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"optical correlation"
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Polarization-Modulated Optical Homodyne for Time-of-Flight Imaging with Standard CMOS Sensors
Indirect time-of-flight (iToF) imaging is a widely applied technique to obtain a depth image from the phase difference of amplitude-modulated signals between emitted light and reflected light. The phase difference is computed via electrical correlation on a conventional iToF sensor. However, iToF sensors face a trade-off between spatial resolution and light collection efficiency because it is hard to downsize the circuit of the electrical correlation in a pixel. Thus, we propose a novel iToF depth imaging system based on polarization-modulated optical homodyne detection with a standard CMOS sensor. A resonant photoelastic modulator is employed to modulate the polarization state, enabling optical correlation through interaction with an analyzer. The homodyne detection enhances noise resistance and sensitivity in the phase difference estimation. Furthermore, the use of a polarization camera allows to reduce the number of measurements. We first validate the successful estimation of the phase difference in both setups with an avalanche photodiode or a CMOS sensor. The experimental results show accurate depth estimation even in challenging factors such as a low signal-to-noise ratio, temporal intensity variations, and speckle noise. The proposed system enables high-resolution iToF depth imaging using readily available image sensors.
Journal Article
High‐contrast QPSK pattern recognition device consisting of a 4× $\\times$ 4 MMI coupler
Pattern recognition of optical label is utilized not only in packet switches but also in the field of data security due to its wide range of applications. In particular, pattern recognition using waveguide devices is highly valued because it eliminates the need for encoder processing. However, existing methods suffer from the problem of degraded contrast ratio because half of the input power are emitted from non‐target waveguides. In this article, a method is proposed to improve the contrast ratio employing a 4× $\\times$ 4 multi‐mode interference (MMI) coupler with multiple input signals. The theoretical results reveal that the proposed method improves the contrast ratio from 3.0 dB to 9.5 dB and ∞ $\\infty$dB for the three‐input and four‐input cases, respectively, for quadrature phase‐shift keying (QPSK)‐modulated signal. Furthermore, numerical simulation was performed through the three dimension finite‐difference time‐domain (3D‐FDTD) method, and the proposed scheme successfully discriminated each QPSK pattern. The power value |E|2 $|E|^2$at all ports closely matches the theoretical value, and the ratios of 9.5 dB and > $>$ 30.0 dB are numerically obtained. This article introduces a novel method to enhance contrast ratio in optical label pattern recognition, crucial for packet switches and data security. By employing a 4× $\\times$ 4 multi‐mode interference coupler with multiple input signals, the proposed approach significantly improves contrast ratio, theoretically from 3.0 dB to 9.5 dB and infinitely for certain cases. Numerical simulations confirm its efficacy, demonstrating successful discrimination of QPSK patterns with results closely matching theoretical predictions.
Journal Article
High‐contrast QPSK pattern recognition device consisting of a 4× imes 4 MMI coupler
Abstract Pattern recognition of optical label is utilized not only in packet switches but also in the field of data security due to its wide range of applications. In particular, pattern recognition using waveguide devices is highly valued because it eliminates the need for encoder processing. However, existing methods suffer from the problem of degraded contrast ratio because half of the input power are emitted from non‐target waveguides. In this article, a method is proposed to improve the contrast ratio employing a 4×4 multi‐mode interference (MMI) coupler with multiple input signals. The theoretical results reveal that the proposed method improves the contrast ratio from 3.0 dB to 9.5 dB and ∞ dB for the three‐input and four‐input cases, respectively, for quadrature phase‐shift keying (QPSK)‐modulated signal. Furthermore, numerical simulation was performed through the three dimension finite‐difference time‐domain (3D‐FDTD) method, and the proposed scheme successfully discriminated each QPSK pattern. The power value |E|2 at all ports closely matches the theoretical value, and the ratios of 9.5 dB and >30.0 dB are numerically obtained.
Journal Article
Brillouin Optical Correlation‐Domain Reflectometry With Polymer Fibers Under Scrambled Polarization Enabled by Angled Connections
Polymer optical fibers (POFs) are attractive for Brillouin optical correlation‐domain reflectometry (BOCDR) because of their flexibility and high strain tolerance. However, their low Brillouin frequency shift causes spectral overlap with Fresnel reflections, limiting the use of polarization scrambling. We show that angled physical contact (APC) connections suppress these reflections and enable reliable distributed sensing under scrambled polarization states. Distributed strain measurements performed with a 6‐m POF reveal that conventional physical contact (PC) connections fail to detect strain, whereas APC connections yield Brillouin signals with a high signal‐to‐noise ratio and correctly measure a 0.65% strain.
Journal Article
Design of an optical test bench (OTB) for an N-bit optical multiplier, optical convolution, and optical correlation circuit using an optical microring resonator in the Z-domain
Present paper proposes the design of an Optical Test Bench (OTB) for an N-bit optical multiplier, optical convolution, and optical correlation circuit. OTB is constructed from a silicon-based optical microring resonator (OMRR). The OTB functions as an optical 4:3 counter, 2 × 2 optical multiplier, and 2 × 2 optical partial product generator circuit. OTB has been designed to be capable of designing any order of optical multiplier, optical convolution, and optical correlation circuit. OTB has been optimized with a small ring radius of 3.546 um and a low power of 1.19 mW. The transfer function of the OTB has been developed in Z-domain. The pole-zero plot is used to validate OMRR optical switching in the frequency domain. The optical switching of the designed OTB has been validated using various critical features such as extinction ratio, contrast ratio with respect to ring radius, and coefficient of coupling to predict the circuit's correctness and feasibility. All the analyses were successfully carried out in a MATLAB environment.
