Journals >Acta Photonica Sinica
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2024
Volume: 53 Issue 7
25 Article(s)
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Special Issue for Photodetectors
Preparation and Performance of Integration Device between Si Microlens Array and Infrared Focal Plane Array （Invited）
Zhijin HOU, Xudong WANG, Yan CHEN, Jianlu WANG, and Junhao CHU
Integration device between silicon (Si) microlens array and Infrared Focal Plane Array (IRFPA) has been a hot research topic domestically and internationally. IRFPA nowadays serves military and commercial equipment fields, such as defense weapons, infrared remote sensing and meteorological environment because of its hiIntegration device between silicon (Si) microlens array and Infrared Focal Plane Array (IRFPA) has been a hot research topic domestically and internationally. IRFPA nowadays serves military and commercial equipment fields, such as defense weapons, infrared remote sensing and meteorological environment because of its high sensitivity and strong anti-interference. Si microlens array can be integrated with IRFPA to solve the problems caused by the low filling factor and chip cracking of IRFPA, thereby improving the performance of IRFPA.In this paper, in order to improve the performance of IRFPA, Si diffractive microlens array is designed. The Si diffractive microlens array and InSb IRFPA are prepared and integrated together. And the performance of integration device is given and discussed.Firstly, design parameters and preparation method of Si microlens array for IRFPA are given in detail. The Si diffractive microlens array is comprised of eight zones within one pixel. The radius of each zone is 6.2 μm, 8.8 μm, 10.8 μm, 12.45 μm, 13.95 μm, 15.3 μm, 16.5 μm, 17.7 μm. The minimum zone width is 1.2 μm. Each etch depth is different. The etching depths are 0.868 μm, 0.434 μm, 0.217 μm. Plasma etching is used in Si diffractive microlens array preparation. The Si diffractive microlens array is prepared by three photolithographic and etching processing steps. The SI500E type equipment is used as reactive ion etching. The etching conditions are the gas flow of CHF3∶O2 of 24 mL∶6 mL, the ICP source power of 400 W, the Radio Frequency (RF) source power of 150 W, and the pressure of reaction room of 0.5 Pa.Secondly, the InSb IRFPA is made using the prepared InSb array and Si Readout Circuit (ROIC). An n-type InSb substrate is used and a P-type layer is obtained through the diffusion Cd. A surface with mesa is obtained by photolithography and etching. After passivation of the mesa, a chrome gold layer is evaporated and then electrodes are obtained through photolithography and corrosion processes. After the chip is prepared, the developed InSb array and the readout circuit array are photolithographed with indium column windows and evaporated with indium film at the same time. The indium column arrays are obtained through stripping process, and then connected through flip-chip bonding. The flip-chip bonding device is assembled and encapsulated after bottom filling, thinning polishing, and vapor deposition of anti-reflection film.Thirdly, the prepared Si diffractive microlens array and InSb IRFPA are integrated together by using the glue without bubbles. Each element of the Si diffraction microlens array and the InSb IRFPA is aligned according to the prepared alignment. The Si diffractive microlens array is thinned and polished to focus on a point.Finally, they are tested by optical system and IRFPA test-bench. Results show that the diffraction efficiency of the Si diffractive microlens array with the double-sided anti-reflecting is 83.6%. The image of response voltage test shows no chip cracking on the integration device. The working band of integrated device is 3.7 μm to 4.8 μm. At this time, the average blackbody responsivity and detectivity of integration device is 4.85×107 V/W and 7.12×109 cm·Hz1/2·W-1, respectively. The working temperature is 77 K. The performance of integration device is superior to the performance of the existing infrared focal plane array.The results indicate that Si microlens array not only increases the filling factor of IRFPA, but also optimizes the stress matching of IRFPA to solve the problem of chip cracking. The results are of reference significance for improving the performance of IRFPA to meet the system application requirements..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753304 (2024)
Multimodal Fusion Detection Method of Tomato Fruit Based on Phase and Hyperspectral
Haichen DAI, Xinyu WEI, Yixin XU, Yuanping CHEN, Yuanyuan XU, and Ying JI
Tomatoes are highly nutritious and popular worldwide as both a vegetable and a fruit. With the improvement of consumers' requirements for food quality and the access standards of tomato products in various countries, tomato quality control has received more and more attention. Traditional manual sorting operations Tomatoes are highly nutritious and popular worldwide as both a vegetable and a fruit. With the improvement of consumers' requirements for food quality and the access standards of tomato products in various countries, tomato quality control has received more and more attention. Traditional manual sorting operations are time-consuming, laborious and inefficient, so it is necessary to develop fast and accurate inspection technology. With the development of machine vision and neural network technologies, automated agricultural product defect detection methods have been widely studied and applied, providing new ideas and methods for agricultural product quality inspection. However, tomatoes and other agricultural products are affected by genetic factors and growth environment, and their external three-dimensional geometric forms and internal physiological information are complex and different, and a single type of detection method can only detect specific defects, so more dimensional detection methods are needed to detect the quality of tomatoes. In view of the needs of automatic detection of tomato quality and the shortcomings of traditional hyperspectral imaging technology in the non-destructive testing of agricultural products, such as incomplete information characterization and spectral reflectance distribution affected by morphology, this work adopts the idea of fusion detection of structured light imaging and hyperspectral imaging, and designs and builds a detection device that can realize the non-destructive diagnosis of the three-dimensional morphology of the appearance of the sample and the internal physiological information in the same imaging room. Based on the deep learning technology to obtain the three-dimensional topography of the sample from the projection fringes, a data fusion algorithm with simple operation and low computational cost was designed to register the heterologous images collected by different sensors, and the multi-dimensional information of the appearance and internal physiological state of the sample was characterized in real time by a single image through the fusion of the three-dimensional topography information and the hyperspectral image.Based on the principle of structured light imaging and deep learning technology, an easy-to-operate and fast automatic three-dimensional topography reconstruction algorithm of samples and a method of matching and fusing spectral distribution data were proposed, and the corresponding detection device was built. For the three-dimensional surface topography of the measured object, based on the fringe imaging principle of monocular camera, the surface height information is mapped through the pixel semantic information output by the semantic segmentation network model. The matching and fusion of the physical morphology information and the biochemical composition information of the analyte were carried out, and the two heterologous images were registered and evaluated based on the line feature fitting of the standard reference object. The edge extraction algorithm, curve fitting algorithm and line feature fusion method are used to recover the spatial position and pixel area of the reference object, and then the spatial position of the object to be tested is restored as the registration element, and the rapid registration of heterologous images is realized through simple operation, and the real-time registration fusion of three-dimensional mapping and hyperspectral images is realized. Taking tomato fruit as an example, the test was carried out by the detection device. For samples with a diameter of 4~8 cm, the trained network model can predict the three-dimensional height distribution within 0.75 seconds, and the diameter and maximum height errors are within 4%. In this paper, the morphology distribution is directly extracted based on a single structured light fringe map, and the heterologous image registration is carried out based on point-line features, and the simultaneous acquisition and fusion characterization of multi-dimensional information around the physical and chemical information of the sample can provide a reference for overcoming the problem of insufficient evaluation index of a single type of image, and realize the simultaneous detection, analysis and characterization of the surface morphology and shallow chemical composition of the analyte. In this work, the feasibility and effectiveness of the proposed method of fusion of three-dimensional morphology image and spectral image from heterologous sensor are verified by experiments, which can provide data and technical reference for solving the problem of insufficient evaluation indicators in the process of fruit quality detection under a single sensor..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0710001 (2024)
Research on Imaging Performance of Annular-5 Sparse Aperture System
Jiankai ZHU, Yonghui LIANG, Jilin LIU, Zhuoxi HUO, and Huizhe YANG
High-resolution imaging plays a crucial role in various fields such as astronomical observations, earth sciences, and national defense. Traditionally, the main approach to improve angular resolution is via increasing the aperture of optical system. However, manufacturing and maintaining large aperture telescopes often High-resolution imaging plays a crucial role in various fields such as astronomical observations, earth sciences, and national defense. Traditionally, the main approach to improve angular resolution is via increasing the aperture of optical system. However, manufacturing and maintaining large aperture telescopes often come with high costs, and space-based optical systems are particularly constrained by payload limitations. Sparse aperture systems have emerged as a solution that can simultaneously reduce cost budgets and process requirements, garnering widespread attention since their inception. The high-resolution imaging capability of sparse aperture systems is essentially achieved through the interference between sub-apertures, resulting in a reduction of the half-width of the sub-aperture's Airy disk. To achieve effective interference between sub-apertures, the control of optical path difference, or the co-phasing of sub-apertures is of great importance and therefore can largely determine the imaging performance of the sparse aperture system. Although adaptive optics systems can provide a relatively flat wavefront, the correction process is performed independently for each sub-aperture, and the relative optical path of the sub-paths used for coherent interference can not be simultaneously controlled. In this study, a annular-5 configuration is firstly discussed based on the constraints imposed by the frequency domain. The annular-5 configuration exhibits a five-fold symmetry, with non-redundant baseline directions between sub-apertures. The resulting modulation transfer function possesses a ten-fold symmetry, providing certain advantages on an equivalent single-aperture telescope. The analytical expression for the point spread function of the annular-5 configuration has been derived based on the theory of Fourier optics. Theoretically, the peak of the point spread function for the annular-5 configuration is 25 times larger than the peak of the point spread function for an individual sub-aperture. This is because the annular-5 configuration collects 5 times more light flux at the entrance pupil compared to a single sub-aperture, and the interference effect causes the energy to shift from dark fringes to bright fringes, enhancing the main peak by 20 times. Therefore, the interference between sub-apertures is crucial for improving the resolution of sparse aperture systems. Considering the constraint of frequency domain coverage without zero frequency, the maximum range for the achievable fill factor of the annular-5 configuration is 27.8% to 68.5%. The discussion on the equivalent aperture highlights the trade-off optimization of fill factor in sparse aperture systems. Based on the analysis under the ideal condition of no aberrations, the influences of piston errors and adaptive optics residual wavefront errors on the annular-5 configuration are investigated numerically by characterizing the point spread function and modulation transfer function. The results demonstrate that the tip/tilt errors in adaptive optics residuals have the most notable impact on the imaging quality. Specifically, tip/tilt errors cause the diffraction patterns of the sub-apertures to be misaligned, resulting in the diffraction envelopes not overlapping with each other, which leads to incomplete coherent interference of the beams. Using a Strehl ratio greater than 0.80 as the evaluation criterion, separate discussions are conducted on the tolerance of piston errors and adaptive optics errors of the annular-5 configuration. Assuming a fill factor of 43.2%, numerical calculations indicate that the piston errors between sub-apertures need to be controlled within λ/6 at a minimum, while the root mean square of wavefront residuals for each sub-aperture, which includes independent adaptive optics systems, needs to be controlled approximately within λ/14. Thus, the co-phasing between sub-apertures relies on the prerequisite of a certain level of adaptive optics correction. The research results on the annular-5 configuration have a certain degree of universality and can provide valuable references for future imaging research on sparse aperture systems..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0711001 (2024)
