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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.

Electro-optic chaotic system based on time-delay feature hiding and key space enhancement based on chaotic post-processing

Xiaoyang Gong, Zou Guoyang, Hongxiang wang, Yuefeng Ji, and Yu Zhang

DOI: 10.1364/AO.457290 Received 16 Mar 2022; Accepted 21 May 2022; Posted 23 May 2022  View: PDF

Abstract: In order to improve the sequence complexity and security of the classical all-optical chaotic system, a new chaotic system based on Logisticmap post-processing is proposed. In terms of the general output performance of the system, the spectrum of the proposed system is flatter than the classical system. Through bifurcation diagram and permutation entropy analysis, it is found that the system is extremely complex. In terms of security, the paper analyzes in detail the sensitivity of chaotic system to Logistic parameters, and the influence of Logistic parameters on system key space. At the same time, the simulation results show that when the parameters of the system are selected reasonably, the key hiding under low system gain can be achieved.

Characterization and alignment of acousto-optic devices using digital tailored RF waveforms

Konstantin Yushkov, Grigory Slinkov, Vasily Gurov, and Vladimir Molchanov

DOI: 10.1364/AO.459256 Received 22 Apr 2022; Accepted 20 May 2022; Posted 23 May 2022  View: PDF

Abstract: Acousto-optic (AO) devices are used in a variety of light control and processing applications in different environments including laboratory conditions, field environment, and air- and space-borne platforms as well. Accurate alignment and calibration of AO deflectors and tunable filters is crucial for correct operation and achieving specified performances of those devices. We describe a simple routine for testing and alignment of AO devices with a programmable RF waveform generator. Using specially tailored RF waveforms as test signals enables single-shot measurement of AO device's diffraction efficiency as a function of applied RF signal frequency and amplitude. The paper is accompanied by MATLAB code for implementation of the testing procedure and application demonstrations for an AO deflector and two types of AO tunable filters.

64-channel label-free fluorescence detection and single-particle counting device

Yinchao Zhang, Chen Siying, Xianda Du, He Chen, Pan Guo, and Huiyun Wu

DOI: 10.1364/AO.458807 Received 17 Mar 2022; Accepted 20 May 2022; Posted 20 May 2022  View: PDF

Abstract: A 64-channel detection system for laser-induced fluorescence (LIF) detection at cell level is established and applied to single event counting. Generally, fluorescence detection at the cellular level requires a dyeing label to enhance the scattered light intensity for the photodetector. However, the dyeing labels, such as fluorophores, probes and dyes, complicate sample preparation and increase cytotoxicity in the process. Therefore, label-free detection becomes essential for in vivo researches. The presented 64-channel detection system is designed for label-free detection with the ability to record feeble emissions. 2 linear photodetector devices are included in the system, extending the wavelength detection range to 366−680 nm, with an average spectral resolution at 4.9 nm. The performance of the system was validated by detecting unlabeled human hepatocytes (L-02) and other cell-level biologic samples. In addition, the 64-channel detection system was also used for particle counting with a quartz microfluidic chip. The counting method based on fluorescence spectra differs from those of other devices (i.e. flow cytometry and cell-sorting equipment), which use isolated irradiance intensities.

Multifunctional Tunable Visible Light Metalens Based on Double-layer Barium Titanate

Shu Yuan Lv, Rong Wang, WenFeng Luo, YuChi Bai, and Fei Meng

DOI: 10.1364/AO.458517 Received 15 Mar 2022; Accepted 19 May 2022; Posted 20 May 2022  View: PDF

Abstract: Tunable metalens plays an indispensable role in the development of integrated optics, multiimaging systems, etc. This paper proposes a multifunctional tunable metalens that combines a double-layer barium titanate (BTO) structure and geometric phase in the visible light band. The refractive index of the upper and lower layer BTO nanorods can be tuned continuously and independently by applying external voltage (0~60V), and the lower layer can be converted between the full-wave plate and the normal scattering unit, while the scatterers of the upper layer can be switched between the half-wave plate and the full-wave plate. The voltages of the upper and lower layer can be adjusted to achieve different functions such as the optical switch, the conversion between monofocal and bifocal metalens,the adjustment of bifocal intensity and broadband focusing (585~690nm). The simulation results show that the multifunctional tunable metalens has a good focusing effect. The metalens with the high focusing efficiency, dynamic reconfigurability and switching function has tremendous application potential in the fields of multifunctional devices, biomedicine, optical communication and imaging and so on.

Self-powered photodetectors with position-controlled array based on ZnO Nanoclusters

Yuanyuan Jing, xu yingtian, Chongyang Xu, Li Li, shi linlin, He Zhang, Liang Jin, Yonggang Zou, and Xiaohui Ma

DOI: 10.1364/AO.458934 Received 25 Mar 2022; Accepted 18 May 2022; Posted 19 May 2022  View: PDF

Abstract: A self-powered ultraviolet (UV) photodetector (PD) with position-controlled array based on ZnO nanoclusters (NCs) has been proposed, in which the structure of the special array provides a mind to reduce the light loss and improve the light trap. It innovatively modifies the structure of ZnO PDs, which is distinguished from other traditional devices. The results demonstrate that the ZnO NCs array can spontaneously generate the carrier and successfully achieve the detection without voltage under the radiation of UV light. In this paper, the structure is fabricated with Si and GaN two different substrates, the Si-based photodetector under 365 nm shows the responsivity, and EQE, reaching up to 14.1 mA/W, 4.79% respectively at zero bias; and the responsivity of GaN-based detector can be obtained up to 59.9 mA/W, its parameter of EQE is 20.04%, the photocurrent is 10-5A, and on/off ratio is 174. This work may be the ideal choice for a new generation self-powered UV device in the future.

An investigation of refractive index sensitivity of Brillouin acoustic modes in single-mode subwavelength-diameter fibers

yongsheng Zhang, Haifei Lu, Shuo Deng, Xiaoyan Wen, and Min Li

DOI: 10.1364/AO.456455 Received 17 Feb 2022; Accepted 18 May 2022; Posted 19 May 2022  View: PDF

Abstract: The acousto-optic interaction is strongly modified and different in sub-wavelength confinement. Here, the optical and acoustic propagation in a subwavelength-diameter fiber (SDF) have been investigated through adopting a two-layer fiber model of air-coated silica rod. Theoretical investigation indicates that SDF with diameter below 1.2 μm supports single mode of light propagation, and various Brillouin acoustic modes with well spectral spaced distribution can be also excited. Due to the light propagation with outer environment as cladding layer, the surrounding medium will greatly affect Brillouin scattering of SDFs. Both of the simulation and experiment results indicate a relatively good linear relationship between Brillouin frequency shift of the lower acoustic modes and surrounding environmental refractive index (RI), and the higher RI sensitivity in finer SDFs can be obtained. In addition, the hybrid acoustic waves have shown higher sensitivity and stability than the surface acoustic modes. A RI sensitivity about 5.1 GHz/RIU has been achieved in a 1.1-μm SDF demonstrating its potential application in RI sensing.

Joint CT-geometry and multigrid strategy for time-domain breast diffuse optical tomography enhancement

Ma Yiwen, Limin Zhang, Mengyu Jia, Pengfei Zhang, and Feng Gao

DOI: 10.1364/AO.457254 Received 08 Mar 2022; Accepted 18 May 2022; Posted 19 May 2022  View: PDF

Abstract: Time-domain diffuse optical tomography (TD-DOT) can efficiently reconstruct absorption and reduced scattering coefficient but is heavily affected by its ill-posed problem and low spatial resolution. Truncated singular value decomposition (TSVD) that based on the whole-weighting-matrix inversion scheme is especially suitable for dealing with these problems, meanwhile, TSVD is still limited by its storage challenge for bulk three-dimensional imaging. With CT anatomical geometry and multigrid strategy, we adopt a fine mesh to ensure the forward calculation accuracy and a coarse mesh for matching the whole-weighting-matrix calculation of TSVD in breast imaging. The interrelated simulation results are validated by the clinical breast patient’s PET images.

