Optical Path Design Research Articles

High-fold optical subdivision blazed grating interferometer based on Mach-Zehnder interferometer

A blazed grating interferometer with high-fold optical subdivision is proposed based on the optical path design of Mach-Zehnder interferometer. In the designed measurement system, multiple diffractions are achieved on the blazed grating surface, fully leveraging the high diffraction efficiency of the blazed grating and avoiding the presence of non-coplanar beams. Furthermore, in order to avoid beam deformation resulting from multiple diffractions, the light path structure returning along the same path is constructed, and this design doubles the optical subdivision fold factor. The experimental results show that 14-fold optical subdivision can be realized in this measurement system, and the maximum calibration difference can reach 34.47 nm within a 0.2 mm travel and 101.07 nm within a 2 mm travel. The designed blazed grating interferometer has the characteristics of a simple structural layout, high-fold optical subdivision and high measurement performance, which lay the groundwork for actual product development.

Single-Shot Fringe Projection Profilometry Based on LC-SLM Modulation and Polarization Multiplexing

Fringe projection profilometry (FPP) is extensively utilized for the 3D measurement of various specimens. However, traditional FPP typically requires at least three phase-shifted fringe patterns to achieve a high-quality phase map. In this study, we introduce a single-shot FPP method based on common path polarization interferometry. In our method, the projected fringe pattern is created through the interference of two orthogonal circularly polarized light beams modulated by a liquid crystal spatial light modulator (LC-SLM). A polarization camera is employed to capture the reflected fringe pattern, enabling the simultaneous acquisition of four-step phase-shifting fringe patterns. The system benefits from advanced anti-vibration capabilities attributable to the common path self-interference optical path design. Furthermore, the utilization of a low-coherence LED light source results in reduced noise levels compared to a laser light source. The experimental results demonstrate that our proposed method can yield 3D measurement outcomes with high accuracy and efficiency.

Diffractive Optical Encryption Systems Based on Multiple Wavelengths and Multiple Distances

Coherent diffractive imaging is an optical methodology that encodes information about an object within the diffraction intensity. Here, we introduce a diffractive optical encryption system that utilizes multiple wavelengths and multiple distances, significantly expanding the size of the secret key space and enhancing the overall security of the system by incorporating these parameters as keys. The system adopts single optical path design, compact structure and is easy to implement, overcoming the disadvantage of single key space of traditional encryption system. This system can encrypt images into a series of diffraction intensity maps (i.e., ciphertexts), and exhibits a high sensitivity to minor variations in wavelength or distance during the process of decryption, showing excellent anti-cracking ability. Furthermore, the system also has considerable robustness, ensuring that the information still can be effectively recovered even in instances of partial loss. Numerical simulation results are presented to demonstrate feasibility and effectiveness of the proposed method. Our study provides novel concepts and methodologies to the advancement of optical encryption technology, while also offering significant technical assistance to the domain of information security.

Light control and optical path design method for stabilized zoom systems based on deformable mirrors

We extend the design methodology for stabilized zoom systems by analyzing the stable convergence of singular points in the solution region for image plane shift compensation and continuous zooming. Using lens group magnification as key parameters, we analyze the stability of singular points related to the descending gradient of the zoom equation and the positions of extremum points within the solution region. These singular points and their solution regions are identified and correspond to solutions of specific optical path structures. With the acquired solution region clusters, we can ensure the performance of stabilized zoom systems and prevent optical performance degradation, especially when a specific zoom ratio is required.

A Dual-FSM GI LiDAR Imaging Control Method Based on Two-Dimensional Flexible Turntable Composite Axis Tracking

In this study, a tracking and pointing control system with a dual-FSM (fast steering mirror) two-dimensional flexible turntable composite axis is proposed. It is applied to the target-tracking accuracy control in a GI LiDAR (ghost imaging LiDAR) system. Ghost imaging is a multi-measurement imaging method; the dual-FSM GI LiDAR tracking and pointing imaging control system proposed in this study mainly solves the problems of the high-resolution remote sensing imaging of high-speed moving targets and various nonlinear disturbances when this technology is transformed into practical applications. Addressing the detrimental effects of nonlinear disturbances originating from internal flexible mechanisms and assorted external environmental factors on motion control’s velocity, stability, and tracking accuracy, a nonlinear active disturbance rejection control (NLADRC) method based on artificial neural networks is advanced. Additionally, to overcome the limitations imposed by receiving aperture constraints in GI LiDAR systems, a novel optical path design for the dual-FSM GI LiDAR tracking and imaging system is put forth. The implementation of the described methodologies culminated in the development of a dual-FSM GI LiDAR tracking and imaging system, which, upon thorough experimental validation, demonstrated significant improvements. Notably, it achieved an improvement in the coarse tracking accuracy from 193.29 μrad (3σ) to 87.21 μrad (3σ) and enhanced the tracking accuracy from 10.1 μrad (σ) to 1.5 μrad (σ) under specified operational parameters. Furthermore, the method notably diminished the overshoot during the target capture process from 28.85% to 12.8%, concurrently facilitating clear recognition of the target contour. This research contributes significantly to the advancement of GI LiDAR technology for practical application, showcasing the potential of the proposed control and design strategies in enhancing system performance in the face of complex disturbances.

