness and low measurement efficiency in the face of measuring such pixelated nanogratings. In this work, aiming at the measurement requirements and challenges of pixelated nanogratings in 3D display, we propose to use a self-designed imaging Mueller matrix ellipsometer (IMME) for grating characterization. A sample containing 6 periods and 10 orientations pixelated gratings was used to verify the effectiveness of the method used. Through the measurement and fitting data, it can be seen that the measurement data obtained by using IMME can be well matched with the theoretical results. At the same time, the extraction results of the structural parameters, periods and orientations are also consistent with the measurement results of the scanning electron microscope. It is expected that IMME could provide a guarantee for the accurate display of 3D holography.

Quasiperiodic light

Laszlo Frazer, Thomas Mercier, Chirenjeevi Krishnan, Zhou Xu, Amelia Liu, Gangcheng Yuan, Junhan Kong, Pavlos Lagoudakis, Martin Charlton, and Alison Funston

DOI: 10.1364/OL.461613 Received 09 May 2022; Accepted 26 Jun 2022; Posted 27 Jun 2022  View: PDF

Abstract: Quasiperiodicity is a form of spatial order which has been observed in quasicrystalline matter, but not light. We construct a quasicrystalline surface out of a light emitting diode. Using a nanoscale waveguide as a microscope (NSOM), we directly image the light field at the surface of the diode. Here we show, using reciprocal space representations of the images, that the light field is quasiperiodic. We explain the structure of the light field with wave superposition. Periodic ordering is limited to at most 6-fold symmetry. The light field exhibits 12-fold quasisymmetry, showing order while disproving periodicity. This demonstrates that a new class, consisting of projections from hyperspace, exists in the taxonomy of light ordering.

Reconfigurable scan lens based on an actively-controlled optical phased array

shengi kuo, Ju-Wei WANG, Zohauddin Ahmad, PoHan Fu, HSIN-HUNG LIN, Jin-Wei Shi, Ding-Wei Huang, and You-Chia Chang

DOI: 10.1364/OL.461697 Received 26 Apr 2022; Accepted 26 Jun 2022; Posted 27 Jun 2022  View: PDF

Abstract: Integrated photonics provides a path for miniaturization of an optical system to a compact chip scale and offers reconfigurability by the integration of active components. Here we report a chip-scale reconfigurable scan lens based on an optical phased array, consisting of 30 actively-controlled elements on the InP integrated photonic platform. By configuring the phase shifters, we show scanning of a nearly diffraction-limited focused spot with a full width at half maximum spot size down to 2.7 μm at the wavelength of 1550 nm. We demonstrate the key functions needed for a laser-scanning microscope, including light focusing, collection, and steering. We also perform confocal measurements to detect reflection at selective depths.

Intrinsic parameter free calibration of FPP using ray phase mapping model

Yang Yang, Yupei Miao, Xiaoli Liu, Giancarlo Pedrini, Qijian Tang, Wolfgang Osten, and Xiang Peng

DOI: 10.1364/OL.462504 Received 02 May 2022; Accepted 25 Jun 2022; Posted 27 Jun 2022  View: PDF

Abstract: This letter presents a ray phase mapping model (RPM) for fringe projection profilometry (FPP) that avoids calibrating intrinsic parameters. The novelty of the RPM is to characterize the imaging system with independent rays for each pixel, and to associate the rays with the projected phase in the illumination field for efficient 3D mapping, avoiding complex imaging-specific modeling about lens layout and distortion. Two loss functions are constructed to flexibly optimize camera ray parameters and mapping coefficients, respectively. As a universal approach, it has the potential to calibrate different types of FPP systems with high accuracy. Experiments on wide-angle lens FPP, telecentric lens FPP and MEMS-based FPP are carried out to verify the feasibility of the proposed method.

2D/3D switchable display based on liquid crystal lens array and rotating specimen shooting method

Li-Lan Tian, Fan Chu, Yu-Xian Zhang, Wuxiang Zhao, and Lei Li

DOI: 10.1364/OL.460263 Received 05 Apr 2022; Accepted 25 Jun 2022; Posted 27 Jun 2022  View: PDF

Abstract: A liquid crystal (LC) lenticular lens array with auxiliary electrode is proposed. The introduction of the auxiliary electrodes helps to obtain LC lens array (LCLA) with relatively large aperture without complex structures. When the LCLA is in the focusing state, the voltage of the auxiliary electrode is less than that of the edge electrode, and the generated electric field in the LCLA can penetrate into the LC layer. Therefore, the ideal phase profile is obtained with a relatively thin LC layer thickness. Experimental results shows that the LCLA has the characteristics of high optical power and low operation voltage. Based on the proposed LCLA, a multi-view 2D/3D switchable display is realized. In the experiment, a series of parallax images are obtained by rotating the sample to replace the convergence shooting method for 3D imaging. Compared with other 2D/3D switchable display devices, the multi-view 2D/3D switchable display based on the LCLA is characterized by thin and compact, high definition and no moiré pattern.

Frequency-modulated continuous-wave 3D imaging with high photon efficiency

Xin Huang, Yu Hong, Zheng-Ping Li, and Feihu Xu

DOI: 10.1364/OL.463007 Received 03 May 2022; Accepted 25 Jun 2022; Posted 27 Jun 2022  View: PDF

Abstract: Frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR), which offers high depth resolution and immunity to environmental disturbances, has emerged as a strong candidate technology for active imaging applications. In general, hundreds of photons per pixel are required for accurate 3D imaging. When it comes to low-flux regime, however, depth estimation has limited robustness. To cope with this, we propose and demonstrate a photon-efficient approach for FMCW LiDAR. We construct a FMCW LiDAR setup based on single-photon detectors where only a weak local oscillator is needed for the coherent detection. To realize the photon-efficient imaging, our approach exploits the spatial correlations among neighboring pixels to amplify the low-flux signals, and employs a total-variation seminorm to smooth out the noise on the recovered depth map while preserving jump discontinuities. Both simulation and experiment results show that our approach can generate high-quality 3D images from $\sim$10 signal photons per pixel, increasing the photon efficiency by 10-fold over the traditional processing method. The high photon efficiency will be valuable for low-power and rapid FMCW LiDAR applications.

Parallel Micro-LED arrays with high modulation bandwidth for visible light communication

Shunan Yao, Huaqing Chai, Lei Lei, Zihe Zhu, Guoqiang Li, and Wenliang Wang

DOI: 10.1364/OL.463399 Received 11 May 2022; Accepted 25 Jun 2022; Posted 27 Jun 2022  View: PDF

Abstract: Over the past few decades, GaN-based light-emitting diodes (LEDs) have been widely used in solid-state lighting due to their energy-saving and long lifetime characteristics. However, the limited modulation bandwidth of conventional commercial LED chips limits their application in high-speed visible light communication system. Herein, this work designs vertical structure parallel micro-LED arrays with different array numbers to develop LED sources for communication and lighting. The as-prepared micro-LEDs in 2 × 2 array reveal a high modulation bandwidth of ~785 MHz at an injection current density up to 6.67 kA/cm2. Meanwhile, the light output power is over 7 mW, which is more suitable for visible light communication in free space. Based on the results, an optical link using an easy non-return-to-zero ON-OFF keying modulation scheme with a data rate of 1 Gb/s has been demonstrated accordingly.

Cancellation of reference update-induced 1/f noise in chirped-pulse DAS

Pedro Vidal-Moreno, Etienne Rochat, Pablo Fermoso Santos, María R. Fernández-Ruiz, Hugo Martins, Sonia Martin-Lopez, Manuel Ocaña, and Miguel Gonzalez-Herraez

DOI: 10.1364/OL.465367 Received 30 May 2022; Accepted 25 Jun 2022; Posted 29 Jun 2022  View: PDF

Abstract: Distributed acoustic sensors (DAS) perform distributed and dynamic strain or temperature change measurements by comparing a measured time-domain trace with a previous fiber reference state. Large strain or temperature fluctuations or laser frequency noise impose the need to update such reference, making it necessary to integrate the short-term variation measurements if absolute strain or temperature variations are to be obtained. This has the drawback of introducing a 1/f noise component, as noise is integrated with each cumulative variation measurement, which is detrimental for the determination of very slow processes (i.e., in the mHz frequency range or below). This work analyzes the long-term stability of chirped pulse phase-sensitive optical time domain reflectometry (CP-ΦOTDR) with multi-frequency database demodulation (MFDD) to carry out “calibrated” measurements in a DAS along an unmodified SMF. It is shown that, under the conditions studied in this work, a “calibrated” chirped pulse DAS with a completely suppressed reference update-induced 1/f noise component is achieved, capable of making measurements over periods of more than 2 months with the same set of references, even when switching off the interrogator during the measurement.

