查看更多>>摘要：We determine the 3D orientation of single gold nano-bipyramids (AuBPs) deposited on a glass substrate. These nanoparticles possess a well-defined localized surface plasmon resonance along their main axis which can be modeled as a single dipole. Orientation is deduced by polarization resolved dark-field scattering. For that purpose, a specific experiment has been built to select, analyze in polarization and resolve the scattering angles at the single nanoparticle level. Usually, the out-of-plane angle is deduced by measuring the degree of polarization (DOP) and doing numerical simulations taking into account the nature of the dipole (1D, 2D) and all experimental parameters. We compare this method with a complete measurement of the DOP as function of the collected numerical aperture (controlled by Fourier filtering). The results provide the accuracy of the polarimetric measurements. The complimentary method proposed in this article can easily be extended to more complex system.
查看更多>>摘要：Using sparse multi-spot patterns, multifocal structured illumination microscopy (MSIM) can retrieve the 3D structures of thick samples with improved lateral resolution. In the existing MSIM techniques, the accurate parameters of microscope and positions of the illumination focus in the captured images are essential for suppressing the out-of-focus light and improving the lateral resolution. Tedious calibration procedures thus should be carried out in these MSIM techniques. Hence, a blind optical sectioning and super-resolution (OS-SR) imaging method in MSIM is proposed in this paper. The proposed method combines a deconvolution method with the standard deviation method. It can achieve OS-SR images without calibrating the accurate parameters of microscope and the positions of the foci. The validity of the proposed method is demonstrated by simulation and experimental results.
查看更多>>摘要：We propose an incoherent encoding system for image encryption utilizing the coded aperture correlation holography (COACH) technique. Incoherent imaging is the core component of this proposal, in which the point spread hologram (PSH) of the imaging system serves as the main key to encode the input intensity distribution. The proposal makes full use of PSH which consists of four point spread functions (PSFs) respectively generated by four coded phase masks (CPMs), so that a multidimensional key space is generated to resist illegal attacks. Incoherent illumination of the imaging system ensures that only the intensity information is manipulated. The encoded information is just an intensity distribution which is advantageous for data storage, simplifying the system structure and processing, and suppressing the information expansion involved in general conventional encryption methods. Both numerical and experimental results illustrate the feasibility and effectiveness of the proposed method. This work represents an effective idea for incoherent optical encryption techniques.
查看更多>>摘要：We propose and demonstrate an optical performance monitoring (OPM) scheme in few-mode fiber (FMF) based elastic optical networks (EONs). In this work, an adversarial transfer learning (TL) assisted by deep neural networks (DNN), which is used to learn the feature of signal constellations, is investigated for modulation format recognition (MFR) and optical signal-to-noise (OSNR) estimation. Because mode interference affects the projected results in FMF, the DNN is trained to increase link damage tolerance through domain adversarial adaptation (DAA). Five modulation formats have been considered for verifying the feasibility of the proposed scheme, including BPSK, QPSK, 8PSK, 8QAM, and 16QAM. The symbol rate of 12.5 Gbaud is experimentally tested for each scheme across a FMF transmission system. The results reveal that DAA scheme outperforms retraining DNN for requiring one-third training data without any accuracy penalty. Furthermore, the root mean square error (RMSE) of OSNR estimation in this paper can achieve less than 0.1 dB. We anticipate that our results can stimulate further research on the OPM tasks with a feasible deep learning scheme and contribute to the development of FMF-based EONs.
查看更多>>摘要：This study introduces a novel nonlinear two-dimensional (2D) warped discrete Fourier transform (WDFT) amplitude demodulation method that allows higher-resolution measurements on specific two-dimensional regions of interest. The specific application in this study addresses the need for the nonlinear 2D amplitude demodulation of fringe-wave fields acquired by a deformed Mach-Zehnder interferometer. The proposed method exploits the properties based on which the WDFT can obtain frequency spectra sampled at non equidistant intervals and the symmetry of the Fourier transform. As a result, this 2D-WDFT-based method can be used to nonlinearly demodulate the amplitude of the 2D interference fringe wave field to obtain a high resolution localized fringe envelope. This study describes the proposed analysis procedure and its application using this 2D WDFT-based demodulation scheme. Experimental verification of the proposed approach was conducted with the use of deformed Mach-Zehnder interferometry. The successful experimental validation proves the efficiency of the proposed algorithm for amplitude demodulation with dense sampling points located in the central part of the envelope. To the best of the authors' knowledge, this is the first investigational report on a 2D nonlinear envelope demodulator.
查看更多>>摘要：A virtual binocular line-structured light measurement method based on a plane mirror is proposed. A checkerboard target and its virtual image in a front coating plane mirror are captured by a camera in a single picture. The target is imaged in several positions to determine the spatial relationship between the camera and plane mirror. The centers of light stripes are matched with its mirror images by the vanishing point constraint between the checkerboard coplanar point and its corresponding mirrored point. By scanning the object on a moving stage, 3D point cloud data can be obtained. Compared with the traditional binocular line-structured light measurement system, the proposed method just needs a single camera, and two images can be obtained in one procedure. It improves the measurement speed, reduces the cost of measurement, and avoids measurement errors caused by non-strict synchronization between the left and right camera in binocular vision. Experimental results demonstrate good performance with the ability to reconstruction surfaces, and measurement accuracy (RMSE = 0.032 mm) can meet the industrial requirement.