Design and Imaging of Multi-frequency Interference System Based on T-lens Arrangement
Yu QIAO, Guixiang CHEN, Yusheng ZHAI, Gang LIU, Weiji HE, and Qian CHEN
The angular resolution of conventional optical systems is limited by the size of the system aperture, and high resolution implies a larger system aperture. However, the increase of system aperture will make the volume, weight and power consumption of the whole system increase dramatically, which greatly increases the dThe angular resolution of conventional optical systems is limited by the size of the system aperture, and high resolution implies a larger system aperture. However, the increase of system aperture will make the volume, weight and power consumption of the whole system increase dramatically, which greatly increases the difficulty of engineering realization. Photonic integrated interferometric imaging technology is a new type of highly integrated detection technology that combines optical interferometric imaging principle and photonic integration technology, which utilizes a photonic integrated chip to replace the sensors in traditional imaging, significantly reducing the volume, weight, and power consumption of the imaging system. However, at present, this technology is still in the stage of theoretical and simulation calculation research, and the research of related experimental imaging system is relatively small, and the existing interferometric imaging system can only collect the spatial frequency of the target point by point.In order to investigate the effect of multi-frequency point sampling on photonic integrated interference technology, this paper proposes and builds a multi-frequency interference imaging system with T-shaped lens arrangement. The system selects laser as the illumination light source. The light from the laser is irradiated to the 2D grating after passing through the fiber collimator. The multi-level diffracted light through the grating is split into multiple paths and incident to the rear fiber collimator. The fiber collimator is used instead of a lens array. The lenses are divided into two groups, S group horizontally and R group vertically, and the T-distributed lens array allows for frequency acquisition of baselines in multiple directions and at different lengths. After the lens array through the optical switch to control the on-off optical path, optical switch on time signal through the optical fiber into the fiber coupler for interference. The detector is used to capture the interference signal and then the spatial frequency information of the target is solved, and the target image can be obtained by doing the inverse Fourier transform of the spectral map.We first simulate the imaging process of the system, the center wavelength of the illumination light source is set to 1 550 nm, the distance from the target to the light source is 1 m, and the orthogonal two-dimensional grating with the spatial frequencies of 80 lp/mm and 40 lp/mm in the transverse and longitudinal directions is selected as the target for the simulation, and the minimum sampling frequency of the system is 40 mm-1. In order to distinguish the target, a pair of black and white stripes of 80 lp/mm is at least 40 mm-1. In order to distinguish the target, a pair of black and white stripes of 80 lp/mm is at least 2 pixels, and the size of the received image is set to 576×576. In order to have a certain degree of redundancy, the size of the spectral image received by the lens is set to 1 152×1 152 in the simulation, corresponding to the highest frequency of 160 lp/mm, which can satisfy the demand for target detection.The actual imaging system is built under the same conditions as the simulation to image the target. After calculation, the Peak Signal to Noise Ratio (PSNR) of the simulated image is 30.79 dB, and the PSNR of the experimental reconstructed image is 27.95 dB, and the overall structure of the reconstructed image has not been changed, so the experiment successfully realizes the reconstruction of the target image. Of course, in the process of the experiment, we also found some problems in the system, such as the lack of spectrum acquisition, the influence of the external environment and other problems, to be further researched and solved. Overall, photon integrated interferometric imaging is a technology with practical value, and the design of the imaging system and the process of system imaging proposed in this paper provide guidance and direction for the practical engineering application of this technology..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0711002 (2024)
Measurement and Analysis of CO2 Hyperspectral Absorption Spectroscopy at High Pressure in the 2 µm Band
Haolong WU, Yamin WANG, Mengmeng TAO, Sheng WANG, Guohua LI, Jingfeng YE, Zhenjie WU, and Lijun WANG
CO2 is one of the important products of combustion processes. In industrial production, food processing, clinical medicine and other application scenarios, monitoring the concentration of CO2 is of great significance. Absorption spectroscopy is a common method based on resonant absorption of molecular energy levels on CO2 is one of the important products of combustion processes. In industrial production, food processing, clinical medicine and other application scenarios, monitoring the concentration of CO2 is of great significance. Absorption spectroscopy is a common method based on resonant absorption of molecular energy levels on the laser transmission path to invert flow field parameters. It has the advantages of high sensitivity, fast response, and small perturbation to the flow field, and has been widely applied in trace gas analysis and environmental monitoring. Compared with tunable diode laser absorption spectroscopy, hyperspectral absorption spectroscopy can cover a wider spectral range, which is beneficial for achieving more accurate environmental parameter measurements. In contrast with communication bands, the CO2 spectral line intensity in the 2 μm band can be increased by two orders of magnitude, and the selection of spectral lines is more abundant. With the help of the broadband tunable thulium-doped fiber laser self-developed by our group, the hyperspectral absorption signals of CO2 in the 2 μm band are measured within the pressure range of 152 kPa to 932 kPa, and compared with the theoretical spectra calculated based on the HITRAN database. At 152 kPa, the peak matching between the measured spectrum and the theoretical spectrum is completed to achieve wavelength calibration, which can verify that the broadband tunable laser has fine frequency linear scanning characteristics. At the same time, the baseline extraction under high pressure environment is a difficult problem in data processing, which directly affects the inversion results of absorption spectral line shape. The commonly used baseline extraction method of extracting the weak absorption part of the original signal by polynomial fitting is only a rough calculation method, which will lead to a low intensity of baseline fitting when the pressure increases, introducing large errors into the subsequent absorption spectrum inversion. Therefore, considering using the simultaneous fitting method. Through synchronous fitting of the original signal baseline and absorption spectrum, the spectrum inversion accuracy of the spectral line can be improved. The specific operation is to describe the original signal as a theoretical model under the joint action of baseline and absorption spectrum, with pressure, temperature, CO2 mole fraction, baseline distribution fitting coefficient as the variable parameters of nonlinear curve fitting, and taking the minimum residual as the goal, using optimization algorithm to calculate the baseline parameters and gas environmental parameters under the optimal matching of theoretical model and measured data. Through the experimental measurement of CO2 hyperspectral absorption data at 932 kPa, it can be found that the CO2 absorption spectrum is greatly broadened, and the overall spectral line tends to be homogenized. Meanwhile the baseline profile of the original signal completely disappears, and it is difficult to obtain the baseline distribution by conventional means without a reference optical path. However, by using the simultaneous fitting method to synchronously fit the baseline and absorption spectrum, this problem can be solved to some extent. From the experimental results, the measured spectra in the pressure range of 152 kPa to 932 kPa are highly matched with the theoretical spectra, and the residuals of the full-band spectral fitting are below 0.04, corresponding to the highly consistent environmental parameter inversion results with the experimental settings. In addition, by comparing the 1 965.98 nm absorption line area retrieved from the narrowband absorption spectrum, the reliability and superiority of the hyperspectral absorption spectrum under high pressure are confirmed. Under the condition of approximately constant temperature and gas mole fraction, the absorption area retrieved from the hyperspectral absorption spectra maintains a good linear relationship with pressure within the measurement range. Overall, the hyperspectral absorption technology has a wide range of environmental applicability and strong reliability. Combined with the advantages of high-intensity absorption spectra in the 2 μm band, the use of simultaneous fitting data processing method can significantly improve the inversion accuracy of spectral line parameters, which can better achieve real-time detection and quantitative analysis of environmental parameters and CO2 gas concentration under wide operating conditions..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0730001 (2024)
Calculation and Experimental Study on the Gradient Refractive Index of Grass Shaped Alumina Microstructure
Xiuhua FU, Jiulin SU, Yonggang PAN, Ben WANG, Zhaowen LIN, Gong ZHANG, and Wenhan SUN
Grass shaped alumina is a nano thin film with extremely low refractive index, which can also have good anti reflection effect when incident at large angles. In recent years, it has been increasingly widely used in consumer electronics fields such as automotive, monitoring, and mobile phones. This article focuses on theGrass shaped alumina is a nano thin film with extremely low refractive index, which can also have good anti reflection effect when incident at large angles. In recent years, it has been increasingly widely used in consumer electronics fields such as automotive, monitoring, and mobile phones. This article focuses on the influence of the micro/nano structure of grass shaped alumina on the refractive index. The volume of alumina is calculated using both the table calculation method and the column calculation method. In order to improve calculation efficiency and accuracy, a higher thickness table calculation method is used on the outer side of the film, and a smaller thickness column calculation method is used on the inner side of the film. The Clausius Mossotti equation is used to calculate the mixed dielectric film layer of alumina and air. A gradient refractive index model of grass shaped alumina was constructed, and the morphology characteristics of its microstructure and distribution of gradient refractive index were studied, and its visible light antireflection performance was calculated. By using electron beam deposition of alumina thin films and optimizing parameters such as deposition temperature and water boiling process, grass shaped alumina nanofilms with different structures were obtained. The visible light band 420~680 nm antireflection film was prepared. Finally, under the conditions of deposition temperature 150 ℃, water boiling time 10 minutes, and water boiling temperature 90 ℃, an antireflection film layer with an average reflectivity of less than 0.5% in the visible light band was prepared, and JPK software and MATLAB software were used to perform hierarchical analysis and simulation fitting on the grass like micro/nano structure. TFC software was used to perform spectral analysis on the gradient refractive index results. The final simulation results still have some differences from the measured results, and the main reason for the error may be the light scattering caused by the non-uniformity of the grass like microstructure; when fitting and calculating the grass like microstructure, the reflection spectrum in the visible light band can only be calculated based on the same refractive index. If the refractive index dispersion distribution in the visible light band is calculated, a specialized software program needs to be developed for calculation; another reason is that there are many methods for calculating the refractive index of mixed media, with varying errors..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0731001 (2024)
Ferroelectric/electret Cooperative Organic Photoelectric Synapse Based on Thin Film Transistor
Zhida LI, Binglin LAI, Bowen LI, Hongyu WANG, Shangchao HONG, and Guocheng ZHANG
