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Tapered Multi-core fiber interferometer for refractiveindex sensing with graphene enhancement

donglai Guo, Lijun Wu, Hongxing Yu, Ai Zhou, Qinyou Li, Mumtaz Farhan, Cheng Du, and Wenbin Hu

DOI: 10.1364/AO.385324 Received 02 Jan 2020; Accepted 27 Mar 2020; Posted 27 Mar 2020  View: PDF

Abstract: An in-line, highly sensitive refractive index (RI) sensor based on tapered Multi-Core fiber (MCF) structuresandwiched between two single-mode fibers (SMF) is proposed and demonstrated. The fiber taperingtechnique was employed to fabricate in-line interferometers based on the multicore fiber. The waistdiameter is one of the dominate factors of the inter-core coupling. The tapered MCF interferometer ishighly sensitive to surrounding refractive index (SRI) with a maximum sensitivity of 9194.6 nm/RIU inthe RI range of 1.4264 to 1.4278 when the waist diameter is 9 µm. The enhancement of the evanescent fieldby graphene coating is proved that to be able to improve the RI sensitivity further. Graphene-coated MCFinterferometer with waist diameter of 9 µm offers the maximum sensitivity of 12617.6 nm/RIU in the RIrange of 1.4144 to 1.4159. The experimental data has good agreement with the simulated results.

Self-localization of an Uncalibrated Camera throughInvariant Properties and Coded Target Location

Mariana Chan-Ley, Gustavo Olague, Gerardo Altamirano-Gomez, and Eddie Clemente

DOI: 10.1364/AO.385841 Received 11 Dec 2019; Accepted 27 Mar 2020; Posted 27 Mar 2020  View: PDF

Abstract: This paper recalls one of the most critical problems forthe area of computer vision, the automatic location ofa single camera. Today, several robotic devices relyon technologies other than visual information to perform self-localization. An artificial optical system willsignificantly benefit from knowing its location withina three-dimensional world since this is a crucial stepto approach other complex tasks. In this article, wewill show how to compute the position of the camerathrough an uncalibrated method making use of projective properties, the projection model of the camera,and some reference points. We introduce a simple yetpowerful way to detect coded targets in photographicimages. Then, we describe an uncalibrated approachused to identify the location of a camera in the threedimensional space. The experiments carried out confirmed the validity of our proposal.

Index of refraction of germanium

John Burnett, Eric Benck, Simon Kaplan, Erik Stover, and Adam Phenis

DOI: 10.1364/AO.382408 Received 06 Feb 2020; Accepted 26 Mar 2020; Posted 27 Mar 2020  View: PDF

Abstract: Measurements of the index of refraction of a sample of high-quality, single-crystalgermanium using the minimum deviation refractometry method are presented fortemperatures near 22 °C and for wavelengths in the range 2 μm to 14 μm. The standarduncertainty for the measurements ranges from 1.5 × 10-5 to 4.2 × 10-5, generally increasingwith wavelength. A Sellmeier formula fitting the data for this range is provided. Details of thecustom system and procedures are presented, along with a detailed analysis of the uncertainty.These results are compared with previous measurements.

Demonstration of wideband metal mesh filters for submillimeter astrophysics using flexible printed circuits

Shinsuke Uno, Tatsuya Takekoshi, Tai Oshima, Keisuke Yoshioka, Kah Wuy Chin, and Kotaro Kohno

DOI: 10.1364/AO.389605 Received 31 Jan 2020; Accepted 26 Mar 2020; Posted 27 Mar 2020  View: PDF

Abstract: We developed a wideband quasi-optical band-pass filter covering 170--520~GHz by exploiting the recent advancements in commercially available flexible printed circuit (FPC) fabrication technologies. We designed and fabricated a three-layered stack of loaded hexagonal grid metal meshes using a copper pattern with a narrowest linewidth of $50~\mu\mathrm{m}$ on a polyimide substrate. The measured frequency pass-band shape was successfully reproduced through a numerical simulation using a set of parameters consistent with the dimensions of the fabricated metal meshes. FPC-based metal mesh filters will provide a new pathway toward the on-demand development of millimeter/submillimeter-wave quasi-optical filters at low cost and with a short turnaround time.

Coherence of vortex Bessel-like beams in a turbulentatmosphere

Igor Lukin

DOI: 10.1364/AO.387549 Received 09 Jan 2020; Accepted 26 Mar 2020; Posted 26 Mar 2020  View: PDF

Abstract: erent properties of vortex conical waves propagating through a turbulent atmosphere are theoretically studiedwith the use of the analytical solution of an equation which describes the evolution of the second-order transversemutual coherence function of an optical radiation field. The following parameters of vortex conical waves areconsidered: the degree of coherence, the coherence radius, the integral scale of the degree of coherence and theintegral scale of the squared degree of coherence. The effect of atmospheric turbulence on these coherencecharacteristics of vortex conical waves is analyzed at different values of their parameters. It turns out that thedegree of coherence of a vortex conical wave, formed from a Gaussian beam while passing through a conical lens(axicon) and a spiral phase plate, at its optical axis is almost independent of the initial radius of the Gaussian beamand the radius of the axicon aperture. In addition, all the coherence characteristics of vortex conical waves dependon the topological charge stronger than on the wave vector component normal to the radiation propagationdirection. A meter of the integral scale of the degree of coherence of vortex Bessel-like optical beams is shown to bea preferred sensor of optical radiation distortions in a turbulent atmosphere as compared to a meter of thecoherence radius of such beams. A lower degree of coherence of vortex conical waves than of fundamental (vortexfree) conical waves in a turbulent atmosphere is proven with the use of the integral scale of the degree ofcoherence of these optical waves as a referent criterion.

Influence of GaAs and GaSb substrates ondetection parameters of InAs/GaSbsuperlattice based mid-infrared interbandcascade photodetectors

Klaudia Hackiewicz, Małgorzata Kopytko, Jarosław Rutkowski, Piotr MARTYNIUK, and Lukasz Ciura

DOI: 10.1364/AO.385916 Received 13 Dec 2019; Accepted 26 Mar 2020; Posted 26 Mar 2020  View: PDF

Abstract: The paper presents electrical and optical properties of interband cascade infraredphotodetectors with InAs/GaSb type-II superlattice absorbers. We compare the detectionparameters of detectors grown on the native GaSb substrate and lattice-mismatched GaAssubstrate and seek solutions to enhance device performance, specifically with using an opticalimmersion. The detectors grown on GaAs have better detection parameters at roomtemperature, but at lower temperatures the misfit dislocations become more important anddetectors grown on GaSb become better.

Precision analysis of turbulence phase screens and itsinfluence on simulation of Gaussian-beampropagating in the turbulent atmosphere

CHEN Zhibin, ZHANG Dong-Xiao, xiao cheng, and QIN Meng-Ze

DOI: 10.1364/AO.389121 Received 24 Jan 2020; Accepted 26 Mar 2020; Posted 26 Mar 2020  View: PDF

Abstract: The slip-step method is widely used in simulating the optical wave propagating in the turbulent atmosphere,which treats propagation and phase perturbations caused by turbulence separately and in discrete steps alongthe propagation axis. The phase perturbations are represented by a series of phase screens, hence, theprecision of phase screen concerns the accuracy of the simulation. In this paper, we firstly discussed theprecision and computational performance of phase screen generated by the subharmonics complemented DFT(DFT-SH) method, three kinds of randomized spectral sampling techniques (Sparse Spectrum (SS) technique,Sparse Spectrum technique with uniform wave vectors (SU), randomized DFT technique) andoptimization-based (OB) method, then, the simulations were implemented with the phase screens generatedby these methods. Some statistical quantities of the received optical field were calculated, such as the beamwander variance, the long-term beam radius, the short-term beam radius and the on-axis scintillation index.Statistical results showed that the undersampling of phase screen in the low-frequency region would cause theunderestimate to the values of the beam wander variance, the long-term beam radius and the focused beamon-axis scintillation index, because these quantities are sensitive to the large-scale inhomogeneities. Whereas,the undersampling would not affect the predicted values of the short-term beam radius and the collimatedbeam on-axis scintillation index, because these quantities are insensitive to the large-scale inhomogeneities.

Hyperspectral remote sensing imageclassification based on random average bandselection and an ensemble kernel extremelearning machine


DOI: 10.1364/AO.386972 Received 30 Dec 2019; Accepted 25 Mar 2020; Posted 25 Mar 2020  View: PDF

Abstract: Hyperspectral remote sensing technology can explore a lot of information aboutground objects, and the information is not explored in multispectral technology. This studyproposes a hyperspectral remote sensing image classification method. First, preprocessing thehyperspectral data to obtain average spectral information of pixels, the average spectralinformation contains spectral-spatial features. Second, the average spectral is randomly bandselected to obtain multiple different datasets. Third, based on ensemble learning and kernelextreme learning machine, an ensemble kernel extreme learning machine is proposed. Finally, ahyperspectral remote sensing image classification model based on the ensemble kernel extremelearning machine was established. Experiments with two common hyperspectral remote sensingimage datasets demonstrate the effectiveness of the proposed method.

Experimental investigation on aero-optical effects of ahypersonic optical dome under different exposuretimes

Haolin Ding, Shihe Yi, Xinhai Zhao, and Yao Xu

DOI: 10.1364/AO.387513 Received 07 Jan 2020; Accepted 25 Mar 2020; Posted 25 Mar 2020  View: PDF

Abstract: The aero-optical effects induced by the complex flow structure around a hypersonic optical dome is highlyunsteady which leads to significant differences in the imaging quality under different exposure times. It is of greatsignificance to study the influence of exposure time on the imaging quality for guiding the design of imagingguidance seekers, and improving the imaging guidance accuracy. Based on the hypersonic gun wind tunnel, theaero-optical effect measurement platform was built to measure the wavefront from transient exposure to longexposure. With the increase of exposure time, the accuracy of OPDhigh-order reconstruction by low-order Zernikepolynomials increased from 62.2% to 88.6%. The increase of exposure time was helpful to reduce the complexityof wavefront spatial distribution structure. In principle, it could reduce the difficulty of wavefront adaptivecorrection systems. With the increase of exposure time, the OPDrms corresponding to OPDhigh-order increasedgradually, the amplitude decreased gradually, and the difference of OPDrms decreased gradually at differenttimes. Under different exposure times, the large aperture approximation (LAA) principle could achieve a betterprediction of Strehl ratio (SR) values. With the increase of exposure time, the imaging integral resolution, R,decreased obviously and it was stable at about 1.43R0. Compared with that, R was improved by about 30%when the exposure time was 6ns.

Filter construction using Ronchi masks and LegendrePolynomials to analyze the noise in aberrationsapplying the Irradiance Transport Equation

Jesús Arriaga Hernández, Bolivia Otahola, Jose Oliveros, Alberto Jaramillo-Núñez, and María Morín Castillo

DOI: 10.1364/AO.389716 Received 04 Feb 2020; Accepted 25 Mar 2020; Posted 25 Mar 2020  View: PDF

Abstract: We tested different optical elements placed in 3 different positions applying the Irradiance TransportEquation (ITE), obtaining the wavefront (W(x, y)) and aberrations surface (AS(r, θ)). The existing noisesin the captures I, as well as in the W and AS were analyzed applying several filters: in the first place a filterbased on Legendre Polynomials (LP), generating the most probable points increasing the data resolution,in the second place a filter based on a 50-degree 2D-LP was used as a multi-lineal fit (multiple linearregression), and in the third place an ideal bandpass filter in the Fourier space after inducing a periodicityusing Ronchi simulated masks with periods in x, y, xy were used to perform a data scanning (similar tothe 4-step Phase-Shifting method). SNR values (Signal-to-Noise Ratio) were obtained for each proposedfilter along with the most probable image free from noise, determined from a linear combination of theoriginal data and the applied filters.

JCW: The Ubiquity of Fourier Transformation in Optical Sciences

Masud Mansuripur

DOI: 10.1364/AO.390342 Received 13 Feb 2020; Accepted 25 Mar 2020; Posted 25 Mar 2020  View: PDF

Abstract: The Fourier transform operation is an important conceptual as well as computational tool in thearsenal of every practitioner of physical and mathematical sciences. We discuss some of its applications inoptical science and engineering, with the goal of providing a broad perspective on the intimate relation betweenthe physical and mathematical concepts that are elegantly interwoven within the theory of Fourier transforms.

All-dielectric bifunctional polarizationconverter with high transmission efficiency innear-infrared region

Ying Cui, Huan Jiang, Li Wang, Bingyi Liu, Jie Song, and Yongyuan Jiang

DOI: 10.1364/AO.388097 Received 13 Jan 2020; Accepted 25 Mar 2020; Posted 26 Mar 2020  View: PDF

Abstract: In this article, we demonstrated a polarization control device with differentfunctions for oppositely propagating directions by two-layer twisted silicon column arrayseparated by a silica layer. The proposed structure can rotate the electric field directions ofbackward-linear polarization waves (BLPWs) by 45º and serve as a linear-to-circularconverter (LCC) for the forward-linear polarization waves (FLPWs). The physicalmechanism is discussed by Jones matrix, and the numerical results show that the maximumtransmissions >0.9 for the two functions of the proposed structure are achieved innear-infrared region. The high transmission originates from the all-dielectric materials, whichis a major advance compared with previously reported bifunctional converters. The proposedsimple-shaped device with high transmission efficiency has potential applications in opticalimaging, sensing, etc.