查看更多>>摘要：Data-driven methods have increasingly been applied to the development of optical systems as inexpensive and effective inverse design approaches. Optical properties (e.g., band-gap properties) of photonic crystals (PCs) are closely associated with characteristics of their light reflection spectra. Finding optimal PC constructions (within a pre-specified parameter space) that generate reflection spectra closest to a targeted spectrum is thus an interesting and meaningful inverse design problem, although relevant studies are still limited. Here we report a generally effective machine learning-based inverse design approach for one-dimensional photonic crystals (1DPCs), focusing on visible light spectra which are of high practical relevance. For a given class of 1DPC system, a deep neural network (DNN) in a unified structure is first trained over data from sizeable forward calculations (from layer thicknesses to spectrum). An iterative optimization scheme is then developed based on a coherent integration of DNN backward predictions (from spectrum to layer thicknesses), forward calculations, and Monte Carlo moves. We employ this new approach to four representative classes of 1DPC systems including periodic structures with two-, three-, and four-layer repeating units and a heterostructure. The approach successfully converges to solutions of optimal 1DPC constructions for various targeted spectra regardless of their exact achievability. Several demonstrating examples are presented and discussed in detail, including the inverse designs toward specially constructed "rectangle-shaped", narrow-bandgap red-, green-, or blue-light reflection spectrum and wide-bandgap reflection spectrum that has high reflectivity in the whole visible light region. Remarkably, the results show that the approach can efficiently find out optimal layer thicknesses even when they are far outside the range covered by the original training data of DNN.
查看更多>>摘要：A polarization-diversified loop structure (PDLS) formed by a four-port polarizing beam splitter has been employed to establish the input polarization independence of optical devices. Here we report a PDLS-based optical fiber birefringence filter, which can provide continuous frequency tunability in passband-squeezed comb spectra by harnessing quarter-wave polarization conversion. The birefringence filter is composed of a four-port PBS, two high birefringence fiber (HBF) segments whose lengths are equal, the first polarization controller (PC) comprised of a quarter-wave retarder (QWR) and a half-wave retarder (HWR), which is located in front of the first HBF segment, and a set of two QWRs as the second PC that lies before the second HBF segment. The dual QWRs, chosen for the second PC, are the simplest form of a PC that can convert arbitrary input polarization into desired polarization. The slow axis of the second HBF segment is oriented at 22.5 degrees with respect to the horizontal axis of the PBS. Through the Jones matrix formulation, we derived the sinusoidal passband-squeezed transmittance function of the filter, whose absolute phase (phi) should be continuously varied for the contiguous wavelength tuning of filter spectra. Then, using this filter transmittance, we found the possible loci of the orientation angles (OAs) of the four wave retarders as the functions of phi. By utilizing the OA loci of the wave retarders, the theoretical passband-squeezed transmission spectra of the filter were calculated for eight equally spaced values of phi from 0 degrees to 315 degrees (with an increment of 45 degrees). This theoretical calculation was also verified by measuring the wavelength-tuned passband-squeezed spectra of the fabricated filter. We theoretically and experimentally confirmed that our filter could provide the wavelength tunability of the polarization-independent passband-squeezed comb spectrum by appropriately controlling the OAs of the wave retarders.
查看更多>>摘要：This paper introduces a novel and promising design of a freeform diversity receiver (FDR) to reduce the interchannel interference (ICI) of multi-cell visible light communication (VLC) system. Based on the potential of rotationally non-symmetric freeform optics, we have established the design of an off-axis VLC receiver frontend. In this study, we have performed the detailed design of the freeform surface profiles and have analysed the corresponding fabrication tolerances. Nonetheless, the communication performance of the VLC system using the proposed design has been evaluated with the help of Monte-Carlo based ray-tracing technique. Results show that the system with the proposed FDR significantly outperforms the existing state-of-the-art multi-cell VLC receivers in terms of signal-to-interference-plus-noise ratio (SINR). The spatial SINR ranges from 98 dB to 137 dB while 120.5 dB average SINR is attained over the communication floor. This compact size receiver (15.12 mm x 15.12 mm x 6.76 mm) with substantial wireless reception reliability has prospective future applications in the emerging field of visible light communication and its counterpart Li-Fi.
查看更多>>摘要：We have proposed an optical see-through near-eye display method, which combines Maxwellian-view and light field displays by a space-division multiplexing method. Recent works have reported that a Maxwellian-view display and a light-field near-eye display are both effective methods to alleviate the vergence-accommodation conflict (VAC). The proposed display method combines the advantages of both the Maxwellian-view and light field displays; the system can provide an accommodation-free virtual image as a background with a large field of view (FOV, 31.5), and a high-resolution full-depth-cue foveal image with a small FOV (10.1) and a large eye-box. To verify the method, a prototype has been developed to superimpose vivid virtual images onto the real environment.
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