Mode power spectrum for Laguerre-Gauss beams in Kolmogorov turbulence

Henry Elder and Phillip Sprangle

DOI: 10.1364/OL.457709 Received 28 Mar 2022; Accepted 24 Jun 2022; Posted 24 Jun 2022  View: PDF

Abstract: We analyze the effects of atmospheric turbulence on the mode power spectrum of beams carrying orbital angular momentum represented by Laguerre-Gauss (LG) modes. For an input (0,m) LG mode, we calculate the power transferred to other modes due to turbulence. The analysis is validated against split-step beam propagation simulations and shows agreement into the strong turbulence regime. These results have applications for the design and characterization of free-space laser communication systems.

Local-flexible coupling optical-resolution photoacoustic microscopy with enhanced sensitivity

Dongfang Li, Chao Tao, Zizhong Hu, Zhengyu Zhang, and XiaoJun Liu

DOI: 10.1364/OL.457652 Received 04 Mar 2022; Accepted 24 Jun 2022; Posted 27 Jun 2022  View: PDF

Abstract: An acoustic coupling scheme largely determines the performance of an OR-PAM, including practicability, sensitivity and stability. In this study, we propose an OR-PAM based on a local-flexible acoustic coupling scheme, which includes a well-designed combiner connecting a set of circulating system. The combiner integrates an objective lens and an ultrasonic transducer, controls the water level, restricts the flow rate, and drains bubbles. The circulating system provides sustained and steady flowing water. The flowing water constrained in the combiner and the circulating system forms flexible and stable local contact between the sample and the transducer. Phantom experiments demonstrated that the proposed method can maintain high optical resolution, but improve the detection sensitivity about 1.9 times in comparison to dry coupling. A series of in vivo imaging experiments of the mouse ear, iris and eyeground were conducted to examine the practicability of the proposed system in biomedicine. Moreover, in vivo experiments showed that OR-PAM based on local-flexible coupling can reveal more details of eyeground microvasculatures, benefitting from its enhanced sensitivity. These merits promise that OR-PAM based on local-flexible coupling may have broad applications in biomedical fields.

Fiber optical parametric oscillator made of soft glass

Imtiaz Alamgir, Mohsen Rezaei, and Martin Rochette

DOI: 10.1364/OL.457711 Received 04 Mar 2022; Accepted 24 Jun 2022; Posted 24 Jun 2022  View: PDF

Abstract: Fiber optical parametric oscillators (FOPO) are compact optical sources of coherent and broadly tunable light, compatible with operation in unconventional spectral bands. Highly nonlinear silica fibers have enabled the development of FOPOs in the telecommunication wavelength band but the strong material absorption of silica glass at wavelengths >2 µm limits its applicability in the mid-infrared (MIR) spectral range. In this work, we overcome this issue and report a FOPO designed entirely out of soft-glass fiber. For this purpose, we combine an As2Se3 single-mode fiber coupler, an As2Se3 parametric gain medium, and a low-loss ZBLAN delay fiber to build the first all-fiber laser cavity made of soft glass. Two FOPOs are presented, one driven by pure parametric gain leading to wavelength tunable Stokes emission within 2.088-2.139 µm, and the other driven by Raman assisted parametric gain leading to Stokes emission within 2.0 -2.048 µm. This demonstration is a promising first step towards the development of fully fiberized MIR light sources.

Multiresonant analysis improves the limit of detection of tilted fiber Bragg grating refractometers

Jacques Albert and Alexandre Kelly-Richard

DOI: 10.1364/OL.462687 Received 04 May 2022; Accepted 23 Jun 2022; Posted 24 Jun 2022  View: PDF

Abstract: A multiresonant approach based on tracking 27 cladding mode resonances of tilted fiber Bragg grating refractometers is shown to improve the limit of detection by factor of 3 to 4 relatively to the conventional approach of tracking the single-most sensitive resonance. Limits of detection between 500 and 600 ppm were achieved for sub-1% dilutions of ethanol in water in repeated experiments. In all cases, wavelengths were referenced to the core mode resonance which eliminates the effect of small temperature changes during and between experiments.

Arbitrary access to optical carriers in silicon photonic mode/wavelength hybrid division multiplexing circuits

Jianzong Tan, Huifu Xiao, Mingyang Ma, Xudong Zhou, Mingrui Yuan, Aditya Dubey, Andreas Boes, Thach Nguyen, Guanghui Ren, Yikai Su, Arnan Mitchell, and Yonghui Tian

DOI: 10.1364/OL.463445 Received 10 May 2022; Accepted 23 Jun 2022; Posted 23 Jun 2022  View: PDF

Abstract: In this letter, an arbitrary optical mode and wavelength carrier access scheme is proposed based on a series of multimode microring resonators and one multimode bus waveguide with constant width. As a proof-of-concept, a three-mode (de)multiplexing device is designed, fabricated and experimentally demonstrated. The mode coupling regions and transmission regions of the microring resonators are designed carefully to selectively couple and transmission different optical modes. The extinction ratio of the microring resonators are larger than 21.0 dB. The mode and wavelength crosstalk for directly (de)multiplexing are less than -12.8 dB and -19.0 dB, respectively. It would be a good candidate for future large-scale multidimensional optical networks.

X-Y sensitive schlieren and shadowgraph system

Adrián Martínez-González and David Moreno-Hernández

DOI: 10.1364/OL.467453 Received 14 Jun 2022; Accepted 23 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: Visualizing and quantifying certain variables is essential in fluid flow studies. If we add that these tasks are achieved in great detail, pay for implementing optical techniques with these characteristics. Based on this premise, we present a z-schlieren setup that allows simultaneous recording of horizontal and vertical sensitivity schlieren images and shadowgraph images. These two visualization techniques complement each other since each method has its strengths and weaknesses. The optical system employs two ultra-thin filters, an RGB Light Emitted Diode (LED), and a color digital camera. As a result, the data obtained is significantly improved over the existing standard schlieren methods. Furthermore, the fluid flow is better analyzed by combining the schlieren and shadowgraph techniques since a straightforward optical system gathers helpful information. The performance of the optical system is demonstrated by visualizing the convective fluid flow of a candle flame and measuring the temperature fields of the flow of a heated rectangular plate.

High-quality fiber Bragg grating inscribed in ZBLAN fiber using femtosecond laser point-by-point technology

Lin Chen, Cailing Fu, zhihao cai, PENG-SHENG SHEN, YU FAN, Chao Du, Huajian Zhong, Yanjie Meng, Yiping Wang, Changrui Liao, Jun He, and Weijia Bao

DOI: 10.1364/OL.464006 Received 13 May 2022; Accepted 23 Jun 2022; Posted 23 Jun 2022  View: PDF

Abstract: We demonstrated for the first time, to the best of our knowledge, the fabrication of a high-quality fiber Bragg grating (FBG) in ZBLAN fiber by using an efficient femtosecond laser point-by-point technology. Two types of FBG, i.e., high coupling coefficient and narrow bandwidth grating, were successfully obtained. The coupling coefficient was strongly dependent on the grating order and pulse energy. A 2rd-order FBG with an ultra-high coupling coefficient of 325 m-1, reflectivity of 97.8% was inscribed in the ZBLAN fiber. A pair of FBGs with a narrow FWHM of 0.30 and 0.09 nm were also demonstrated.

Integrated orbital angular momentum mode sorters on vortex fibers

LAVI SOMERS, Shlomi Lightman, Ilan Bleyhman, Gilad Hurvitz, Raz Gvishi, Leslie Rusch, and Ady Arie

DOI: 10.1364/OL.462948 Received 05 May 2022; Accepted 22 Jun 2022; Posted 23 Jun 2022  View: PDF

Abstract: We design, fabricate and characterize integrated mode sorters for multimode fibers that guide well-separated vortex modes. We use 3D-direct laser printing to print a collimator and a Cartesian to log-polar mode transformer on the tip of the fiber. This polarization insensitive device can send different modes into different exit angles and is therefore useful for space division multiplexed optical communication. Two types of fibers with two corresponding sorters were used, enabling to sort either 4 or 8 different modes in a compact and robust manner. The integration of the vortex fiber and multiplexer opens the door for widespread exploitation of OAM for data multiplexing in fiber networks.

LED-pumped Cr:LiSAF laser system operating at 100 Hz based on a multipass amplifier

Hussein Taleb, Catherine LeBlanc, Elio THELLIER, Pierre Pichon, Frederic Druon, Francois Balembois, and Patrick Georges

DOI: 10.1364/OL.465115 Received 25 May 2022; Accepted 22 Jun 2022; Posted 23 Jun 2022  View: PDF

Abstract: The LED-pumping technology is used for the first time, to the best of our knowledge, to develop a complete MOPA (Master Oscillator Power Amplifier) system including a multipass amplifier. A pumping head using an original slab architecture has been developed integrating a Cr:LiSAF slab pumped by 2112 blue LEDs via a Ce:YAG luminescent concentrator. The slab configuration allows to reach a large number of passes – up to 22 - together with an access to an efficient cooling, allowing the operation at 100 Hz repetition rate. For 22 passes, the amplifier delivers up to 2.4 mJ pulses with a slightly saturated gain of 4.36 at 825 nm. A complete study of the MOPA including temperature issues is described, concluding in nearly constant performances versus the repetition rate, up to 100 Hz.