In recent years, the level of computerisation in society has increased significantly, resulting in a surge in demand for data processing. Consequently, traditional computing technologies based on Von Neumann architectures are encountering limitations. The separation of processors and storage units in traditional computIn recent years, the level of computerisation in society has increased significantly, resulting in a surge in demand for data processing. Consequently, traditional computing technologies based on Von Neumann architectures are encountering limitations. The separation of processors and storage units in traditional computers makes them less efficient and power-efficient when processing large amounts of data. Biological neural network computing presents a potential alternative solution to the Von Neumann bottleneck. Neuromorphic computing at the physical level relies on synaptic devices that mimic the function of biological synapses in neural networks. Significant progress has been made in artificial synaptic devices, such as phase-change memories, amnesia, and field-effect transistors. Organic thin-film transistors are currently a popular research topic due to their simple manufacturing process and low cost. In contrast to inorganic thin-film transistors, which require fabrication under high vacuum and high temperature conditions, organic electronic devices only require the formulation of organic materials into a solution for thin-film processing and annealing below 200 degrees Celsius. This reduces equipment requirements and manufacturing costs. To improve the simulation of synaptic function in thin film transistors, researchers have added a functional layer between the insulation and semiconductor layers. Various synaptic transistors have been prepared by combining materials with different properties. The three most common types of synaptic transistors are electret, ferroelectric, and floating gate, classified based on their functional layer. Ferroelectric synaptic transistors are a popular research topic among artificial synaptic devices due to the plasticity of their polarisation, which closely resembles that of biological synapses. However, the retention time of these ferroelectric synapses is short due to the gradual decrease of the ferroelectric polarization state over time. The rough ferroelectric film results in poor interface characteristics, including high leakage current and easy mutual diffusion between the ferroelectric film and the semiconductor layer. This is because the ferroelectric layer is in direct contact with the semiconductor. These issues negatively impact the device's basic performance, limiting the potential applications and development of ferroelectric synapses. This paper proposes adding an electret functional layer to ferroelectric synaptic transistors. The electret PVN can help passivate the rough surface of the ferroelectric material and improve the interface quality. The root-mean-square roughness of the film surface has been reduced from 2.95 nm to 0.66 nm. The film's homogeneity facilitates smooth carrier transportation at its interface. Additionally, the P(VDF-TrFE) layer has a higher dielectric constant than the PVN layer, resulting in a stronger electric field applied to the PVN layer. This allows for better electron trapping, resulting in a larger postsynaptic current and longer retention time after stimulation. These findings suggest a transition from short-term to long-term plasticity. Compared to conventional ferroelectric synaptic transistors, the switching ratio has been increased by an order of magnitude, and the threshold voltage has been reduced by 10 V. This leads to lower operating voltage and energy consumption. Photoelectrical synapses have become a popularresearch topic in recent years due to their advantages over traditional electrical synapses. These advantages include low crosstalk, low energy consumption, high bandwidth, and high transmission speed. Unlike traditional electrical synapses, which use a single electrical stimulus as the input signal, photoelectrical synapses offer a more efficient alternative. The combination of light and electricity in the input mode is more similar to the operational mechanism of biological synapses than a single electrical input. This is because a single device simulating a synapse has an insignificant impact on an entire biological neural network. However, constructing a complete artificial neural network requires a vast number of components and intricate circuits. Multilevel optoelectronic synapses hold great potential in reducing the number of devices and simplifying neural networks. This paper demonstrates that the electret layer of the device can capture different numbers of electrons depending on the colour of light. As a result, the device exhibits four distinct synaptic states under different colours of light, highlighting the potential of multi-stage photoelectric synapses. The hybrid input mode of light and electricity brings it closer to biological synapses, enabling more complex synaptic behaviours. The function of multi-stage photoelectric synapses gives them unlimited potential in the field of neural networks..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0731002 (2024)
[in Chinese]
Qiang Li, Xudong Wang, Mingsheng Xu, and Weizong Xu
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753300 (2024)
Fiber Optics and Optical Communications
Deep Learning Aided Signal Detection Algorithm Experimental Research for Underwater Optical Communication
Pengfei YE, Peng ZHANG, Hao YU, Shuang HE, Dongsheng TIAN, Yuanxin WANG, and Shoufeng TONG
Underwater wireless optical communication has garnered significant attention in the wireless communication field due to its high data rate, enhanced security, and lightweight nature. However, seawater can induce absorption and scattering of light. Absorption results in a reduction of the received optical power at the rUnderwater wireless optical communication has garnered significant attention in the wireless communication field due to its high data rate, enhanced security, and lightweight nature. However, seawater can induce absorption and scattering of light. Absorption results in a reduction of the received optical power at the receiver, which is an irreversible process, while scattering causes alterations in the received photons at the receiver. Moreover, the ocean typically contains turbulence, a phenomenon caused by temperature variations and irregular movements, leading to random fluctuations in the optical signal. Consequently, the underwater channel is intricate and challenging to predict. To achieve reliable communication performance, a more dependable signal detection method is required at the receiver. In this study, a deep learning-assisted signal detection method is proposed for underwater optical communication. A convolutional neural network (a specialized form of deep neural network) is developed to directly detect the Original On-off Keying (OOK) signal, and two distinct training methods for the Deep Neural Network (DNN) are proposed during the training phase. Initially, an indoor underwater optical communication experimental platform is designed and constructed, incorporating three types of water tank channels (flowing water, turbid flow 1, turbid flow 2). The attenuation coefficients and probability density functions of the channels are measured. Subsequently, a simulated underwater optical channel is derived based on the measured channel mathematical models, and a simulated dataset of OOK signals for the neural network is obtained. The proposed methods are tested using the dataset, and the performance of the two different DNN training methods and the adaptive threshold method is simulated under different simulated channels. The proposed methods exhibit an improvement in Bit Error Rate (BER) compared to the adaptive threshold method at any signal-to-noise ratio in the three channels. The improvement is most notable in the simplest flow channel, with up to a two-order-of-magnitude enhancement, and it increases with higher signal-to-noise ratios in the relatively complex turbid flow channel 2. Additionally, due to DNN training method 1 learning multiple datasets from different channels, it exhibits worse BER performance compared to training method 2, which only learns one channel dataset. However, thanks to the powerful fitting capability of DNN, the BER is still superior to the adaptive threshold method. To validate the simulation results, experimental datasets of OOK signals are obtained based on the experimental platform. The DNN is retrained and tested using the experimental datasets, and the BER performance of the two different DNN training methods and the adaptive threshold method is experimentally studied. For 5 Mbps communication transmission in the three water tank channels, the DNN method achieves a reduction in BER of two orders of magnitude, one order of magnitude, and one order of magnitude, respectively, compared to the adaptive threshold method. The trend of the experimental results is consistent with the simulation. For turbid flow 1 and different communication rates (5 Mbps, 10 Mbps, 25 Mbps), the DNN method achieves a reduction in BER of one order of magnitude at all three rates, and the proposed method requires lower received optical power compared to the adaptive threshold method when the BER is the same. The simulation and experimental results demonstrate that the proposed method enhances the performance of underwater wireless optical communication in complex channels compared to the adaptive threshold method, validating the reliability of the method. Therefore, the method can offer valuable insights for the design of high-speed and reliable underwater wireless optical communication systems..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0706001 (2024)
Instrumentation, Measurement and Metrology
Influence of Infrared Window on the Radiation Ideality of Package Blackbody and Correction Method
Jingyang ZHANG, Lingqi MENG, Xinzhu MOU, Ping SHEN, and Sheng XU
The blackbody is an ideal calibration target source for correcting the photoelectric conversion characteristics of infrared detectors. According to the theoretical radiation flux provided by the blackbody target surface, the detector can correct the quantitative relationship between the gray value of the output temperaThe blackbody is an ideal calibration target source for correcting the photoelectric conversion characteristics of infrared detectors. According to the theoretical radiation flux provided by the blackbody target surface, the detector can correct the quantitative relationship between the gray value of the output temperature field and the radiation flux, thus obtaining an accurate response gain coefficient. In order to meet the demand for real-time and accurate detection of targets with large temperature variations in fast-changing environments such as airborne, missile-borne, and space-borne scenarios, the wide-temperature-range blackbodies are typically vacuum-packaged by infrared windows to solve the problems of non-uniformity and low temperature dew and frost caused by large temperature differences in the environment. However, during calibration, the blackbody is affected by the attenuated target surface radiation and stray radiation from the window, there will be an error between the apparent temperature corresponding to the actual apparent radiation flux of the blackbody and the calibration temperature given by the measurement of blackbody surface. If the infrared detector still gives the calibration temperature according to the measured target surface temperature, it will affect the ideality of the blackbody and the calibration accuracy of the infrared detector. Most researchers consider the infrared window as a graybody and analyze the impact of environmental stray radiation reflected by the window on the infrared detector under high-temperature conditions, without systematically considering the influence of the spectral transmissivity, emissivity and reflectivity of the window on blackbody calibration technology. Therefore, in this paper, starting from the window spectral characteristics, aiming at the problem that wide-temperature blackbody packaged with infrared window affects the blackbody ideality, the influence law and internal causes of Ge and BaF2 typical windows on the error between the calibration temperature and the apparent temperature corresponding to the actual radiation flux were analyzed under different environment temperatures and calibration temperatures. Furthermore, a calibration temperature correction method, which is associated with both the calibration temperature and the environment temperature, was proposed and experimentally validated.Firstly, a thermal-optical coupling simulation model for the extended source blackbody surface was established. By using Monte-Carlo ray tracing method, the diffuse gray blackbody surface, the infrared window surface with selective radiation and the environmental radiation parallel to the window were dispersed into energy-carrying sub-beams. The actual apparent radiation flux, apparent temperature, and the variation trend of the error between the apparent temperature and the calibration temperature of the blackbody were calculated by the integrating sphere under the conditions where the atmospheric transmittance band was 7.5 μm~13 μm, and the environment temperature and calibration temperature ranged from -50 ℃ to +50 ℃. The actual apparent radiation flux included the attenuated radiation flux of the blackbody target surface under the influence of window spectral transmission, as well as the stray radiation flux from the window's spontaneous emission and reflective environment. The results show that when the calibration temperature is between -50 ℃ and +50 ℃, if the calibration temperature is lower than the environment temperature, the apparent temperature is higher than the calibration temperature, and the positive error between the calibration temperature and the apparent temperature corresponding to the actual radiative flux increases with the increase of the environment temperature. Conversely, if the calibration temperature is higher than the environment temperature, the apparent temperature is lower than the calibration temperature, and the negative error increases with the decrease of the environment temperature. The maximum error for the blackbody packaged with a Ge window can reach -4 ℃ to +13 ℃, while for the blackbody packaged with a BaF2 window, the maximum error can reach -6 ℃ to +20 ℃. This is because there the window's enhanced stray radiation and attenuated radiation from the target surface have a positive-negative game effect. Additionally, the