Artificial Neural Network Estimation of Data andChannel Characteristics in Free-space UltravioletCommunications

Sudhanshu Arya and Yeon-ho Chung

DOI: 10.1364/AO.386509 Received 19 Dec 2019; Accepted 25 Mar 2020; Posted 26 Mar 2020  View: PDF

Abstract: In this paper, we develop an artificial neural network (ANN) based algorithm for signal classification,i.e., data demodulation, and the estimation of channel characteristics, such as channel DC gain and turbulence distribution parameters, in free-space ultraviolet (UV) communication systems. In this scheme,the ANN-based receiver adaptively tracks the UV channel variation and is directly trained using the datagenerated from UV channel models. To evaluate the performance of the proposed algorithm across allturbulence regimes, log-normal, Gamma-Gamma, and negative exponentially distributed UV turbulencechannels are considered. We demonstrate that the proposed algorithm is robust to perform accurate andreliable signal classification and UV channel estimation without knowing underlying UV channel models or channel state information (CSI). In addition, time complexity analysis is presented. It is shown that,even under the strong turbulence regime, the accuracy of the proposed algorithm is found to be higherthan 97% in terms of correct classification. It is also demonstrated that the classification error rate performance of the proposed ANN-based detector is superior to that of a maximum-likelihood (ML) baseddetector with perfect CSI.

High fidelity underwater wireless opticalcommunication with a phase-conjugatedframe structure

Deli Qin, Yingchun Li, You Sun, yifan li, Nan Ye, Min Wang, and Junjie Zhang

DOI: 10.1364/AO.388536 Received 27 Jan 2020; Accepted 25 Mar 2020; Posted 26 Mar 2020  View: PDF

Abstract: In this paper, the influence factors of phase noise are first analyzed in detail andverified by experiments, and its principle is theoretically derived. Besides, we propose a novelframe structure for m-quadrature amplitude modulation-orthogonal frequency divisionmultiplexing (m-QAM-OFDM) in underwater wireless optical communication (UWOC). Theframe structure contains OFDM signals and their phase-conjugated signals. At the receivingend, by the simple superposition of phase-conjugated symbols, the noise suppression can beachieved. The feasibility is experimentally demonstrated by transmitting m-QAM-OFDMsignal in different modulation formats and scenarios. The results show that bit error rate(BER) performance can be significantly improved, and there is also a significant increase intransmission capacity compared with traditional phase-conjugated method. Moreover, theproposed frame structure can provide a robust and simple compromise between transmissioncapacity and distance.

Optical monitoring of two-substance structuredarea with non-matrix detectors

Artur Martirosyan, Radik Kostanyan, Pavel Muzhikyan, Hrayr Azizbekyan, and David Zargaryan

DOI: 10.1364/AO.381864 Received 31 Oct 2019; Accepted 24 Mar 2020; Posted 27 Mar 2020  View: PDF

Abstract: In this paper, we describe a novel concept, to the best of our knowledge, tomonitor changes in the landscape with two arbitrarily distributed substances. To recordsignals from the mock-up scene, the non-matrix detectors are used which work in thelinear sensitivity range. The formulas that describe the parameters of distributedsubstances are derived. They allow one to find distribution centers of the two substances,drift and drift speed of the centers, radial standard deviations and their changing rates,areas of each substance. The technique has been applied to monitor remotely the mock-upscene which imitates the landscape of vegetation restoration after a fire.

Information content of absorption spectra and implications for ocean color inversion

B. B. Cael, Alison Chase, and Emmanuel Boss

DOI: 10.1364/AO.389189 Received 28 Jan 2020; Accepted 24 Mar 2020; Posted 25 Mar 2020  View: PDF

Abstract: The increasing use of hyperspectral optical data in oceanography, both \emph{in situ} and via remote sensing, holds the potential to significantly advance characterization of marine ecology and biogeochemistry because, in principle, hyperspectral data can provide much more detailed inferences of ecosystem properties via inversion. Effective inferences, however, require careful consideration of the close similarity of different signals of interest, and how these interplay with measurement error and uncertainty to reduce the degrees of freedom (DoF) of hyperspectral measurements. Here we discuss complementary approaches to quantify the DoF in hyperspectral measurements in the case of in situ particulate absorption measurements, though these approaches can also be used on other such data, e.g. ocean color remote sensing. Analyses suggest intermediate DoF for our dataset, meaning that these data can yield coarse community structure information. Empirically, chlorophyll is an effective first-order predictor of absorption spectra, meaning that error characteristics and the mathematics of inversion need to be carefully considered for hyperspectral data to provide information beyond that which chlorophyll provides. We also discuss other useful analytical tools that can be applied to this problem and place our results in the context of hyperspectral remote sensing.

Fabrication of mesoporous silica film based opticalwaveguide sensor for detection of small molecules

Guiqiang Wang and Shuqing Sun

DOI: 10.1364/AO.389118 Received 27 Jan 2020; Accepted 24 Mar 2020; Posted 25 Mar 2020  View: PDF

Abstract: In this paper, a thick MSF (more than 700 nm) was fabricated via the two-step enhancing Stöber solution growthapproach (ESSGA). According to the optimization based on transfer matrix method, a thicker MSF sensor has higherwaveguide index sensitivity and is more suitable for the adsorbent detection, while a thinner MSF sensor hashigher covered medium index sensitivity and is more appropriate for non-adsorbent detection. The coveredmedium index sensitivity and refractive index resolution of fabricated MSF optical waveguide sensor werecalculated to be 53.18 deg/RIU and 1.28 × 10-6 RIU, respectively. For the detection of small molecule, CTAB wasused as a model of small molecule to verify its sensing property and its limit of detection (LOD) as low as 1.879 nMwas obtained. In order to detect heavy metal ions, MSF was modified with amino group by post-grafted method.The response of resonance angle shift is more sensitive to Pb2+ ion than Cu2+ ion and both their LODs could reachthe nM detection level, those are 17.30 and 6.44 nM, respectively.

JCW: High energy yield bifacial spectrum-splitting photovoltaic system

Benjamin Chrysler and Raymond Kostuk

DOI: 10.1364/AO.391821 Received 03 Mar 2020; Accepted 24 Mar 2020; Posted 25 Mar 2020  View: PDF

Abstract: In this paper a photovoltaic system is proposed that achieves high energy yield by integrating bifacial silicon cells into a spectrum-splitting module. Spectrum-splitting is accomplished using volume holographic optical elements to spectrally divide sunlight onto an array of photovoltaic cells with different bandgap energies. Light that is reflected from the ground surface onto the rear side of the module is converted by the bifacial silicon cells. The energy yield of the system is optimized by tuning the volume holographic element parameters, such as film thickness, index modulation, and construction point source positions. An example is presented for utility scale illumination parameters in Tucson, Arizona that attains an energy yield of 1010(kw∙hr)/(yr∙m^2 ), which is 32.8% of the incident solar insolation.

Angular Dependent Circular Dichroism of Tai Chi ChiralMetamaterials in Terahertz Region

Xiaoxiang Dong, Changji Liu, Yuanyuan Huang, Fangrong HU, Yiwen E, Yanping Jin, Yixuan Zhou, and Xinlong Xu

DOI: 10.1364/AO.387150 Received 02 Jan 2020; Accepted 23 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: Chirality has received wide attentions due to its promising applications in biopharmaceuticals, chemical detection,and polarized optoelectronic devices. Herein, metamaterials with layered Tai Chi patterns are proposed to getstrong and tunable chirality. Based on the surface current distribution analysis, a coupling model considering boththe magnetic and electric dipoles in the upper and bottom metallic structures is proposed to understand thecircular dichroism. Accordingly, both an external chiral modulation by changing the incident angle and an internalchiral modulation by changing the twist angle are achieved. Incident angle dependent circular dichroismmodulation exhibits a range of 0.44~0.62 and the twist angle dependent modulation range is -0.6~0.42, where thenegative value means the polarity of the circular dichroism can also be tuned. This work deepens theunderstanding of angular dependent chirality in metamaterials and expands the potential for terahertzpolarization optoelectronic applications.

Single Preloaded Piezoelectric Ceramic Stack ActuatorBased Fast Steering Mirror with Ultrahigh NaturalFrequency

Ziye Zhou, ZhongYi Feng, Hao Xian, and Huang Linhai

DOI: 10.1364/AO.387262 Received 07 Jan 2020; Accepted 23 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: To meet the requirements of the adaptive optics systems with high-bandwidths and large excursion angles, wepropose a fast steering mirror (FSM) with an ultrahigh natural frequency and a large angular range. The proposedFSM is driven by a preloaded piezoelectric ceramic stack actuator (PCSA), which has a higher shear stress limit inthe working direction. We describe the structure of the preloading device (PD) and analyze the stiffnessimprovement of the preloaded PCSA. Then we introduce the structure of the proposed FSM, and performtheoretical analysis based on the established statics modal and dynamical model. We also build an experimentalsetup of the proposed FSM. The experimental results show that the angular range of the proposed FSM is up to8.4mrad and its first natural frequency (FNF) is 6660Hz, which surpass the performances of current FSMs.

The soft x-ray laser beamline for surface processingand damage studies

Masahiko Ishino, Thanh-Hung Dinh, Yuji Hosaka, Noboru Hasegawa, kimio yoshimura, hiroki yamamoto, Hatano Tadashi, Takeshi Higashiguchi, Kazuyuki Sakaue, Satoshi ICHIMARU, Masatoshi Hatayama, Akira Sasaki, Masakazu Washio, Masaharu Nishikino, and Yasunari Maekawa

DOI: 10.1364/AO.387792 Received 15 Jan 2020; Accepted 23 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: We have developed a soft x-ray laser (SXRL) beamline equipped with an intensity monitor dedicated to the ablationstudy such as surface processing and damage formation. The SXRL beam having the wavelength of 13.9 nm, pulsewidth of 7 ps, and pulse energy of around 200 nJ is generated from Ag plasma mediums using an oscillatoramplifier configuration. The SXRL beam is focused onto the sample surface by the Mo/Si multilayer coatedspherical mirror. To get the correct irradiation energy/fluence, an intensity monitor composed of a Mo/Simultilayer beam splitter and an x-ray charge-coupled device camera has been installed in the beamline. Mo/Simultilayer beam splitter has a large polarization dependence in the reflectivity around the incident angle of 45°.However, by evaluating the relationship between reflectivity and transmittance of the beam splitter appropriately,the irradiation energy onto the sample surface can be derived from the energy acquired by the intensity monitor.This SXRL beamline is available to not only the ablation phenomena but also the performance evaluation of soft xray optics and resists.

Analytical design of high-performing +1st order diffraction convexgrating imaging spectrometer

Yuhang Shen, Zhengni Ni, Yuanshen Huang, Bing Sheng, Banglian Xu, MoQiang Guo, and MengJing Xu

DOI: 10.1364/AO.387901 Received 10 Jan 2020; Accepted 23 Mar 2020; Posted 24 Mar 2020  View: PDF

Abstract: A novel concentric spectrometer having one convex grating and one concave mirror, working at +1st orderdiffraction, with a small size, high resolution, and high diffraction efficiency is proposed. It can simultaneously achieve highresolution and compactness by increasing the grating groove density. A compact spectrometer operating at a wavelength of740–790 nm with excellent imaging quality is designed. Its spectral resolution reaches 0.049 nm, and its diffraction efficiencyimproves by 27 % compared to the conventional Offner spectrometer with convex grating working at -1st order diffraction.This is suitable for small, light, and low-cost atmospheric gas monitoring satellites.

Research on the surface morphological andelectrochemical modification of Polyvinylchloride (PVC) induced by KrF and ArFexcimer lasers direct writing

jian Wu, Tingting Zeng, Chunyan Wang, Tao Chen, and Chong Zheng

DOI: 10.1364/AO.388823 Received 22 Jan 2020; Accepted 23 Mar 2020; Posted 24 Mar 2020  View: PDF

Abstract: To obtain superior performance in adhesion, polyvinyl chloride (PVC) substrateswere modified by excimer laser direct writing with different operating wavelengths, scanningspeeds and laser fluences. The induced morphological and electrochemical changes weredetailedly tested and analyzed. Microchannels were formed on the surfaces of the PVCsubstrates due to the laser ablation, where the melted-resolidified droplet-like structures weredistributed uniformly and can significantly improve the mechanical interlock. Besides,according to the FT-IR and XPS analyses, Lewis bases such as hydroxyl and carbonyl wereformed after laser treatment which is beneficial to the adhesion strength. These mechanicaland chemical modifications may play positive roles in enhancing the bonding strength of thePVC edge bandings.

A robust and fast filtering method for enhancement ofquality-guided path two dimensional unwrappingalgorithms

Jafar Amjad

DOI: 10.1364/AO.386064 Received 16 Dec 2019; Accepted 23 Mar 2020; Posted 24 Mar 2020  View: PDF

Abstract: This paper presents a new filtering algorithm for reducing the phase noise based on Bicubic interpolation method (BIM). The unwrapped phase map accuracy is enhanced by the combination of BIM with aconventional unwrapping algorithm. The Bicubic interpolation filtering (BIF) and Bicubic interpolationsmoothed filtering (BISF) methods presents as two powerful low pass filters. The simulation shows thatthe BIF and BISF convert the initial noise distribution to the Gaussian distribution. The Mirau interferometer is used to approve the performance of proposed filtering algorithms. The root mean square errorbetween two QGP and BISF method has estimated approximately 31 nm.

Area coding method in frequency comb profilometryfused with optical interferometry for measuringcentimeter-depth object with nanometer-accuracy

Quang Pham and Yoshio Hayasaki

DOI: 10.1364/AO.386464 Received 24 Jan 2020; Accepted 23 Mar 2020; Posted 24 Mar 2020  View: PDF

Abstract: Area coding masks in a frequency comb profilometer (FCP) based on a single-pixel imaging architecture areintroduced for measuring a practical metal object that has weaker reflection than a specular object. In such a case,it is important to increase the intensity of the encoded object light on the photodetector area because a photodiodeoperated at a high frequency of more than 1 GHz is generally small. The area coding masks can concentrate morelight on the focal point compared with random coding masks that are commonly used. The increased intensity alsoincreases the number of pixels in the FCP, and consequently, accurate matching is achieved between the dataobtained by optical interferometry and the FCP data. It was demonstrated that the introduction of area codingmasks increased the detected light intensity and allowed us to measure a practical metal object with 16-times moresampling points.