Squeezed light generated with hyperradiance without nonlinearity

Jun Li, Chengjie Zhu, and Yaping Yang

DOI: 10.1364/OL.464060 Received 19 May 2022; Accepted 21 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: We propose that the squeezed light accompanied by hyperradiance is induced by quantum interference in a linear system consisting of a high quality optical cavity and two coherently driven two-level qubits. When two qubits are placed at the crest and trough of the standing wave in the cavity respectively (i.e., they have the opposite coupling coefficient to the cavity), we show that squeezed light is generated in the hyperradiance regime under the conditions of strong coupling and weak driving. Simultaneously, the Klyshko's criterion alternates up and down at unity when the photon number is even or odd. Moreover, the orthogonal angles of the squeezed light can be controlled by adjusting the frequency detuning pressure between the driving field and the qubits. It can be implemented in a variety of quantum systems, including but not limited to two-level systems such as atoms, quantum dots in single-mode cavities.

Compact and Broadband Silicon TE-Pass Polarizer Based on Tapered Directional Coupler

Zakriya Mohammed, Bruna Paredes, and Mahmoud Rasras

DOI: 10.1364/OL.457260 Received 28 Feb 2022; Accepted 21 Jun 2022; Posted 22 Jun 2022  View: PDF

Abstract: We demonstrate a novel TE-pass polarizer on a silicon-on-insulator (SOI) platform. The device's working principle is based on the phase-matched coupling of unwanted TM0 mode in an input waveguide to TM1 mode in a tapered directional coupler, which is then guided to a low-loss bending (180-degree) and scattered in a terminator section with low back reflections. On the other hand, the input TE0 mode is routed through the tapered section uncoupled with negligible loss. An S-bend is added before the output for filtering any residual TM0 mode present in the input waveguide. Tapering the directional coupler helps maintain phase matching for broadband operation and increases the tolerance towards fabrication errors. The measurement shows low insertion loss (IL < 0.44 dB), high extinction ratio (ER > 15 dB), and wide bandwidth (BW = 80 nm). The overall device length is only 13 µm. A high performing TE-pass polarizer (IL < 0.89, ER > 30, and BW = 100 nm) is also demonstrated by cascading two of the proposed polarizers.

Laser-Induced damage of Anti-Resonant Hollow-Core Fiber for High-Power Laser Delivery at 1 μm

xinyue zhu, Fei Yu, Dakun Wu, Shufen Chen, Yi Jiang, and Lili Hu

DOI: 10.1364/OL.457749 Received 07 Mar 2022; Accepted 21 Jun 2022; Posted 22 Jun 2022  View: PDF

Abstract: We demonstrate high-power laser delivery exceeding 1 kilowatt through a 5-meter homemade anti-resonant hollow-core fiber (AR-HCF) at 1 μm wavelength. Laser-induced damages to fiber coating and jacket glass are experimentally observed respectively for different incident laser powers from a few hundred watts up to nearly 1.5 kilowatts. The cladding microstructure of AR-HCF is free of damage at the incident end when 80 % of 1.5 kW incident power is coupled in. The deviation of incident laser beam from the core to the cladding causes no damage but deterioration of coupling efficiency only. The potential of AR-HCF for higher-power laser delivery are discussed.

Moiré modulated non-Hermitian mode-locking

Zengrun Wen, Song Gao, Weiming Wang, Kaile Wang, Yangjian Cai, and Yuanmei Gao

DOI: 10.1364/OL.464199 Received 17 May 2022; Accepted 20 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: We study the pulse characteristics in a laser mode-locked by active modulators with non-Hermitian moiré driven signals. The signal assembles a parity-time (PT) symmetric and an anti-parity-time (APT) symmetric function with fundamental and harmonic frequencies, respectively, inducing the complex coupling between modes in the frequency domain. A one-dimensional synthetic lattice is used to analyze the spectral mode coupling. By enlarging the weight and harmonic order of the APT part of the signal, the optical spectrum can be adjusted from red shift to blue shift. Simultaneously, the pulse duration and spectral width are shortened and broadened, respectively. The work explores the role of non-Hermitian moiré modulation in the laser area.

A robust binary fringe generation method with defocus adaptability

zhuojun zheng, Jian GAO, Yizhong Zhuang, Lanyu Zhang, and Xin Chen

DOI: 10.1364/OL.462657 Received 02 May 2022; Accepted 20 Jun 2022; Posted 23 Jun 2022  View: PDF

Abstract: Current binary defocus technology mainly focuses on fringe generation suitable for specific frequencies without considering fringe adaptability for defocus-degree variation, which decreases the measuring accuracy for this scenario. To achieve a high-quality measurement, this paper proposes a robust binary fringe generation method to minimize the phase error caused by changes in defocus and the random error in measurement. In the method, we establish a complete phase error model and construct a novel objective function to optimize the binarization threshold of each pixel. Through derivation of the threshold gradient calculation formula, we quickly obtain optimal binary fringes that can adapt to different fringe pitches and various degrees of defocus. The experimental results verify that the proposed method can generate robust binary fringes adaptive to different fringe pitches and defocus degree variation, and thus achieve high-quality 3D measurements.

Pulsewidth-dependent critical power for self-focusing of ultrashort laser pulses in bulk dielectrics

Sergey Kudryashov, Pavel Danilov, Sergey Kuzmin, Yulia Gulina, Alexey Rupasov, George Krasin, Iosif Zubarev, Alexey Levchenko, Michael Kovalev, Peter Pakholchuk, Sergey Ostrikov, and Andrey Ionin

DOI: 10.1364/OL.462693 Received 29 Apr 2022; Accepted 20 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: Micro-scale filamentation of 0.25-NA focused linearly- and circularly-polarized 1030-nm and 515-nm ultrashort laser pulses of variable pulsewidths in fused silica, fluorite, natural and synthetic diamonds, demonstrates Raman-Kerr effect in the form of critical pulse power magnitudes, proportional to squared wavelength and inversely proportional to laser pulsewidth of 0.3-10 ps. The first trend represents the common spectral relationship between the quantities, while the second indicates its time-integrated inertial contribution of Raman-active lattice polarization, appearing in transmission spectra via ultrafast optical-phonon Raman scattering. The optical-phonon contribution to the non-linear polarization could come from laser field-induced spontaneous/stimulated Raman scattering and coherent optical phonons generated by electron-hole plasma with its clamped density in the non-linear focus. Almost constant product value of the (sub)picosecond laser pulsewidths and corresponding critical pulse powers for self-focusing and filamentation in the transparent dielectrics (“critical pulse energy”) apparently implies constant magnitude of the non-linear polarization and other “clamped” filamentation parameters at the given wavelength for each material.

A 64-pixel Mo80Si20 superconducting nano-wire single-photon imager with saturated internal quantum efficiency at 1.5 μm

Hui Wang, Qingyuan Zhao, Lingdong Kong, Yanghui Huang, Shi Chen, Hao Hao, Jiawei Guo, Danfeng Pan, xuecou tu, Labao Zhang, Xiaoqing Jia, Jian Chen, Lin Kang, and Peiheng Wu

DOI: 10.1364/OL.461915 Received 26 Apr 2022; Accepted 20 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: Superconducting nanowire single-photon imager (SNSPI) uses a time multiplexing readout, which is built in the nanowire designed into a microwave transmission line, for sensing the position and arrival time of photons. This readout method significantly reduces the readout complexity. However, due to the serial connection, the nanowire should be uniform so that a common bias can set all segments of the nanowire to their maximum detection efficiency, which becomes more challenging as the scalability (i.e. the length of nanowire) increases. Here, we have developed a 64-pixel SNSPI based on amorphous Mo80Si20 film, which yielded uniform nanowire and slow transmission line. Adjacent detectors were separated by delay lines with a distance of 38 μm in horizontal direction and 35 μm in vertical direction, giving an imaging area of 270 μm × 240 μm. Benefiting from the high kinetic inductance of Mo80Si20 films, the delay line gave a phase velocity as low as 4.6 μm/ps (1.5% of the speed of light). By optimizing the microwave and geometry design of the detectors and delay lines, positions of all pixels can be read out with negligible electrical crosstalk (0.02%) by using cryogenic amplifiers. The timing jitter was 100.8 ps. Saturated internal quantum efficiency were observed at a wavelength of 1550 nm. These results demonstrate that amorphous film is a promising material for achieving SNSPIs of large scalability and high efficiency.