average transmissivity of the BaF2 window is lower than that of the Ge window, resulting in increased attenuation of the blackbody target surface and the stray radiation from the window.Secondly, based on the fitting of the error variation curve between the apparent temperature and the calibration temperature, the relationship between the error correction amount of typical Ge and BaF2 window-packaged blackbodies and the calibration temperature change under different environment temperatures was obtained. In addition, the calibration temperature and apparent temperature measurement experiments of windowless open blackbody and Ge window-encapsulated blackbody were designed. Comparing the experimental value of the apparent temperature with the corrected calibration temperature, it was found that the effect of the blackbody calibration temperature correction was significant. For example, at an environment temperature of -10 ℃, the maximum absolute error between the corrected calibration temperature and the measured apparent temperature was 2.6 ℃, while at an environment temperature of 20 ℃, the maximum absolute error between the two was only 1.4 ℃.In this paper, through theoretical analysis, simulation correction and experimental measurement, it was found that the window has a positive-negative game effect on enhancing stray radiation and attenuating target surface emission radiation. Consequently, the larger the difference between the environment temperature and the calibration temperature, the larger the error between the apparent temperature and the calibration temperature. Additionally, the error increases as the average transmissivity of the window decreases. Furthermore, the effectiveness of the calibration temperature correction method was validated. The result shows that the maximum error between the corrected calibration temperature and the measured apparent temperature is reduced by more than 50%. This method provides a new solution for correcting the non-ideal characteristics of blackbody radiation sources with infrared window packaging and offers more accurate engineering guidance for the high-precision calibration of low-temperature infrared detectors..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0712001 (2024)
Planar Array Lidar and Camera Calibration Method Based on Tetrahedral Features
Xiaobin XU, Chenfei CAO, Lei ZHANG, Jinchao HU, Yingying RAN, Zhiying TAN, Linsen XU, and Minzhou LUO
Compared with traditional mechanical multi-line Lidar, area array Lidar can achieve greater field of view coverage through non-repetitive scanning, and has many applications in industrial production and robotics. A single sensor often has some limitations, while the fusion of multi-sensor data has higher precision and Compared with traditional mechanical multi-line Lidar, area array Lidar can achieve greater field of view coverage through non-repetitive scanning, and has many applications in industrial production and robotics. A single sensor often has some limitations, while the fusion of multi-sensor data has higher precision and accuracy. Point cloud data contains accurate depth information of the environment, while image data contains rich color and texture information of the environment. The fusion of Point cloud and image can increase the dimensionality of the sensor's perception of environmental, and also enable robots and automation equipment to achieve more complex tasks and reconstruct colorful three-dimensional environments. The prerequisite for achieving the fusion of point cloud data and image data is to calibrate the extrinsic parameters of the Lidar and camera. The purpose of sensors external parameter calibration is to find the accurate position conversion relationship between the two sensor coordinate systems. In order to improve the calibration accuracy of array Lidar and monocular camera, this paper proposes a calibration method based on tetrahedral structure for array Lidar and camera. The tetrahedron structure formed by two isosceles right triangle calibration plates and the ground is used as the calibration object. Using the random sampling consensus algorithm to extract three plane features from point cloud data, The straight line parameter equations of the edges of the tetrahedral structure are obtained through the intersection of the three planes. The common points of the three planes are the vertices of the tetrahedral structure. The line segment detection algorithm is used to extract the straight line features of the intersection of three planes in the image data, and the vertex coordinates of the tetrahedral structure are obtained through the straight line intersection. The method of indirectly obtaining point and linear features through plane extraction is more accurate than the direct extraction method. The back-projection rays of the corner points in the image and the straight-line features in the point cloud form multiple sets of skew lines. The distance between the skew lines is used to construct the residual equation of the rotation and translation relationship. The angle error between the projection of the straight line feature in the point cloud on the image and the real imaging straight line is used to establish the residual equation of the rotation relationship. The “point-three-line” correspondence relationship between point cloud data and image data is established, which improves the constraint strength between corresponding features in point cloud and image data. Based on the Rodriguez formula, a rotation vector is used to represent the transformation matrix between the Lidar and camera coordinate systems. The transformation vector between the camera and radar coordinate systems is solved through nonlinear optimization and the transformation matrix is finally obtained. The distance from the projected point of the edge in the point cloud to the edge in the image is used as the projection error from the point cloud data to the image data. The proposed method is experimentally compared with the Livox company's open-source calibration method and the University of Hong Kong's targetless calibration method. The tetrahedral structure data collected in this paper and the open-source algorithm data were tested, respectively. The calibration results on images with a resolution of 1 920×1 080 shows that the average projection error of the proposed method is within 0.6 pixels, which is superior to the other two calibration methods. At the same time, without a specific tetrahedral structure calibration object. The proposed method can use the wall corner tetrahedral structure to complete the calibration, which reflects the flexibility of the proposed method. The proposed high-precision calibration method of Lidar and camera provides a research foundation for the subsequent research on the fusion of Lidar data and image data..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0712002 (2024)
Three-dimensional Morphology Measurement of Highly Reflective Objects Based on Three Channel Parallel Processing
Hexiang HAN, Nan GAO, Guofeng ZHANG, Tong GUO, Yajing BAI, Yubo NI, Zhaozong MENG, and Zonghua ZHANG
Currently, optical 3D measurement technology is widely applied in various fields including industrial inspection and reverse engineering, due to non-contactness, high speed, and high precision. However, traditional fringe projection methods face challenges for the measurement of highly reflective surfaces. In such caseCurrently, optical 3D measurement technology is widely applied in various fields including industrial inspection and reverse engineering, due to non-contactness, high speed, and high precision. However, traditional fringe projection methods face challenges for the measurement of highly reflective surfaces. In such cases, the projected images may experience overexposure in bright regions, which may result in camera distortion. Currently, commonly used methods such as the multiple exposure time method and the intensity adjustment of projection patterns have issues such as requiring a large number of images to be captured and having poor algorithm adaptability. Therefore, to ensure both the measurement efficiency and accuracy while adapting to varying surface reflectivity of highly reflective objects has become a challenging research topic.With respect to the three-dimensional surface measurement of highly reflective objects, this investigation presents an approach for fringe projection intensity prediction and image fusion based on three-channel parallel acquisition of color camera. In the first place, a uniform gray image is pre-projected onto the object's surface. Based on the histogram distribution of light intensity of the object being measured, regions with similar surface reflectivity are grouped into clusters. The specific values for either three significant clusters or two significant clusters plus one minor cluster are calculated. By considering the scattering effects of light of different wavelengths, the optimal projection intensity ratio for the three channels specific to the object is determined. The corresponding RGB fringes are then re-projected onto the surface of the object. Secondly, the corresponding RGB fringes are re-projected onto the object's surface, and a color 3CMOS camera with three independent sensors captures images in parallel. Under multi-channel illumination conditions, the camera exhibits distinct responses to fringe patterns projected the projector with varying intensity ratios, subsequently isolating the corresponding channel-specific fringe images. Following this, pixels in positions with both unsaturation and maximum modulation are selected from the images of the three channels to generate image masks for each channel. Finally, based on the masks and fringe images from the three channels, a high dynamic range fringe pattern is synthesized.A hardware measurement system is constructed using a 3CMOS camera and a color DLP projector. Camera calibration is performed to obtain the internal parameters, and system calibration is carried out to acquire the geometric correspondence parameters between phase and space. The captured high dynamic range fringe images are processed using the four-step phase-shifting method and the optimal three-fringe selection method to calculate the phase and obtain unwrapped phase information. Utilizing the parameters obtained from the system calibration, the three-dimensional reconstruction is then completed. Using the proposed method, measurements were taken of highly reflective metal planar and spherical parts. The experimental results indicate that the method can adaptively predict the optimal projection intensity ratios for different highly reflective objects across the three channels of the color camera. Profile data from four locations on the two reflective objects were selected for fitting, and the root mean square error, maximum residual and correlation coefficient of the original data and the fitted data were analyzed. The measurement error of this method is reduced to 61.2% of the measurement error of traditional methods. In contrast to the multiple exposure time method and the adjustment of projection pattern intensity method, this approach utilizes only one pre-projected image and 12 fringe images, which greatly reduces the number of image acquisition in the process of multiple exposures or adaptive pre-projection, improves the measurement efficiency of the system, and has high measurement accuracy. In conclusion, the presented method may find promising applications in scenarios involving highly reflective metal components, and shows potential for industrial inspection and similar applications..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0712003 (2024)
Grayscale Distortion Correction Method for Hysteresis Characteristics of Electrowetting Display
Ziyu XIE, Ting MEI, Shanling LIN, Bipeng CAI, Mingzhen CHEN, and Zhixian LIN
Electrowetting Display (EWD) not only has the advantages of ultra-low power consumption, can reading under strong light, paper-like reading experience, but also has the advantages of high response speed and video playback that Electronic Paper Displays (EPD) does not have. However, problems such as oil splitting, oil bElectrowetting Display (EWD) not only has the advantages of ultra-low power consumption, can reading under strong light, paper-like reading experience, but also has the advantages of high response speed and video playback that Electronic Paper Displays (EPD) does not have. However, problems such as oil splitting, oil backflow, charge trapping, hysteresis effect, hinder the development of EWD. Hysteresis is an important reason for the gray distortion of EWD. Aiming at the phenomenon that the luminance displayed by the same driving voltage is different in the voltage rise stage and the voltage drop stage due to the hysteresis characteristics of EWD, this paper proposes a gray distortion correction method for the hysteresis characteristics of electrowetting display.Firstly, we designed and built a test platform. The test platform is used to measure the change of EWD aperture ratio under different voltages. The test platform consists of a microscope (with a high-speed CCD camera), a function generator, a power amplifier, and a PC. At the same time, we developed a program to measure the aperture ratio with Labview, which was run on PC. Part of the function of the program is to output test voltage. This function uses PC as the master computer and function generator as the slave computer, and uses SPCI to communicate between them. The output voltage of the function generator is amplified by the power amplifier and then applied to the EWD. The second part of the program is to detect the degree of ink shrinkage. This function uses PC as the master computer and microscope with camera as the slave computer. When the voltage is applied to the EWD, the ink begins to shrink, and the camera collects the ink status in the form of image data and sends it back to the master computer. The last part of the program is to calculate the aperture ratio