Compact wide-angle capsule endoscopic lens design

Sehui Chang, Dongmok Kim, and Hyuk-Sang Kwon

DOI: 10.1364/AO.386939 Received 01 Jan 2020; Accepted 23 Mar 2020; Posted 24 Mar 2020  View: PDF

Abstract: Capsule endoscopes require a high-quality imaging system in terms of the wide field of view, imagebrightness, and resolution to provide accurate diagnostic information. However, due to the wide-anglelens design, the first element of the lens inevitably becomes larger in diameter, which makes it difficultto reduce the overall size of the lens. In this study, the compact wide-angle lens for a capsule endoscopeis reported. The proposed system allows the first element to be compact in diameter and increases imagequality by utilizing all aspheric surfaces for optical aberration control. The specification of the proposedcapsule endoscope lens shows the wide field of view (FOV) of 160 deg, F-number 2.8, and total tracklength of 5mm. In the overall field of view, relative illumination is still over 60%. To achieve a high imagequality in the proposed system, the modulation transfer function (MTF) is over 30% at 180 lp/mm for a1920 × 1080 1/6" CMOS image sensor in a pixel size of 1.4 µm.

Influence of the arrangement of vacuum chuck holeon transmittance wavefront of large-aperture KDP inSPDT

Xiangyang Lei, Shuang Zhang, Shengfei Wang, Jianfeng Zhang, Wenhu Su, Liping Zhang, chenhui an, Jian Wang, Qinghua Zhang, Mincai Liu, and Qiao Xu

DOI: 10.1364/AO.382447 Received 08 Nov 2019; Accepted 22 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: Serious edge effect of potassium dihydrogen phosphate (KH2PO4, KDP) manufactured using single pointdiamond turning (SPDT) often results in disqualification of transmittance wavefront for high-power laser systems.In this paper, based on the theoretical analysis of suck hole configuration and pressure distribution law undervacuum chuck condition of crystal elements, the influence of sucker hole configuration on transmittance wavefrontroot-mean-square gradient (GRMS) is verified through fly-cutting experiments. By adopting the new designedvacuum chuck, the vacuum chucking quality is effectively improved, and the edge effect is accordingly suppressedin SPDT. And the accuracy of transmittance wavefront GRMS has an improvement about 25% under the sameprocessing parameters.

Radial and tangential velocity effects of a probedscanning mirror on laser Doppler frequency shift

Kusuma Agusanto, Gih-Keong Lau, Ting Liu, and Chuangui Zhu

DOI: 10.1364/AO.387267 Received 06 Jan 2020; Accepted 22 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: A laser Doppler vibrometer (LDV) is precise and fast in measuring the translational velocity of a vibratingdiffuse surface. However, it could fail to measure the tangential velocity of a rotating mirror. While thespecular reflection away from the mirror can be recovered by a retroreflective collector, the recoveredLDV reading is found to deviate from the true tangential velocity of the probed scanning mirror. Thishappens because the probed spot shifts radially along the rotating mirror surface and thus introducesextra Doppler shift, while the laser beam was aimed at a constant height on the scanning mirror. Here,we derive an analytical relationship between the laser Doppler shift and the tangential velocity of themeasured spot. With the input of the prescribed scan profile, we recovered the true reading of tangentialvelocity of the scanning mirror even at the large rotational angle. This corrected LDV reading is as preciseas the measurement by a high-speed camera.

Morphological and chemical dynamics uponelectrochemical cyclic sodiation of electrochromictungsten oxide coatings extracted by in situellipsometry

Alexandre ZIMMER, Mickael Gilliot, Laurent Broch, Clotilde Boulanger, Nicolas Stein, and David Horwat

DOI: 10.1364/AO.389063 Received 23 Jan 2020; Accepted 22 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: The sodiation-desodiation process of sputtered amorphous electrochromic tungsten oxide coatings in aqueousbased medium was simultaneously monitored over 99 cycles by cyclic voltammetry and in situ spectroscopicellipsometry. This allowed extracting the evolution of optical and geometrical parameters upon cycling. Theresulting electrochemical coloring-bleaching process was dynamically fitted in the 1.8-2.8 eV optical range with afour-phase model including a constrained spline parametrization of the dielectric function. This allows real timeaccess to thickness, surface roughness and dielectric function of NaxWO3. The temporal evolution of the latter in thefully colored state was used to highlight a porosity extent of the probed coating of opened morphology. Thedesigned spectro-electrochemical approach was applied to map the temporal evolution of the Na content (x inNaxWO3) during and between cycles, taking into account the intricate interplay between charge density, thicknessand electrolyte uptake.

Adaptive niche-genetic algorithm based onbackpropagation neural network for atmosphericturbulence forecasting

DONG SU, Xiaoqing Wu, Tao Luo, Su Wu, and Chun Qing

DOI: 10.1364/AO.388959 Received 23 Jan 2020; Accepted 21 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: Because systematic direct measurements of the refractive index structure constant (C_n^2) are not available for many climates and seasons, we develop an indirect method to forecast atmospheric turbulence. The C_n^2 data is estimated from a backpropagation neural network optimized by an adaptive niche-genetic algorithm. The estimated result was validated against the corresponding 6-day C_n^2 data from a field campaign of the 〖30〗^th Chinese National Antarctic Research Expedition. We also compared the proposed model with the Weather Research and Forecasting (WRF) model. The results suggest that the algorithm can improve the learning ability of neural networks to achieve the training objective.

Modeling Retinal Detachment Associated with Hemorrhageby Monte Carlo Simulation

Tarek Al-Saeed

DOI: 10.1364/AO.385247 Received 19 Dec 2019; Accepted 20 Mar 2020; Posted 25 Mar 2020  View: PDF

Abstract: In this work we study fundus reflection in the case of retinal detachment. Vitreous humor builds upbeneath the retina through a break in the retina or when there is traction on the retina Further, we assume that thisdetachment is associated with hemorrhage in both regions above and below the retina. To discuss hemorrhage, weassume erythrocytes to be spheres of different radii. Then we apply Mie scattering theory to these spheres where wecalculate the scattering coefficient, the absorption coefficient and the anisotropy factor. Using these parameters, weapply Monte Carlo simulation to calculate reflection. In order to model fundus reflection under retinal detachmentwe define three types of reflection. First, reflection from the vitreous body. Second, retinal reflection where photonsare reflected from retinal vitreous interface once. Third, retinal reflection where photons are reflected many timesfrom retinal vitreous interface.

Designing an anamorphic illumination system witha RTIR prism for a TRP type projector

Yu Jia Chen and Jui Wen Pan

DOI: 10.1364/AO.390072 Received 12 Feb 2020; Accepted 20 Mar 2020; Posted 20 Mar 2020  View: PDF

Abstract: A relay lens system design for a mini-projector with telecentric illumination is described. The reverse total internal reflection (RTIR) prism for angularmagnification and lateral magnification is discussed in detail, and magnifications under different digital micro mirror devices (DMD) are compared. TheTRP DMD chip (tilt angle is ±17°) is the latest spatial light modulator, and the F-number of illumination system is 1.71. Using the tilt and roll (TRP) DMD,the lateral magnification and the angular magnification for the RTIR prism can be increased by 3.77% and 8.73% over that obtainable using theconventional DMD chip (tilt angle is±12°). In order to solve for the angular magnification of an RTIR prism, the baffle is set at the aperture stop of therelay lens system. There is a trade-off between the efficiency and the contrast ratio with the baffle. When B (the position of the baffle) is at 0.11, thecontrast ratio of the illumination system is 7590:1 and the efficiency is 57%. The spot size at the edge and corner of DMD active area is controlled to beless than 250μm and the optical distortion is less than 1%.

Realization of all optical comparator using beaminterference inside photonic crystal waveguides

HuGe Jile

DOI: 10.1364/AO.385744 Received 11 Dec 2019; Accepted 20 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: Using optical beam interference inside photonic crystal based waveguides is a promising method for designing andrealizing all optical logic gates and other digital devices. In this paper we are going to design and propose an alloptical 1-bit comparator using optical beam interference. In the proposed structure the logic state of input portsare determined based on their initial phase. The 180 degrees and Zero degrees phases are used as logic 0 and 1.However the logic state of the output ports are determined based on the amplitude of the optical signal at theoutput ports. For the proposed structure the maximum rise and fall times are about 0.6 ps and 0.3 ps respectively.

Nanosecond pressure transient detection oflaser-induced thermal lens

Otávio Capeloto, Vitor Zanuto, Vinicius Camargo, Gabriel Flizikowski, Gustavo Bassi Lukasievicz, Leandro Herculano, Marcos Belançon, Nelson Astrath, and Luis Malacarne

DOI: 10.1364/AO.389545 Received 31 Jan 2020; Accepted 19 Mar 2020; Posted 19 Mar 2020  View: PDF

Abstract: We use the thermal lens technique in the nanosecond time scale to describe acousticwave effect in liquids and the corresponding correlation with the speed of sound in the fluid,volumetric thermal expansion and piezo-optic coefficient. These physical properties are found tobe directly correlated to the anomalous effects observed in the transients at the nanosecond timescale, where acoustic waves dominate the thermal lens signal inducing an oscillating transient.Our results suggest the application of the thermal lens to study the generation and the detectionof thermo-acoustic waves in liquids, which make this method interesting for all-optoacousticultrasound detection and imaging.

The active vibration isolation system basedon LADRC algorithm for atom interferometryYIN ZHOU,1†DONGYUN LUO,1,2†BIN WU,1 BING CHENG,1* AND QIANG LIN1*

Yin Zhou, Dongyun Luo, Bin Wu, Bing Cheng, and Qiang Lin

DOI: 10.1364/AO.390168 Received 12 Feb 2020; Accepted 19 Mar 2020; Posted 20 Mar 2020  View: PDF

Abstract: A new method based on the linear active disturbance rejection control (LADRC)algorithm is proposed to design and build a vertical vibration isolator below 0.1 Hz for coldatom interferometry. This system combines the control system which is used to process and tofeedback vibrations measured by a seismometer, and a voice coil which is used to cancel themotion of a commercial passive vibration isolation platform. When the feedback is on, thevertical vibration is reduced by an additional factor of up to 1000 from 0.1 to 5 Hz, while thesystem has a steady oscillation with a natural period of 66 s. The experimental results showthat the LADRC is an effective control algorithm for this application and performs better thanthe classic lag compensation filters in our case. In addition, fewer parameters to adjust in thismethod and we only need to tune the feedback gain of system state error for its application.

Extended field-of-view adaptive optics inmicroscopy via numerical field-segmentation

Pouya Rajaeipour, Alex Dorn, Kaustubh Banerjee, Hans Zappe, and Caglar Ataman

DOI: 10.1364/AO.388000 Received 13 Jan 2020; Accepted 19 Mar 2020; Posted 20 Mar 2020  View: PDF

Abstract: Sample-induced optical aberrations in microscopy are in general field-dependent,limiting their correction via pupil Adaptive Optics (AO) to the center of the available Field-of-View(FoV). This is a major hindrance particularly for deep tissue imaging, where AO has a significantimpact. We present a new wide-field AO microscopy scheme, in which the deformable element islocated at the pupil plane of the objective. To maintain high quality correction across its entirety,the FoV is partitioned into small segments, and a separate aberration estimation is performed foreach via a modal decomposition based indirect wavefront sensing algorithm. A final full-fieldimage is synthesized by stitching of the partitions corrected consecutively and independently viatheir respective measured aberrations. The performance and the limitations of the method isexperimentally explored on synthetic samples imaged via a custom-developed AO fluorescencemicroscope featuring an optofluidic refractive wavefront modulator.

Focal shift of an axisymmetric Bessel-Gaussian beam under airy mixing modulation

SITONG DING, Yue Li, Ziyan Li, Guanxue Wang, Jitong Xu, Yang Li, Dong Xiangmei, and Xiumin Gao

DOI: 10.1364/AO.388065 Received 13 Jan 2020; Accepted 19 Mar 2020; Posted 20 Mar 2020  View: PDF

Abstract: In this paper, focusing characteristics of Bessel-Gaussian beams are studied bymeans of vector diffraction theory. The vector field distribution of the axisymmetric BesselGaussian of a cylindrical vector is derived by calculating and adding Airy mixing modulationto the Bessel-Gaussian beam. It is found that a series of regular focusing changecharacteristics, focusing presents strong stability of optical chain structure, and the number ofoptical chain links can be adjusted. At the same time, it is pointed out that in the case of atightly focused helically polarized beam, the polarization in the focal region is not uniform,but there was a similar horizontal shift in focus. Finally, the relevant practical applicationscenarios are briefly introduced. The correlation focus shift conversion can be widely used inelectronic acceleration, optical sampling and operation, and biological imaging.

Novel Schlieren masks: square root monomials,sigmoidal functions and off-axis Gaussians

Jorge Ojeda-Castaneda and Cristina Gomez-Sarabia

DOI: 10.1364/AO.387370 Received 02 Jan 2020; Accepted 19 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: By using an effective transfer function, one can describe conveniently the nonlinear mapping between an input thintransparent structure, and its image irradiance distribution. This effective transfer function is useful for makingsound comparisons between several spatial filters, employed for phase rendering. Here, we unveil threenonconventional Schlieren techniques, which employs absorption masks whose amplitude distributions aredescribed by: square root monomials, or by sigmoidal functions, or by off-axis Gaussian functions. We apply theeffective transfer function for analyzing the similarities between the proposed masks and other Schlierentechniques.