A dual chirped-pulse electro-optical frequency comb method for simultaneous molecular spectroscopy and dynamics studies: Formic acid in the THz region

Jasper Stroud and David Plusquellic

DOI: 10.1364/OL.465823 Received 07 Jun 2022; Accepted 19 Jun 2022; Posted 27 Jun 2022  View: PDF

Abstract: An electro-optic dual comb system based on chirped-pulse waveforms is used to simultaneously acquire temporally magnified rapid passage signals and normal spectral line shapes from the back-transformation to the time domain. Multi-heterodyne THz wave generation and detection is performed with the difference frequency mixing of two free-running lasers. The method is used to obtain THz spectra of formic acid in the 10 cm-1 to 20 cm-1 (300 GHz – 600 GHz) region over a range of pressures. The method is widely applicable across other spectral regions for investigations of the transient dynamics and spectroscopy of molecular systems.

Spatial Bessel-like Beams along Arbitrary Convex Trajectories Based on 3D-Printed Metasurface

Meijun Qu, Renwen Tian, Wenyu Li, and Jianxun Su

DOI: 10.1364/OL.465481 Received 30 May 2022; Accepted 19 Jun 2022; Posted 23 Jun 2022  View: PDF

Abstract: A 3D-printed all-dielectric metasurface is presented in this letter which can generate accelerating beam with circularly symmetric non-spreading transverse profile that can propagate along arbitrary convex trajectories. The curved trajectory is mapped to the corresponding direct-space spatial phases by the basic cube units with different geometrical heights. The required phase distribution is derived in detail based on the enveloping theory of differential geometry and Bessel beam generation method. A metasurface with a preset trajectory is simulated and measured for demonstrating the validity of the phase distribution calculated by the proposed theory. The full-wave simulation and measurement results verify that the Bessel-like beam whose intensity follows curved (off-axis) trajectory can be produced by the proposed metasurface. The generated hybrid beam merges the advantages of non-accelerating and accelerating diffractive-free beams. Therefore, the proposed metasurface has great potential in ultra-high-speed communication, secure communication, near field imaging and wireless energy transmission applications and so on. All-dielectric characteristic makes the proposed metasurface have competitive advantages of low cost and easy large-scale processing.

Linearly polarized ytterbium laser enabled by anti-resonant hollow-core fiber inline polarizer

Charu Goel, Huizi Li, Jichao Zang, and Seongwoo Yoo

DOI: 10.1364/OL.465662 Received 01 Jun 2022; Accepted 18 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: We report a linearly polarized ytterbium-doped fiber (YDF) laser cavity configured by integrating an antiresonant hollow-core fiber-based inline polarizer. The 5 cm long compact fiber polarizer was fusion-spliced to a commercial large mode area, polarization-maintaining YDF. Near-diffraction limited linearly polarized signal output with polarization extinction ratio >21 dB was achieved for up to 25 W power that was limited only by available pump power. The performance of the hollow-core fiber polarizer is found to be temperature insensitive, which obviates the need for precise temperature control required in all-fiber, high-power polarized laser cavities employing crossed fiber Bragg gratings. We use the tapering technique to scale down the geometry of the polarizing fiber and shift its operating wavelength by ~100 nm, which makes it an attractive candidate for a variety of fiber laser applications.

Mode-locking induced by coherent driving in fiber lasers

Carlos Mas Arabi, Nicolas Englebert, Pedro Parra-Rivas, Simon-Pierre Gorza, and François Leo

DOI: 10.1364/OL.463061 Received 04 May 2022; Accepted 18 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: Mode-locking is a broad concept that encompasses different processes enabling short optical pulse formation in lasers. It typically requires an intracavity mechanism that discriminates between single and collective mode lasing, which can be complex and sometimes adds noise. Moreover, known mode-locking schemes do not guarantee phase stability of the carrier wave.Here we theoretically propose that injecting a detuned signal seamlessly leads to mode-locking in fiber lasers. We show that phase-locked pulses, akin to cavity solitons, exist in a wide range of parameters. In that regime the laser behaves as a passive resonator due to the non-instantaneous gain saturation.

All-fiber low frequency shifter based on acousto-optic interaction and its heterodyne vibration response

Xianglong Zeng, zhengwei zhang, jiangtao xu, longkun zhang, Linping Teng, and Jianfeng Sun

DOI: 10.1364/OL.463739 Received 11 May 2022; Accepted 18 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: We demonstrate two all-fiber low frequency shift schemes based on acousto-optic interaction in few-mode fiber (FMF). Two acoustically induced fiber gratings (AIFGs) are cascaded in reverse to achieve efficient cycle conversion between LP11 and LP01 core modes in FMF while obtaining a frequency shift of 1.8 MHz. In addition, a long-period fiber grating (LPFG) is employed to replace the AIFG, which achieves a lower-frequency shift of 0.9 MHz, and its tunable wavelength range exceeds 100 nm. Both schemes show the characteristics of upward frequency shift. Moreover, we also present a heterodyne detection system based on the above frequency shift schemes, which is verified in response to micro-vibration signals ranging from tens to hundreds of kilohertz, as well as speech signals in a lower frequency range. The experimental results show that these all-fiber frequency shift schemes have the potential application, such as fiber optic hydrophones, laser speech detection, and fiber optic sensors.

High spatial resolution fast BOTDA enabled by frequency-agility digital optical frequency comb

Huan He, Zhiyong Zhao, Songnian Fu, Deming Liu, and Ming Tang

DOI: 10.1364/OL.458100 Received 09 Mar 2022; Accepted 18 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: A significant spatial resolution enhancement scheme for digital optical frequency comb (DOFC) -based fast Brillouin optical time-domain analysis (BOTDA) is proposed and experimentally demonstrated by utilizing frequency-agility probes, without sacrificing the frequency resolution. The proposed system ensures high spatial resolution by using short frame duration, meanwhile enabling high frequency resolution retrieval of Brillouin gain spectrum using frequency interleaving of multiple frequency-agility DOFC probes. Additionally, quadratic phase coding is introduced to release the influence of the high peak to average power ratio of the probes. Eventually, the proposed BOTDA sensor achieves a record 5 m spatial resolution over 10 km fiber with less than 2 MHz frequency uncertainty, and 1 GHz dynamic measurement range. For proof of concept, 10 Hz vibration sensing is also successfully demonstrated at 40 Hz sampling rate, showing great potential for fast measurement. It’s worth mentioning that higher spatial resolution can be achieved by using more frequency-agility DOFC probes, at the expense of increasing the measurement time.

Cascaded Raman fiber lasers with ultra high spectral purity

Rashmita Deheri, Sarthak Dash, V R Supradeepa, and V Balaswamy

DOI: 10.1364/OL.463950 Received 19 May 2022; Accepted 18 Jun 2022; Posted 22 Jun 2022  View: PDF

Abstract: Random distributed feedback (RDFB) Cascaded Raman fiber lasers (CRFLs) are simple, wavelength agile and enable high power fiber lasers outside emission bandwidths of rare-earth doped fiber lasers. However, spectral purity, defined as the percentage of total output power in the desired Stokes wavelength band, and Relative intensity noise (RIN) of these systems are limited due to the intensity noise of the pump source used for Raman conversion. RIN gets amplified and gets transferred to Raman Stokes orders which causes incomplete Raman conversion and hence limits the spectral purity. Here, we demonstrate a low-intensity noise (<-100dBc/Hz from 9kHz to 10GHz) CRFL with a record ~99% spectral purity tunable over 6 Stokes orders, using a very low intensity noise, narrow linewidth Ytterbium fiber amplifier as a pump source

Novel cavity design with single-mirror THz frequency tuning for polariton lasers

Ondrej Kitzler, Andrew Lee, Ameera Jose, Helen Pask, and David Spence

DOI: 10.1364/OL.465375 Received 30 May 2022; Accepted 17 Jun 2022; Posted 17 Jun 2022  View: PDF

Abstract: We demonstrate a new cavity design for THz lasers based on stimulated polariton scattering (SPS). The design simplifies the angle tuning of these lasers, which require non-collinear cavity fields at fundamental and Stokes wavelengths to cross in an SPS crystal with adjustable crossing angle. A mirror shared by both the fundamental and Stokes cavities ensures stationary overlap of the fields within the crystal, with the angle between the fields tunable by adjustment of one axis of a single mirror. We demonstrate the design for an intracavity SPS laser using an RTP crystal, and achieve single-mirror tuning of the THz output in bands between 3 and 5.8 THz, with a maximum output of 78 μW at 4.08 THz.

Passively phase-locked Er:fiber source of single-cycle pulses in the near infrared with electro-optic timing modulation for field-resolved electron control

Christoph Schönfeld, Philipp Sulzer, Daniele Brida, Alfred Leitenstorfer, and Takayuki Kurihara

DOI: 10.1364/OL.461076 Received 22 Apr 2022; Accepted 17 Jun 2022; Posted 17 Jun 2022  View: PDF

Abstract: A single-cycle light source in the near infrared is demonstrated enabling sensitive applications of ultrafast optical field control of electronic transport. The compact Er:fiber system generates passively phase-locked pulses with broadband spectra covering 150 THz to 350 THz at a duration of 4.2 fs and 40 MHz repetition rate. A second output arm is equipped with an electro-optic modulator that switches the arrival time of the pulses by 700 ps at arbitrary frequencies up to 20 MHz, enabling timing modulation of the pump pulse without changing the average intensity. As a benchmark demonstration, we investigate the carrier relaxation dynamics in low-temperature-grown InGaAs using quantum interference currents.