Contrast ratio enhancement method of a pancake virtual reality head‐mounted display

AbstractFolded optical path designs have been widely applied in Virtual Reality (Pancake VR) displays in recent years. Compared with the traditional straight‐through and Fresnel optical path design, the Pancake design has obvious advantages in smaller size and clearer virtual image. However, the Pancake optical path uses polarization devices to fold the optical path and, light undergoes multiple refractions and reflections between lens groups, thus inevitably introducing stray light. This stray light greatly reduces the contrast ratio even if taking high‐contrasting Mini‐LED backlight LCD as panel, and seriously affects the user experience. In this paper, we first analyze the causes of stray light in the Pancake design and then propose an effective optical design method. In addition, an effective process scheme for improving image contrast is proposed by analyzing the impact of lens and tube reflectivity. Further, a prototype of the Pancake VR optical module is successfully implemented with low stray light and high contrast ratio.

PASAT: pathfinder in solar adaptive telescope

In the forefront of quantitative solar physics research using large-aperture ground-based solar optical telescopes, high-contrast observation along with high-accuracy polarimetric measurement in the solar active region are required. In this paper, we propose a novel high-contrast imaging telescope construction with a 60 cm medium aperture, namely, the PAthfinder in Solar Adaptive Telescope (PASAT), in which a deformable secondary mirror is used as the adaptive optical correction device and a symmetrical optical path design is employed, leading to the least Muller matrix polarization instruments. The telescope can provide a high-resolution magnetic field with high accuracy for the solar active regions, as well as high-contrast images with a superior signal-to-noise ratio and photometric accuracy of the solar photosphere and chromosphere. These data will be directly used for a better understanding of the evolution and release of magnetic energy, which will help in improving space weather forecasting. Meanwhile, PASAT will accumulate the relevant techniques for constructing similar, larger solar telescopes in the future.

Internal surface inspection method under linear structured light illumination based on dual non-coaxial optical paths

The inner space of tubular and hole-like workpieces, such as oil pipes and cylinders, is limited in volume and has no effective means of measuring the inner surface under geometric constraints.This paper proposes a non-coaxial optical path line structured light method for inner surface inspection, which can significantly reduce the device size and working distance. The method constructs two non-coaxial optical paths for light source and imaging, and uses two fixed reflectors to achieve the deflection of the optical axes of the light source and imaging paths.After theoretical derivation and verification, a sample device was designed and fabricated for experiments. The device measures approximately 22 mm by 24 mm in cross-section, the maximum insertion distance is about 200 mm, and the minimum inner diameter of the accessible space is 50 mm.The results show that the optical path design does not destroy the original homography relationship, and can still ensure the measurement capability comparable to the existing methods when reducing the device size to 10% of the original. The method has obvious advantages when applied to the inspection of tubular and hole-like workpieces in fields such as petrochemical industry, military equipment, etc.

Incident angle optimization with multiple conflicting objectives based on BP-MOPSO in oblique laser interferometry

The oblique incident phase-shifting interferometric measurement method is an effective technique for assessing gear tooth form deviation. In the measurement process, the tooth flank incident angle is a crucial factor determining the quality of interferograms. Addressing the challenge in traditional optical path design, where the selection of the tooth flank incident angle encounters a trade-off among quality features such as measurable tooth area (MTA), interference fringe density (IFD) and interferogram compression ratio (ICR), this paper proposes an optimized method for the tooth flank incident angle. Firstly, a comprehensive evaluation model is established to calculate and analyze the MTA, IFD and ICR of the helical gear. Secondly, by integrating BP neural network and Multi-Objective Particle Swarm Optimization (MOPSO) algorithm, a tooth flank incident angle optimization method is devised to simultaneously optimize the measurement light incident angle γ and the rotation angle of the gear axis β. Finally, simulation analyses and physical experiments are employed to demonstrate the feasibility of the proposed method, compared to before optimization, the pseudocorrelation (PSD) value has increased by an average of 34%, and the residual points have decreased by an average of 80%, confirming its capability to improve quality interferogram and measurement accuracy.