Underwater image enhancement based on color correction and complementary dual image multi-scale fusion

xiaoyan lei, huibin wang, jie shen, and haiyun liu

DOI: 10.1364/AO.456368 Received 17 Feb 2022; Accepted 17 May 2022; Posted 19 May 2022  View: PDF

Abstract: Underwater images often suffer from the color cast, poor contrast, and detail loss owing to the scattering and absorption of light in water. To solve these problems, we propose a novel underwater image enhancement method based on color correction and dual image multi-scale fusion. We first use color correction method to solve the problem of color cast, we compensate the other two-color channels with the highest mean value color channel; further, all the color channels are dynamically stretched. Next, a complementary dual image multi-scale fusion method is used to improve the contrast, pairs of complementary adaptive gamma correction with weighted distribution enhanced images are used as the two inputs of multi-scale fusion, and appropriate weight maps are selected.Then, a multi-scale detail sharpening method is used to enhance the image details. Qualitative and quantitative evaluations prove that the proposed method can produce high-quality underwater images. Moreover, the proposed method has relatively high evaluator values compared to the state-of-the-art methods.

Indirect and direct estimation of pharmacokinetic parameters in dynamic diffuse fluorescence tomography by adaptive extended Kalman filtering

Limin Zhang, Yingxue Pan, Zhichao Zhao, Nan Cheng, Xin Wang, Yiwen Ma, Mengyu Jia, and Feng Gao

DOI: 10.1364/AO.457343 Received 03 Mar 2022; Accepted 17 May 2022; Posted 18 May 2022  View: PDF

Abstract: Pharmacokinetic parameter estimation with the support of dynamic diffusefluorescence tomography (DFT) can provide helpful diagnostic information for tumordifferentiation and monitoring. Adaptive extended Kalman filtering (AEKF) as a nonlinearfilter method has the merits of high quantitativeness, noise-robustness, and initializationindependence. In this paper, indirect and direct AEKF schemes combining with a commonlyused two-compartment model were studied to estimate the pharmacokinetic parameters basedon our self-designed dynamic DFT system. To comprehensively compare the performances ofboth schemes, the selection of optimal noise covariance matrices affecting estimation resultswas first studied, then a series of numerical simulations with the metabolic time ranged from 4.16 min to 38 min were carried out and quantitatively evaluated. The comparison resultsshow that the direct AEKF outperforms the indirect EKF in estimation accuracy at different metabolic velocity, and demonstrates stronger stability at the large metabolic velocity. Furtherly, the in vivo experiment was conducted to achieve the indocyanine green pharmacokinetic-rate images in the mouse liver. The experimental results testified the capability of both schemes to estimate the pharmacokinetic-rate images, and in agreementwith the theory predictions and the numerical simulation results.

Cryptanalysis of optical cryptosystem with uncertainty quantification in probabilistic model

Xinkai Sun, Sanguo Zhang, and Yishi Shi

DOI: 10.1364/AO.457681 Received 08 Mar 2022; Accepted 17 May 2022; Posted 18 May 2022  View: PDF

Abstract: In this paper, a modified probabilistic deep learning method is proposed to attack the double random phase encryption by modeling the conditional distribution of plaintext. The well-trained probabilistic model gives both predictions of plaintext and uncertainty quantification, the latter of which is first introduced to optical cryptanalysis. Predictions of the model are close to real plaintexts, which shows the success of the proposed model. Uncertainty quantification reveals the level of reliability of each pixel in the prediction of plaintext without ground truth. Subsequent simulation experiments demonstrate that uncertainty quantification can effectively identify predictions with poor quality to avoid the risk of unreliability from deep learning models.

Heterodyne spectrometer sensitivity limit for quantumnetworking

Joseph Chapman and Nicholas Peters

DOI: 10.1364/AO.459172 Received 22 Mar 2022; Accepted 16 May 2022; Posted 18 May 2022  View: PDF

Abstract: Optical heterodyne detection-based spectrometers are attractive due to their relatively simple constructionand ultra-high resolution. Here we demonstrate a proof-of-principle single-mode optical-fiber-basedheterodyne spectrometer which has picometer resolution and quantum-limited sensitivity around 1550 nm.Moreover, we report a generalized quantum limit of detecting broadband multi-spectral-temporal-modelight using heterodyne detection, which provides a sensitivity limit on a heterodyne detection-based opticalspectrometer. We then compare this sensitivity limit to several spectrometer types and dim light sources ofinterest, such as, spontaneous parametric downconversion, Raman scattering, and spontaneous four-wavemixing. We calculate the heterodyne spectrometer is significantly less sensitive than a single-photondetector and unable to detect these dim light sources, except for the brightest and narrowest-bandwidthexamples.

Investigation of computed tomography in resolvingflame topology with internal optical blockageinvolved

Haifeng Wu, Yu Gao, Yue Wu, Bugao Gong, and Chen LIng

DOI: 10.1364/AO.459725 Received 29 Mar 2022; Accepted 16 May 2022; Posted 18 May 2022  View: PDF

Abstract: This work reports the modification and optimization of computed tomography (CT) algorithm to become capable ofresolving the optical field with internal optical blockage (IOB) presented. The IOB, practically the opaque mechanicalparts installed inside the measurement domain, would prevent a portion of emitted light from transmitting to the opticalsensors. Such blockage disrupts the line-of-sight intensity integration on recorded projections and eventually leads toincorrect reconstructions. In the modified algorithm developed in this work, the positions of the obstacle are measuredas a prior, then the discretized optical field (i.e., the voxels) are classified as those that participate in the CT process(named effective voxels) and those that are expelled, based on the relative positions of the imaging sensors, IOB and lightsignal distribution. Finally, the effective voxels can be iteratively reconstructed by combining their projections on thesensors that provide direct observation. Moreover, the impact of IOB on reconstruction accuracy is discussed underdifferent sensor arrangements to provide hands-on guidance on sensor orientation selection in practical CT problems.The modified algorithm and the sensor arrangement strategy are both numerically and experimentally validated bysimulated phantoms and a two-branch premixed laminar flame in this work.

The transversal energy flow of tightly focused Off-axis circular polarized vortex beams

Liping Gong, Xiaolei Wang, Zhuqing Zhu, Shengying Lai, Hongyan Feng, Jun Wang, and Gu Bing

DOI: 10.1364/AO.459816 Received 31 Mar 2022; Accepted 16 May 2022; Posted 18 May 2022  View: PDF

Abstract: The transversal energy flow characteristics of tightly focused circular polarized beamscarrying off-axis vortices are examined in this research work. The results reveal that the symmetry of the focal fields are destroyed and energy flow is offset by the existence of off-axis vortices. Therefore, the focal field and energy flow distribution of polygons (bar-type-like, triangle-likeand square-like) can be realized by superposition of multiple off-axis vortices with controllable positions. Furthermore, based on off-axis vortex energy flow characteristics, the force exertedon metal particles in polygon focal fields is found to rotate the particles clockwise along the outlines of the polygon energy flow. The results will potentially provide new ideas and theoretical guidance for exploring novel focal field and particle control methods.