Optimization of a lightweight mirror with reduced sensitivity to mounts location

ping jiang and Pingwei Zhou

DOI: 10.1364/AO.383391 Received 20 Nov 2019; Accepted 18 Mar 2020; Posted 19 Mar 2020  View: PDF

Abstract: Due to the requirement on the optical performance, the primary mirror assembly must have the ability to beunaffected by environmental influences. These environmental influences include gravity, axial assembly error,flatness error of mounting interface and thermal change, under which the mirror surface accuracy is degraded. Theflexure mounts can be used to isolate the loads transfer to the mirror in case of flatness error and thermal change.The mirror surface accuracy will degenerate significantly when the flexure mounts have deviations from theoptimum axial mount location due to mirror fabrication and the testing error of the center of gravity. These twoerror terms introduce an accuracy of mount locations on the order of millimeters. In this paper, we describe amethod to reduce the sensitivity of lightweight mirror to mounts location. Firstly, we introduce a design criterionthat determine the sensitivity. Then, the topology and parametric optimization are used to specify selectivereinforcement of the mirror structure in which the design criterion is taken as the objective function. With ourmethod, the lightweight ratio of a 2 m mirror has been improved from 86.8% to 88.5%, and the sensitivity tomounts location has been reduced from 1nm/±1mm to 0.6nm/±1mm.

Measurement of the adjustable slightroughness emulated by spatial lightmodulator employing the vortex beam specklepattern

Can Cui, Zhi Wang, Xiangkong Zhan, Jian Wang, lanlan LIU, Zhi-Yong Li, and Chongqing Wu

DOI: 10.1364/AO.385176 Received 05 Dec 2019; Accepted 17 Mar 2020; Posted 26 Mar 2020  View: PDF

Abstract: : In this paper, we analyze the speckle patterns produced via the scattering of opticalvortex with different roughness surface comparing with that of Gaussian light, the roughnessof the surfaces is emulated by a spatial light modulator (SLM) and adjustable. The schemeand experiments demonstrate the improvement with the vortex beam especially for slightroughness measurement. In addition, since the topological charge, which is used to producespeckle patterns, has a great influence on speckle size and can be optimized to adjust thespeckle size for different object measurements, we also investigate the dependence of theroughness on the topological charge.

Design of reconfigurable broadband greyscalemultiplexed metasurface hologram

Tianhang Chen, jun li, Tong Cai, dashuang liao, Lijun Guo, YI RUAN, and Bin Zheng

DOI: 10.1364/AO.386811 Received 27 Dec 2019; Accepted 17 Mar 2020; Posted 17 Mar 2020  View: PDF

Abstract: Hologram is a promising state-of-the-art technique that is able to reproduce fully three-dimensional image.However, most elementary holograms only recover nonadjustable image restricted by a certain amplitude andphase. Recently, the concept of the reconfigurable metasurface has come into sight. The reconfigurablemetasurfaces can be tuned dynamically through physics control signal from outside. Here, we design and realize aseries of novel reconfigurable metasurfaces. Using these devices, an advanced metasurface hologram effect couldbe easier to achieve. Moreover, the reconfigurable property of such tunable metasurface enables independentcontrol of advanced multiplexed channel functionalities to be exist in comparison with the conventional staticmetasurface holograms. Our method creates unprecedented display and virtual effects, opens a novel way to moreflexible methodology of dynamically control of the electromagnetic waves.

Low-stray-light concave holographic gratingsprocessed by combining the methods of photoresisthot-melting and oxygen-ion ashing

HUI CHEN, Zhengni Ni, Yuanshen Huang, Banglian Xu, and Dawei Zhang

DOI: 10.1364/AO.386465 Received 19 Dec 2019; Accepted 17 Mar 2020; Posted 18 Mar 2020  View: PDF

Abstract: The principal motivation for this paper is to reduce stray light and line roughness in concave holographic gratings(CHG). Compared with other previously reported grating line-smoothing techniques such as dynamic exposurenear-field holography, we successfully improve the line smoothing of CHG to approximately 10 nm from 2 nmpreviously. The method that we use is the combination and optimization technologies of photoresist hot-melting(PHM) and oxygen-ion ashing (OIA), thereby improving the degree of stray light before and after optimization byone order of magnitude, the level processed by OIA, PHM and OIA successively is 7.85 × 10-5. Combining the twotechnologies, we achieve lower stray light and straighter groove lines for the concave gratings, which is moreeffective, easy to implement, and incurs a low cost.

Determination of 1-propanol, ethanol and methanolconcentrations in water based on 1D phoxonic crystalsensor

Samar Shaban, Ahmed Mehaney, and Arafa H Aly

DOI: 10.1364/AO.388763 Received 21 Jan 2020; Accepted 17 Mar 2020; Posted 18 Mar 2020  View: PDF

Abstract: In this research, the photonic and phononic response of 1D multilayer phoxonic crystal (1D- PxCs) with normal incident ofelectromagnetic and acoustic waves is discussed. The presented design can work as high-sensitive sensor for measuring threebinary alcohol/water mixtures (i.e. 1-propanol/water, ethanol/water and methanol/water) for a wide range of concentrations.The PxC sensor is able to detect small changes in the refractive index and longitudinal sound velocity of the alcohol/watermixture with initially neglecting the acousto-optical interaction. The sensor design is a defective structure as [(Si/SiO2)4(Mixturewt%) (SiO2/Si)4]. Also, we studied the effects of changing mixture concentrations from 0 wt% to 100 wt% on the physio-chemicalparameters and resonant mode frequency. In our results, we have achieved high performance for the three alcohol mixtures inboth phononic and photonic sensors especially for low concentrations. For example, in the PhC sensor we obtained sensitivity, Qvalue and figure of merit of the values 873 nm/RIU, 755 and 290 RIU-1, respectively, for methanol of concentration 10% in water.The phononic sensor showed higher results compared with the photonic sensor, as for ethanol with concentration 26.8 % inwater we obtained sensitivity, Q-value and figure of merit of the values 37 MHz/ms-1, 1604 and 8.4 (m/s)-1, respectively. Theproposed structure has different merits; operation at high temperatures, compact size, eases of fabrication and feasibility ofalcohol detection with two different methods which could be used in many chemical applications.

Narrow linewidth distributed feedback Moiré-gratinglaser for high-speed optical communications

Yingming Zhao, Yu Li, and Wei Ping Huang

DOI: 10.1364/AO.389583 Received 03 Feb 2020; Accepted 17 Mar 2020; Posted 18 Mar 2020  View: PDF

Abstract: A time-domain traveling wave model is described to simulate the novel distributed feedback Moirégrating laser (DFM), which can suppress the longitudinal spatial hole burning effect (LSHB) and improve thespectral linewidth for high-speed optical communications. The longitudinal photon distribution, linewidth anddynamic modulation characteristics of the DFM lasers are calculated and compared with the state of art DFB lasers.We found that the DFM laser can also improve the light-current (L-I) slope efficiency and modulation bandwidth byintroducing multiple π-phase shifts at Moiré envelope index changes while suppressing the LSHB effectively.

Optical characterization of high numericalaperture microlenses for quality assessmentand fabrication process optimization

Jeremy Béguelin, Michail Symeonidis, Wilfried Noell, Reinhard Voelkel, and Toralf Scharf

DOI: 10.1364/AO.387346 Received 28 Jan 2020; Accepted 16 Mar 2020; Posted 17 Mar 2020  View: PDF

Abstract: An accurate characterization of high numerical aperture aspheric microlensesis a non standard procedure and remains an open challenge. Here, we present and discussa characterization method based on interferometric and point spread function measurementsperformed in transmission by a high resolution interferometric microscope. In particular, weshow that a single phase measurement performed under fixed testing conditions can be processedin a simple way that yields wavefront aberration as well as surface topography for plano-convexmicrolenses with arbitrary asphericity. Consequently, this approach allows, at the same time andwithout heavy modification of the testing setup, both fabrication process optimization and opticalquality testing for microlenses with different optical functions. As an illustration, we present thecase of a microlens with a numerical aperture of ∼ 0.4.

Improving the transmission efficiency of theCassegrain optical system for Bessel Gaussian beam

Renxuan Liu, Yang Huajun, Ping Jiang, Yan Qin, Wei Caiyang, Biao Cao, miaofang zhou, and Qian Mao

DOI: 10.1364/AO.388121 Received 15 Jan 2020; Accepted 16 Mar 2020; Posted 17 Mar 2020  View: PDF

Abstract: With the improvement of the transmission efficiency, the Cassegrain antenna canbe widely used in space optical communication. In this paper, the Bessel-Gaussian (BG)beam is used to avoid the central energy loss of a Cassegrain antenna system. The intensitydistribution and the phase distribution of the BG beam passing through a Cassegrain antennaare theoretically derived and simulated. At a wavelength of 1550 nm, this method cantheoretically improve the transmission efficiency to approach 100% under the situation ofobscuration ratio is nonzero, and the transmission efficiency can reach more than 80% whenobscuration ratio is in the range of from 0 to 0.1252 with l=4. The effects of on-axialdefocusing on the light field and the transmission efficiency are studied. The methodproposed in this paper can remarkably improve the transmission efficiency of a Cassegrainantenna in a practical and uncomplicated approach.

Long-wave infrared absorption measurementof undoped germanium using photothermalcommon-path interferometry

Yu-Jen Lee, Avijit Das, Merlin Mah, and Joseph Talghader

DOI: 10.1364/AO.390374 Received 11 Feb 2020; Accepted 16 Mar 2020; Posted 17 Mar 2020  View: PDF

Abstract: Germanium is one of the most commonly used materials in the longwave infrared(λ ~ 8–12 μm), but ironically, its absorption coefficient is poorly known in this range. Aninfrared photothermal common path interferometry system with a tunable quantum cascadepump laser is used to measure the absorption coefficient of >99.999% pure undopedgermanium as a function of wavelengths between 9 and 11 μm, varying between about 0.15cm-1 and 0.45 cm-1 over this range.

Design and Development of Volume PhaseHolographic Grating based Digital HolographicInterferometer for Label-Free Quantitative CellImaging

Vivek Rastogi, Shilpi Agarwal, Satish Dubey, Gufran Khan, and Chandra Shakher

DOI: 10.1364/AO.387620 Received 09 Jan 2020; Accepted 15 Mar 2020; Posted 17 Mar 2020  View: PDF

Abstract: In this paper, a volume phase holographic optical element based digital holographic interferometer is designedand used for quantitative phase imaging of biological cells (white blood cells, red blood cells, platelets, andStaphylococcus aureus (S. aureus) bacteria cells). The experimental results reveal that sharp images of the S. aureusbacteria cells of the order of ~1 µm can be clearly seen. Volume phase holographic grating will remove the straylight from the system reaching towards the grating and will minimize the coherent noise (speckle noise). This willimprove the sharpness in the image reconstructed from the recorded digital hologram.

Charged Particle Radiation Induced Changes to OpticalProperties of Acousto-Optic Materials

Barrett Taylor, Adam Bourassa, and Michael Bradley

DOI: 10.1364/AO.387947 Received 29 Jan 2020; Accepted 15 Mar 2020; Posted 17 Mar 2020  View: PDF

Abstract: We report on the measurement of the transmittance and reflectance of unpolarized light (425 - 700 nm) inthree birefringent, acousto-optic materials, including quartz, lithium niobate, and tellurium dioxide, afterexposure to varying fluences of proton radiation (1014- 1018 protons/cm2) delivered by a 10 keV hydrogenion beamline. We observe a general monotonic decrease of transmittance with increasing fluence for allthree materials, but with varying rates of change and critical points of change. Reflectance measurementsalso exhibit a general monotonic trend with fluence, but increases in quartz are observed versus decreasesin both lithium niobate and tellurium dioxide. These observations are used to assess the suitability ofthe materials for acousto-optic applications in the space environment where charged particles from thesolar wind are dominant and pose a threat to device operation. Our measurements agree with previouslyreported work concluding that tellurium dioxide is suitable for space applications at low fluences (below1016 ions/cm2), but our findings also raise previously unreported concerns for higher accumulated fluencesobserved for longer mission lifetimes of greater than 5-10 years in space in an unshielded configuration.

The phase information extraction for moiré fringe based onmulti-resolution analysis (MRA)

Yunyun Chen, Meng Xu, Wei-hao Cheng, and Fang Gu

DOI: 10.1364/AO.384679 Received 29 Nov 2019; Accepted 14 Mar 2020; Posted 17 Mar 2020  View: PDF

Abstract: In this paper, the multi-resolution analysis (MRA) method is used to preprocessmoiré fringes, which can reduce the number of data points and increase the computation speed.To discuss the applicability of the method, a candle combustion flow field is chosen as anexample for experiment by moiré deflectometry. First of all, moiré fringes are preprocessedby MRA method. And then, phase information extraction and refractive index reconstructionare performed on the three-level low-frequency approximation components. Finally, theinvolved results prove that the calculation time required for phase information extraction andrefractive index reconstruction is greatly reduced based on the moiré fringes are preprocessedby MRA method. And, the relative error could be accepted if the suitable approximation level is applied.

Weld quality inspection of small-diameter thin-walled pipes by laser ultrasonic method

Jiujian Liu, Xuehan Feng, Anmin YIN, Liping Cheng, Li Fan, xiaodong Xu, and Shuyi Zhang

DOI: 10.1364/AO.387293 Received 02 Jan 2020; Accepted 14 Mar 2020; Posted 17 Mar 2020  View: PDF

Abstract: Defect inspection of small-diameter thin-walled pipes is a difficult problem in the field of non-destructive testing. In this paper, a new detection method based on laser ultrasonics and guided circumferential waves technology is proposed and used to inspect the defect in pipes. Firstly, a theoretical model based on the theory of acoustic propagation in solids is proposed for the small-diameter thin-walled pipes. The dispersion characteristics of the guided circumferential waves of thin-walled pipes are obtained by numerical simulation. Secondly, a laser ultrasonic system was constructed and used to detect the flaw in the small-diameter thin-walled pipes. Finally, the laser ultrasonic system is used to analyze the welding quality of stainless steel pipes with a diameter of 4.20 mm and a wall thickness of 0.30 mm. The experimental results are in agreement with the theoretical analysis, which demonstrates the reliability and practicability of the laser ultrasonic method in the weld quality inspection of small-diameter thin-walled pipes.