Journal Article
Recent Progress in Long-Range Brillouin Optical Correlation Domain Analysis
Distributed optical fiber sensing technology has been widely applied in the areas of infrastructure health monitoring, national defense security, etc. The long-range high-spatial-resolution Brillouin optical correlation domain analysis (BOCDA) has extensive development and application prospects. In this paper, long-range BOCDAs are introduced and summarized. Several creative methods underpinning measurement range enlargement, including the interval enhancement of the adjacent correlation peak (CP), improvements in the signal-to-noise ratio, and the concurrent interrogation of multiple CPs, are discussed and experimentally verified, respectively. The main drawbacks in the present BOCDA schemes and avenues for future research and development have also been prospected.
Journal Article
Phase singular point localization of vortex beam using optical correlation
The study of optical vortex beams has garnered significant attention due to their wide-ranging applications. These beams exhibit a phase singularity and accurately identifying the location of the singular point is crucial for various vortex-based applications. This study introduces a novel method for localizing the phase singularity of optical vortex beams using a hybrid optical correlator. In contrast to machine learning-based techniques, the proposed approach eliminates the need for complex architectures, reducing computational demands and facilitating real-time implementation. The method demonstrates robust performance under varying conditions, including different contrast levels and aberrations such as astigmatism.
Journal Article
Brillouin Optical Correlation-Domain Technologies Based on Synthesis of Optical Coherence Function as Fiber Optic Nerve Systems for Structural Health Monitoring
Brillouin optical correlation-domain technologies are reviewed as “fiber optic nerve systems” for the health monitoring of large structures such as buildings, bridges, and aircraft bodies. The Brillouin scattering property is used as a sensing mechanism for strain and/or temperature. Continuous lightwaves are used in the technologies, and their optical coherence properties are synthesized to realize position-selective measurement. This coherence manipulation technology is called the “synthesis of optical coherence function (SOCF)”. By utilizing SOCF technologies, stimulated Brillouin scattering is generated position-selectively along the fiber, which is named “Brillouin optical correlation domain analysis (BOCDA)”. Spontaneous Brillouin scattering, which takes place at any portion along the fiber, can also be measured position-selectively by the SOCF technology. This is called “Brillouin optical correlation domain reflectometry (BOCDR)”. When we use pulsed lightwaves that have the position information, sensing performances, such as the spatial resolution, are inherently restricted due to the Brillouin scattering nature. However, in the correlation-domain technologies, such difficulties can be reduced. Superior performances have been demonstrated as distribution-sensing mechanisms, such as a 1.6-mm high spatial resolution, a fast measurement speed of 5000 points/s, and a 7000-με strain dynamic range, individually. The total performance of the technologies is also discussed in this paper. A significant feature of the technologies is their random accessibility to discrete multiple points that are selected arbitrarily along the fiber, which is not realized by the time domain pulsed-lightwave technologies. Discriminative and distributed strain/temperature measurements have also been realized using both the BOCDA technology and Brillouin dynamic grating (BDG) phenomenon, which are associated with the stimulated Brillouin scattering process. In this paper, the principles, functions, and applications of the SOCF, BOCDA, BOCDR, and BDG-BOCDA systems are reviewed, and their historical aspects are also discussed.
Journal Article
Magneto‐Optical Correlations in a High Symmetry Dysprosium Complex Reveal an Almost “Ideal Non‐SMM” and Orange‐to‐Red DyIII‐Based Emitter
The importance of investigating high‐symmetry systems in order to reveal properties that would otherwise be concealed in less symmetrical compounds is demonstrated. This is particularly true for discrete coordination complexes that tend to adopt low symmetries. The magnetic, optical, and theoretical investigation of [DyN(SiMe3)23], an amido complex that features an almost trigonal electrostatic environment around the DyIII ion, is reported here. While this specific coordination is ideally suited to the stabilization of high magnetic ground state for “prolate” YbIII‐based single‐molecule magnet (SMM), it is the opposite for oblate DyIII. Hence, [DyN(SiMe3)23] is expected to display the lowest conceivable magnetic anisotropy. This is confirmed herein by magneto‐optical and theoretical correlations. An extremely pure Kramers doublet composition is observed on a totally reversed energetic profile compared to the standard DyIII‐SMM. This results in a paramagnetic but dynamically silent compound, even when an external dc field is applied. Additionally, this unusual energetic profile induces an exceptional optical signature, with orange (300 K) to red (4 K) emission, far from the traditional white‐to‐yellow emission expected for a DyIII ion. Dysprosium in high‐symmetry environment: an original crystal‐field energetic profile provides an experimental demonstration of the oblate/prolate theory and is also responsible for an unprecedented orange‐to‐red emission.
Journal Article