Computational optical system design: a globaloptimization method in simplified imagingsystem

Jiangyong Li, Lin Zhao, Xiaoqin Wu, Fei Liu, Yazhe Wei, Chun Yu, and Xiaopeng Shao

DOI: 10.1364/AO.456939 Received 24 Feb 2022; Accepted 16 May 2022; Posted 18 May 2022  View: PDF

Abstract: Optical imaging system often meets the problems with high complexity and lowenergy transmittance to compensate for aberrations. Here we proposed a method to correct theaberration by coupling the optical subsystem with the digital subsystem. Specifically, in theglobal optimization process, the two subsystems correct their respective easily handledaberrations so that the final imaging aberration is minimized. We design simple lenses in thismethod and assess the imaging quality. In addition, we conducted a tolerance analysis forproposed method, and verified the effectiveness of the deconvolution using spatially-varyingpoint spread function (SVPSF) in the actual imaging process. The simulation results show thesuperiority of the proposed method compared with the conventional design and the feasibilityof simplifying optical system. The experimental results prove the effectiveness of thedeconvolution using SVPSF.

Microwave Photonics BroadbandUnambiguous Frequency Measurement basedon a Sagnac Loop and a Linear Optical Filter

Yinling Zhang, Tao Shang, Gufeng Li, Xiongchao Liu, dan chen, and Zhaokun Li

DOI: 10.1364/AO.456821 Received 24 Feb 2022; Accepted 16 May 2022; Posted 23 May 2022  View: PDF

Abstract: We propose an instantaneous frequency measurement (IFM) scheme featured withunambiguous measurement utilizing a Sagnac loop with an embedded bi-directional phase modulator (BPM) and an optical filter with a linear frequency response. The frequency of the microwave signal to be measured is instantaneously estimated by calculating an amplitude comparison function (ACF) of photocurrents from the up and low branches in the proposed structure. Compared to previous IFM schemes, the ACF in the proposed scheme is monotonic,by which the frequency of the unknown microwave signal can be uniquely confirmed without ambiguity. Meanwhile, only one single laser source and a phase modulator are needed, whichsimplifies the measurement system. In addition, the monotonous ACF can guarantee the measurement accuracy in a wide range from low frequency to high frequency. The IFM system has robustness in optical and RF power shift. The simulation results show that, frequency measurement over the range of 30 GHz with measurement error of 0.4 GHz is achieved.

Analysis of the smoothing characteristics and shape-retaining ability of conformal vibration polishing and suppression strategy for full-spatial frequency errors of optics

liu shiwei, Hongxiang Wang, Hou Jing, Qinghua Zhang, Chen Xianhua, Bo Zhong, and Mingzhuang Zhang

DOI: 10.1364/AO.460786 Received 08 Apr 2022; Accepted 16 May 2022; Posted 18 May 2022  View: PDF

Abstract: Conformal vibration polishing (CVP) employing flexible polishing tools is expected to be an efficient means of optical processing, and all current research on it is limited to planar components. Hence, the smoothing characteristics of the middle-spatial frequency (MSF) errors and the ability to maintain the surface shape of different types of optics in CVP are analyzed. A combined processing method based on magnetorheological finishing and CVP for full-spatial frequency errors is proposed and verified by experiment. The peak-to-valley value, MSF errors, and surface roughness of the large-diameter component can reach 75nm, 1.1nm, and 0.37nm after 9 hours of processing. The research not only demonstrates the excellent removal characteristics of CVP and the effectiveness of the proposed method but also provides an additional choice for the high-precision manufacturing of optics.

Nanostructured photosensitive layerfor Tamm-plasmon-polariton-based organic solar cells

Bikbaev Rash, Dmitrii Pykhtin, Stepan Vetrov, Ivan Timofeev, and Vasiliy Shabanov

DOI: 10.1364/AO.456413 Received 01 Mar 2022; Accepted 16 May 2022; Posted 19 May 2022  View: PDF

Abstract: The influence of the volume fraction of plasmonic nanoparticles on the efficiency of the Tamm-plasmonpolariton-based organic solar cell is investigated in the framework of the temporal coupled mode theoryand confirmed by the transfer matrix method. It is shown that, unlike a conventional plasmonic solar cells,in which the efficiency is directly proportional to the volume fraction of nanoparticles in the photosensitivelayer, the efficiency of the proposed solar cell reaches the highest value at low volume fractions. Thiseffect is explained by the fact that at these volume fractions the critical coupling condition of the incidentfield with the Tamm plasmon polariton is fulfilled. Thus, for the incoming radiation range from 350to 500 nm the maximal cell efficiency of 28% is achieved with a volume fraction of nanoparticles equalto 10%. Additionally, the optical properties of the photosensitive layer are compared for the cases ofdetermining its complex refractive index by effective medium theory and S-parameter retrieval method. Agood agreement between the results is demonstrated, which encourages the use of the effective mediumtheory for preliminary calculations.

Off-axis common-path digital holography using a cube beam splitter

YUNHAO LI, lei liu, YIZHE LIU, MENGYAO WANG, Zhong Zhi, and Shan Mingguang

DOI: 10.1364/AO.458168 Received 10 Mar 2022; Accepted 16 May 2022; Posted 20 May 2022  View: PDF

Abstract: An off-axis common-path digital holography is built up by inserting a 45° tilted cube beam splitter(CBS) into a 4f system in this paper. Two apertures are set as the input of the 4f system, where one supports the object and the other is vacant. The CBS divides the incoming beam into two copies, which are symmetrical with each other along the semireflecting layer. Due to the separation of two beams in Fourier plane and the flipping of the field of view(FOV) induced by the CBS, an off-axis hologram can be captured. Moreover, the carrier frequency can be easily modulated by translating the beam splitter perpendicular to the optical axis. The new proposed scheme has high light utilization, compact setup and high temporal stability. Experiments are carried out to demonstrate the validity and stability of the proposed method.

Reflective astronomical telescopes with a large fieldof view and a wide waveband

Xiaoheng Wang and Jun Zhu

DOI: 10.1364/AO.456073 Received 11 Feb 2022; Accepted 15 May 2022; Posted 19 May 2022  View: PDF

Abstract: Large-aperture ground-based astronomical telescopes are expected to have a large field of view and a wide workingwaveband. In this paper, we design two coaxial reflective telescopes based on a low-order even asphere and a highorder Q-con polynomial. Both telescopes have a primary mirror with a diameter of 6.5 m, a focal length of 24 m and aworking wavelength that stretches from ultraviolet to near-infrared (0.365–2.4 µm). The telescopes using an asphereand a Q-con polynomial have spectroscopic survey fields of 3° and 3.4°, respectively. In these fields, the EE80D (diameterof 80%-enclosed light energy) values that can characterize the telescope image quality are less than 0.58", and thespectral data can be obtained using fibers at the focal surface of the telescopes. Additionally, the two reflectivetelescopes can image celestial targets in a 0.4° field of view, and the root mean-square diameters of the standard spotdiagrams are less than 27 µm. By combining precise imaging measurements with the spectral data, the properties ofcelestial bodies can be better analysed. The designed telescopes could enable the realization of astronomicalspectroscopic surveys with both a large field of view and a wide waveband.

Laser stripe segmentation and centerlineextractionbased on 3D scanning imaging

Chuan Ye, Wenrong Feng, Qiyan Wang, Chao Wang, Bo Pan, Youchun Xie, Yuanyao Hu, and Jian Chen

DOI: 10.1364/AO.457427 Received 02 Mar 2022; Accepted 15 May 2022; Posted 20 May 2022  View: PDF

Abstract: Ambient noise and illumination inhomogeneity will seriously affect the high-precision measurement of structuredlight3D morphology. To overcome the influences of these factors, a new sub-pixel extraction method for the centerof laserstripes is proposed. First, an automatic segmentation model of structured light stripe based on UNet deeplearningnetwork and level set is constructed. Coarse segmentation of laser stripes using the UNet network caneffectivelysegment more complex scenes and automatically obtain a prior shape information. Then, the a prior informationisusedas a shape constraint for fine segmentation of the level set, and the energy function of the level set is improved. Finally, the stripe normal field is obtained by calculating the stripe gradient vector, and the center of the stripe is extractedbyfusing the gray center of gravity method according to the normal direction of the stripe distribution. The experimentalresults show that the average width error of different rows of point cloud data of workpieces with different widthsisless than 0.3mm, and the average repeatability extraction error is less than 0.2mm.