Dispersion engineering for optimizing scattering, emission and radition properties

Mauro Cuevas, Ricardo Depine, and Marcelo Gingins

DOI: 10.1364/AO.385414 Received 10 Dec 2019; Accepted 13 Mar 2020; Posted 13 Mar 2020  View: PDF

Abstract: We present a dispersion engineering method based onthe rigorous electromagnetic theory to study the scatteringproperties of a double graphene layer spherical structure.The localized surface plasmons (LSPs) supported bythe structure provide resonance channels which leadto an enhancement of the electromagnetic cross section.The method is used to find conditions under which two different multipolar LSP resonances occur at the same frequency value. Thesuperscattering feature under these conditions is revealed by an extraordinary enhancement of the scattering cross section when the structure is illuminated by a plane wave field. Moreover,by studying the behavior of a single emitter localized near thegraphene sphere, we show that the spontaneous emission and the radiation efficiency are also largely enhanced when the two different LSP resonances overlap.

Configuration design for the variable pupilshaping unit of a photolithography machine

Youbao Zhang, Xiaozhe Ma, Fang Zhang, and Huijie Huang

DOI: 10.1364/AO.385352 Received 09 Dec 2019; Accepted 13 Mar 2020; Posted 17 Mar 2020  View: PDF

Abstract: This work provides an integrated design and simulation method for a pupilshaping unit, which combines optical design and simulation software using the Pythonprogramming language. The novel approach presented here allows for systematicoptimization and solves the inverse problem to obtain the configuration of a pupil shapingunit with given partial coherence factors (sigmas). The relationships among sigma, focallength, zoom lens separation, axicon separation, and ring width are investigated forconventional and annular illumination modes. Results of the pupil shaping unit for aNA0.75 193-nm photolithography machine are presented, and a new interpolation tabledesign method that simplifies the original method is proposed. The maximum residualexperimental error for sigma is 0.01106.

Broadband and low crosstalk silicon on-chip modeconverter and demultiplexer for mode divisionmultiplexing

Devendra Chack, Shamsul Hassan, and MOHD QASIM

DOI: 10.1364/AO.390085 Received 07 Feb 2020; Accepted 13 Mar 2020; Posted 17 Mar 2020  View: PDF

Abstract: In this paper, a compact and broadband mode converter and demultiplexer based on multimode interference(MMI) is designed and experimentally demonstrated on silicon on insulator. We have designed a mode converterusing cascaded MMI to convert fundamental mode into higher-order (first-order mode) and vice-versa.Subsequently, we have demonstrated an on-chip two-mode demultiplexer with a compact footprint and low loss.The proposed mode demultiplexer shows low insertion loss (0.22 dB for TE0 and 0.36 dB for TE1 mode) andcrosstalk (–25.2 dB for TE0 and –24.4 dB for TE1 mode) at wavelength 1550 nm using Eigenmode expansionmethod. Moreover, the device supports a broad bandwidth having crosstalk < – 20 dB over a wavelength range of1520 – 1580 nm. The proposed device can be used in mode division multiplexing for photonic network-on-chip.

Development of a Position-Velocity-Time modulatedtwo dimensional ion beam figuring system forsynchrotron X-ray mirrors fabrication

Tianyi Wang, Lei Huang, Yi Zhu, Matthew Vescovi, Dennis Kuhne, Hyukmo Kang, Heejoo Choi, Dae Wook Kim, Kashmira Tayabaly, Nathalie Bouet, and Mourad Idir

DOI: 10.1364/AO.389010 Received 07 Feb 2020; Accepted 12 Mar 2020; Posted 12 Mar 2020  View: PDF

Abstract: With the rapid evolution of synchrotron X-ray sources, the demand for high-quality precision X-ray mirrors has greatly increased. Single nanometer shape accuracy is required to keep imaging capabilities atthe diffraction limit. Ion Beam Figuring (IBF) has been frequently used for ultra-precision finishing ofmirrors, but achieving the ultimate accuracy depends on three important points: careful alignment, accurate dwell time calculation and implementation, and accurate optical metrology. The Optical MetrologyGroup at National Synchrotron Light Source II (NSLS-II) has designed and built a Position-Velocity-Timemodulated two dimensional IBF system (PVT-IBF) with three novel characteristics: 1) a beam footprinton the mirror was used as a reference to align the coordinate systems between the metrology and the IBFhardware. 2) The Robust Iterative Fourier Transform-based dwell time Algorithm (RIFTA) proposed byour group was applied to obtain an accurate dwell time map. 3) The dwell time was then transformedto velocities and implemented with the Position-Velocity-Time (PVT) motion scheme. In this study, thetechnical aspects of the PVT-IBF systems are described in details, followed by a experimental demonstration of the figuring results. In our first experiment, the 2D RMS in a 50 mm × 5 mm clear aperture wasreduced from 3.4 nm to 1.1 nm after one IBF run. In our second experiment, thanks to a 5 mm pinholeinstalled in front of the source, the 2D RMS in a 50 mm × 5 mm clear aperture was reduced from 39.1 nmto 1.9 nm after three IBF runs, demonstrating that our PVT-IBF solution is an effective and deterministicfiguring process.

Propagation of twisted EM GaussianSchell-model array beams in anisotropicturbulence

Miaomiao Tang, Hehe Li, and Xinzhong Li

DOI: 10.1364/AO.389577 Received 03 Feb 2020; Accepted 12 Mar 2020; Posted 12 Mar 2020  View: PDF

Abstract: The behavior of the twisted EM Gaussian Schell-model array beams in anisotropicrandom turbulence is investigated. An example illustrates that a twisted EM source canproduce lattice-like patterns in degree of polarization with rotation or not, which depends onthe setting of the initial twist phase. One also finds that the anisotropy of the medium leads toan anisotropic beam spreading, and we can effectively limit such turbulence-induced effect byoptimizing the initial twist and source correlation widths. Moreover, after transmittingthrough the turbulence for sufficiently long distances, the intensity and coherence are mainlyaffected by turbulence statistics, however, for the case of polarization, the initial twist plays adominate role for determining its distribution profile.

An Exact Frequency Domain Method for theAnalysis of Scattering from Multilayer Bianisotropic Cylindrical Structures

Noushin vaseghi and Mohammad sadegh Abrishamian

DOI: 10.1364/AO.388258 Received 21 Jan 2020; Accepted 12 Mar 2020; Posted 13 Mar 2020  View: PDF

Abstract: Bi-anisotropic materials have enormous and interesting applications in electromagnetic (EM) engineering. Inthis study, based on the state space concept, an exact and rigorous analysis of EM propagation and scattering frommultilayer bi-anisotropic cylindrical structures of general case is proposed. In comparison to the other commonly usedmethods in the literature, the presented method reveals faster and more accurate analytical framework. The similarworks mostly presented approximated and numerical methods for the analysis of cylindrical structures containing biisotropic and/or anisotropic materials as special bi-anisotropic cases. Throughout the study, the geometrical specificationsand the EM excitations are chosen based on practical considerations. Since the multilayer composite is practical especiallyfor the realization of the inhomogeneous material, the proposed approach is applied to analyze inhomogeneous bianisotropic cylindrical structures with more degrees of freedom in manipulation of EM waves. Our results depict anexcellent conformity to the other possible solutions to compute scattering from bi-anisotropic cylindrical configurations.The mentioned comprehensiveness is one of the main advantages of our work. The suggested approach can be used as abasic step for future researches related to the analysis of forward and inverse scattering problems of practical types ofcylindrical structures made by complex media..

Pixel super-resolved lensfree on-chip microscopybased on dual laterally shifting modulation

He Zhang, Weibo Wang, Liu Chenguang, and Jian Liu

DOI: 10.1364/AO.387428 Received 06 Jan 2020; Accepted 11 Mar 2020; Posted 12 Mar 2020  View: PDF

Abstract: Achieving high spatial resolution over a wide field of view (FOV) is the goal of many imaging systems. In atraditional lens-based microscope, designing a complex objective with high numerical aperture (NA) to achieve thisgoal is a tough and challenging task. The lensfree wide-field imaging method based on phase retrieval provides anew way to bypass the trade-off between the spatial resolution and FOV of conventional microscopy. However, thetypical lensfree microscopy usually requires mechanical devices with high precision and repeatability. In thispaper, we report a robust and cost-effective pixel super-resolved lensfree imaging method based on dual laterallyshifting modulation. A thin diffuser is inserted between the object and the image sensor to be used as themodulator. The diffuser and the object are transversely scanned at the same time to add diversities for phaseretrieval and pixel super-resolution, respectively. In this way, the positional shifts of both the diffuser and theobject can be directly recovered with registration algorithm, addressing the low stability and inaccuracy issues oftranslation stages. We also propose a pixel super-resolution phase retrieval algorithm to recover the object and theunknown diffuser. We first use numerical simulations to evaluate the proposed scheme. Then we validate thisapproach by imaging a resolution target and a pollen sample, achieving a FOV of ~30 mm2 and a half-pitchresolution of 0.78μm, which surpasses 2.14 times of the theoretical Nyquist-Shannon sampling resolution limit.Finally, the 3D refocusing ability is also verified by imaging a thick mosquito sample.

Width determination for deep grooves based on avariable point spread function imaging model

Xiaoyu You, Yuhang Wang, Richard Leach, Kang Gu, Yushu Shi, Shu Zhang, and Jian Liu

DOI: 10.1364/AO.388279 Received 15 Jan 2020; Accepted 11 Mar 2020; Posted 12 Mar 2020  View: PDF

Abstract: In three-dimensional confocal microscopy, two-dimensional width measurement can be significantly influenced bythe groove height. The groove height not only results in deformation of the input light field due to the effect of edgeocclusions, but also introduces a defocus error to the detection plane. This paper proposes a new edge-settingmethod to determine groove width, which engineers the point spread function to correct for the groove edgeobstruction effect and develops an edge obstruction imaging model (EOIM) based on the variable point spreadfunction. This model gives a relationship between the groove height and the normalized intensity at the grooveedge and can use this relationship to determine the groove edge position that would result from focusing at thegroove’s lower surface. Experimental results show that EOIM-based width determination method is more accuratethan the traditional 1/4 edge-setting method. Compared to the 1/4 edge-setting method, the deviation from areference width measured with traceable scanning electron microscopy is reduced by a factor of 2.1 with a 1.3times smaller standard deviation.

Specular signal return through a range-compensating lens

Jason Mudge

DOI: 10.1364/AO.389184 Received 27 Jan 2020; Accepted 10 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: A range-compensating lens has been developed which alleviates, to a certain degree, the oneover-range-squared attenuation in the signal (laser) return for active optical systems [Mudge,Appl. Opt., 58(28), 7921-7928, (2019)]. This compensation applies to the diffuse return and,in particular, the perfectly diffuse return which is an assumption used to develop theequations. However, there is another component of the return which is equally important andthat is the specular signal return. Often this return is a result of a very shiny and close targetsince the return needs to closely follow the outgoing beam path in order for the light to bereturned to the detector. This implies a high sensitivity to target orientation. For this reason,specular returns are not counted on as a signal return, and the sensor is generally not designed 2to use this type of return which can lead to an undesired detector saturation should a highreflectivity specular return occur. This return, with respect to a range-compensation lens, wasonly discussed briefly and qualitatively. The work here means to address this specular signalreturn quantitatively as it applies to a range-compensating lens as compared to that of atraditional lens and considers the specular performance on the sensor-level.

Harmonic analysis and reduction of thescattered field from electrically large cloakedmetallic cylinders

Barbara Cappello and Ladislau Matekovits

DOI: 10.1364/AO.387246 Received 02 Jan 2020; Accepted 10 Mar 2020; Posted 11 Mar 2020  View: PDF

Abstract: In this paper an analysis of the spectral composition of the scattered field fromcoated metallic cylinders is performed, focusing particularly on the cloaking of electrically largestructures. An expression of the scattering coefficients is derived considering both a dielectric anda metasurface coating. Modelling the metasurface as a surface impedance boundary condition,the surface impedance which annuls one harmonic of the scattered field is formulated in aclosed and compact form. Moreover, in the case of cylinders with radius comparable with thewavelength of interest, it is demonstrated that a reduction of the scattering is possible by using ahomogeneous metasurface coating which presents a positive surface reactance. In particular, areduction of the scattering width of 4 dB is achieved for a cylinder radius a = 0.917λ0.

Switchable generation of sub-200 fs dissipative solitonand noise-like pulse in normal dispersion Tm-dopedmode-locked Fiber Laser

Yiwu Zhao, Desheng Zhao, Runmin Liu, Wanzhuo Ma, and Tianshu Wang

DOI: 10.1364/AO.389594 Received 04 Feb 2020; Accepted 10 Mar 2020; Posted 11 Mar 2020  View: PDF

Abstract: We report on the switchable generation of dissipative soliton (DS) pulse and noise-like pulse (NLP) in an allfiberized Tm-doped fiber laser under normal dispersion region. The mode-locking operation is achieved throughnonlinear polarization rotation (NPR) component and the cavity dispersion is compensated by using ultra-highnumerical aperture (UHNA4) fiber that is ease of integration and low cost. At a pump threshold of 510 mW, DSoperation can first achieve without additional filter. The 3-dB spectrum bandwidth of DS pulse is greater than 50nm and the duration of de-chirped pulse is 193 fs. By increasing the pump power to 880 mW, the mode-lockingstate can evolve into NLP operation with properly cavity polarization state. The 3-dB spectrum bandwidth andduration of de-chirped coherence spike are 105.6 nm and 121 fs, respectively. Meanwhile, ultra-broadband NLP(over 150 nm considering 3-dB spectrum width) can also be observed with appropriate cavity parameters. All theproposed pulse patterns present good capacities of achieving narrow pulse width and withstanding high pulseenergy.