RETRACTED: Design of fiber optic lidar for high temperature and humidity detection based on multiphysical simulation

The background radiation of sunlight seriously affects the performance of Raman LiDAR in daytime detection. In order to improve the height and accuracy of Raman LiDAR daytime detection, the author designed a Raman LiDAR system with a laser wavelength of 354.8 nm. The influence of 354.8 nm and 532 nm laser sources on the detection performance of Raman LiDAR was discussed, and the optical path design of the system was completed. The combination of a polarizing beam splitter prism and a 1/4 wave plate optical switch with a combined telescope reduces the receiving field angle of the system and optimizes the performance of daytime detection. The detection performance of the system was simulated with the minimum temperature uncertainty as the standard. During the simulation process, the laser energy is taken as 200 mJ, the frequency is 50 Hz, the integration time is 20 min, and the distance resolution is 105 m. The Raman LiDAR system with integrated transmission and reception considers depolarization, and the temperature uncertainty detected during the day is less than 1 K below 3180 m. The statistical error of detecting the water vapor mixing ratio during the day is below 2400 m, less than 0.001gkg. The simulation results show that the performance of daytime detection has been improved to a certain extent.

A Laser Triangulation Displacement Sensor Based on a Cylindrical Annular Reflector

The ellipticity of the spot caused by laser jitter has a significant effect on the measurement accuracy of the traditional laser triangulation method. In order to overcome the influence of laser characteristics on measurement and improve the accuracy of displacement measurement, this paper proposes a measurement model for a laser displacement sensor based on a cylindrical annular reflector. A physical prototype is designed through parameter optimization using NSGA-II, and a two-step detection algorithm is proposed for the imaging ring of the prototype. The algorithm performs contour thinning after rough positioning of the imaging annular ring, and then performs precise detection. Through physical experiments, it is verified that the repeatability error of this method can reach below 0.02%, and the accuracy is significantly improved compared to traditional laser triangulation displacement sensors. Meanwhile, the measurement results of displacement show linearity. The optical path design of this sensor is simpler than the previously proposed rotational symmetrical laser triangulation displacement sensor, which has good application prospects.

Algorithm for Reconstruction of Three-Dimensional Images in X-Ray Computed Tomography with a Cone Beam of Radiation

Purpose: Development of an algorithm for the reconstruction of three-dimensional images in X-ray
 computed tomography with a cone beam.
 Material and methods: A new approach to the development of the reconstruction algorithm is proposed.
 The algorithm is based on the exact analytical representation of the 3D Radon transform of the projection data. For such a representation, an iteration-invariant point spread function (PSF) is introduced.
 From the existing approximate algorithms of Feldkamp, Katsevich and other authors, the developed algorithm differs in increased accuracy, is applicable for high-performance spiral X-ray tomography, and
 provides a practical design of the X-ray optical path of the tomograph.
 Results: Mathematical modeling of the developed three-dimensional reconstruction algorithm for the
 helical trajectory of the radiation source was performed; satisfactory results were obtained on a phantom model simulating an object of study with contrast inserts. The influence of the distance of the radiation source from the center of coordinates with respect to the radius of the object of study is shown, for
 which a mathematical model of a special phantom in the form of a cube, consisting of separate uniform
 elliptical plates (ellipsoids) of the same density, was developed.
 The quality of the reconstructed tomographic images was assessed through by measurement of the difference between the image of the section of the phantom model and the reconstructed image, presented
 as the root mean square error.
 Conclusion: Studies have shown that for the ratio of the radius of the spiral trajectory to the radius of
 the object (R/Rm
 ), equal to about 3.0, i.e. at sufficiently large angles of the radiation cone of the source,
 the developed algorithm for three-dimensional reconstruction with a cone beam of radiation gives a tomographic image of high quality. This can be applied in the devel-opment of medical X-ray computed tomography.

Optical Design of an LCoS-Based 1 × 10 WSS with High Coupling Efficiency and Compact Light Paths

In the field of communication, the utilization of Liquid Crystal On Silicon (LCoS) in Wavelength Selective Switch (WSS) systems holds great promise. However, the lack of research on the optical path design of LCoS-based WSS makes it challenging to realize high-port-count and perfect performance with a compact structure. In this paper, the conceptual optical path design method of a compact LCoS-based 1 × 10 WSS system working in C-band (1529 nm–1568 nm) is proposed, where there exists 1 input port and 10 output ports in the same array. The optical powers in both the wavelength and deflection directions have been meticulously considered separately, while the polarization-independent structure has been designed novelty, which boost system compactness and lowers manufacturing costs. Finally, a high fiber-to-fiber coupling efficiency of an idealized system ranging from 95.07 to 99.18% with only five components is achieved. Furthermore, a brief tolerance analysis to demonstrate the instrumentation feasibility is also conducted and the additional losses that will be introduced by real experiments are discussed. Our work is pioneering in providing a more straightforward methodology and conceptual model for WSS system design and offering reference significant for high-port-count systems.