with Matlab. After the image data is collected and transmitted to Matlab, the image is processed by using the program we wrote in advance in Matlab. The corresponding aperture ratio at that applied voltage will be calculated and saved.Secondly, the influence of hysteresis characteristics on the photoelectric curve was measured at different voltage range. The lowest driving voltage of EWD, above which the ink begins to shrink, and the highest driving voltage, above which the ink will cross the pixel wall, are used as the measurement boundary. The measured aperture ratio data is used as the basis for curve fitting, and quadratic polynomial is used for curve fitting. The correction methods is designed based on the obtained curves. The main correction methods are as follows: when the image data enters, it is converted to the corresponding gray scale and the aperture ratio. The initiation voltage is determined according to the changing trend of the image data According to the difference of starting voltage, select the appropriate fitting curve, calculate the corrected driving voltage, achieve the correct luminance. The judging method of the initiation voltage is as follows: when the three consecutive frames of image data have a increasing-decreasing or increasing-decreasing change, the initiation voltage is the knee-point voltage, and vice versa.Finally, we use the luminance meter to measure the luminance in the darkroom environment. The experimental results show that the actual luminance of each gray scale will be affected by the electrowetting hysteresis characteristics, and there is a significant difference between the voltage rising stage and the voltage dropping stage. The maximum relative luminance difference can reach 20.43%. After correction by the proposed correction method, the relative luminance difference of gray scale decreases from 20.07% to 0.01%, with a reduction ratio of 99.93%. The relative luminance difference decreased by 10.84% on average, and the reduction ratio was 80.98%. The highest degree of aperture ratio distortion was reduced from 5.67% to 0.13%, with the reduction ratio was 97.7%. On the other hand, using human eyes to observe the correction results, it can be found that the actual display effect after correction is significantly improved compared with that before correction..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0712004 (2024)
Research on Rough Road Detection Link Model
Yi YANG, Leilei ZHANG, Chi RUAN, Fengtao HE, Zixuan ZHAO, and Liang JIAO
Non-contact road surface meteorological detection technologies have emerged as a significant area of development due to their non-destructive impact on the road foundation and the simplicity of installation and maintenance. Typically, these non-contact road surface meteorological detection technologies utilize optical Non-contact road surface meteorological detection technologies have emerged as a significant area of development due to their non-destructive impact on the road foundation and the simplicity of installation and maintenance. Typically, these non-contact road surface meteorological detection technologies utilize optical detection methods, and factors such as the roughness of the road surface and the optical angle of incidence significantly influence the system's performance and the accuracy of the meteorological measurements.According to the optical geometric ray method, an improved microfacet model is proposed, which introduces multiple random parameters generated by the reflection of light from rough road surfaces, and establishes a hemispherical equivalent simulation model. This model microscopically elucidates the reflective properties of photons when interacting with rough road surfaces, and it allows for the convenient and precise simulation and analysis of the distribution of photons after reflecting off rough surfaces. Building on this, a rough road surface link transmission model based on wireless laser transmission theory has been developed to study and simulate the optical power characteristics received by the detection system under different road roughness levels and angles of incidence.The random distribution function of the normals of road microfacets under varying degrees of roughness is obtained by using refusal sampling technique, which determines the changes in photon reflection direction, and the distribution state of photons after reflection from the rough surface is statistically analyzed by using the Monte Carlo method, which derived the variations in reflected optical power under different angles of incidence and road roughness conditions. Subsequently, the validity of the model is confirmed. For the experimental design, a non-contact laser-based road surface meteorological condition detection system operating at a wavelength of 850 nm is constructed, which mainly consists of the light source drive circuit with emitting the light power of 50 mW, the laser receiving unit, and the optical system (including an optical antenna, the optical filters, and an optical collimator, etc.). The system is positioned at a vertical height of 2 m from the road surface to be measured, which is capable of not only monitoring road conditions in real time but also validating the photon distribution and optical power variation predicted by the simulation model. The simulation results and experimental data both reveal a trend where the received optical power gradually decreases as the incident angle between the incident light and the road surface normal increases. Notably, at an incidence angle less than 15°, the greater the road surface roughness, the lower the received optical power. Conversely, at angles greater than 15°, the trend reverses—the greater the road surface roughness, the higher the optical power, and this relationship tends to become linear at certain roughness levels. When the incidence angle reaches 60°, the received optical power stabilizes and undergoes minimal further change. Additionally, the experimental results indicate that the signal-to-noise ratio of the received optical signal does not change with the variation of road roughness, but closely correlates with the incident angle.This study presents and validates an equivalent simulation model for the reflection of light from rough road surfaces, and confirms the model's accuracy and feasibility in practical applications through experiments with an actual non-contact road surface meteorological detection system. The findings not only enhance our understanding of road surface reflective properties but also offer practical insights for the optimization of road detection techniques and meteorological condition monitoring. Thus, the research provides a theoretical and technical support for further improving road detection technology and monitoring meteorological conditions, ultimately contributing to the advancement of road safety measures..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0712005 (2024)
Special Issue for Attosecond Optics
Progress on Ultraviolet Photodetection Based on Narrow Bandgap Semiconductors （Invited）
Chunyan WU, Yuliang ZHANG, Xinhui HE, Xiaoping YANG, and Xiujuan WANG
Ultraviolet (UV) photodetection is characterized by relatively lower background noise, higher sensitivity and stronger anti-interference capability than its visible and infrared counterparts, which greatly facilitate its application in fields including optical imaging, security monitoring and space-to-space communicatiUltraviolet (UV) photodetection is characterized by relatively lower background noise, higher sensitivity and stronger anti-interference capability than its visible and infrared counterparts, which greatly facilitate its application in fields including optical imaging, security monitoring and space-to-space communications. Photomultiplier tubes and Si photodetectors dominate the commercial UV photodetectors, which normally operate at high bias voltage or adopt elaborate filters to eliminate the effect of visible and near infrared spectra. Wide bandgap semiconductors with bandgap larger than 3.4 eV, such as AlGaN, SiC, ZnMgO and Ga2O3, are prominent candidates for highly sensitive UV photodetection due to their relatively high radiation hardness and intrinsic visible blindness. However, expensive apparatuses and intricate processes, such as Metal Organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE), Plasma-Enhanced Chemical Vapor Deposition (PECVD), and highly corrosive and toxic chlorine (Cl2)-based dry Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE), are normally required for the wide bandgap semiconductor technology. What is more, for the solar-blind photodetection, a higher concentration of Al (～0.4) or Mg (～0.5) will be needed to tune the bandgap up to 4.42 eV, which increases the difficulty in epitaxial growth of high-quality film. Phase segregation may occur in the film, introducing defects and dislocations and degrading the detecting performance. Therefore, development of a facile and effective strategy for UV photodetection remains challenging.Recently, narrow bandgap semiconductor nanostructures emerged in the field of UV or even solar-blind UV photodetection. In this paper, we reviewed two kinds of nanostructures (nanowires and nanosheet) with the potential application in UV photodetection. Nanowires can be viewed as ultimately scaled-down versions of microcylinder resonators that can trap light in circulating orbits by multiple internal reflections from its boundary. Owing to their subwavelength size, the resonant modes in nanowires become leaky and interact more effectively with the outside world, carrying out a valuable antenna function. Different Leaky Mode Resonances (LMRs), including TM (Transverse Magnetic, HZ=0), TE (Transverse Electric, EZ=0), HE (magnetoelectric, TM-like), and EH (electromagnetic, TE-like) can be induced, which can selectively enhance the optical absorption in a particular spectral region and facilitate the tailoring of related optical absorption properties. When the illumination wavelength matched one of the allowed LMRs, there is an enhanced electromagnetic field in the nanowire. As a consequence, light absorption and the photocurrent could be enhanced at a desired wavelength by tuning the nanowire diameter. Horizontal nanowires tend to support TM and TE LMRs, the number of which reduces with the decrease of diameters. The wavelength corresponding to the specific leakage mode also decreases, resulting in a blue shift of the absorption peak. 36 nm Si nanowires was found to be sensitive to UVB light and almost blind to visible and near-infrared illumination, showing peak absorption at 310 nm. For vertical nanowires, only HE1m transverse resonance modes result in absorption enhancements. The HE11 leaky mode is separated from the HE12 mode by a large spectral gap, which enables the high wavelength selectivity. When the diameter of Si nanowire decreases from 120 nm to 40 nm, the peak absorption due to the HE11 leaky mode resonance shifts to short wavelengths while the absorption attributable to the HE12 leaky mode begins to gradually weaken. By using Si nanowires array with a diameter of 45 nm as building blocks, a UV photodetector with peak absorption at 365 nm was fabricated.On the other hand, most semiconductors show wavelength-dependent absorption coefficient, which decreases with increasing wavelength. The short-wavelength incident light has a higher photon absorption rate on the top surface, which attenuates quickly when penetrating into the crystal, giving a smaller penetration depth (defined as the distance where the energy of incident light is reduced to 1/e of its initial value when it propagates in the medium), while the long-wavelength incident light has a larger penetration depth. Therefore, absorption of long-wavelength illumination can ben suppressed by thinning the crystal and the peak absorption blueshifts with the decreasing thickness, revealing the possibility of thinning narrow bandgap semiconductors for UV or even solar blind UV photodetection. Several kinds of nanosheets, including ultrathin Si etched from SOI, perovskite nanosheets grown by the space-confined method (MAPbBr3 and CsPbBr3 nanosheet) and Chemical Vapor Deposition (CVD) grown 2D layered semiconductors nanosheets (GaSe nanosheet), have been researched, all of which show UV sensitive photoresponse. The UV-to-visible rejection ratio increases gradually with the decrease of thickness. Further, simulation by Finite Element Method (FEM) reveals that through integration with an asymmetric Fabry-Pérot (F-P) resonator, selective absorption enhancement at the resonant wavelength can be realized and the UV-to-visible rejection ratio can be improved by about 2 orders of magnitude, comparable to that of the commercial GaN and SiC based Schottky photodiodes.Comparing to its wide bandgap semiconductor and Si-based counterparts, the narrow bandgap semiconductor-based photodetectors provide a filterless strategy for UV photodetection with easier manufacturing process and lower manufacturing cost. However, it still suffers from the poor detection performance such as lower UV-to-visible rejection ratio. The further research should focus on: 1) improving the nanofabrication technology to uniformly control the characteristic parameters of semiconductors such as diameters and thickness for the stable and reliable photodetection; 2) improving the manufacturing capability of integrated device to facilitate the application in fields including image sensing and real-time monitoring; 3) combing with light regulation technology such as Localized Surface Plasmon Resonance (LSPR) and optical microcavity resonance to realize the highly selective absorption and therefore the high-performance UV photodetection..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753303 (2024)
Special Issue for Micro/Nanophotonics
Vacuum Ultraviolet Photodetectors with MSM Structure Based on Hexagonal Boron Nitride Films via Magnetron Sputtering （Invited）
Wannian FANG, Qiang LI, Qifan ZHANG, Ransheng CHEN, Jiaxing LI, Kangkang LIU, and Feng YUN