Feasibility of multimodal multi-photonmicroscopy to facilitate surgical marginassessment in pancreatic cancer

Thu Pham, Bhaskar Banerjee, Benjamin Cromey, Soroush Mehravar, Bethany Skovan, Hao Chen, and Khanh Kieu

DOI: 10.1364/AO.391315 Received 02 Mar 2020; Accepted 10 Mar 2020; Posted 13 Mar 2020  View: PDF

Abstract: Pancreatic cancer is a common cancer with poor odds of survival with surgicalresection offering the only hope of cure. Current surgical practice is time consuming and doesnot sample the whole cut surface to check for remaining cancer sufficiently due to timeconstraints. Although microscopy with hematoxylin and eosin (H&E) stain is the goldstandard for microscopic evaluation, multi-photon microscopy (MPM) has emerged as analternative tool for imaging tissue architecture and cellular morphology without labels. Weexplored the use of multimodal MPM for the label-free identification of normal andcancerous tissue of the pancreas in a mouse model by comparing the images to H&Emicroscopy. Our early studies indicate that MPM using second harmonic generation, thirdharmonic generation and multiphoton excitation of endogenous fluorescent proteins can eachcontribute to the label-free analysis of the pancreatic surgical margin.

All-optical 3R regeneration for DPSK signal based on SOA scheme

Yaya Mao, Bo Liu, Delin Zhao, Tingting Sun, lilong zhao, Rahat Ullah, and Yongfeng Wu

DOI: 10.1364/AO.389952 Received 27 Feb 2020; Accepted 09 Mar 2020; Posted 11 Mar 2020  View: PDF

Abstract: This paper presents experimental demonstration of an all-optical 3R (re-amplification, re-shaping, re-timing)regeneration scheme for differential phase shift keying (DPSK) signal, which consists of a clock recovery moduleand a phase regeneration module. The clock recovery module is based on a mode-locked fiber laser and the opticalclock is extracted with low timing jitter of 29 ps from a degraded 10 Gb/s DPSK signal. The phase regeneratorconsists of a one-bit delay interferometer (DI) demodulation stage and a semiconductor optical amplifier (SOA) inwhich cross-phase modulation (XPM) and nonlinear polarization rotation (NPR) occur simultaneously. The resultsshow that after 3R regeneration, the receiver sensitivity is improved by more than 1.6 dB for a bit error rate (BER)of 1E-9.

Tunable mode-locked erbium-doped fiberlaser based on digital micro-mirror device

Wenhao Wang, Meng Tian, Yang Yan, Yanhua Huang, Cong Li, Guoliang Chen, and Min Lv

DOI: 10.1364/AO.388878 Received 22 Jan 2020; Accepted 09 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: A tunable mode-locked erbium-doped fiber laser (EDFL) with digital micro-mirrordevice (DMD) as the wavelength tuner and nonlinear amplifying loop mirror (NALM) as themode-locked device is proposed and experimentally demonstrated. The mode-locked pulsewith the center wavelength of 1538 nm - 1565 nm continuously tunable is achieved. Theaverage power of the output pulse is 1.028 mW, the pulse repetition frequency is 1.7 MHz,the pulse duration is 616 fs and the single pulse energy is 0.6 nJ. By controlling the DMD, thecenter wavelength can be fine-tuned with the tuning accuracy of 0.07 nm. With the increaseof the pump power, the traditional soliton pulse is transformed into noise-like pulse (NLP),and the power of NLP can reach 34 mW. This mode-locked process can work for a long timeand is almost unaffected by the external environment. These results are very useful forapplications where pulsed lasers with different wavelengths are needed.

Micro mirror array allocation algorithm basedon deconvolution

Zhifan Liu, Chaoxing Yang, Yang Bu, Si Li, Zhang Jianhua, Xiangzhao Wang, and Gang Sun

DOI: 10.1364/AO.389891 Received 06 Feb 2020; Accepted 09 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: Freeform illumination is one of the necessary techniques in 28nm technology nodeand beyond. The micro mirror array has been widely used in lithography freeformillumination system due to its programmability and high free degree. The micro mirror arrayallocation algorithm is the key to generate the target freeform illumination source. Itscomputational speed and precision affect the generation speed and precision of targetillumination source, as well as the process window size of the generated illumination pupildirectly. In this paper, a micro mirror array allocation method based on deconvolution isproposed. The target freeform illumination source can be obtained directly with thedeconvolution and quantization processes. As without the iterative optimization process, thecomputational speed of the proposed method is much faster than that of the traditional method.The numerical simulation results show that, the difference between the target source and theMMA source generated by using the proposed method is less than 0.2%. Compared with theprocess window loss of the target source, the process window loss of the MMA sourcegenerated by the proposed deconvolution method is less than 0.5%. Compared with thetraditional allocation method, the runtime of the proposed method is less than 0.05 second andhas improved by 1463 times.

Deep ghost phase imaging

Koshi Komuro, Takanori Nomura, and George Barbastathis

DOI: 10.1364/AO.390256 Received 11 Feb 2020; Accepted 09 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: Deep-learning-based single-pixel phase imaging is proposed. The method, termed deep ghost phaseimaging (DGPI), succeeds the advantages of computational ghost imaging, i.e. has the phase imagingquality with high signal-to-noise ratio derived from the Fellgett’s multiplex advantage and the point-likedetection of diffracted light from objects. A deep convolutional neural network is learned to outputa desired phase distribution from an input of a defocused intensity distribution reconstructed by thesingle-pixel imaging theory. Compared with the conventional interferometric and transport-of-intensityapproaches to single-pixel phase imaging, the DGPI requires neither additional intensity measurementsnor explicit approximations. The effects of defocus distance and light level are investigated by numericalsimulation, and an optical experiment confirms the feasibility of the DGPI.

Recommended optic system design for the SSST

Hao Tan and Donglin Ma

DOI: 10.1364/AO.387948 Received 10 Jan 2020; Accepted 09 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: The Southern Spectroscopic Survey Telescope (SSST) is a planned multi-wavelength space survey telescope by China located in Chile. In this paper, we present a feasible optical system design based on wide-field Cassegrain corrector configuration for the SSST of China. Our recommended design has a large field of view (FOV) of 2.4° × 2.4° with its image spot size less than 0.3 arc second in diameter for its full FOV in 80% encircled energy (EE80). The atmospheric dispersion effect and actual science requirements are taken into consideration. In addition, a trade-off study is presented. This paper can also provide a reference to the next generation of spectroscopic survey telescopes.

Density Functional Theory Study of Mixed HalideInfluence on Structures and OptoelectronicAttributes of CsPb(I/Br)3

Ahmed Jbara, Junaid Munir, Bakhtiar Ul Haq, and m. a. Saeed

DOI: 10.1364/AO.389100 Received 24 Jan 2020; Accepted 09 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: This paper reports the influence of the Bromine (Br) atoms substitution on thestructures and optoelectronic traits of CsPbI3 wherein the DFT simulation was performedusing all electrons full-potential linearized augmented plane wave method. Furthermore, theGGA, LDA, and modified Becke-Johnson exchange-correlation potential were used toimprove the optimization and band structure calculations. The calculated lattice constants ofCsPbI3 and CsPbBr3 were consistent with the experimental values. All the studied compoundsrevealed wide and direct bandgap energies at the R-symmetry point that varied from 1.74 -2. eV. The obtained refractive indices of the CsPbI3, CsPbBrI2, CsPbIBr2, and CsPbBr3compounds were correspondingly 2.265, 2.245, 2.090, and 2.086. Present findings maycontribute towards the development of experimental studies on the proposed compounds withcontrolled properties useful for the solar cells.

Three-Dimensional Measurement of Particle FieldUsing Phase Retrieval Digital Holography

Hangjian Ling

DOI: 10.1364/AO.389554 Received 31 Jan 2020; Accepted 08 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: Digital Inline Holography (DIH) has long been used to measure the three-dimensional (3D) distributionof micrometer particles in suspensions. However, the DIH experiences virtual image problem whichlimits the particle density and the placement of hologram plane relative to the sample volume. Here, weapply the virtual-image-free Phase Retrieval Digital Holography (PRDH) to detect opaque particles in 3Dvolumes that exceed 2000 particles/mm3. The PRDH is based on recording two holograms whose planesare displaced along the optical axis, and then reconstructing the complete optical waves estimated by theiterative phase retrieval algorithm. Both numerical and experimental tests are performed, and resultsshow that the PRDH recovers the original 3D particle distributions even when the hologram planes arewithin the particle suspensions. Moreover, compared to the single-hologram based DIH, the PRDH isproved to have better particle detection qualities. The uncertainty in the localization of particle centers isreduced to less than one particle diameter.

Wide-Field Optical Design for a Sixty MeterSubmillimeter Telescope

Zheng Lou, Yingxi Zuo, Qijun Yao, Sheng-Cai Shi, Ji Yang, and Xue-Peng Chen

DOI: 10.1364/AO.388320 Received 16 Jan 2020; Accepted 08 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: We present a practical wide-field optical design for a sixty meter aperture submillimeter telescope, which iscurrently under conceptual design study in China. The telescope is specified to operate over a wavelength range of0.65~3mm and provide a wide field of view (FOV) of 1 degree in diameter. We designed an F/6 RC system with aquasi-planar tertiary corrector, which cancels all spherical, coma, and astigmatism aberrations. It also achieves agood balance between the mirror sizes, central obscuration, and focal-plane curvature. The problems of focalsurface curvature and non-telecentricity are treated in the sub-field instrumental design, which employs a simplesilicon wedge prism to obtain a flat and telecentric focal planes for each sub-field instrument module. Our studiesshow that by such a design, more than 105 detector pixels can be efficiently and uniformly fed at the shortestwavelength band with Strehl ratios above 0.85 across the entire 1o FOV. Several practical issues related to thetelescope optics are also discussed.

Study of linear and nonlinear temperature dependenttransmission/absorption characteristics of Cadmium Telluridecrystal for terahertz generation

Archana Kumari, Anil Chaudhary, and Mottamchetty Venkatesh

DOI: 10.1364/AO.366208 Received 01 Dec 2019; Accepted 07 Mar 2020; Posted 09 Mar 2020  View: PDF

Abstract: The paper reports the temperature dependentinvestigation of linear and nonlinear transmission/absorption characteristics of CdTe crystal between 300-408 K range using 780-970 nm tunable wavelengths of 140fs pulses obtained from Ti: sapphire laser at 80 MHzrepetition rate. The same pulses were also used for THzgeneration. The linear transmission/absorption propertieswere measured using specially improvised temperaturetuned spectrophotometer between 500-1500 nmwavelength range. The linear absorption of 750 nmwavelength gradually increases with respect to rise in thetemperature and transmission becomes zero at 408K,whereas nonlinear absorption induced by femtosecondspulses shows sudden drop of 18% in transmission above800 nm range is due to electron-phonon interaction whichaffects the strength of THz signal. It is also responsible forchange in the temperature along with the linear shift in therefractive index of the crystal.

Impact of coherence length on the field of view indark-field holographic microscopy for semiconductormetrology: theoretical & experimental comparisons

Christos Messinis, Vasco Tenner, Johannes de Boer, Stefan Witte, and Arie den Boef

DOI: 10.1364/AO.379236 Received 30 Sep 2019; Accepted 07 Mar 2020; Posted 09 Mar 2020  View: PDF

Abstract: Semiconductor manufacturers continue to increase the component densities on computer chips by reducing thedevice dimensions to less than 10 nm. This trend requires faster, more precise and more robust optical metrologytools that contain complex and high-precision optics with challenging imaging requirements. Here, we presentdark-field Digital Holographic Microscopy as a promising optical metrology technique that uses optics withacceptable complexity. A theoretical analysis and an experimental demonstration of this technique is presented,showing the impact of the coherence length of the light source on the Field-of-View. Finally, we also present thefirst holographically obtained images of metrology targets.

ffective Fresnel diffraction field extension ofdiffractive optical elements with plane wave incident

Zhe Kong, Ning Xu, Huan Xiao, and Qiaofeng Tan

DOI: 10.1364/AO.387646 Received 13 Jan 2020; Accepted 07 Mar 2020; Posted 09 Mar 2020  View: PDF

Abstract: Diffractive optical elements (DOEs) are widely used to realize special diffraction fields nowadays, but the sizeof the effective Fresnel diffraction field of the DOEs with plane wave incident is limited by the wavelength ofthe incident beam, the sampling interval of the DOE and the distance between the DOE and the output plane.In this paper, a method is proposed to extend the size of the effective Fresnel diffraction field with anintroduced intermediate plane and two-step diffraction calculation. Zero padding is used on the DOE plane,the sampling interval on the intermediate plane is correspondingly decreased, and the size of the Fresneldiffraction field on the output plane is finally extended. The accompanied aliasing is eliminated by placing alow-pass filter on the intermediate plane. Both numerical simulations and experimental results show thevalidity of the proposed method to extend the size of the effective Fresnel diffraction field of the DOEs withplane wave incident.

Geometrical and physical optics analysis formm-wavelength refractor telescopes designed to mapthe cosmic microwave background

Jon Gudmundsson

DOI: 10.1364/AO.387842 Received 22 Jan 2020; Accepted 06 Mar 2020; Posted 09 Mar 2020  View: PDF

Abstract: We present a compact two-lens HDPE f/1.6 refractor design that is capable of supporting a 28-deg diffractionlimited field of view at 1-mm wavelengths and contrastit to a similar two-lens refractor using silicon lenses.We compare the optical properties of these two systems as predicted by both geometrical and physicaloptics. The presented analysis suggests that by relaxing telecentricity requirements, a plastic two-lensrefractor system can be made to have a surprisinglylarge field of view. Furthermore, this HDPE system isfound to perform comparably to a similar silicon system across a wide field of view and wavelengths up to1 mm. We show that for both telescope designs, coldstop spillover changes significantly across the field ofview in a way that is somewhat inconsistent with Gaussian beam formalism and simple f-number scaling. Wepresent results that highlight beam ellipticity dependence on both pixel location and pixel aperture size—an effect that is challenging to reproduce in standardgeometrical optics. We show that a silicon refractor design suffers from larger cross-polarization compared tothe HDPE design. Our results address the limitationsof solely relying on geometrical optics to assess relativeperformance of two optical systems. We discuss implications for future refractor designs.