Multibit NOT logic gate enabled by function programmable optical waveguide

Tao Chen, Zhangqi Dang, Zhenming Ding, Zexu Liu, and Ziyang Zhang

DOI: 10.1364/OL.458516 Received 07 Apr 2022; Accepted 17 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: Introduced in this work is an optical computing/switching engine based on a multimode waveguide and a series of thermal electrodes that can alter the mode profiles, their propagation constants, and hence the interference patterns at the output. Instead of forward design based on time-consuming simulations, we have built a system that can update the thermal electrodes automatically and monitor the change of the interference in a synchronized and fast way until the desired function is reached, all experimentally. We name it function programmable waveguide engine, upon which an optical NOT logic gate is demonstrated, capable of processing up to 4 bits in parallel. Different from the solutions where the phase or amplitude of light is taken as the signal, the input stays in the electronic domain, while the output is converted into optical intensity variations, calculated from the truth table. This simple, low-cost yet powerful engine may lead to the development of a new set of devices for on-chip photonic computing and signal switching.

3D medical images security via light-field imaging

xiaowei Li, Ying Li, Tianhao Wang, Dahai Li, and YANHENG LIAO

DOI: 10.1364/OL.464184 Received 17 May 2022; Accepted 17 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: This letter proposes a selective encryption scheme for 3D medical images using light-field imaging and 2D Moore cellular automata (2D MCA). In our work, we first utilize convolutional neural networks (CNNs) to obtain the saliency of each elemental image (EI) originate from 3D medical image with different viewpoints, and successfully extract the region of interest (ROI) in each EI. In addition, we use 2D MCA with balanced rule to encryptROI of each EI. 2D MCA supports parallel computing and has more advantages in terms of expansion and confusion compared with 1D CA. Finally, the decrypted elemental image array (EIA) can be reconstructed into a full-color and full-parallax 3D image using the display device, which can be visually displayed to doctors so that they can observe from different angles to design accurate treatment plans and improve the level of medical treatment. Our work also requires no preprocessing of 3D images, which is more efficient than the method of using slices for encryption.

A local dielectric tunnel junction to manage the current distribution for AlGaN-based deep-ultraviolet light-emitting diodes with thin p-GaN layer

Qingqing Li, Chunshuang Chu, Weidong Wang, Jiamang Che, Hua Shao, Qianqian Liu, Yonghui Zhang, and Zi Hui Zhang

DOI: 10.1364/OL.461732 Received 25 Apr 2022; Accepted 17 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: In this report, a p+-GaN/SiO2/Ni tunnel junction with a local SiO2 insulation layer is designed to manage the current distribution for commercial-structured AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) with thin p-GaN layer. The experimental and calculated results prove that besides the increased hole injection at the p+-GaN/SiO2/Ni tunnel junction, the local SiO2 layer produces an in-plane unbalanced energy band in the p-GaN layer for the proposed DUV LEDs, thus modulating the carrier transport paths and making holes more spreaded. Then the enhanced optical power is obtained when compared to the conventional DUV LEDs. In addition, the influence of SiO2 insulation layer at different positions on the current distribution is also investigated in this work. The SiO2 insulation layer in the middle position of the p+-GaN layer is most helpful to increase the hole injection efficiency for commercial-structured DUV LEDs.

Time-Frequency Joint Mappings of Terahertz Metasurface for Multi-Dimensional Analysis of Biological Cells

Zhang Zhang, Xinyue Guo, Yang Maosheng, qili Yang, Xin Yan, Lanju Liang, Longhai Liu, and Jian-Quan Yao

DOI: 10.1364/OL.464443 Received 20 May 2022; Accepted 16 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: Traditional fast Fourier transform is to extract the frequency component at the cost of losing time domain information, which is critical for metasurface biosensing. In this letter, a more comprehensive algorithm, continuous wavelet transform (CWT) is introduced to process signals from THz time-domain spectroscopy. By comparing the metasurface-enhanced 2D time-frequency mappings (TFMs) of HaCaT and HSC3 cells, the two types of biological cells can be clearly differentiated, showing the great potential of CWT in the label-free recognition of biological cells. Also, the 2D TFMs serves as effective visualized indicators to successfully detect the concentration of cancer cells from of 1×105 cells/mL to 7×105 cells/mL, supplying a new path to the sensitive detection for cancer diseases. In addition, the 2D TFMs of different metasurfaces under the same cell concentration reveal the correlation of TFMs and localized fields. Such a feature supplies the evidence of interaction between biological cells and electromagnetic waves, implying the possibility that the absorption of biological cells to THz radiation can be effectively controlled by properly designing SRRs structure of metasurfaces.

Giant Electro-Optic Effect in Paraelectric Nanodisordered KTa1-xNbxO3 Crystal

jianwei zhang, Xiaoping Du, Jiguang Zhao, Xuping Wang, Bing liu, Yishuo Song, Zhengjun Liu, and Hang Chen

DOI: 10.1364/OL.460885 Received 11 Apr 2022; Accepted 16 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: Recent experiments have revealed that the order of the electro-optic (EO) effect depends on the frequency of electric field in paraelectric nanodisordered KTa1-xNbxO3 (KTN) crystal. Through the dielectric frequency spectrum under the bias electric field, giant linear and quadratic EO effect was discovered at the resonance frequencies, which breaks the cognition that only quadratic EO effect exists. Applying only a small AC electric field of 6V/mm, the effective linear EO coefficient reached 478pm/V at 609kHz, and the effective quadratic EO coefficient reached 4.39*〖10〗^(-13) m^2 V^(-2)at 302kHz. The reason why extremely low electric field resulting in giant EO coefficient was attributed to the resonance between the polar nanoregions (PNRs) and electric field induced by the field-driven reorientation of free dipoles on the boundary of PNRs. And the order of EO effect depending on the frequency of electric field was attributed to the frequency dependence of vibration of KTN crystal. This finding promotes the understanding for the EO effect caused by field-driven PNR dynamics, but also provides a basis for the development of EO devices.

Generic saturation‐induced phase error correction for structured light 3D shape measurement

Ji Tan, wenqing su, zhaoshui he, yulei Bai, Bo Dong, and Shengli Xie

DOI: 10.1364/OL.461663 Received 25 Apr 2022; Accepted 16 Jun 2022; Posted 17 Jun 2022  View: PDF

Abstract: Intensity saturation is a challenging problem in structured light 3D shape measurement. Most of the existing methods achieve high dynamic range (HDR) measurement by sacrificing measured speed, making them limited in high-speed dynamic applications. This letter proposed a generic efficient saturation-induced phase error correction method for HDR measurement without increasing any fringe patterns. We first theoretically analyze the saturated signal model and deduce the periodic characteristic of saturation-induced phase error. Based on this, we specially design a saturation-induced phase error correction method by jointing Fourier analysis and Hilbert transform. Furthermore, the relationship between phase error, saturation degree, and phase-shifting steps is established by numerical simulation. Since the proposed method requires no extra captured images or complicated intensity calibration, it is extremely convenient in implementation and is applicable to performing high-speed 3D shape measurements. Simulations and experiments verify the feasibility of the proposed method.

Dual-mode optical thermometry design in K3YSi2O7: Eu multi-site phosphor

Jiawen Wang, QingYang Feng, Ruo Lei, Xiaohan Chen, Degang Deng, and Shiqing Xu

DOI: 10.1364/OL.462252 Received 28 Apr 2022; Accepted 16 Jun 2022; Posted 16 Jun 2022  View: PDF

Abstract: In this study, a dual-mode optical thermometer was designed based on radiative transitions from Eu3+ and Eu2+ ions at different K3YSi2O7 lattice sites. In the luminescence-intensity-ratio strategy, a ratiometric signal composed of Eu3+:5D0→7F1 and Eu3+:5D0→7F2 emissions at 593 and 616 nm, respectively, was employed. Meanwhile, the intensity ratio of the 593 nm emission under O2-→Eu3+ charge transfer excitation (λex=249 nm) to the one upon Eu2+:4f7→4f65d1 excitation (λex=349 nm) was selected as a thermometric parameter in the single-band-ratio approach. The study findings showed that combining the two strategies were conducive to the improvements in sensing sensitive and anti-interference performance.