High performance Vacuum Ultraviolet (VUV) photodetectors are of great significance for space science, radiation monitoring, electronics industry, and basic science. The ultra-wide bandgap semiconductor material of hexagonal Boron Nitride (hBN) has high band edge absorption coefficient, thermal conductivity, and excelleHigh performance Vacuum Ultraviolet (VUV) photodetectors are of great significance for space science, radiation monitoring, electronics industry, and basic science. The ultra-wide bandgap semiconductor material of hexagonal Boron Nitride (hBN) has high band edge absorption coefficient, thermal conductivity, and excellent thermal and chemical stability, making it very suitable for application in the field of VUV detection. At present, there are still some challenges in the preparation and transfer of large-scale high-quality hBN films.In this work, two-inch wafer-level hBN films were successfully deposited on silicon and sapphire substrates using radio frequency magnetron sputtering technique. Characterization of the surface morphology by scanning electron microscope and atomic force microscope confirmed the production of uniformly continuous and dense films with an root meam square value of 4.04 nm (the film thickness was 154 nm); Raman peaks were located in the 1 366 cm-1, and the full width at half maxima was about 33 cm-1, which confirmed that the hBN films had hexagonal phase, and the quality of the crystalline was relatively high; X-ray photoelectron spectroscopy verified B-N bonding with a B/N ratio of 1.05∶1, indicating that the films had a small amount of nitrogen vacancies; the UV-vis absorption spectrum indicated that the films only had strong absorption of deep ultraviolet light below 220 nm, with the intrinsic absorption edge located at 212.5 nm, the absorption coefficient was as high as 1.52×105 cm-1, and the optical bandgap of hBN was about 5.95 eV.Furthermore, the MSM-type photodetectors based on hBN films were fabricated, and the effects of electrode material, film thickness, and interdigital electrode width and spacing on performance were investigated.According to the Schottky contact model, the higher the work function of the metal, the Schottky barrier height formed with the hBN material would be higher, and the junction current density would be lower. During the preparation of electrodes, the actual barrier height was difficult to analyze and determine due to the combined effects of the presence of interface states, the introduction of impurities, and the quality of the Schottky contacts. The length, width, and spacing of the interdigital electrode were 1.5 mm, 25 μm, and 25 μm, respectively, with a logarithm of 25 and an electrode thickness of 70 nm. When Ni was used as the electrode, the detector had the minimum dark current and the maximum photocurrent, and its performance was stable and not easily oxidized.As the thickness of the hBN films increased, the dark current slowly increased, while the photocurrent first increased and then decreased. The optimal thickness was 135 nm. In the thickness range of tens of nanometers, films were still in the process of island growth connection and not dense enough, which inhibited the transmission of the current signal, and the light and dark currents were weak. As the film continued to grow, the islands connected with each other to form dense films. The signal transmission ability was improved, and the number of photogenerated carriers increased, which resulted in a large increase in the photocurrent and a small increase in the dark current. Due to this growth mechanism, the polycrystalline defects became more numerous and the resistance of the whole bulk material was greater with the further increased of thickness, leading to a gradual decrease in the value of the detector photocurrent.The influence of interdigital electrode width on the dark current and photocurrent was very weak, while the interdigital electrode spacing affected the device photocurrent significantly. As the interdigital electrode spacing increased, the active area of the hBN films became larger and more photogenerated carriers were generated, which contributed to the increase of photocurrent (Mechanism Ⅰ). On the other hand, when the interdigital electrode spacing increased, the electric field strength between the neighboring interdigital electrodes decreased, the transit distance of the carriers increased, and the number of carriers collected by the electrodes decreased, which contributed to the decrease of photocurrent (Mechanism Ⅱ).The ultimately selected hBN detectors had an extremely low dark current (<3 pA@100 V) and significant photoresponse to 185 nm wavelength light. When the applied bias voltage was 25 V, the responsivity and specific detectivity of the detectors were 0.697 mA/W and 7.47×108 Jones, respectively; when the voltage was increased to 100 V, the responsivity and specific detectivity were 2.769 mA/W and 2.969×109 Jones, respectively..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753302 (2024)
Special Issue for Photodetectors
Preparation and Properties of PEN Substrate Gallium Oxide Based Flexible Ultraviolet Detector （Invited）
Yue DING, Qianqian HUANGFU, Qingyuan ZUO, Jinlong LIANG, Wei MI, Di WANG, Xingcheng ZHANG, Zhen LIU, and Linan HE
The emerging wide-band gap semiconductor material gallium oxide is a very promising solar blind ultraviolet detector material, which has the advantages of good stability, simple preparation process, low production cost, high temperature and high pressure resistance, etc. And the preparation materials used as flexible pThe emerging wide-band gap semiconductor material gallium oxide is a very promising solar blind ultraviolet detector material, which has the advantages of good stability, simple preparation process, low production cost, high temperature and high pressure resistance, etc. And the preparation materials used as flexible photodetectors can maintain good performance even when they are twisted and extended into complex non-planar shapes. However, due to the limitation of substrate temperature (generally less than 200 ℃), it is difficult to directly grow high-quality gallium oxide films on flexible substrates, which seriously affects the improvement and promotion of the performance of flexible ultraviolet detectors.At present, most of the transparent conductive thin flexible substrates Ga2O3 reported were prepared by magnetron sputtering method, so in order to improve reliability, we also adopted magnetron sputtering method in this experiment. The experimental process of preparing the flexible gallium oxide Ultraviolet (UV) detector on the PEN substrate is planned as follows: First, a Ga2O3 adhesive layer is formed by pre-sputtering with DE500 magnetron sputtering equipment, and on this basis, a Ga2O3 thin film with a thickness of about 160 nm is further deposited. Finally, ITO electrode layer with thickness of about 150 nm was grown on the thin film by magnetron sputtering through the mask. The process parameters of growing Ga2O3 film on PEN substrate and ITO electrode on Ga2O3 film were set.It can be seen from the results of the structure characterization of the thin films that the XRD patterns of the PEN substrate and the PEN substrate growing gallium oxide thin films are compared, and there is only a strong diffraction peak at 25.9° in the curve, but no other diffraction peaks. This indicates that the prepared GAN films have amorphous or microcrystalline structure. The full spectrum scanning of 0~1 200 eV and fine scanning of Ga 2p and O 1s were obtained. The atomic ratio of Ga and O in the prepared film is about 0.67, which is very close to the theoretical stoichiometric ratio of gallium oxide, indicating that the chemical composition of the film is accurate. The optimal spectral response of the gallium oxide photodetector from 200~400 nm corresponds to the excitation at 214 nm. The analysis shows that the average transmittance of the sample in the visible region exceeds 80%. The sample transmittance of Ga2O3 films grown in some wavelength region is higher than that of PEN substrate, which is caused by the anti-reflection effect of refractive index modulation.By observing the surface morphology of the film, it can be seen that the Ga2O3 UV detector film and ITO electrode on the PEN substrate only show slight bending traces in the bending region, and the ITO electrode of the whole sample does not appear to be broken. Therefore, it is proved that the prepared PEN substrate gallium oxide UV detector has good flexibility and bending resistance.By comparing the light and dark current curves of the device graph before and after 20 000 bending, it can be observed that the light and dark current ratio of the UV detector after 20 000 bending does not decrease significantly. According to the I-t characteristic curve of the response of the flexible Ga2O3 UV detector to 254 nm UV switch at 10 V bias voltage after 20 000 bending, it can be seen that after the alternating opening and closing of the UV light source for 10 cycles, the current response of the detector shows a continuous rapid rise and fall, and the I-t characteristic curve presents periodic stability.It is proved that the Ga2O3 UV detector prepared on PEN substrate has excellent photoelectric performance and mechanical resistance, which provides an experimental basis and theoretical support for the development of high-performance flexible UV photodetectors..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753305 (2024)
Preparation and Properties of ZnO/Spiro-MeOTAD Heterojunction Self-powered Photodetector （Invited）
Pengfan LI, Yuxin HUANG, Xuewei YU, Shiliang FENG, Yanfeng JIANG, Dawei YAN, and Pingping YU
A photodetector is a sensing element capable of converting an optical signal into an electrical signal. ZnO is widely used in photodetectors due to high stability, low cost and wide band gap, however the long response speed limits their development. The photoelectric performances of ZnO can be effectively improved by fA photodetector is a sensing element capable of converting an optical signal into an electrical signal. ZnO is widely used in photodetectors due to high stability, low cost and wide band gap, however the long response speed limits their development. The photoelectric performances of ZnO can be effectively improved by fabricating the inorganic-organic heterostructure. The Li-TFSI doped Spiro-MeOTAD as one of organic semiconductor exhibits high hole regeneration ability, high conductivity and the hole mobility, but the stability is low. In this paper, Zn(TFSI)2 and CNT∶TiO2 are used as mixed dopants to replace Li-TFSI to improve the conductivity and stability of Spiro-MeOTAD and achieve higher photoelectric performances. The doped Spiro-MeOTAD is closely combined with ZnO thin films by spinning coating method. ZnO/Spiro-MeOTAD photodetectors were prepared by Ag paste as electrodes covered on the ZnO thin films and ZnO/Spiro-MeOTAD heterojunction, respectively. The morphologies and structure of ZnO, Spiro-MeOTAD and ZnO/Spiro-MeOTAD devices were characterized by scanning electron microscope, X-ray diffractometer, Raman spectrum, UV-Vis absorption spectrum, suggesting the successful preparation of ZnO/Spiro-MeOTAD heterojunction. The thickness of the ZnO film is about 9 μm, while the thickness of Spiro-MeOTAD is about 400 nm, suggesting the thin Spiro-MeOTAD is benefit to the light absoption and photodetection performances. The optical absorption coefficient of ZnO/Spiro-MeOTAD is higher than that of ZnO in the whole wavelength range, and is significantly improved in the wavelength range of 350~450 nm. The addition of Spiro-MeOTAD extends the absorption cutoff edge of ZnO and expands the response wavelength range. Under dark conditions, the forward bias voltage and the reverse bias voltage of ZnO/Spiro-MeOTAD devices have different current change rates, showing a rectification effect with the rectification ratio of 28±2. The open circuit voltage and short circuit current of the device under 368 nm illumination are 0.4 V and 14 nA respectively, indicating a good self-powered characteristic. At 0 V, ZnO/Spiro-MeOTAD device exhibits the highest photoelectric performances at 368 nm, with a responsivity of 27.34 mA·W-1, specific detectivity of 3.62×1011 Jones, switching ratio of 2 029, and rise/fall time of 0.71 s/0.55 s, respectively. Compared with ZnO, the photoelectric performances of ZnO/Spiro-MeOTAD (responsivity 17.74 mA·W-1, specific detection 5.11×1010 Jones, switching ratio 63.6, rise/fall time 11.76 s/1.49 s) is improved by 1.5 times, 7 times and 32 times, respectively. Compared with ZnO devices (response of 0.01 mA·W-1, specific detectivity of 3.53×107 Jones), ZnO/Spiro-MeOTAD device still shows the responsivity and specific detectivity of 2.48 mA·W-1 and 3.32×1010 Jones at 550 nm, which is increased by 248 times and 940 times, respectively. The ZnO/Spiro-MeOTAD device has a wide spectral response of UV-visible light with the addition of Spiro-MeOTAD. The p-n heterojunction can fast separate the electron-hole pairs due to the build-in potential, improving the electronic properties. The photocurrent of ZnO/Spiro-MeOTAD device without packaging protection only decreases to 78.6% of the original photocurrent after one month, and the switching ratio is 1.25 at 140 ℃. The comparison of ZnO/Spiro-MeOTAD-O (doped with Li-TFSI and TBP) device remains 50% photocurrent after one day, not a stable periodic cycle after one week, and switching ratio of 1.08 at 100 ℃. The excellent stability can be contributed to enhanced hydrophobic characteristics with doping by zinc salt not lithium salt, as well as the improved thermal stability and conductive properties by CNT∶TiO2 mixed dopants. The Zn(TFSI)2 and CNT∶TiO2 doped Spiro-MeOTAD can improve the e responsivity, switching ratio and response speed of ZnO film, and promote the thermal stability and environmental stability of the ZnO/Spiro-MeOTAD heterojunction. This preparation method provides a new idea for new composite structure heterojunction, which has theoretical research and practical application value..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753306 (2024)