Adjustable Panoramic Inspection System forSub-Millimeter Fasteners

Yung-Jhe Yan, Ming-Shiou Tsai, Wen-Bin Chen, You-Bo Chen, Ching-Cherng Sun, and Mang Ou-Yang

DOI: 10.1364/AO.386555 Received 24 Dec 2019; Accepted 06 Mar 2020; Posted 09 Mar 2020  View: PDF

Abstract: : Fasteners are critical and indispensable locking components in the mechanicalassembly. The sub-millimeter fasteners are massively and widely used in electronic devices.This study proposed an adjustable panoramic inspection system for M2 to M0.8 submillimeter fasteners. The system mainly consists of a panoramic imaging module, a backlightmodule, and an image grabbing and computing module. The panoramic imaging modulewould form four equal optical path lengths (OPLs) to keep the same imaging amplificationbetween the different directions of the field of view (FOV). The back-light module wasdesigned to provide uniform illumination and enhance the contrast of the pitch edge betweenfasteners and background. The image grabbing and computing module with a high speedcamera was designed as adjustable for different sizes of sub-millimeter fasteners. The realizedsystem can offer the function of four images in a one-shot to make a panoramic scene,independent illumination for recognizing, inspect screws possible from M0.8 to M2.0 screws,and short time consuming of image processing, such as 3.284 milliseconds for M0.8 screwand 2.384 milliseconds for M2.0 screw to achieve the speed of the examination of 6000pieces in one minute.

A single/dual-pulse repetition rate variablesupercontinuum light source with peak wavelengtharound 1.7 μm using a modulated pump

Xiaoyan Li, Peng Zhang, Di Wu, kexuan han, Shou Tong, and Huilin Jiang

DOI: 10.1364/AO.387225 Received 07 Jan 2020; Accepted 06 Mar 2020; Posted 09 Mar 2020  View: PDF

Abstract: A single/dual-pulse repetition rate variable supercontinuum (SC) light source witha peak wavelength around 1.7 μm (SLS around 1.7 μm) is proposed and experimentallydemonstrated. In our scheme, a 1.5 μm modulated pump source included a laser and anintensity modulator (IM). The pump source can generate pulse trains with different repetitionsand pulse durations. A 1 km high nonlinear fiber (HNLF) was used as the nonlinear gainmedium. A picosecond-pulsed SC signal was obtained by pumping the HNLF, and awavelength division multiplexer (WDM) was used for filtering residual pump. Additionally, aSagnac loop was applied to create a multi-wavelength pulse SC light source. The generatedSC source covered from 1.59 μm to 1.96 μm, and its peak wavelength was around 1.7 μm.The single/dual-pulse train can be produced and switched by adjusting the direct current (DC)bias and radio frequency (RF) driving voltages of the input signal to the IM. When therepetition rate of the generated pulse train was between 170 MHz and 2 GHz, the pulseduration of dual-pulse train was between 60 ps and 180 ps. Additionally, the duty cycle ofdual pulse operation was 40%. The single pulse SLS around 1.7μm can be a choice toimprove OCT performance, and the dual-pulse source will be a reference for laser drillingapplication.

High extinction ratio and low loss polarization beamsplitter based on multimode interference for PICs

Shamsul Hassan, Devendra Chack, and Varad Mahajan

DOI: 10.1364/AO.387418 Received 06 Jan 2020; Accepted 05 Mar 2020; Posted 06 Mar 2020  View: PDF

Abstract: A high extinction ratio polarization beam splitter (PBS) based on multimode interference (MMI) is proposed andexperimentally demonstrated on silicon on insulator. The PBS is designed using cascaded MMI to enhance theextinction ratio (ER) and minimize insertion loss (IL) as compared to conventional MMI structure. The proposeddevice has high extinction ratio (22.3 dB for TE and 25.6 dB for TM) and low insertion loss (0.7 dB for TE and 0.1 dBfor TM) at wavelength 1550 nm while the device supports broad bandwidth of 60 nm (ER > 16 dB) for bothpolarizations over wavelength 1520-1580 nm. Moreover, Eigen mode expansion method shows that the device haslarge fabrication tolerance of MMI width ± 40 nm and length ± 1500 nm. The proposed PBS can be used in on-chipsilicon photonic integrated circuits for polarization division multiplexing

Quantitative inspection of coatings thickness by flashpulse thermography and time-power transformationevaluation

Michal Svantner, Lukáš Muzika, and Šárka Houdková

DOI: 10.1364/AO.388440 Received 28 Jan 2020; Accepted 05 Mar 2020; Posted 06 Mar 2020  View: PDF

Abstract: Thermographic testing is an inspection method, which primarily indicates the presence of discontinuities in a testedsample. Its application to coatings can indicate a presence of local thickness variations; however, it mostly does not bring anyquantitative information about the thickness of the coatings. This contribution is focused on a quantification of the thermographicinspection, which would make possible an evaluation of coating thickness differences. A flash pulse thermographic testing wasapplied to thermally sprayed coatings. The importance of a precise synchronization of a flash-source and thermographic recordingwas determined. Different evaluation methods were analyzed and their comparison showed that a time-power transformationmethod is the most suitable for quantification of the inspection results.

Analysis of caustics of partially coherentlycombined truncated Gaussian beams

Jan Jabczynski and Przemyslaw Gontar

DOI: 10.1364/AO.389415 Received 30 Jan 2020; Accepted 05 Mar 2020; Posted 06 Mar 2020  View: PDF

Abstract: A theoretical model of the caustics of partially coherently combined beams CBCwas derived to model CBC in the case of truncated Gaussian beams. The model enables theanalysis of different lattice structures and partial coherence effects, including incoherentbeam combining (ICBC). The impacts of the coherence state, geometry of the array andtruncation losses were analyzed. An optimal truncation level of about 6% was found and amaximum CBC efficiency of 62% was determined for this CBC system. With an increase inthe beam numbers in the lattice, the relative caustics length decreases, which is consistentwith the general rules of diffraction theory.

Dual Polarized Highly Sensitive Surface PlasmonResonance based Chemical and Bio Molecular Sensor

Mohammad rakibul Islam, Nayem Iftekhar, Kazi Rakibul Hasan, Julkar Nayen, and Saimon Bin Islam

DOI: 10.1364/AO.383352 Received 15 Nov 2019; Accepted 03 Mar 2020; Posted 06 Mar 2020  View: PDF

Abstract: As the research work in surface plasmon resonance (SPR)-based Photonic Crystal Fiber (PCF) is getting tighter; aperfectly circular shaped PCF with elliptical air holes is proposed where the performance parameters are improvedsignificantly. Performances between our designed elliptical, circular and rectangular air holes are compared and thebest result is achieved for the elliptical air holes. The technique used for the investigation is Finite Element Method(FEM) and for the simulation of data COMSOL Multiphysics 5.3a software was used. The method covers a widerrange of optical spectrum from 0.59 ࣆm to 1.05 ࣆm. The highest confinement loss achieved through our design is 340dB/cm. The wavelength sensitivity and amplitude sensitivity are 13,000nm/RIU and 1,189.46 RIU-1 respectively. Thesensor resolution is 7.69 × 10-6 for our proposed design. The proposed sensor also achieved a maximum birefringenceof 2.8×10−3 which is to our knowledge the highest birefringence reported so far for PCF-SPR sensor. This enables thefiber to be operated in a dual polarized mode. The refractive index for the analyte ranges from 1.33 to 1.40. Based onall the characteristics, the proposed PCF structure can be used effectively for chemical and biomolecular sensing.

Rectangular illumination method using LED arrays formachine vision

Liang Zhang, Ling Peng, Kang Luo, and Sheng Yu

DOI: 10.1364/AO.384833 Received 03 Dec 2019; Accepted 03 Mar 2020; Posted 03 Mar 2020  View: PDF

Abstract: Machine vision image quality is significantly affected by illumination. Uniform illumination of a rectangular targetsurface requires a function for evaluating the illumination system. In this study, based on an LED array light sourceilluminance model, such an evaluation function was established. Further, the influence of the light source’s structureon illumination was analyzed using a single factor analysis method to determine the boundary conditions and it wasthen solved using a genetic algorithm to finalize the structural design. An experimental platform was built tomeasure the illuminance uniformity. The experimental results were consistent with the numerical results, verifyingthe effectiveness and feasibility of the proposed illumination method. Thus, this research provides a theoreticalreference for the illumination of a rectangular target surface for vision-based detection.

Characterization of a compact low cost Stokes lens forastigmatism compensation in optical instruments

Sara Ferrer-Altabás and Vicente Mico

DOI: 10.1364/AO.386247 Received 18 Dec 2019; Accepted 03 Mar 2020; Posted 03 Mar 2020  View: PDF

Abstract: Variable power cross-cylinder lenses (or Stokes lenses) are widely known in the literary from decades ago. In thismanuscript, we describe how to build a low cost Stokes lens, its calibration and its application to two significantcases. The construction is in virtue of a phoropter’s Risley prism mount for assembling a couple of equal butopposite sign cylindrical lenses (we have selected ±1.50 D). Thus, variable astigmatic power is achieved by relativerotation of the lenses in opposite directions, and the resulting astigmatic axis is defined by the global rotation ofthe device. Calibration measurements are performed using an automatic lensmeter (Topcon CL-300) and anaberrometer (Zeiss iProfiler plus) for low and high order, respectively, aberration characterization. The proposeddevice has been adapted to a manual Topcon LM-8 lensmeter and to a regular Olympus BX-60 upright microscopefor experimental validation concerning astigmatism compensation in a digital microscope and astigmatismcancellation in ophthalmic lenses, respectively. The device can be easily adapted to any ophthalmic/opticinstrument for the compensation and/or measurement of astigmatism up to a maximum range of |3|D ofastigmatism.

White-light circular-polarization imaging using pairs of polarization gratings and wedge prisms

Kohei Noda, KOYA YAMADA, Ryusei Momosaki, Moritsugu Sakamoto, Tomoyuki Sasaki, Nobuhiro Kawatsuki, Kimiaki Tsutsui, and Hiroshi Ono

DOI: 10.1364/AO.384303 Received 02 Dec 2019; Accepted 03 Mar 2020; Posted 04 Mar 2020  View: PDF

Abstract: Novel method for circular-polarization imaging with white-light is presented. The key optical elements of proposed system are two polarization gratings (PGs) and a wedge prism. The chromatic dispersion of the PG diffraction angle is compensated by difference of the grating period for the two PGs. In addition, the distance between the diffracted lights on the imaging plane is controlled by using a wedge prism. As a result, S3 of the Stokes parameter including the wavelength dependence of scarab beetle was observed at a time, and the S3 contribution to each color was determined by using the color filter of the light receiving element. Because white-light polarization image includes a lot of information about the illuminated structure, proposed method should be applied to a biomedical sensing and a remote sensing.

Compact, high-performance, and fabricationfriendly two-mode division multiplexer basedon a silicon bent directional coupler

Kolsoom Mehrabi, Abbas Zarifkar, and Mahsa Babaei

DOI: 10.1364/AO.385585 Received 11 Dec 2019; Accepted 02 Mar 2020; Posted 03 Mar 2020  View: PDF

Abstract: In response to the increasing demands of the capacity enhancement of opticalcommunication, a compact and high performance silicon mode division multiplexer isproposed which multiplexes the fundamental and first-order transverse magnetic modes. Thedevice structure is based on an asymmetric bent directional coupler with an ultasmallcoupling length of 3.67 μm. Utilizing the single layer silicon waveguides with the sameheights allows the proposed device to be fabricated using a single-step CMOS-compatiblefabrication process, which provides a cost-effective design in comparison with the previouslyreported structures. The three-dimensional finite-difference-time-domain (3D FDTD)simulation results confirm that the device has a low loss of 0.87 dB, low cross talk of -21.8dB, and high mode conversion efficiency of 98.3%, at the communication wavelength of 1.55µm. Furthermore, the device shows a broad bandwidth of about 110 nm, completely coveringthe C and L bands with the crosstalk less than -10 dB. Moreover, it is shown that the proposedmode (de)multiplexer is fabrication tolerant for the coupling gap variation of -40 nm<Δg< nm and the waveguides width variation of –25 nm<ΔW<25 nm for a low loss of <-1.67 dBand low crosstalk of <-10 dB.

Elemental mercury sensing by synchronouslysweeping two multimode diode lasers

Tie Zhang, Xiutao Lou, Lianjie Xu, and Sailing He

DOI: 10.1364/AO.386105 Received 16 Dec 2019; Accepted 28 Feb 2020; Posted 04 Mar 2020  View: PDF

Abstract: We propose a sum-frequency-generation (SFG) laser-based elemental mercurysensing method by mixing two low-cost multimode diode lasers (MDLs). The wavelengths ofthe two MDLs are synchronously scanned, which enlarges the whole coverage range ofwavelength and improves the measurement stability. Correlation spectroscopy was used toeliminate the impact of environmental change and enhance trace the absorption signal of thesample accurately. A novel data processing method was employed to extract the weakabsorption signals from the background efficiently. A sensitivity of 0.1 μg/m3 (11 ppt) wasachieved for 1-m path length and 10-s integration time. The sensing range was efficientlyincreased up to 200 μg/m3 using a calibration curve based on a new mathematical analyticalformula. Real-time monitoring of the mercury volatilization and diffusion process wasexperimentally demonstrated with a time resolution of 10 s. The performance of the systemshows a great practical value for the detection of elemental mercury in industrial applications.