Ultrafast multiple motion-pictures recording technique for propagating light pulses with an ultrashort time difference

Tomoyoshi Inoue, Koki Nagao, Kenzo Nishio, Toshihiro Kubota, and Yasuhiro Awatsuji

DOI: 10.1364/OL.458194 Received 10 Mar 2022; Accepted 16 Jun 2022; Posted 17 Jun 2022  View: PDF

Abstract: Ultrafast optical imaging techniques involving light propagation, which can record light pulse propagation as a motion-picture, are commonly applied in the fields of physics, chemistry, and biomedicine. However, conventional ultrafast optical imaging techniques cannot obtain multiple motion-pictures with an ultrashort time difference. In this Letter, we proposed and demonstrated an imaging technique to obtain multiple motion-pictures of propagating light pulses with an ultrashort time difference. To record multiple motion-pictures of propagating light pulses without superposition of the motion-pictures, we employed a space division multiplexing technique for recording holograms. Also, we constructed and introduced an optical delay setup for generating light pulses with an ultrashort time difference. In the experimental demonstration of the proposed technique, we observed the first and second light propagations for 6.9ps with 1.78 ps time difference.

Interleave-sampled photoacoustic (PA) imaging: a doubled and equivalent sampling rate for high-frequency imaging

Jesse Jokerst and Lei Fu

DOI: 10.1364/OL.464293 Received 20 May 2022; Accepted 16 Jun 2022; Posted 17 Jun 2022  View: PDF

Abstract: Abstract: High-frequency photoacoustic (PA) imaging (>20 MHz) requires data acquisition (DAQ) with commensurately high sampling rate, which leads to hardware challenges and increased costs. We report here a new method—interleave-sampled PA imaging that enables high-frequency imaging with a relatively low sampling rate, e.g., a 41.67-MHz sampling rate with a 30-MHz transducer. This method harnesses two acquisitions at a low sampling rate to effectively double the sampling rate which consequently reduces the frame rate by a factor of two. It modulates the delay of the light pulses and can thus be applied to any PA DAQ system. We performed both phantom and in vivo studies with a 30-MHz transducer. The results demonstrate that interleaved sampling in 41.67 MHz can capture high frequency information above 30 MHz but 41.67-MHz sampling rate cannot. The axial and lateral resolution are as high as 63 µm and 91 µm via interleaved sampling which are much higher than those of conventional 41.67-MHz sampling (130 µm and 136 µm). © 2020 Optica Publishing group

High-performance lensless diffraction imaging from diverse holograms by three-dimensional scanning

Xiu Wen, xuyang Zhou, Yutong Li, Yu Ji, Keya Zhou, Shutian Liu, Dong Jia, Wei Liu, Dazhao Chi, and Zhengjun Liu

DOI: 10.1364/OL.464864 Received 25 May 2022; Accepted 16 Jun 2022; Posted 17 Jun 2022  View: PDF

Abstract: For lensless diffraction imaging, it is a challenging dilemma to achieve a large field of view and high resolution with a small amount of data at the same time. In ptychography system, the high resolution is realized by removing illumination background from the reconstructedimage. But the illumination is limited to a small size by a probe in typical ptychography. For large samples, it takes much time to collect abundant patterns and has strict requirements for computing power of computers. Another widely applied method, multiheight measurement, can realize a wide field of view with several holograms. But, the recovered image is easily destroyed by the background noise. In this letter, a lensless diffraction imaging method by threedimensional scanning is proposed. All positions of the object are different in three directions instead of scanning schemes only on a plane or along optic axis, so more diversity of diffraction information is obtained. We apply the illumination without the limit of a confined aperture, which means that the imaging FOV of a pattern is equal to the size of the utilized image sensor. In comparison with the multi-height method, our method can separate the illumination background noise from the retrieved object. Consequently, the proposed method realized high resolution and contrast, large field-of-view and removing background simultaneously. Experimental validations and comparisons to other methods are presented.

Towards high-power-density laser-driven lightings: Enhancing heat dissipation in phoshor-in-glass film by introducing h-BN

Ping Sui, Hang Lin, Yue Lin, Shisheng Lin, Jiajing Huang, Ju Xu, Yao Cheng, and Yuansheng Wang

DOI: 10.1364/OL.460008 Received 31 Mar 2022; Accepted 16 Jun 2022; Posted 17 Jun 2022  View: PDF

Abstract: It is demonstrated that the h-BN nanocrystals as functional additives into phosphor-in-glass film substantially increases the luminous performance under blue laser driven. The latent mechanism is analyzed via the microstructural and spectroscopic studies. The developed composite material with fine thermal manipulation could be a promising phosphor color converter for high-power-density laser-driven lightings.

Nonlinear pulse compression to 51 W average power GW-class 35 fs pulses at 2 µm wavelength in a gas-filled multi-pass cell

Philipp Gierschke, Christian Grebing, Mathias Lenski, Mahmoud Abdelaal, Joachim Buldt, Ziyao Wang, Tobias Heuermann, Martin Gebhardt, Michael Müller, Jan Rothhardt, and Jens Limpert

DOI: 10.1364/OL.462647 Received 13 May 2022; Accepted 15 Jun 2022; Posted 17 Jun 2022  View: PDF

Abstract: We report on the generation of GW-class peak power, 35 fs pulses at 2 µm wavelength with an average power of 51 W at 300 kHz repetition rate. A compact, krypton-filled Herriott-type cavity employing metallic mirrors was used for spectral broadening. This multi-pass compression stage enabled the efficient post compression of the pulses emitted by an ultrafast coherently combined Thulium-doped fiber laser system. The presented results demonstrate an excellent preservation of the input beam quality in combination with a power transmission as high as 80 %. These results show that multi-pass cell based post-compression is an attractive alternative to nonlinear spectral broadening in fibers, which is commonly employed for thulium-doped and other mid-infrared ultrafast laser systems. Particularly, the average power scalability and the potential to achieve few-cycle pulse durations make this scheme highly attractive.

Semi-analytic Fresnel diffraction calculation with polynomials decomposition

Lei Zhao, Wenhui Fei, yuejia li, Kaiwei Wang, and Jian Bai

DOI: 10.1364/OL.462972 Received 03 May 2022; Accepted 15 Jun 2022; Posted 17 Jun 2022  View: PDF

Abstract: The numerical method based on the fast Fourier transform (FFT) is generally applied to calculate the Fresnel diffraction field, which would suffer from sampling constraints. To break this limit, in this Letter, the semi-analytic Fresnel diffraction calculation method is proposed based on polynomials decomposition. The diffraction field could be flexibly computed by using the properly analytic Fresnel diffraction basis function terms according to the application requirements. Analytic Fresnel diffraction basis functions are calculated based on Legendre or Chebyshev polynomials by using the object-domain frequency division multiplexing method. The proposed method provides arbitrary sampling, high-flexibility, and high-accuracy diffraction calculation in the full-path Fresnel region. The computational efficiency and accuracy of the proposed method are compared with FFT-based methods. It is potentially applied in light field analysis, wavefront sensing, and image processing.

Fano effect induced giant and robust enhancement of photon correlations in cavity QED systems

Yuwei Lu, Jingfeng Liu, Runhua Li, Haishu Tan, and Yongyao Li

DOI: 10.1364/OL.459643 Received 30 Mar 2022; Accepted 15 Jun 2022; Posted 16 Jun 2022  View: PDF

Abstract: Fano effect arising from interference between two dissipation channels to the radiation continuum enables to tune the photon statistics. Understanding the role of Fano effect and exploiting to achieve strong photon correlations are of both fundamental and applied significance. We present an analytical description of Fano-enhanced photon correlations based on cavity quantum electrodynamics to show that, the Fano effect in atom-cavity systems can improve the degree of antibunching by over four orders of magnitude. The enhancement factors and the optimal conditions are explicitly given, and found related to the Fano parameter q. Remarkably, the Fano enhancement manifests robustness against the decoherence processes, and can survive in the weak coupling regime. We expect our work to provide insight in tuning the photon statistics through Fano effect, which offers a new route to enhance the photon correlations, as well as the possibility of generating nonclassical light in a wider diversity of systems without the need of strong light-matter interaction.

High-aperture low-coherence interferometer with diffraction reference wave

Michael Toropov, Nikolay Chkhalo, Ilya Malyshev, and Nikolay Salashchenko

DOI: 10.1364/OL.460708 Received 18 Apr 2022; Accepted 15 Jun 2022; Posted 16 Jun 2022  View: PDF

Abstract: A high-aperture low-coherence interferometer with a diffraction reference wave based on tipped single mode optical fiber was proposed and investigated. Due to the usage of the central and least aberrated region of the diffracted wavefront, the interferometer comprise record working aperture. The interferometer makes it possible to study samples with a reflectance that varies over a wide range. The demonstration of the use of this interferometer for high-precision measurements of a spherical mirror was presented. Sub-nanometer reproducibility of measurements in terms of the PV parameter and sub-angstrom reproducibility in terms of RMS were demonstrated.