Multilayer thermal control for high-altitude verticalimaging aerial cameras

Yanwei Li, Guoqin Yuan, Xinwang Xie, Leigang Dong, and Longhai Yin

DOI: 10.1364/AO.460335 Received 06 Apr 2022; Accepted 14 May 2022; Posted 18 May 2022  View: PDF

Abstract: Aerial cameras play an important role in obtaining ground information. However, the complex and changeable aviationenvironment limits its application. Thermal control is vital in improving the environmental adaptability of the camera toobtain high-quality images. Conventional thermal control of aerial cameras is to directly implement active thermalcontrol on the optical system, which is a single layer thermal control method. Such method cannot isolate the opticalsystem from the external environment. It results in a sharp increase in thermal control power consumption and intemperature gradient which increases the difficulty of thermal control. Here, we propose a multilayer system-levelthermal control approach by partitioning the aerial camera into two parts, i.e. the imaging system and the outline cabin.Two parts are connected by materials with poor thermal conductivity, and an air insulation interlayer is formed inbetween. Theoretical analysis is carried out to model the internal and external thermal environment of the aerial camerain complex high-altitude environment. We study the passive thermal control of the thermal insulation layer of the outlinecabin, optical window, imaging optics, CCD device, and the phase change material, active thermal control of thermalconvection and heating film. Numerical modelling on the multilayer thermal control of system is carried out and verifiedby the thermal equilibrium test and actual field flight test. The total power consumption of the thermal control system is270 W. High quality images are obtained with the temperature gradient of the optical lens is less than 5 ℃, and thetemperature of CCD is lower than 30 ℃. Our technology is simple, accurate, low cost, and easy to implement comparing tothe conventional thermal control method. It effectively lowers the power consumption and reduces the difficulty ofthermal control.

High-speed three-dimensional shape measurementbased on tripartite complementary Gray-coded light

Dongsong Li, Jie Chen, Tianhang Tang, XueLei Shi, zixin tang, and Yi-Guang Liu

DOI: 10.1364/AO.457024 Received 28 Feb 2022; Accepted 13 May 2022; Posted 18 May 2022  View: PDF

Abstract: In phase-shifting profilometry based on Gray code, the jump error is inevitably generated and is furtheramplified in dynamic scenes. To tackle this problem, we propose a robust method called TCG (TripartiteComplementary Gray-code method). Without projecting additional patterns, TCG uses different combinations of Gray code to calculate three complementary orders that are able to avoid jump error in theunwrapping process. TCG is efficient and robust, as it fully utilizes the redundant information of Graycode. Experimental results demonstrate that TCG can realize high-efficiency and high-speed 3D shapemeasurement at a rate of 500 fps.

Quantifying the quality of optical vortices by evaluating their intensity distributions

Mateusz Szatkowski, Brandon Norton, Jan Masajada, and Rosario Porras Aguilar

DOI: 10.1364/AO.456106 Received 15 Feb 2022; Accepted 13 May 2022; Posted 16 May 2022  View: PDF

Abstract: Optical vortices are widely used in optics and photonics, impacting the measurements and conclusions derived from their use. Thus, it is crucial to evaluate optical vortices efficiently. This work aims to establish metrics for evaluating optical vortex quality to support the implementation procedure and, hence, provide a tool supporting research purposes andtechnological developments. We propose to assess vortex quality using the following intensity parameters: eccentricity, cross-sectional peak-to-valley, cross-sectional peak difference, and the doughnut ratio. This methodology provides a low-cost, robust, and quantitative approach to evaluating optical vortices for each specific optical technology.

Measurement of stress-induced birefringence ina thin-disk laser with full-Stokes polarimetry

Johanna Dominik, Michael Scharun, Benjamin Dannecker, Veronika Bühner, Klaus Ertel, Dominik Bauer, and Thomas Dekorsy

DOI: 10.1364/AO.457145 Received 25 Feb 2022; Accepted 13 May 2022; Posted 16 May 2022  View: PDF

Abstract: Stress-induced birefringence leads to losses in solid-state laser resonators and amplifiers withpolarized output beams. A model of stress-induced birefringence in thin disks is presented, aswell as measurements of stress-induced birefringence in a thin disk in a multi-kilowatt oscillator.A full-Stokes imaging polarimeter was developed to enable fast and accurate polarimetricmeasurements. Experimental and simulated results are in good agreement qualitatively andquantitatively and show that the polarization loss due to stress-induced birefringence is negligiblefor ytterbium-doped thin disks with a thickness around 100 µm, but becomes relevant in thickerdisks. It is concluded that stress-induced birefringence should be taken into consideration whendesigning a thin-disk laser system.

Wavelength selection of multispectral imaging for oilpalm fresh fruit ripeness classification

Minarni Shiddiq, Herman Herman, Dodi Arief, Edy Fitra, IKHSAN HUSEIN, and Sinta Ningsih

DOI: 10.1364/AO.450384 Received 23 Dec 2021; Accepted 13 May 2022; Posted 16 May 2022  View: PDF

Abstract: Multispectral imaging has been recently proposed for high-speed sorting and grading machine vision of fruits.It is a prospective method applied in yet traditional sorting and grading of oil palm fresh fruit bunches (FFB). Theripeness of oil palm FFBs determines the quality of crude palm oil (CPO). Implementation of multispectral imaging forthe task needs wavelength selection from hyperspectral datasets. This study aimed to obtain the optimum wavelengthsand used them for oil palm FFB classification based on three ripeness levels. We have selected eight optimumwavelengths using Principal Component Analysis (PCA) regression which represented the ripeness levels.

Ultra-fast detail enhancement for short-waveinfrared image

Yaohong Chen, Hui Zhang, Zehao Zhao, Zhen Wang, HAO WANG, and Chiman Kwan

DOI: 10.1364/AO.455947 Received 11 Feb 2022; Accepted 13 May 2022; Posted 18 May 2022  View: PDF

Abstract: Image detail enhancement is critical to the performance of short-wave infrared(SWIR) imaging systems, especially to the long-range systems. However, the existing highperformance infrared (IR) image enhancement methods typically have difficulty in meeting therequirements of the imaging system with high resolution and high frame rate. In this paper, wepropose an ultra-fast and simple SWIR image detail enhancement method based on theDifference of Gaussian (DoG) filter and plateau equalization. Our method consists of efficientedge detail information extraction and histogram equalization. The experimental resultsdemonstrated that the proposed method achieves outstanding enhancement performance with aframe rate around 50 fps for 1280x1024 SWIR images.

Areal measurement of vibration modes ofhemispherical shell resonator bydeflectometry

Rui Zhu, Xiangchao Zhang, Shaoliang Li, Yunuo Chen, Wei Lang, and Lu Ye

DOI: 10.1364/AO.456744 Received 22 Feb 2022; Accepted 12 May 2022; Posted 13 May 2022  View: PDF

Abstract: The hemispherical shell resonator (HSR) is the core and sensitive part of ahemispherical resonator gyro. The geometrical accuracy and vibration properties of HSRdetermine the navigating performance of the system. Lack of the areal measurement methodsof the vibration modes limits the investigation of kinetic mechanism and the improvement ofnavigating performance. Consequently, an areal measurement method is developed based ondeflectometry. The blurry spots on the image plane reflected from the vibrating HSR areextracted, and the blurring trajectories are obtained by the Wiener deconvolution method. Thevibrating amplitude distribution of a standing wave mode is transformed into the swing angledistribution of the normal vectors. The parameters of vibration mode are fitted by theLevenberg-Marquardt method. This method can find widespread applications in the arealinspection of vibration modes.