Optical reflectivity of an interface with randomrefractive-index-contrast patterns

Anays Acevedo-Barrera, Omar Vazquez-Estrada, and Augusto Garcia-Valenzuela

DOI: 10.1364/AO.383166 Received 12 Nov 2019; Accepted 28 Feb 2020; Posted 02 Mar 2020  View: PDF

Abstract: We develop simple models for the optical reflectivity of an interface in opticalcontact with random media consisting of discrete volumes of arbitrary form and differentrefractive indices. Examples of interest are surfaces sprinkled with microdroplets or aninterface with biological cells adhered to it at random locations. We focus our attention to thecase of internal reflectivity, in which the incidence medium has a larger refractive index thanthe refractive indices at the other side of the interface. Assuming an incident plane wave, weprovide simple approximate expressions for the surface’s coherent reflectance and for thesurface’s total reflectance. We compare predictions of the surface coherent-reflectance modelwith numerical simulations. Then, we use the surface’s reflectance models to interpretexperimental measurements obtained with an optical prism and a thin vegetable tissueadhered to its base. In general, the surface reflectivity can be used to determine fractionalcontact area between the interface and microdroplets or biological cells and infer theirrefractive indices with an accuracy of about 0.5%.

Digital image correlation with improved efficiency by pixel selection

Xinxing Shao, Fuqiang Zhong, Wei Huang, xiangjun dai, Zhenning Chen, and Xiaoyuan He

DOI: 10.1364/AO.387678 Received 09 Jan 2020; Accepted 28 Feb 2020; Posted 02 Mar 2020  View: PDF

Abstract: With the increase in digital image correlation (DIC) applications, its computational efficiency is becoming increasingly important. In previous studies, real-time DIC was realized with a relatively small subset. However, a small subset does not always include sufficient gray gradient information. In this paper, a pixel selection strategy is proposed to improve the computational efficiency of DIC further, allowing real-time deformation measurement with a large subset. Within the subset, zero weight is assigned to unreliable pixels for pursuing maximum efficiency. The modulus of local intensity gradient vector (MLIGV) of each pixel in the reference image is used as the criterion of reliability. Numerical and real experiments conducted to validate the feasibility and effectiveness of the strategy showed the computational speed of DIC can be improved about two times.

Simulation analysis and preparation of a highoptical density laser protection filter

Liangyi Hang, Weiguo Liu, Shigeng Song, Des Gibson, SUN ZHOU, Zhang Xu, cheng li, and SAM AHMADZADEH

DOI: 10.1364/AO.386799 Received 01 Jan 2020; Accepted 26 Feb 2020; Posted 04 Mar 2020  View: PDF

Abstract: High optical density (OD) filters have been widely used in space observation,optical detection, and laser protection. However, the lack of high OD value filters isrestricting their application. This paper reports the formulation of a three-dimensional meshmodel that can help predict the effects of pinhole defects, thickness error, and uniformity onthe transmittance and OD value of optical filters. A laser protection filter (LPF) with a highOD value was prepared on fused silica using a microwave plasma-assisted pulsed DC reactivesputtering technique. The transmittance and OD value of the LPF were measured. Comparingthe designed, measured, and simulated results, we found that the thickness error anduniformity of the layers mainly affected the passband transmittance of the LPF and had littleeffect on the OD value of the blocking band. In contrast, the pinhole defects were the mainfactor that decreased the OD value of the blocking band. The average OD values of theprepared LPF in the blocking bands of 527–532 and 755–833 nm were 8.832 and 10.191,respectively. By comparing the transmittance and OD value of the simulated and measuredresults, we found that the LPF has ±1% uniformity error and 0.5% pinhole ratio. Suggestionsfor preparing high OD optical filters are provided and further improvements are summarized.

Compression of 3D dynamic holographic scenes in theFresnel domain

Sorayda Trejos Gonzalez, Melisa Gómez, Alejandro Velez, Jonh Freddy Barrera, and Roberto Torroba

DOI: 10.1364/AO.383578 Received 19 Nov 2019; Accepted 25 Feb 2020; Posted 02 Mar 2020  View: PDF

Abstract: In this paper, we present an optodigital protocol for the compression of 3D dynamic scenes recorded withan off-axis Fresnel holography system. The compression protocol involves optical scaling, sampling with binarymasks and multiplexing of the optical field data obtained after a filtering process applied to Fresnel holograms.Volume reduction of up to 93.71% and a 16-fold decrease in the transfer time are achieved. Virtual-opticalreconstruction is performed for different values of the parameters involved in the compression protocol. Thecorrelation coefficient is used as a metric to measure the loss caused by the volume reduction process. Furthermore,we show that a high level of lossy compression can be achieved with this protocol, with better reconstruction qualitythan the MPEG-4 video compression technique. Finally, we perform the experimental reconstruction using aholographic projection system based on phase only spatial light modulator, highlighting the potential of ourproposal.

Broadband, millimeter-wave antireflection coatings for large-format, cryogenic aluminum oxide optics

Andrew Nadolski, Joaquin Vieira, Joshua Sobrin, Anna Kofman, Peter Ade, Zeeshan Ahmed, Adam Anderson, Jessica Avva, Ritoban Basu Thakur, Amy Bender, Bradford Benson, Lincoln Bryant, John Carlstrom, Faustin Carter, Tom Cecil, Clarence Chang, James Cheshire, Grace Chesmore, Jean-Francois Cliche, Ari Cukierman, Tijmen de Haan, Marion Dierickx, Junjia Ding, Daniel Dutcher, Wendeline Everett, John Farwick, Kyle Ferguson, Lina Florez, Allen Foster, Jianyang Fu, Jason Gallichio, Anne Gambrel, Robert Gardner, John Groh, Sam Guns, Robert Guyser, Nils Halverson, Angelina Harke-Hosemann, Nicholas Harrington, Robert Harris, Jason Henning, William Holzapfel, Doug Howe, Nicholas Huang, Kent Irwin, Oliver Jeong, Michelle Jonas, Adam Jones, Milo Korman, John Kovac, Donna Kubik, Steve Kuhlmann, Chao-Lin Kuo, Adrian Lee, Amy Lowitz, Jeff McMahon, Jason Meier, Stephan Meyer, Daniel Michalik, Joshua Montgomery, Tyler Natoli, Hogan Nguyen, Gavin Noble, Valentine Novosad, Stephen Padin, Zhaodi Pan, Pascal Paschos, John Pearson, Chrystian Posada, Wei Quan, Sasha Rahlin, Dave Riebel, John Ruhl, James Sayre, Erik Shirokoff, Graeme Smecher, Tony Stark, Judith Stephen, Kyle Story, Aritoki Suzuki, Chris Tandoi, Keith Thompson, Carole Tucker, Keith Vanderlinde, Gensheng Wang, Nathan Whitehorn, Vlad Yefremenko, Ki Won Yoon, and Matt Young

DOI: 10.1364/AO.383921 Received 05 Dec 2019; Accepted 25 Feb 2020; Posted 26 Feb 2020  View: PDF

Abstract: We present two prescriptions for broadband (~77 - 252 GHz), millimeter-wave antireflection coatings for cryogenic, sintered polycrystalline aluminum oxide optics: one for large-format (700 mm diameter) planar and plano-convex elements, the other for densely packed arrays of quasi-optical elements, in our case 5 mm diameter half-spheres (called "lenslets"). The coatings comprise three layers of commercially-available, polytetrafluoroethylene-based, dielectric sheet material. We review the fabrication processes for both prescriptions then discuss laboratory measurements of their transmittance and reflectance. In addition, we present the inferred refractive indices and loss tangents for the coating materials and the aluminum oxide substrate.

Wavelength locking in a large-smile diode-laser array using dual-beam transformation systems

liu bin, Hui Liu, fenning chen, Haiyan LI, and liu sheng

DOI: 10.1364/AO.388241 Received 15 Jan 2020; Accepted 25 Feb 2020; Posted 26 Feb 2020  View: PDF

Abstract: Dual-beam transformation systems (dual BTSs) are used to obtain a wide wavelength-locking range for high-power large-smile diode-laser array. The collimating residual divergence-angle can be reduced from 9 mrad to less than 6.5 mrad, using a set of two angled BTSs that are located in front of a diode-laser array with about 2μm smile. Due to the reduced collimating residual divergence-angle, the external cavity with a set of two angled BTSs and a volume Bragg grating (VBG) achieved a wide wavelength-locking range for temperatures ranging from 20°C-30°C. In addition, the side-mode suppression-ratio (SMSR) exceeds 30dB.

General formula to design a freeform singletfree of spherical aberration and astigmatism:Reply to Comment

Rafael Gonzalez Acuña, Héctor Chaparro Romo, and Julio Gutierrez-Vega

DOI: 10.1364/AO.389840 Received 03 Feb 2020; Accepted 25 Feb 2020; Posted 26 Feb 2020  View: PDF

Abstract: The comment made by Valencia-Estrada and García-Márquez [App. Opt.....] to our paper [Appl. Opt. 58, 1010, 2019] consists on a trivial generalization of our formulation.

Microlens testing on back-illuminated image sensors for space applications

Frédéric Zanella, Guillaume Basset, Christian Schneider, Angélique Luu-Dinh, Sören Fricke, Ana Madrigal, Dirk Van Aken, and Mustapha Zahir

DOI: 10.1364/AO.383454 Received 18 Nov 2019; Accepted 24 Feb 2020; Posted 26 Feb 2020  View: PDF

Abstract: The optoelectronic properties of image sensors, among which the photosensitivityand resolution, are key quality factors for imaging as well as spectrometry in Earthobservation and scientific space exploration missions. Micro-Lens Arrays (MLAs) furtherimprove state-of-the-art CMOS Image Sensors (CIS) by redirecting more photons into thephotosensitive surface/volume of each pixel. This paper reports the design, deposition, opticalcharacterization and reliability assessment of such MLA made from a UV-curable hybridpolymer and replicated on a packaged back-illuminated CIS (BI-CIS) having a pixel pitch of15.5 µm. We find that such MLAs are highly stable to temperature variations, exposure tohumidity, mechanical shocks and vibrations as well as irradiation by gamma rays, whileimproving the parasitic light sensitivity (PLS) by a factor of 1.8. Such MLAs can be appliedon a large variety of image sensors, back- but mostly front-illuminated, with pixel pitchesranging from few microns to several hundreds, making them suitable for most specificationsof the space industry.

Differential Interference Contrast Microscopy with AdjustablePlastic Sanderson Prisms

Sonika Rathi, Nicholas Zoubek, Vivian Zagarese, and Daniel Johnson

DOI: 10.1364/AO.381056 Received 22 Oct 2019; Accepted 20 Feb 2020; Posted 06 Mar 2020  View: PDF

Abstract: Differential interference contrast microscopy is a technique to image spatially dependent gradients in optical path lengths.Contrast is produced through the splitting of polarized light with quartz Wollaston prisms. Here we demonstrate that light splitting forDIC microscopy can also be achieved with Sanderson Prisms consisting of polycarbonate bars under a bending load. Comparableimage contrast while imaging cultured cells was achieved with this alternative technique. These results demonstrate an inexpensiveand easily adjustable alternative to traditional quartz Wollaston prisms.

Reconciling models of primary production and photoacclimation

Shubha Sathyendranath, Trevor Platt, Zarko Kovac, James Dingle, Thomas Jackson, Robert Brewin, Peter Franks, Emilio Maranon, Gemma Kulk, and Heather Bouman

DOI: 10.1364/AO.386252 Received 17 Dec 2019; Accepted 14 Feb 2020; Posted 26 Feb 2020  View: PDF

Abstract: Primary-production models and photo-acclilmation models are two important classes of physiological models that find applications in remote sensing of pools and fluxes of carbon associated with phytoplankton in the ocean. They are also key components of ecosystem models designed for studying biogeochemical cycles in the ocean. So far, these two classes of models have evolved in parallel, somewhat independently of each other. Here we examine how they are coupled to each other through the intermediary of the photosynthesis-irradiance parameters. We extend the photo-acclimation model to accommodate spectral effects in light penetration in the ocean, and the spectral sensitivity of the initial slope of the photosynthesis-irradiance curve, making the photo-acclimation model fully compatible with spectrally-resolved models of photosynthesis in the ocean. The photo-acclimation model contains a parameter $\theta_m$, which is the maximum carbon-to-chlorophyll ratio that phytoplankton can attain, when available light tends to zero. We explore how size-class-dependent values of $\theta_m$ could be inferred from field data on chlorophyll and carbon content in phytoplankton, and show that the results are generally consistent with lower bounds estimated from satellite-based primary-production estimates, with empirical models linking phytoplankton carbon and chlorophyll concentration, and with the range of values obtained in culture measurements. We study the equivalence between different classes of primary-production models at the functional level, and show that availability of chlorophyll-to-carbon ratio from photo-acclimation model facilitates the translation between these classes. We discuss the importance of better assignment of parameters in primary-production models as an important avenue for reducing model uncertainties and for improving the usefulness of satellite-based primary production calculations in climate research.

Impact of nonlinear effects on transmission losses ofhollow-core anti-resonant negative-curvature opticalfiber

Shouyue Wu, Bartlomiej Siwicki, Richard Carter, Fabio Biancalana, Jonathan Shephard, and Duncan Hand

DOI: 10.1364/AO.382350 Received 13 Nov 2019; Accepted 04 Feb 2020; Posted 05 Feb 2020  View: PDF

Abstract: We investigate the impact of input pulse duration and peak power of a femtosecond laser on pulsebroadening and propagation losses in selected hollow-core anti-resonant fiber (HC-ARF). The mixed effects ofstrong self-phase modulation and relatively weak Raman scattering broaden the spectral width, which in turncauses a portion of the output spectrum to exceed the transmission band of the fiber, resulting in transmissionlosses. By designing and setting up a gas flow control system and a vacuum system, the nonlinear behavior ofthe fiber filled with different pressurized gases is investigated. The experimental results show that replacingthe air molecules in the fiber core with argon can weaken pulse broadening and increase the transmittablepeak power by 14 MW for a given 122 MW input, while a vacuum system can reduce the nonlinearity to alarger extent, therefore enhancing the transmission of HC-ARF by at least 26 MW.

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