Research Progress on Fabrication of Two-dimensional Hexagonal Boron Nitride and Its Optoelectronic Devices （Invited）
Man LUO, Yang ZHOU, Tiantian CHENG, Yuxin MENG, Yijin WANG, Jiachi XIAN, Jiayi QIN, and Chenhui YU
Boron Nitride (BN) is Ⅲ-Ⅴ binary compound crystal material formed by B and N atoms in 1∶1 stoichiometric ratio, which primarily comprises four major crystallographic structures: wurtzite BN (w-BN), cubic BN (c-BN), rhombohedral BN (r-BN), and hexagonal BN (h-BN). In w-BN and c-BN, the B and N atoms undergo sp3 hybridizBoron Nitride (BN) is Ⅲ-Ⅴ binary compound crystal material formed by B and N atoms in 1∶1 stoichiometric ratio, which primarily comprises four major crystallographic structures: wurtzite BN (w-BN), cubic BN (c-BN), rhombohedral BN (r-BN), and hexagonal BN (h-BN). In w-BN and c-BN, the B and N atoms undergo sp3 hybridization to form tetrahedral structures. Conversely, in r-BN and h-BN, these atoms exhibit sp2 hybridization within the plane, resulting in the formation of hexagonal ring structures. These structures are similar to those of graphene, with layers stacked upon each other through weak van der Waals (vdWs) forces, forming bulk materials. The spacing between the basal planes and the in-plane lattice constants of the two crystal structures are identical, with the difference being in the stacking order of the basal planes. h-BN is a representative material with wide band gap and two-dimensional (2D) layered structure, possessing unique properties such as excellent physicochemical stability and high thermal conductivity. It is considered as a novel 2D functional material with significant application potential in electronics, photonics, energy catalysis, and surface protection.Controllable preparation of large-area, high-quality h-BN is a challenging and active research direction. In this paper, recent research results are presented by categorizing the main ways of preparing h-BN into two broad categories: “top-down” exfoliation and “bottom-up” growth methods. The “top-down” method refers to the exfoliation of large-sized or bulk materials into monolayers to nanosheets ranging from monolayers to layers by different material preparation methods, such as mechanical exfoliation, liquid-phase exfoliation, and electrochemical exfoliation. In this process, the interlayer vdWs forces within the 2D materials are primarily disrupted by the application of external forces. The “bottom-up” method refers to the direct preparation of nanosheets by chemical synthesis using atoms, ions or molecules, which is mainly implemented by chemical vapor deposition, physical vapor deposition and molecular beam epitaxy. For h-BN, on the one hand, controlling nucleation presents a certain level of difficulty, making it challenging to grow large single crystals from individual nuclei. On the other hand, the crystal structure of h-BN exhibits three-fold symmetry, leading to the easy formation of antiparallel structures and twins during epitaxial growth on most substrates. Currently, chemical vapor deposition stands as the predominant method for growing large-area, high-quality h-BN. Ongoing research into the development of new technologies for the controllable production of large area, high quality materials is key to promoting the industrialization and application of h-BN. The aim is to improve yield while ensuring structural integrity and performance consistency of the target materials, and to precisely control the size, number of layers and other parameters of the materials to meet the needs of different application scenarios.Following the study of the structure, the properties and the synthetic preparation of the 2D h-BN, this paper reviews the research progress of h-BN in optoelectronic devices by focusing on three aspects, namely, substrate/dielectric layer, tunneling layer and absorber layer. Firstly, h-BN possesses unique intrinsic properties such as a wide bandgap, atomically smooth surface, absence of dangling bonds and surface trap states, and chemical inertness. These outstanding properties make h-BN highly suitable for serving as key functional layers such as gate dielectrics, passivation layers, and substrates in electronic and optoelectronic devices. Secondly, the wide band gap and large electron affinity of h-BN result in the formation of a higher tunneling potential barrier in heterostructures, which can effectively suppress the occurrence of direct tunneling current, thereby enhancing the on-state resistance of the devices. Several research results show that the transport mechanism is dominated by Fowler-Nordheim (FN) tunneling when thin layer of h-BN is used as the tunneling layer. In addition, h-BN is an indirect bandgap material, but due to its unique flat electronic band structure, 2D h-BN exhibits distinctive properties in light-matter interactions. The highly localized electrons in h-BN result in a higher effective electron density involved in the Ultraviolet (UV) light absorption process, giving 2D h-BN an inherent UV light response capability. h-BN also has natural hyperbolic properties in the mid-infrared wavelength range. The hyperbolicity gives rise to a unique physical property, i.e., the sign of the dielectric constant along the in-plane direction is opposite to that of the dielectric constant along the out-of-plane direction. The directional propagation of hyperbolic phonon polaritons is confined within sub-wavelength dimensions, similar to behavior in metals. Based on this inherent structural advantage in the mid-infrared, h-BN has become a potential material for detecting mid-infrared signals.Large-area, high-quality, low-cost material synthesis, damage-free transfer onto any substrates, and compatibility with traditional CMOS processes represent common challenges that 2D materials encounter on the path to industrialization, which are equally true for h-BN. Furthermore, direct growth of additional 2D materials on h-BN offers potential for significant process simplification and enhanced device performance. Finally, this paper delves into the prevailing research landscape of h-BN, highlighting the challenges and opportunities it faces..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753307 (2024)
Effect of Atomic Layer Deposition Al2O3 Passivation on the Luminescence Properties of InAs/InGaAsSb Type-II Superlattices
Chao XIANG, Dengkui WANG, Xuan FANG, Dan FANG, Hao YAN, Jinhua LI, Xiaohua WANG, and Peng DU
As an emerging mid-infrared semiconductor material, InAs/InGaAsSb superlattice possesses a wide working range covering the infrared spectrum from 2~30 μm, holding promising potential for applications in fields of infrared imaging. Compared to traditional InAs/GaSb superlattices, InAs/InGaAsSb superlattice has the advanAs an emerging mid-infrared semiconductor material, InAs/InGaAsSb superlattice possesses a wide working range covering the infrared spectrum from 2~30 μm, holding promising potential for applications in fields of infrared imaging. Compared to traditional InAs/GaSb superlattices, InAs/InGaAsSb superlattice has the advantages of high electronic effective mass, low Auger recombination efficiency, and long carrier lifetimes, making it a potential material for designing third-generation infrared photodetectors. Hence, the study on InAs/InGaAsSb superlattice has become the current research hotspot. However, the surfaces and cross-sections of InAs/InGaAsSb superlattices are easily oxidated in air, resulting in the formation of gallium oxide and arsenious oxide. These oxides act as non-radiative recombination centers, reducing minority carrier lifetimes and severely limiting the performance improvement of infrared photodetectors. Therefore, it is of great significance for surface treatment to remove surface oxides and reduce surface state density in InAs/InGaAsSb superlattice materials.Recently, research on the passivation of InAs/InGaAsSb superlattices focuses solely on surface treatment. However, the cross-sections, consisting of distinct InAs and InGaAsSb structures, respectively, exhibit heightened susceptibility to being oxidated. Consequently, it is necessary to remove the inherent oxide layers from the cross-section by etching and passivate the surfaces to prevent further oxidation. Accordingly, this paper proposes a passivation technique integrating dry etching and atomic layer deposition. Dry etching is employed to remove the inherent oxide layers from the surface and cross-section of InAs/InGaAsSb superlattices, followed by the deposition of an Al2O3 thin film through atomic layer deposition to passivate the etched surfaces. This approach aims to enhance the emission performance and long-term optical stability of InAs/InGaAsSb superlattices.In order to characterize the crystal quality of the InAs/InGaAsSb superlattice, the double-crystal X-ray diffraction (XRD) is employed. It is easy to find six orders of satellite peaks in XRD patterns, indicating excellent crystal and interface quality between InAs layers and InGaAsSb layers. Additionally, a tiny difference between the 0th-order diffraction peak and the substrate peak is observed, which is attributed to internal strain-induced effects. The surface roughness before and after treatment is analyzed by using atomic force microscopy, showing a significant reduction in surface roughness from 6.32 ? for untreated samples to 1.93 ? for the treated superlattice material. To verify the successful elimination of surface and cross-section oxides, X-ray Photoelectron Spectroscopy (XPS) is employed on the superlattice before and after treatment. For the As 3d spectrum of the untreated superlattice, the peak related to the As-O bond is observed in addition to the As 3d1/2 and As 3d3/2 peaks. However, this peak associated with the As-O bond disappears in the spectrum of the surface-treated superlattice, indicating complete removal of the surface oxide layer.The Photoluminescence (PL) characteristics of the superlattice are measured before and after treatment. The PL spectra reveal an increase in emission intensity and a decrease in full width at half maximum after passivation, which is attributed to the effective reduction of non-radiative recombination through the removal of surface oxides. Continuous PL measurement over five days showed that the emission intensity of the treated samples decreased to 89% of the original intensity, while the emission intensity of untreated samples decreased to 76% of the original intensity. These results indicate better emission stability of the superlattice after treatment. The power-dependent and temperature-dependent PL spectra are employed to analyze the mechanism of the increase in emission intensity and the improvement in emission stability. The relationship between PL intensity and excitation power is analyzed to verify the origin of the emission. The fitting coefficient α decreased from 1.17 to 1.02 after treatment, indicating an increased proportion of exciton-dominated emission. The Arrhenius formula is used to fit the relationship between emission intensity and measurement temperature, revealing that the activation energy E1 increased by 5.13~13.73 meV and E2 increased by 121.92~130.04 meV for the treated samples compared to untreated samples, which indicates a significant suppression of non-radiative recombination, especially at high temperatures. This work lays the foundation for enhancing the performance of InAs/InGaAsSb superlattices and promoting their applications in the field of optoelectronic detection..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753308 (2024)
Measurement of Key Terminal Ballistic Parameters of Small Arms Based on Sparse Distribution Optoelectronic Detection Array
Ziyu YANG, Ding CHEN, and Lingnan SHEN
The article proposes a measurement method to efficiently and accurately obtain the key terminal ballistic parameters (i.e., the hitting coordinates, the flight velocity, the flight direction angle of the projectile and the weapon firing rate) of small arms using the sparse distribution detector array. Compared with theThe article proposes a measurement method to efficiently and accurately obtain the key terminal ballistic parameters (i.e., the hitting coordinates, the flight velocity, the flight direction angle of the projectile and the weapon firing rate) of small arms using the sparse distribution detector array. Compared with the traditional methods of uniformly and densely arranged detectors, this method greatly reduces the number of lasers and detectors required, thus saving costs. In addition, because the detector distribution can be non-uniform, installation and commissioning are more flexible and convenient. First, the detection principle and the composition of the system based on the propagation characteristics of the shock wave are described. Then, the measurement model of the system is established, and the calculation equations are derived by combining the relevant structural parameters and the shock wave propagation velocity. In addition, the systematic errors of the parameters such as the impact coordinates and the flight velocity are analyzed, and the effectiveness and practicality of the measurement method are verified by simulation. The simulation results show that in the effective target area of 10 m×10 m, the measurement error distributions of x and y coordinate values are the same, both decrease with the increase of the over-curtain time and increase with the increase of the extraction time of the shock wave propagation. The maximum deviation of x, y coordinate values is 1.55 mm. The azimuth error decreases with the increase of x coordinate difference, and the maximum azimuth error does not exceed 0.08°. The pitch angle error decreases as the difference of x coordinate and y coordinate increases, and the maximum error does not exceed 0.95×10-3 °. When the target distance varies from 0.5 m to 2 m, the velocity error of the projectile gradually decreases as the target distance increases. The velocity error of the projectile shows a trend of first increases and then decreases as the difference of the x and y coordinates increases. The maximum deviation of the velocity of the projectile is 0.65 m/s. In order to quantitatively compare the proposed method with the measurement results of the light screen array, live fire experiments are conducted. Two sky targets and two sparse distribution detector arrays are placed alternately along the trajectory line, each with a target distance of 1.5 m. The wooden target is placed 1.26 m behind the sparse distribution detector array. Three high-speed cameras are placed on either side of the trajectory line and above the wooden target, respectively. The rifle is placed on a gun rack and 100 standard projectile shots are fired at a distance of 30 m from a start target of the six-light screen array. The coordinates of the center of the bullet hole on the wooden target are considered as the reference values, and the high-speed camera measurements are considered as the reference values of velocity and attitude angle. To verify the feasibility and validity of the proposed method, the sparse detection array measurements and the light screen array measurements are compared with each other and with the reference data. The measurement data of the proposed system show that the maximum deviation of coordinates is 2.4 mm, the average deviation of coordinates is 1.0 mm, the maximum deviation of azimuth and pitch angle is 0.128°, and the maximum deviation of flight velocity is 0.99 m/s. The proposed method reduces the average coordinate error by 35%, the average azimuth and pitch angle error by 31%, and the average velocity error by 33% compared with the six-light screen array measurement. The results show that the measurement method can meet the requirements for testing the terminal ballistic parameters of supersonic projectiles. Compared with the previous measurement system, it has the advantages of sufficiently large detection area, no detection blind area, low cost, easy installation and commissioning..