B-247 Rapid and Field-deployable Microchip-based Real-time PCR for Hepatitis B Virus DNA Detection

Abstract Background Hepatitis B is one of the most common infectious diseases with global significance, seriously causing chronic liver complications and a heavy health burden in developing countries. There is no doubt that real-time polymerase chain reaction (RT-PCR) has been a golden standard for monitoring the Hepatitis B virus (HBV) level in clinical health management. However, the conventional PCR protocol cannot fulfill the field test requirement in some resource-poor areas due to its drawbacks, such as huge size, long turnaround time, and demand for professional laboratory facilities. For solving these problems, a portable microfluidic chip-based PCR detection system was developed to enable the nucleic acid test in a flexible, rapid, and economical way. With the efficient temperature control module and advanced optical path design, this novel panel can achieve fast thermal circulation with a 30°C/s heating rate and multiple fluorescent detection with a throughput of 6 samples at a time. Methods In this study, we assessed the detection performance of the system using a commercial HBV nucleic acid detection kit. The reproducibility, limit-of-detection (LoD), and linearity were validated by reference samples with gradient concentrations. We evaluated the clinical sensitivity and specificity of the microdevice by a total of 200 extracted serum samples (100 positive and 100 negative cases). The analytical results were compared with a traditional PCR device with FDA certification. Results The variation coefficients of the microdevice for reference samples with different concentrations are 1.78%, 1.98%, and 1.50% (n = 10), respectively. The field-deployable PCR system can provide the HBV DNA assay with a detection limit of 300 IU/ml, whose reaction time was approximately 67 mins rather than the 108 mins performed by the comparator. During the establishment of the standard curve, this fast PCR test shows a strong linear correlation (R2 = 0.9919) between targeted gene concentration and dilution factor. Additionally, among the 200 clinical samples, we used the microchip-based system to rapidly complete quantitative detection for each sample with high sensitivity of 100% (100/100) and specificity of 100% (100/100), which is critically consistent with the traditional PCR method. Conclusion Hence, the point-of-care microfluidic PCR system exhibits great feasibility in offering timely, accurate, and reliable molecular diagnosis for early epidemic disease screening and therapeutic guidance of chronic infections.

Automatic Pico Laser Trimming System for Silicon MEMS Resonant Devices Based on Image Recognition

Laser trimming promises an increasing yield in microfabrication for the high performance Micro Electro-Mechanical Systems (MEMS) resonant devices by overcoming manufacturing tolerances and tuning sensors or actuators for certain operating conditions. How to achieve a high precision and efficiency trimming at low cost is the critical issue that the technical communities are most concerned. In this paper, we proposed an automatic laser trimming system for silicon MEMS devices based on a picosecond laser source and image recognition technique (IRT). Through the design of laser focusing optical path and coaxial imaging optical path, the observation of laser machining process is realized. A set of picosecond laser trimming parameters is determined by experiments, which enables a 4um width trench on the silicon resonator. Compared with the femtosecond laser trimming systems, the cost of the pico-laser system is reduced by more than 60%. The shape matching algorithm based on OpenCV and the chord-to-point distance accumulation (CPDA) algorithm for MEMS resonators image measurement solve the problem of inefficiency of manual trimming for complex resonators. A dual-mass tuning fork resonator is used to demonstrate the feasibility of the trimming approach. It is shown that the system realizes a fine-tuning (< 0.3Hz) of the resonant frequencies. The trimming time of a single device using the automatic trimming method is reduced from more than 1 hour manual trimming to less than 1 minute. Finally, the structural stiffness imbalance of tuning fork resonator caused by the manufacturing error is eliminated, which verifies the feasibility of the system.