Improvement of beam shaping on metasurface byeliminating the interaction between coding units

Pengwei Zhou, Bo Fang, Tianqi Zhao, and Xufeng Jing

DOI: 10.1364/AO.458232 Received 11 Mar 2022; Accepted 12 May 2022; Posted 13 May 2022  View: PDF

Abstract: The interaction between sub-wavelength elements must be considered when constructing the metasurface. Generally, onesignore the interaction between cell structures when designing metasurface optoelectronic devices, which results in a significant decrease inthe design performance and efficiency of the overall metasurface structure. In order to reduce or further eliminate the interaction betweencell structures, we propose a cell structure with borders to construct coded metasurface sequences. At the same time, we design a commonframeless cell structure to construct a traditional coding metasurface. By numerical simulation of the near field distribution and far fieldscattering characteristics of these two types of coded metasurface sequences, we find that the element structure with medium frame canattenuate the interaction between adjacent encoded particles. In the process of transmission on the encoding metasurface with frame,different encoded particles can express their transmission phase independently, and are not affected by adjacent structures, thus realizingthe low coupling coding metasurface.

Effect of Doppler shift on preamplifier DPSK receiversusing balanced detection for optical satellite networks

Liying Tan, XINLEI WANG, Sixun Cheng, Jing Ma, and Dongpeng Kang

DOI: 10.1364/AO.458555 Received 15 Mar 2022; Accepted 12 May 2022; Posted 13 May 2022  View: PDF

Abstract: Optical satellite networks using laser intersatellite links (ISLs) are recognized to be capableto satisfy the increasing broadband communication demands. However, the Doppler shift due torelative movement between satellites must be taken into consideration. A convenient method thatdoesn't require complicated mathematical calculation is adopted to derive the relationship between theresidual Doppler shift and the bit error rate (BER) for the balanced differential phase-shift keying(DPSK) detection system. It is shown that the DPSK receiver is sensitive to the residual Doppler shift,when the residual Doppler shift Δfres ∕ Rb is 0.05, 0.10, and 0.15, the BER has been reduced from a levelof 10−17 to a level of 10−14, 10−11, 10−6, respectively. The BER of a certain node pair under different linkassignment schemes is calculated in a typical multi-hop LEO constellation. The results show that thecommunication BER of the same node pair is not related to the step change of the Doppler, but relatedto the accumulation of the Doppler shift in the optical path. The results obtained here will be helpful inrouting selection, link assignment, topology design, and system compensation.

Methodology of Designing Compact Schlieren SystemsUsing Off-Axis Parabolic Mirrors

Lingzhi Zheng, Adam Susa, and Ronald Hanson

DOI: 10.1364/AO.457151 Received 03 Mar 2022; Accepted 11 May 2022; Posted 12 May 2022  View: PDF

Abstract: Schlieren imaging is widely adopted in applications where fluid dynamics features are of interest. However, traditional Z-type schlieren systems utilizing on-axis mirrors generally require large system footprintsdue to the need to use high f-number mirrors. In this context, off-axis parabolic (OAP) mirrors providean attractive alternative for permitting the use of smaller f-number optics, but well-documented methodologies for designing schlieren systems with OAP mirrors are lacking. The present work outlines aray-tracing-based workflow applied to the design of a modified Z-type schlieren system utilizing OAPmirrors. The ray-tracing analysis evaluates the defocus and distortion introduced by schlieren optics. Theresults are used along with system size and illumination efficiency considerations to inform the selectionof optimal optical components capable of producing high-quality schlieren images while minimizing thesystem footprint. As a step-by-step demonstration of the design methodology, an example schlieren systemdesign is presented. The example schlieren design achieved an image resolution of 1.1 lp/mm at 50%contrast with a 60% reduction in system length compared to traditional Z-type systems with f/8 mirrors;distortion characterizations of the designed schlieren system showed good agreement with ray-tracingpredictions and the distortion can be corrected through image post-processing. The current work providesa systematic approach for the design of compact schlieren systems with OAP mirrors and demonstrates theutility of this underutilized option.

Laser Radius Measurement Method Based on Amplitude Jumpof Thermal Wave

Dongjin Hu, Xunpeng Qin, Zeqi Hu, Yan Zeng, and Feilong Ji

DOI: 10.1364/AO.460098 Received 04 Apr 2022; Accepted 11 May 2022; Posted 12 May 2022  View: PDF

Abstract: The laser radius should be calculated with high precision when analyzing the characteristics of Lamb wave excited bylaser in thin plate. However, the traditional methods are complex and rough to measure the radius of laser beam. The paper aimsto propose a novel convenient method for measuring the radius of laser ultrasonic beam. A laser interferometer (receiving laser)is used to receive ultrasonic signals excited by the laser to be measured (exciting laser) on the surface of a test block. Consideringthe characteristics represented by the thermal wave, positions where the receiving beam contacts and separates from the excitingbeam is determined, and the spot of radius is calculated by corresponding geometric relations. Experiments show that accuracyof the proposed method is in the order of magnitude of 0.01 mm, and the relative errors of experimental data are within 2%. Thispaper provides an alternative method for the measurement of laser beam radius, and has great significance for the application oflaser ultrasonic detection in thin plate and the calculation and analysis of dispersion curve.

A dissolved oxygen sensor based on fluorescence quenching method with optimal modulation frequency

Zhixuan Er, Ping Gong, Jian Zhou, Yiming Wang, Xiaokang Jiang, and Liang Xie

DOI: 10.1364/AO.457805 Received 09 Mar 2022; Accepted 11 May 2022; Posted 11 May 2022  View: PDF

Abstract: Measurement of dissolved oxygen (DO) in liquid samples is of vital importance inboth industrial and biomedical fields. In this paper, a DO sensor based on fluorescencequenching method has been built. The measurement principle is based on fluorescencelifetime detection, which is indicated by the phase difference between excitation light signaland fluorescence signal. The nonlinear effect of the fluorescent material has been taken intoconsideration to obtain a more accurate fitting model. The performance of the system varyingwith the modulation frequency of excitation light signals is also reported in this paper.Modulation frequency mainly affects the sensitivity and phase resolution ratio of the system.The system at the optimized modulation frequency has a good degree of fitting with 2 R valueof 0.9981 and a small relative error of 0.79%. The study presents that this kind of sensor withoptimal modulation frequency has a good performance, which can be used in many important fields.

Performance of resonant fiber-optic gyroscope basedon broadband source

shuang Liu, Lu Liu, Junyi Hu, Li hanzhao, Qingwen Liu, Huilian Ma, and Zuyuan He

DOI: 10.1364/AO.460419 Received 04 Apr 2022; Accepted 11 May 2022; Posted 11 May 2022  View: PDF

Abstract: A resonant fiber-optic gyroscope (RFOG) based on a broadband source can avoid the fundamental drawback ofcoherence detection process while possess the greater sensitivity afforded by the finesse of the fiber-optic ring resonator.In this paper, the basic operation principle is presented and demonstrated in detail, and various noise sources as wellas temperature effect encountered in this broadband source-driven RFOG are studied and analyzed. Then a combinedmodulation technique is proposed to suppress the residual backscattering noise. To further reduce the effect oftemperature transience, an asymmetric fiber ring resonator is designed. In the experiment, a bias stability of 0.01°/h issuccessfully demonstrated with a 100-meter-long fiber ring resonator of 8 cm diameter in a laboratory environmentwithout temperature control.