Demonstration of turbulence mitigation in a 200-Gbit/s orbital-angular-momentum multiplexed free-space optical link using simple power measurements for determining the modal crosstalk matrix

Nanzhe Hu, Haoqian Song, Runzhou Zhang, Huibin Zhou, Cong Liu, Xinzhou Su, Hao Song, Kai Pang, Kaiheng Zou, Brittany Lynn, Moshe Tur, and Alan Willner

DOI: 10.1364/OL.464217 Received 17 May 2022; Accepted 15 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: We experimentally demonstrate turbulence mitigation in a 200-Gbit/s quadrature-phase-shift-keying (QPSK) orbital-angular-momentum (OAM) mode-multiplexed system using simple power measurements for determining the modal coupling matrix. To probe and mitigate turbulence, we: (i) sequentially transmit multiple probe beams on 1550-nm wavelength each with a different combination of Laguerre Gaussian (LG) modes; (ii) detect the power coupling of each probe beam to LG00 for determining the complex modal coupling matrix; (iii) calculate the conjugate phase of turbulence-induced spatial phase distortion; (iv) apply this conjugate phase to a spatial light modulator (SLM) at the receiver to mitigate the turbulence distortion for the 1552-nm mode-multiplexed data-carrying beams. The probe wavelength is close enough to the data wavelength such that it experiences similar turbulence, but yet is far enough away such that the probe beams do not affect the data beams and can all operate simultaneously. Our experimental results show that with our turbulence mitigation approach: (a) the inter-channel crosstalk is reduced by ~25 and ~21 dB for OAM +1 and -2 channels, respectively; (b) the optical signal-to-noise ratio (OSNR) penalty is <1 dB for both OAM channels for a bit error rate (BER) at the 7% forward error correction (FEC) limit, compared with the no turbulence case.

High-speed two-dimensional terahertz spectroscopy with echelon-based shot-to-shot balanced detection

Frank Gao, Zhuquan Zhang, Zi-Jie Liu, and Keith Nelson

DOI: 10.1364/OL.462624 Received 02 May 2022; Accepted 15 Jun 2022; Posted 23 Jun 2022  View: PDF

Abstract: By utilizing a reflective-echelon-based electro-optic sampling technique and a fast detector, we develop a two-dimensional terahertz (THz) spectrometer capable of shot-to-shot balanced readout of THz waveforms at a full 1 kHz repetition rate. To demonstrate the capabilities of this new detection scheme for high-throughput applications, we use gas-phase acetonitrile as a model system to acquire two-dimensional THz rotational spectra. The results show a two-order-of-magnitude speedup in the acquisition of multidimensional THz spectra when compared to conventional delay-scan methods while maintaining accurate retrieval of the nonlinear THz signal. Our report presents a feasible solution for bringing the technique of multidimensional THz spectroscopy into widespread practice.

Single-wavelength transmission at 1.1-Tbit/s net data rate over a multi-modal free-space optical link using commercial devices

Zhouyi Hu, Yiming Li, David Benton, Abdallah Ali, Mohammed Patel, and Andrew Ellis

DOI: 10.1364/OL.463941 Received 13 May 2022; Accepted 15 Jun 2022; Posted 15 Jun 2022  View: PDF

Abstract: We employ commercial mode-selective photonic lanterns to implement mode multiplexing and demultiplexing for high-capacity free-space optical communications. Moreover, we design a time-division-multiplexed frame structure to efficiently emulate multiple independent transmitters with channelized precoding using only one transmitter. To maximize the throughput of the system, we optimize the modes selected for carrying data, and apply adaptive loading to different channels. By leveraging mode- and polarization-division multiplexing, the free-space optical data link comprising multiple independent channels provides an aggregate net data rate of 1.1 Tbit/s and net spectral efficiency of 28.35 bit/s/Hz. Different from many previous demonstrations based on delayed or partially delayed copies of identical data streams, to the best of our knowledge, it is a record-high net data rate and net spectral efficiency achieved by a single-wavelength mode-division multiplexed free-space optical communication system with fully independent channels. Moreover, all key devices used in this work, including optical transponder, multiplexer and demultiplexer are commercially available.

Demonstration of a Cross-Thin-Slab Pre-Amplifier for High Peak and Average Power Ti:Sa Laser Systems

Vladimir Chvykov, Han Chi, Yong Wang, KRISTIAN DEHNE, Mark Berrill, and Jorge Rocca

DOI: 10.1364/OL.460743 Received 08 Apr 2022; Accepted 15 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: We demonstrate a room temperature Ti:Sa amplifier that uses a cross pump-seed geometry (Cross-Thin-Slab) to generate 30mJ output pulses at 0.5 kHz repetition rate, and 25mJ at 1 kHz when pumped by 100 mJ =515nm pulses from a diode pumped Yb:YAG laser. The geometry allows to maintain a crystal temperature of ~ 300C using cooling water at 100C. The amplifier is an attractive solution for use in the first stages of amplification in high peak and high average power chirped pulse amplification laser systems.

Inverse Regular Perturbation with ML-Assisted Phasor Correction for Fiber Nonlinearity Compensation

Hubert Dzieciol, Toshiaki Koike-Akino, Ye Wang, and Kieran Parsons

DOI: 10.1364/OL.460929 Received 12 Apr 2022; Accepted 14 Jun 2022; Posted 16 Jun 2022  View: PDF

Abstract: We improve an inverse regular perturbation (RP) model using a machine learning technique. The proposed learned RP (LRP) model jointly optimizes step-size, gain and phase rotation for individual RP branches. We demonstrate that the proposed LRP can outperform the corresponding learned digital back-propagation (DBP) method based on a split-step Fourier method (SSFM), with up to 1dB gain in a 800km standard single mode fiber link. Our LRP also allows a fractional step-per-span (SPS) modelling to reduce complexity while maintaining superior performance over a 1-SPS SSFM-DBP.

Parametric downconversion via vibronic transition

Kentaro Miyata, Masaki Yumoto, Yasushi Kawata, Shinichi Imai, and Satoshi Wada

DOI: 10.1364/OL.460560 Received 05 Apr 2022; Accepted 14 Jun 2022; Posted 14 Jun 2022  View: PDF

Abstract: This Letter presents the first demonstration of noncritically birefringent-phase-matched parametric downconversion, which is associated with stimulated emission via vibronic laser transition. The so-called self-difference frequency generation is realized along the a-axis of a Cr:CdSe single crystal pumped by a Tm:YAG laser pulse at 2.013 μm, directly producing an infrared spectrum centered at 9 μm with maximized effective nonlinearity. The light source, benefitted from the broad vibronic spectroscopic properties together with the wide transparency range of the host material, is expected to generate noncritically phase-matched, mid-infrared spectra beyond 20 μm along with birefringence engineering in the solid solution Cr:CdSxSe1–x.

Hyperspectral image super-resolution based on transfer of both spectra and multi-level feature

Xuheng Cao, Yusheng Lian, Zilong Liu, Han Zhou, xiangmei Hu, Beiqing Huang, and Wan Zhang

DOI: 10.1364/OL.463160 Received 06 May 2022; Accepted 14 Jun 2022; Posted 15 Jun 2022  View: PDF

Abstract: Existing hyperspectral image super-resolution methods fusing a high-resolution RGB image (HR-RGB) and a low-resolution hyperspectral image (LR-HIS) always rely on spatial degradation and handcraft priors, which hinders their practicality. To address these problems, we propose a novel method with two transfer models, i.e., window-based linear mixing model (W-LM) and feature transfer model. Specifically, W-LM initializes an HR-HSI by transferring the spectra from LR-HSI to the HR-RGB. By using the proposed feature transfer model, the HR-RGB multi-level features extracted by a pre-trained convolutional neural network (CNN) are then transferred to the initialized HR-HSI. The proposed method fully exploits spectra of LR-HSI and multi-level features of HR-RGB, and achieves super-resolution without requiring the spatial degradation model and any handcraft priors. The experimental results for 32× super-resolution on two public datasets and our real image set demonstrate the proposed method outperforms five state-of-the-art existing methods.

Designing thermal radiation metamaterials via hybrid adversarial autoencoder and Bayesian optimization

Dezhao Zhu, Jiang Guo, Gang Yu, Changying Zhao, Hong Wang, and Shenghong Ju

DOI: 10.1364/OL.453442 Received 14 Jan 2022; Accepted 14 Jun 2022; Posted 15 Jun 2022  View: PDF

Abstract: Designing thermal radiation metamaterials is challenging especially for high degrees of freedom and complex objective problems. In this letter, we have developed a highly efficient and hybrid framework which combines the adversarial autoencoder and Bayesian optimization to design thermal radiation metamaterials. The proposed materials informatics approach was applied to design narrowband thermal emitters at different target wavelengths. With only several hundreds of training data sets, new structures with better target properties can be quickly figured out in a compressed 2-dimensional latent space. This enables the optimal design by calculating far less than 1% of the total candidate structures, which greatly decreases the design period and cost. The proposed design framework can be easily extended and applied to any other thermal radiation metamaterials design with high dimension feature.