Dynamic Optical Path Provisioning for Alien Access Links: Architecture, Demonstration, and Challenges

With the spread of datacenter interconnect (DCI) and private 5G, there is a growing demand for dynamically established connections between customer locations via highcapacity optical links. However, link parameters, such as signal power profile and amplifier gains, are often unknown and have to be measured by experts, which prevents dynamic path provisioning because of time-consuming manual measurements. Several techniques have been proposed for estimating the unknown parameters of such alien access links; however, no work has presented the architecture and protocol driving the estimation techniques to establish an optical path between the customer locations. This study aims to automatically connect customerowned transceivers via alien access links with maximum data rate. First, we propose an architecture and protocol for cooperative optical path design between a customer and carrier, utilizing a state-of-the-art technique for estimating link parameters. Second, we implement the proposed protocol in a software-defined networking controller and white-box transponders using an open API. The experiments demonstrate that the optical path is dynamically established via alien access links in 137 seconds from the transceiver's cold start. Finally, we discuss the possible reduction of required OSNR margin with this method and the remaining issues.

Development and Performance Evaluation of a Infrared Rain Sensor

We design a rain sensor to automatically control the car wiper action. In the circuit and optical path design, innovative design of four rain detection channel, that increase the rain sensing area. In the design of optical lens, the main compensating lens and airfoil compensating lens are designed to enhance the signal strength and improve the sensitivity of detection. In the software design, we use self-calibration technology, anti-interference technology, so that wiper control accurate and reliable. We also design a device to test the rain sensing area of the sensor, and evaluated the sensor performance by compared the rain sensing area. The results show that the sensing area of the designed rain sensor is far beyond the standard.

Design of a dual scattering angle multi-pass Thomson scattering system with signal separation function on Heliotron J.

This paper proposes a design of dual scattering angles multi-path Thomson scattering system with a signal separation function to solve the overlapping phenomenon of scattered light signals and to increase the measurement accuracy for the investigation of anisotropic electron velocity distribution. Furthermore, an optical path design is proposed to demonstrate how overlapping scattered light signals can be separated by setting the optical path in a limited room with a compact layout, which makes the incident interval between two overlapping scattered light signals 1.7 times longer than that of our current system. The specific position of each optical component existing in the system is determined via a Gaussian beam analysis to avoid damage caused by overexpansion of spot size with the application of two cooperating image relay systems. Conversely, a polychromator is optimized by resetting the pass waveband of the interference filter combination to achieve high accuracy in electron temperature (Te) measurement corresponding to two scattering angles simultaneously.

Colored Silicon Heterojunction Solar Cells Exceeding 23.5% Efficiency Enabled by Luminescent Down-Shift Quantum Dots.

Colored solar panels, realized by depositing various reflection layers or structures, are emerging as power sources for building with visual aesthetics. However, these panels suffer from reduced photocurrent generation due to the less efficient light harvesting from visible light reflection and degraded power conversion efficiency (PCE). Here, color-patterned silicon heterojunction solar cells are achieved by incorporating luminescent quantum dots (QDs) with high quantum yields as light converters to realize an asthenic appearance with high PCE. It is found that large bandgap (blue) QD layers can convert UV light into visible light, which can notably alleviate the parasitic absorption by the front indium tin oxide and doped amorphous silicon. Additionally, a universal optical path model is proposed to understand the light transmission process, which is suitable for luminescent down-shift devices. In this study, solar cells with a PCE exceeding 23.5% are achieved using the combination of a blue QD layer and a top low refractive index anti-reflection layer. Based on ourbest knoledge,the obtained PCE is the highest for a color-patterned solar cell. The results suggest an enhanced strategy involving incorporation of luminescent QDs with an optical path design for high-performance photovoltaic panels with visual aesthetics.

Contactless GSR Sensing Using mmWave Radar

The galvanic skin response (GSR), which is a manifestation of the activity in eccrine sweat glands, has always been an important psychological test to evaluate emotional arousal and mental stress. Although researches have focused on the radio reflections of skin and revealed that sweat gland activity can change the reflection signal of skin, the complicated experimental settings including vector network analyzer (VNA) and even optical path design limit further daily life application. In this article, we demonstrate the potential of using commodity millimeter-wave (mmWave) multiple-input multiple-output (MIMO) radar for contactless GSR sensing. To simulate the reflected signals of the frequency-modulated continuous-wave (FMCW) radar to the skin of different individuals, a four-layered skin model focused on the sweat duct is used and the change in conductivity in sweat ducts is regarded as mapping of sweat gland activity. Extensive experiments are conducted, consisting of three different physiological statuses: relaxing status, mental stress status, and physical stress status. We design a beamformer to transform the raw signal to the space domain so that the reflection signals from the palm are separated. The principal components of the processed signal are extracted to eliminate the interference caused by breathing and random noise. We evaluate the performance in terms of the correlation between the radar signal and the GSR before and after stress-induced events. The experimental results preliminarily verify the feasibility of contactless GSR sensing.