Silicon Photonics 2×2 Trench Coupler Design andFoundry Fabrication

Hiva Shahoei, Ifeanyi Achu, Evan Stewart, Unaiza Tariq, William Oxford, Mitchell Thornton, and Duncan McFarlane

DOI: 10.1364/AO.453464 Received 12 Jan 2022; Accepted 10 May 2022; Posted 13 May 2022  View: PDF

Abstract: A 2×2 photonic coupler is realized at the intersection of two 480nm × 220nm Silicon on Insulator (SOI) ridgewaveguides. The designed 2×2 coupler is simulated in both HFSS and Lumerical and shows an equal split of an inputsignal into a transmitted and a reflected signal for a 45 degree, ~100 nm SiO2 filled trench. The principle of operationof the coupler is frustrated total internal reflection (FTIR). Thus, this behavior is reasonably flat across wavelengthwhich is confirmed by Lumerical simulations and by experiment in this paper. Also, it has been shown that this couplerhas a flat behavior across trench thickness for the chosen geometry and material system which makes it insensitive tofabrication variation and resolution. We are interested to make this coupler a part of silicon photonic foundry processdevelopment kits. Therefore, fabrication is done at the AIM Photonics foundry to study the performance in the contextof the foundry’s design rules and process flow of the foundry. Good agreement between theory and experiment isreported herein. A 2×2 trench coupler is, when operated in the single photon or quantum regime, an integratedphotonic realization of a Hadamard gate.

Pulsed laser source digital holography efficiency measurements

Steven Owens, Mark Spencer, Douglas Thornton, and Glen Perram

DOI: 10.1364/AO.453344 Received 07 Jan 2022; Accepted 10 May 2022; Posted 12 May 2022  View: PDF

Abstract: In this paper, a 1064 nm pulsed laser source and a short-wave infrared (SWIR)camera are used to measure the total-system efficiency associated with a digital-holographysystem in the off-axis image plane recording geometry. At zero path-length difference betweenthe signal and reference pulses, the measured total-system efficiency (15.9%) is consistent withthat previously obtained with a 532 nm continuous-wave laser source and a visible camera[Appl. Opt. 58, G19-G30 (2019)]. In addition, as a function of temporal delay between thesignal and reference pulses, the total-system efficiency is accurately characterized by a newcomponent efficiency, which is formulated from the ambiguity function. Even with multi-modebehavior from the pulsed laser source and substantial dark-current noise from the SWIRcamera, system performance is accurately characterized by the resulting ambiguity efficiency.

Viscosity of fluoride glass fibers for fused componentsfabrication

Edith Ducharme, Stephane Virally, Rodrigo Itzamnà Becerra-Deana, Caroline Boudoux, and Nicolas Godbout

DOI: 10.1364/AO.455528 Received 04 Feb 2022; Accepted 09 May 2022; Posted 10 May 2022  View: PDF

Abstract: Fluoride glasses show great promise for mid-IR fiberbased applications. Their brittleness and low glass transition temperature have thus far been obstacles towardsobtaining low-loss fused components. Here, we suggest a simple method to measure glass viscosity over arange of process temperatures of interest for fused coupler fabrication. We achieved tapers of inverse taper ratio (ITR) 0.12 in multimode fluoroindate fibers. Taperswith loss < 0.1 dB at ITR 0.3 and no visible defects werefabricated with high repeatability. This work paves theway towards low-loss fused optical coupler in fluorideglass fiber.

Polarimetric characterization of segmented mirrors

Adur Pastor Yabar, Andres Asensio Ramos, Rafael Manso Sainz, and Manuel Colladas Vera

DOI: 10.1364/AO.460201 Received 01 Apr 2022; Accepted 06 May 2022; Posted 09 May 2022  View: PDF

Abstract: We study the impact of the loss of axial symmetry around the optical axis on the polarimetric propertiesof a telescope with segmented primary mirror when each segment is present in a different aging stage.The different oxidation stage of each segment as they are substituted in time leads to non-negligiblecross-talk terms. This effect is wavelength dependent and it is mainly determined by the properties of thereflecting material. For an aluminum coating, the worst polarimetric behavior due to oxidation is found forthe blue part of the visible. Contrarily, dust —as modeled in this work— does not significantly changethe polarimetric behavior of the optical system . Depending on the telescope, there might be segmentsubstitution sequences that strongly attenuate this instrumental polarization.

A hybrid ray-tracing/Fourier optics method to analyze multilayer diffractive optical elements

Victor LABORDE, Jerome Loicq, Juriy HASTANIN, and Serge Habraken

DOI: 10.1364/AO.456055 Received 11 Feb 2022; Accepted 05 May 2022; Posted 09 May 2022  View: PDF

Abstract: The performance (paraxial phase delay) of conventional diffractive optical elements is generally analyzedusing the analytical scalar theory of diffraction, based on thin-element approximation (TEA). However,the high thickness of multilayer diffractive optical elements (MLDOEs) means that TEA yields inaccurateresults. To address this, we tested a method based on ray-tracing simulations in mid-wave and long-waveinfrared wavebands and for multiple F-numbers, together with the effect of MLDOE phase delay on acollimated on-axis beam with an angular spectrum method. Thus, we accurately generated optical figuresof merit (point spread function along the optical axis, Strehl ratio at the "best" focal plane, and chromaticfocal shift), and by using a finite-difference time-domain method as a reference solution, demonstrate it asa valuable tool to describe and quantify the longitudinal chromatic aberration of MLDOEs.

In-Flight Measurement of Atmospheric-Imposed Tilt: Experimental Results and Analysis

Matthew Kalensky, Eric Jumper, Matthew Kemnetz, and Stanislav Gordeyev

DOI: 10.1364/AO.460717 Received 06 Apr 2022; Accepted 05 May 2022; Posted 09 May 2022  View: PDF

Abstract: The work presented here experimentally measured the tilt imposed onto a laser beam by the atmosphere from Shack-Hartmann Wavefront Sensor measurements collected in-flight. Tip/tilt is imposed onto the laser beam by propagating through optical turbulent structures larger than or on the order of the size of the beam diameter. This tip/tilt causes a dynamic, net deflection of the beam in the far-field, referred to as jitter, which poses a serious problem for tracking in directed energy applications. The practical measurement of turbulence-induced tip/tilt at altitude is challenging since mechanical contamination in the form of vibrations also manifests as tip/tilt. In this paper, a procedure referred to as the stitching method was used to quantify the turbulence-induced component of tilt without the influence of mechanical corruption. It was found that the measured tilt aligned with what analytic solutions predict and that the turbulence environment through which the beam propagated had Kolmogorov-like characteristics.

DIC measurement for large-scale structures basedon adaptive warping image stitching

Long Sun, Chen Tang, Min Xu, and Zhenkun Lei

DOI: 10.1364/AO.455564 Received 10 Feb 2022; Accepted 05 May 2022; Posted 06 May 2022  View: PDF

Abstract: As a representative method of optical non-interference measurement, digital image correlation (DIC) technology isa non-contact optical mechanics method that can measure the displacement and deformation of the whole field.However, when the measurement range of the field is too large, existing DIC method cannot measure the full fieldstrain accurately, which limits the application of DIC measurement in the case of large-size and wide-field view. Toaddress this issue, a DIC measurement method for large-scale structures based on adaptive warping imagestitching is proposed in this paper. Firstly, multiple adjacent high-resolution images are collected at differentlocations of large-scale structures. Secondly, the collected images are stitched by applying the adaptive warpingimage stitching algorithm to obtain a panoramic image. Finally, the DIC algorithm is applied to solve the wholedeformation field. In the experiments, we first verify the feasibility of the proposed method for image matching andfusion through the numerical simulation of rigid body translation experiment. Then, the accuracy and robustnessof the proposed method in practical application is verified by rigid body translation and three-point bendingexperiment. The experimental results demonstrate that the measurement range of DIC is improved significantlywith the adaptive warping image stitching algorithm.