Microsecond-resolved smartphone time-gated luminescence spectroscopy

Qisheng Deng, Yulei Liu, Zece Zhu, and Xuewen Shu

DOI: 10.1364/OL.467458 Received 10 Jun 2022; Accepted 12 Jun 2022; Posted 14 Jun 2022  View: PDF

Abstract: Time-gated luminescence spectra are usually measured by the lab instruments equipped with high-speed excitation sources and spectrometers, which are always bulky and expensive. In order to reduce the reliance on the expensive lab instruments, we demonstrate the first use of smartphone for the detection of time-gated luminescence spectra. A mechanical chopper was used as the detection shutter and an optical switch was placed at the edge of the wheel to convert the chopping signal into a TTL signal which was used to control the excitation source and achieve the synchronization. The time-gated luminescence spectra at different delay time of Eu(TTA)3 powder and the solutions of Eu-tetracycline complex were successfully detected with a temporal resolution of tens of microseconds by the proposed approach. We believe our approach offers a route toward portable instruments for measuring the luminescence spectra and lifetimes.

Data compression in heterodyne phase-sensitive OTDR using quantization technique

Feihong Yu, Shuaiqi Liu, Liyang Shao, Weijie Xu, Dongrui Xiao, FANG ZHAO, jie Hu, Weihao Lin, Guoqing Wang, WeiZhi Wang, Feng Wang, Huanhuan Liu, and Perry Shum

DOI: 10.1364/OL.456925 Received 01 Mar 2022; Accepted 12 Jun 2022; Posted 13 Jun 2022  View: PDF

Abstract: Phase-sensitive optical time-domain reflectometry (Φ-OTDR) based on heterodyne detection is widely used for its simple structure and high signal-to-noise ratio (SNR). However, the large amount of raw data of Φ-OTDR places a heavy burden on the storage device and also limits the transferability of the data. In this letter, we propose a data compression approach using quantization technique to solve the data storage problem in heterodyne Φ-OTDR. Experimental results show that the optical phase variations induced by external vibrations can be successfully demodulated from the 1-bit-resolution raw data, and a compression ratio of 16 is achieved. In addition, this work also reveals that data acquisition device with extremely low sampling resolution is sufficient for heterodyne Φ-OTDR, signifying that the cost of the system can be further decreased.

High dynamic range electro-optic dual-comb interrogation of optomechanical sensors

David Long, Benjamin Reschovsky, Thomas LeBrun, Jason Gorman, Joseph Hodges, David Plusquellic, and Jasper Stroud

DOI: 10.1364/OL.460028 Received 05 Apr 2022; Accepted 09 Jun 2022; Posted 14 Jun 2022  View: PDF

Abstract: An interleaved, chirped electro-optic dual comb system is demonstrated for rapid, high dynamic range measurements of cavity optomechanical sensors. This approach allows for the cavity displacements to be interrogated at measurement times as fast as 10 µs over ranges far larger than can be achieved with alternative methods. While the performance of this novel readout approach is evaluated with an optomechanical accelerometer, this method is applicable to a wide range of applications including temperature, pressure, and humidity sensing as well as acoustics and molecular spectroscopy.

Terahertz polarimetry with a monolithic metasurface

Thomas Nowack, Yash Shah, Ivonne Escorcia Carranza, James Grant, Mitchell Kenney, Daniele Faccio, Edward Wasige, David R. S. Cumming, and Vincenzo Pusino

DOI: 10.1364/OL.463143 Received 06 May 2022; Accepted 07 Jun 2022; Posted 22 Jun 2022  View: PDF

Abstract: The state of polarization (SoP) is a fundamental property of electromagnetic radiation that can carry a rich set of important information in light transmitted through a test sample. Despite a wide range of applications in material identification, (thin-film) characterization and defect analysis, the SoP remains difficult to exploit - especially at terahertz frequencies since its measurement requires complex apparatus with multiple moving parts. We have addressed these challenges by designing a metasurface polarimeter (MSP) that incorporated the entire functionality of a division-of-aperture-polarimeter (DoAP) with high efficiency into a single silicon layer without the need for moving parts. Collective simulations are in perfect agreement with experimental data, both confirming the intended operation. Furthermore, we present an automated analysis algorithm that allowed for the complete determination of the SoP from a single image with an experimental accuracy of 92.1 % ± 4.2 %, following an initial calibration. We anticipate that the presented MSP will find applications in polarimetric sensing and imaging for non-destructive evaluation at terahertz frequencies.

Spatio-temporal observation of higher-order modulation instability in a recirculating fiber loop

Francois Copie, Pierre Suret, and Stephane Randoux

DOI: 10.1364/OL.462389 Received 03 May 2022; Accepted 06 Jun 2022; Posted 06 Jun 2022  View: PDF

Abstract: We experimentaly investigate higher-order seeded modulation instability in an optical fiber experiment. The recirculating loop configuration with round-trip losses compensation enables the observation in single-shotof the spatio-temporal evolution of an initially modulated continuous field revealing intricate yet deterministic dynamics. By tuning the modulation period, a continuous transition between perfectly coherent and purely noise-driven dynamics is observed that we characterise by means of a statistical study.

Simultaneous multi-channel near-eye display: A holographic retinal projection display with large information content

Zi Wang, Kefeng Tu, Yujian Pang, Guoqiang Lv, Qibin Feng, Anting Wang, and Hai Ming

DOI: 10.1364/OL.461918 Received 25 Apr 2022; Accepted 06 Jun 2022; Posted 07 Jun 2022  View: PDF

Abstract: The augmented reality (AR) near-eye displays (NED) are emerging as the next-generation display platform. The existing AR NED only present one single video channel at one time, same as traditional media such as TV and smart phone. In this paper, to the best of our knowledge, we first propose a multi-channel holographic retinal projection display (RPD), which can provide multi-channel image sources simultaneous, thus greatly increasing the information volume. Due to the superposition capacity of hologram, multiple images are projected to different viewpoints simultaneously through multiple spherical wave encoding, so that the viewer can switch among playing channels very fast through eye rotation. A full-color dynamic multi-channel holographic near-eye display was demonstrated in optical experiment. The proposed method provides a good prospect that the future AR glasses can play dozens of video channels in parallel, and the user can switch among channels freely and efficiently just through a simple eye rotation.

Complex-valued decision feedback equalizer for optical IMDD signals with adaptive manipulations in time and amplitude domains

Lin Sun, Jiawang Xiao, Yi Cai, Gangxiang Shen, Ning Liu, and Chao Lu

DOI: 10.1364/OL.462524 Received 03 May 2022; Accepted 05 Jun 2022; Posted 06 Jun 2022  View: PDF

Abstract: In this work, we innovatively equalize optical intensity-modulated and directly-detected (IMDD) PAM-4 signals using a complex-valued decision feedback equalizer (CDFE). Through mapping the adjacent symbols of PAM-4 signals onto the complex domain, the influence of strongest inter-symbol interference (ISI) can be alleviated during the decision process in DFE, which effectively alleviate the burst-error propagation when signals are noisy. Moreover, signal-adaptive manipulations of DFE parameters on both time- and amplitude-domain are performed by using an ultra-stable timing recovery and level-adaptive decision. Performance evaluations are made on VCSEL-modulated and MMF-transmitted 100-Gbps optical PAM-4 signals. Based on experimental results of the short-reach optical communication, the proposed DFE outperforms the traditional DFE with 0.5-dB system power budget gain at the 7%OH-FEC BER threshold.

An effective integration of MOSFET phototransistor to GaN LED for UV sensing

Jinlong Piao, Junhua Wu, Ziqi Ye, Hao Zhang, Jinjia Li, Pengzhan Liu, Hao Wang, Ziping Cao, and yongjin wang

DOI: 10.1364/OL.463236 Received 06 May 2022; Accepted 31 May 2022; Posted 03 Jun 2022  View: PDF

Abstract: In this letter, we report an effective monolithic integration of metal oxide semiconductor field effect (MOSFET) phototransistor (PT) and light-emitting diode (LED) on a GaN-on-Si LED epitaxial (epi) wafer. Avoiding additional growth or Si diffusion, the phototransistor was directly fabricated on LED epi layer, providing a cost-effective and facile method. As a driver, the phototransistor can modulate both peak value of the light intensity and output current of the integrated LED. As a ultraviolet (UV) detector, our phototransistor showed sufficient responsivity. It was found that the gate-voltage-dependent photocurrent-response of our fabricated phototransistor device had shorter response time and higher responsivity were obtained at a higher gate-voltage bias. The device showed the switching effect that the photo-induced current from the phototransistor drove the LED when the UV lamp is turned on whereas photo-induced current stopped driving upon powering off the UV lamp. The experiment demonstrated that the integrated device working as a UV detector exhibited a fast response time and a longstanding stability. We anticipate that such an approach could have potential applications for UV light detection and visible light communication (VLC).