A parallelism measurement method for nontransparent flat parts

Juntao Zhang, Bo Pan, Huan Liu, Xu Zhu, Kang Renke, and Jiang Guo

DOI: 10.1364/AO.457755 Received 08 Mar 2022; Accepted 05 May 2022; Posted 10 May 2022  View: PDF

Abstract: Non-transparent flat parts with weak rigidity are widely used in precision physics experiments, aerospace, and otherfields, in which parallelism is highly required. However, existing methods cannot meet requirements due to the limitationof measurement size and accuracy. This paper proposes a new method for measuring parallelism of non-transparent flatparts with high accuracy, and then built a submicron level parallelism measuring system. The 3D model of the whole partis reconstructed by thickness and flatness, which are measured respectively. Subsequently, parallelism is evaluated bythe principle of minimum directional zone. The method is verified by an experiment with a thin copper substrate sizedø200 mm × 2.48 mm on the parallelism measuring system. The experiment result shows that the part's parallelism is 7.41µm and the expanded uncertainty of parallelism measurement system is 0.34 µm, k = 2.

Novel broadband tunable coding metasurfaces basedon metal patch and graphene for beam control at theterahertz frequencies

Panpeng Ge, ying Zhang, Lihua Xiao, and Binggang Xiao

DOI: 10.1364/AO.459343 Received 25 Mar 2022; Accepted 04 May 2022; Posted 05 May 2022  View: PDF

Abstract: In this paper, we present a broadband tunable coding metasurfaces structure usingcruciate metal patch and circular graphene on multilayer substrate. By changing the Fermilevel of graphene, we can achieve obvious reflection phase variation to design multi-bitcoding metasurfaces. In the research of 1-bit coding metasurfaces, we combine theadvantages of graphene and cooper to realize the real-time adjustment of reflected waves infour broadband frequency bands. In this case, we can control the number of far-fieldreflected waves in the frequency range of 5.45THz ~ 6.45THz. Then, we create 2-bit and3-bit coding mode on the basis of 1-bit coding metasurfaces to obtain a single beam ofreflected waves. Finally, we use the convolution calculation to realize the real-timeadjustment of the single beam reflection direction from 0° to 360° in the azimuthal plane.The research of 2-bit and 3-bit coding mode also provide a way to control the number anddirection of reflect beam specifically in 1-bit coding mode. The present codingmetasurfaces structure provide inspirations for the design of functional devices infuture-oriented intelligent communication.

Femtosecond 3D photolithography through a digitalmicromirror device and a microlens array

Balaji Baskar, Aravind Jakkinapalli, and Sy Wen

DOI: 10.1364/AO.457847 Received 08 Mar 2022; Accepted 04 May 2022; Posted 09 May 2022  View: PDF

Abstract: Based on the microscale 3D point cloud projection with a digital micromirror device (DMD) and a microlens array(MLA) developed recently, we explored the capabilities of this specific type of 3D projection in 3D lithography withfemtosecond light in this study. Unlike 3D point cloud projection with UV continuous light demonstrated before, highaccuracy positioning between the DMD and the MLA is required to have rays simultaneously arrive at the designedvoxel positions to induce two-photon absorption with femtosecond light. Because of this additional requirement, anew positioning method through direct microscope inspection of the relative positions of the DMD and the MLA isdeveloped in this study. Because of the usage of a rectangular microlens array, around four rays can arrive at eachprojecting voxel at the same time. Thus, a new algorithm for determining the pixel map on the DMD to the 3D pointcloud projection with a femtosecond laser is also developed. It is observed that a very long exposure time is requiredto generate 3D patterns with the new 3D projection scheme because of the very limited number of rays used forprojecting each voxel with the new algorithm. It is also found that 3D structures with desired shapes should beprojected far away from the MLA (~15f to 30f, with f being the focal distance of the MLA) in the 3D lithography withthis femtosecond 3D point cloud projection. For patterns projected closer than 10f, shapes are distorted because ofunwanted voxels cured with the 3D projection technique using DMD and MLA.

High-efficiency InGaN blue LEDs with reducedpositive sheet polarization

Ravi Teja Velpula, Barsha Jain, Moulik Patel, FATEMEH MOHAMMADI SHAKIBA, Ngoc Quoc Toan, Hoang-Duy Nguyen, and Hieu Nguyen

DOI: 10.1364/AO.458463 Received 17 Mar 2022; Accepted 02 May 2022; Posted 03 May 2022  View: PDF

Abstract: The formation of positive sheet polarization charges at the interface of the last quantum barrier (QB) andconventional p-type electron-blocking layer (EBL) creates significant band-bending, leading to severeelectron leakage and poor hole injection in III-nitride light-emitting diodes. In this study, we report thatthe positive sheet polarization charges are mitigated by employing a lattice matched AlGaN last QB.Electron leakage is dramatically reduced due to the increased effective conduction band height at the lastQB and EBL. Furthermore, it favors the hole injection into the active region due to the reduced effectivevalance band height for EBL

Integrated refractive index sensor based onAlN-PSiO2 hybrid plasmonic microdiskresonator

Caixia Guo, Chenghao Wang, Tao Ma, Linqing Zhang, and fang wang

DOI: 10.1364/AO.458340 Received 14 Mar 2022; Accepted 30 Apr 2022; Posted 06 May 2022  View: PDF

Abstract: In this paper, a microdisk resonator (MDR) based on an AlN-PSiO2 hybridplasmonic waveguide (HPW) and its refractive index (RI) sensing characteristics areinvestigated. The plasmonic characteristics of the MDR based on the AlN-PSiO2 HPW(APHPW-MDR) in near-infrared wavelengths are studied by using the finite element method(FEM). Through the structure parameter optimizations, the propagation length (Lprop) of theAPHPW-MDR is ~165 µm, which is ~2.5 times as long as that of the MDR based on the AlNHPW (AHPW-MDR). The simulation results show that the quality factor (Q) and extinctionrate (ER) of the APHPW-MDR are ~3100 and ~30 dB, respectively. The RI sensing sensitivity(S) of the RI sensor based on the APHPW-MDR is ~276.6 nm/RIU. The RI sensor based on theAPHPW-MDR has wide application prospects in high-performance biochemical sensing, andit can also be used in integrated optical filters, modulators, switches, routers, delay circuits.

LASER BEAM STEERING AUTOMATION WITHARDUINO-BASED CNC SHIELD FOR STANDOFFFEMTOSECOND FILAMENT INDUCED BREAKDOWNSPECTROSCOPIC STUDIES

lingamurthy Narlagiri, BYRAM CHANDU, Sampath Kumar Satani, and Venugopal Rao Soma

DOI: 10.1364/AO.453824 Received 16 Jan 2022; Accepted 30 Apr 2022; Posted 02 May 2022  View: PDF

Abstract: In this study, we report a novel instrumentation procedure in the automation of laserbeam steering for raster/spiral scanning of the samples used in standoff femtosecond laserinduced breakdown spectroscopy (LIBS) experiments. We have used a readily available andeasy-to-handle Arduino-based computerized numerical control (CNC) shield along with thefree software, universal G-code sender (UGS), for the automation. Standoff femtosecondfilamentation induced breakdown spectra (St-fs-FIBS) of metals, three compositions of Ag-Aualloy, and polyvinyl chloride (PVC), unplasticized polyvinyl chloride (UPVC), chlorinatedpolyvinyl chloride (CPVC) plastic samples were recorded using the developed automatedexperimental setup. The St-Fs-FIBS spectra were recorded at a standoff distance of ~5 metersutilizing a simple hand-held spectrometer. Furthermore, principal component analysis (PCA)technique was utilized for the successful classification of three compositions of Au-Ag alloyspectra using their St-Fs-FIBS spectral data.

One Metal Ions-regulated AgTNPs Etching Sensor Array for Visual Discrimination of Multiple Organic Acids

Miao He, Jiawei Li, Dong Zhao, Yi Ma, Jing Zhang, Cailin Qiao, Zhihua Li, qun Huo, and Changjun Hou

DOI: 10.1364/AO.456278 Received 16 Feb 2022; Accepted 26 Apr 2022; Posted 27 Apr 2022  View: PDF

Abstract: The detection and discrimination of organic acids (OAs) is of great importance in the early diagnosis of specific diseases. In this study, we established an effective visual sensor array for the identification of OAs. This is the first time metal ions were used to regulate the etching of silver triangular nanoprisms (AgTNPs) in OAs discrimination sensor array. The sensor array was based on the oxidation etching of AgTNPs by three metal ions (Mn2+, Pb2+, and Cr3+) and accelerated etching of AgTNPs by OAs. The introduction of metal ions alone led to a slight wavelength shift of the AgTNPs colloid solution, signifying the incompletely etching of the AgTNPs. Nevertheless, when both metal ions and OAs were introduced simultaneously to the solution, a significant blue shift of the localized surface plasmon resonance (LSPR) peak was detected, and a color change of the AgTNPs was observed, which were the consequences of morphological transitions of the AgTNPs. The addition of different OAs accelerated AgTNPs etching in varying degrees, generating diverse colorimetric response patterns (i.e., RGB variations) as “fingerprints” associated with each specific organic acid. Pattern recognition algorithms and neural network simulation were employed to further data analysis, indicating the outstanding discrimination capability of the provided array for eight OAs at 33 μM level. Moreover, excellent results of selective experiments as well as real samples tests demonstrate that our proposed method possessed great potential for practical applications.

Numerical Analysis of Grating Embedded BidirectionalIntegrated Optical Coupler Pressure Sensor

Sanjeev Raghuwanshi, Yadvendra Singh, and Talabattula Srinivas

DOI: 10.1364/AO.456410 Received 21 Feb 2022; Accepted 24 Apr 2022; Posted 11 May 2022  View: PDF

Abstract: A numerical analysis of grating embedded bidirectional optical coupled waveguide structure is presentedfor the first time. Finite difference method (FDM) based scheme has been devised to extract the allowedeigen TE and TM modes of the structure. Sensing characteristics of grating employed between two highrefractive index couplers are then explored. The influence of strain on composite structure has beennumerically analyzed for better understanding of guiding phenomena. Numerical method based on3-point central finite difference scheme with proper boundary conditions at the point of discontinuity hasbeen developed. To be an accurate sensitivity analysis a large number of mesh points (N = 1000) havebeen used in FDM algorithm, while whole analysis being done on MATLAB software. To the best of theauthors knowledge, Bragg grating sensitivity of individual TE and TM modes have been estimated for thefirst time. It is found that higher order TE and TM modes shows the improved sensitivity performance.The physics behind the improved sensitivity of proposed structure is correlated with the existing cases.The proposed technique is based on effective refractive index theory, and hence easy to implement. ThisWork can be easily extended to obtain the temperature, humidity and vibration sensitivity of other novelstructure.

Ultra-broadband high-efficiency circular polarizationconversion and terahertz wavefront manipulationbased on all-metallic reflective metasurface

Mucheng Wang, Yongzhi Cheng, and Ling Wu

DOI: 10.1364/AO.454099 Received 18 Jan 2022; Accepted 22 Apr 2022; Posted 27 Apr 2022  View: PDF

Abstract: In this paper, an all-metal metasurface (MS) is proposed and investigated theoretically,which can achieve the high-efficient reflective circular-polarization conversion and multi-functionalterahertz (THz) wavefront manipulation in an ultra-broadband frequency range. The proposed all-metalMS is consisted of the periodic array of the gold vertical-split-ring (VSR) structure adhered on the goldsubstrate. Numerical simulation results indicate that the proposed MS structure can convert the incidentcircular-polarization (CP) wave into its orthogonal component after reflection with conversioncoefficient over 95% from 0.8THz to 1.65THz (relative bandwidth of 68.3%). The full 2π phase shiftof the proposed MS in this frequency range can be obtained by changing the rotation angle of the VSRstructure along the wave propagation direction. As proofs of concept for the multi-functional wavefrontmanipulation, anomalous reflection, reflective planar focusing and vortex beam generation arenumerically demonstrated based on the Pancharatnam-Berry (PB) phase principle. Our work canprovide an effective method of enhancing the performance of reflective-type all-metal MS and showendless potential in wavefront manipulation and communication applications in THz and even opticalregion.

All-fiber high-power erbium-doped laser systemgenerating optical pulses with a duration of 200 μs to5 ms for fractional photo-rejuvenation

Maksim Koptev, Andrey Morozov, Ksenia Shatilova, Sergey Muravyev, Alexander Zapryalov, Mikhail Likhachev, and Arkady Kim

DOI: 10.1364/AO.455761 Received 08 Feb 2022; Accepted 31 Mar 2022; Posted 13 May 2022  View: PDF

Abstract: An all-fiber high-power erbium-doped fiber laser (EDFL) source generating optical pulses from 200 μs to 5 ms with astable rectangular envelope for fractional photo-rejuvenation is proposed and experimentally demonstrated. A masteroscillator power amplifier (MOPA) configuration composed of a master oscillator, an acousto-optic modulator (AOM)and a one-stage amplifier is designed and employed in the EDFL to serve as an efficient laser system with excellentoutput performance. To avoid multistage amplifiers, the master oscillator generates 1.5 W and for one-stage poweramplifier a Yb-free Er-doped large-mode-area (LMA) active fiber is used, in which we have two benefits: first,modulation of both pump and seed pulses is used to achieve clear rectangular shaped pulses without amplifiedspontaneous emission (ASE) growth, and second, there are no power limitations in amplifier and undesirable 1 µm ASEcompared to Er/Yb systems. We have reached 28.6 W of peak power with 26% slope efficiency limited only by availablepump power, so the system can be easily scaled for achieving a higher peak power.

Ultra-Broadband Perfect Absorber Using Triple-layer Nanofilm in Long Wave Near-Infrared Regime

Kaili Kuang, qiao Wang, Xiaomin Yuan, Li Yu, Yuzhang Liang, Yang Zhang, and Wei Peng

DOI: 10.1364/AO.454217 Received 18 Jan 2022; Accepted 21 Mar 2022; Posted 30 Mar 2022  View: PDF

Abstract: Plasmonic absorbers have drawn extensive attentions because of their promising applications in solar cells, controllable thermal emission and infrared detection. Most proposed plasmonic absorbers are with precise designed surface-pattern, which require complex manufacturing process and high cost. Herein, we propose a simple plasmonic absorber composed of triple-layer Ti/SiO2/TiN nanosystem. The maximal absorption reaches 99.8% from 1554 nm to 1565 nm and an average absoption of 95.3% is achieved in the long wave near-infrared range (from 1100 nm to 2500 nm). The synergistic effect of the upper surface plasmon resonance and the Fabry-Perot resonance in the Ti/SiO2/TiN cause the high absorption. Besides, the effects of the incident angle, polarization state, structural materials and geometric parameters on the absorption performance are investigated in detail. The proposed near-infrared absorber has a potential application prospect in solar collectors, thermal emitters, and solar cells, owing to its high absorption, ultra-broadband bandwidth, insensitivity to incident angle and polarization state, low cost and simple preparation process.

This is a test submission

Dan McDonold and Keith Jackson

DOI: 10.1364/AO.443911 Received 20 Sep 2021; Accepted 20 Sep 2021; Posted 20 Sep 2021  View: PDF

Abstract: This is a test submission