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753309 (2024)
Preparation and Performance of the Self-powered Ultraviolet Photodetector Based on the Bi2O3/g-C3N4 Composite
Xiangming FANG, Qicheng ZHOU, Zhuangpeng GUO, Enke ZHU, Yurui HAO, and Shiyong GAO
Self-powered Ultraviolet (UV) photodetectors have attracted great attention for the fast detection of UV light without external bias voltage, as well as for their high sensitivity, light weight and low energy consumption. In order to obtain high-performance self-powered UV photodetector, Bi2O3 nanoblocks and g-C3N4 nanSelf-powered Ultraviolet (UV) photodetectors have attracted great attention for the fast detection of UV light without external bias voltage, as well as for their high sensitivity, light weight and low energy consumption. In order to obtain high-performance self-powered UV photodetector, Bi2O3 nanoblocks and g-C3N4 nanosheets were synthesized by thermal polymerization method. Subsequently, Bi2O3/g-C3N4 composites were prepared via solution method, and their morphology, crystal structure, chemical composition and valance state were characterized. The results of morphological characterization show that Bi2O3 present as a honeycomb-structured block, which are attached to the surface of g-C3N4 nanosheets with layered structure. The characteristic peaks of Bi2O3 nanoblocks and g-C3N4 nanosheets can be observed in the XRD pattern of the as-prepared composite, indicating successfully constructing of the Bi2O3/g-C3N4 heterojunction. Further, XPS measurement of the Bi2O3/g-C3N4 composite was performed to study the valence states of the elements compositing the composite, in which the results of high-resolution XPS of Bi 4f, O 1s, C 1s and N 1s also confirm the prepared composite as Bi2O3/g-C3N4 heterojunction. Based on the as-prepared Bi2O3/g-C3N4 heterojunction, the UV photodetector that can operate without an external power source was fabricated. At zero bias voltage, the photodetection performance of the Bi2O3/g-C3N4 UV photodetector was investigated under darkness and UV illumination by repeating 10 s with light on and 10 s with light off. When irradiated with UV light, the Bi2O3/g-C3N4 UV photodetector immediately generates photocurrent and rapidly rises to the maximum value (0.43 μA) and remain stable. After turning off the UV light, the photocurrent immediately decreases and returns to the initial state. Notably, the maximum photocurrent of the device remains essentially unchanged after 7 cycles, indicating that the Bi2O3/g-C3N4 UV photodetector has good stability and repeatability. In addition, the performance of the UV photodetector prepared based on Bi2O3 nanoblocks was also investigated under the same conditions. The results show that when the Bi2O3 nanoblocks UV photodetector was exposed to UV light, its photocurrent can rise rapidly to reach the maximum value of about 0.21 μA. Remarkably, the maximum photocurrent of the Bi2O3/g-C3N4 UV photodetector is enhanced by about 1.05 times compared with that of the Bi2O3 nanoblocks UV photodetector. And the Bi2O3/g-C3N4 UV photodetector exhibits a fast response time (~181.7 ms), which demonstrates that the device is capable of stable and fast detection of UV light. The photoresponse characteristics of the Bi2O3/g-C3N4 UV photodetector were also investigated under UV light irradiation with different intensities. It is found that even under UV irradiation at a lower light intensity (2 mW/cm2), the photocurrent generated by the device increases rapidly as well as still reaches a maximum value of about 0.098 μA. And there is no significant attenuation of the maximum photocurrent after several cycles of cycling. Meanwhile, note that the photocurrent increases approximately linearly with the increase of the light intensity, which indicates that there has a well linear relationship between the photocurrent and incident light intensity. And the device also exhibits excellent recyclability and stability for the detection of UV light of different intensities, which demonstrates the ability of the device to achieve effective detection of UV light over a wide range of UV intensities. The device also exhibits a large switching ratio with a value of about 1 313, which demonstrates the high sensitivity of the Bi2O3/g-C3N4 UV photodetector. And its responsivity is as high as 0.17 mA/W under UV irradiation of 2 mW/cm2, demonstrating the potential application of the device in the field of photodetectors. In addition, the detection mechanism of the Bi2O3/g-C3N4 UV photodetector is analyzed. The high-performance Bi2O3/g-C3N4 self-powered UV photodetector prepared in this work may be used in the field of future optoelectronic devices..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753310 (2024)
Characteristics of Al-doped ZnO Nanowire Arrays Ultraviolet Photodetectors
Zhaolin YUAN, Qingpeng XU, Zhiwen XIE, Jianfeng HE, Shengyu YOU, and Xueyuan WANG
ZnO, an II-VI semiconductor, has a direct wide bandgap of 3.37 eV and a large exciton binding energy of 60 meV. Also ZnO has many advantages, such as low cost, nontoxicity, rich raw materials, good chemical stability and excellent photoelectric properties. Up till now, ZnO has been widely investigated for various potenZnO, an II-VI semiconductor, has a direct wide bandgap of 3.37 eV and a large exciton binding energy of 60 meV. Also ZnO has many advantages, such as low cost, nontoxicity, rich raw materials, good chemical stability and excellent photoelectric properties. Up till now, ZnO has been widely investigated for various potential applications, such as solar cells, catalyses, piezoelectric devices, gas sensors, light-emitting diodes and Ultraviolet (UV) photodetectors.UV photodetectors have received great attention because they play key roles in many important fields, such as military, civilian, space communication, industrial automation, wastewater treatment and environmental monitoring. In particular, UV photodetectors based on some wide bandgap semiconductors, such as gallium nitride, titanium dioxide, diamond, silicon carbide, gallium oxide and ZnO, have attract increasing interest due to their excellent performances. Among these wide bandgap semiconductors, ZnO is considered as one of the most ideal candidates for UV photodetectors. In order to achieve high-performance ZnO UV photodetectors, various nanostructured ZnO, such as nanoparticles, nanorods, nanowires and nanoflowers, were used as photosensitive layers to fabricate UV photodetectors. Well-aligned ZnO nanowire arrays, a unique structure, have high specific surface area, good photoelectronic performance as well as a more direct and effective conduction path for electrons, high-performance UV photodetectors based on well-aligned ZnO nanowire arrays are easy to realize. Unfortunately, the performances of the reported well-aligned ZnO nanowire arrays UV photodetectors have still been poor so far. Normally, the performance of photoconductive well-aligned ZnO nanowire arrays UV photodetector mainly depends on electric property of ZnO nanowire arrays, the metallic elements doping, such as Ga, In, Mg and Al, is one of the most well-known means for improving electric property of ZnO nanowire arrays. Among these metallic elements, the radius of Al3+ ions is smaller than that of Zn2+ ions, Al are easily doped into ZnO matrix, which results in improving electric property of Al-doped ZnO nanowire arrays.Low-cost and high-performance of ultraviolet photodetectors with good reliability have widely applications in many important fields. In this paper, fluorine-doped tin oxide coated glass substrates were cut into 2 cm×2 cm in size and etched into interdigital patterns using the laser technology, the substrates were rinsed in detergent, deionized water, ethanol, isopropanol for 15 min via an ultrasonic cleaning bath, respectively, and air-dried at 50 ℃. ZnO thin films were first deposited on the clean interdigital patterned fluorine-doped tin oxide coated glass substrates by the spin coating technique and acted as seed layers, zinc nitrate hexahydrate and hexamethylenetetramine was used as precursors, aluminum nitrate nonahydrate acted as an Al dopant, deionized water was the solvent, several well-aligned Al-doped ZnO nanowire arrays were then grown on the ZnO seed layers by a facile hydrothermal method at low temperature, five Al doping concentrations were designed, the atomic ratios of Al to Zn were 0% (undoped ZnO nanowire arrays), 0.5%, 1%, 2% and 4%, respectively. Firstly, the crystal structures of all the Al-doped ZnO nanowire arrays were measured using an X-Ray Diffractometer (XRD), the XRD results indicated that all the Al-doped ZnO nanowire arrays were hexagonal wurtzite structure of ZnO, no any other impurities and compounds were found. Then the morphology of all the Al-doped ZnO nanowire arrays were observed by a Scanning Electron Microscope (SEM), it was found that a large number of ZnO∶Al nanowires grew onto the surface of substrate along the approximate vertical direction to the surface. Energy dispersive spectroscopy results of the 1% Al-doped ZnO nanowire arrays demonstrated that Al ions were substitutionally incorporated into the ZnO lattice. As a result, well-aligned Al-doped ZnO nanowire arrays were successfully built. Furthermore, the resulting five Al-doped ZnO nanowire arrays were used as photosensitive layers, respectively, the corresponding UV photodetectors were fabricated, their performances were investigated in detail. I-V characteristics of all the Al-doped ZnO nanowire arrays UV photodetectors in the dark and under 365 nm light illumination revealed that the currents of all the devices under illumination were much larger than their dark currents, indicating that all the devices showed good responses to 365 nm light. Also, the main performance parameters of all the devices were obtained by calculation, their performance parameters were compared, it was noted that the 1% Al-doped ZnO nanowire arrays UV photodetector had the optimal performance among these devices. For 1% Al-doped ZnO nanowire arrays UV photodetector, at a wavelength of 365 nm, its responsivity, specific detectivity, sensitivity, external quantum efficiency, response time and decay time were 6 180 mA/W (5 V), 1.51×1012 Jones (5 V), 83.2 (0 V), 6 090% (5 V), 4.12 s and 14.45 s, respectively. These results indicated that high-performance Al-doped ZnO nanowire arrays UV photodetectors could be achieved when ZnO nanowire arrays were doped with a proper Al concentration.This work will be helpful for developing low-cost, high-performance and large-area UV photodetectors and other related devices based on Al-doped ZnO nanowire arrays. Also, it can provide some reference for investigating other related UV photodetectors..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753311 (2024)
Preparation and Characterization of Aggregation-induced Dual Emission Solid Red Carbon Dots
Zhehao YONG, Wenjie SUN, Shouwang KANG, Xinyue ZHU, Min WANG, Congrui KANG, and Liu DING
Due to the unique luminous properties, Carbon Dots (CDs) has become one of the research hotspots in the field of new materials. The existence of aggregation-induced fluorescence quenching effect, however, severely limits the application of carbon dots in the field of solid-state luminescence. The development of long waDue to the unique luminous properties, Carbon Dots (CDs) has become one of the research hotspots in the field of new materials. The existence of aggregation-induced fluorescence quenching effect, however, severely limits the application of carbon dots in the field of solid-state luminescence. The development of long wavelength red CDs in solid state has always been a difficult problem. Most long-wavelength red CDs display quenching phenomenon and single fluorescence emission, which greatly limits their utilization in the field of anti-counterfeiting. Therefore, in this study, an environmentally friendly and easy to prepare solid red fluorescent CDs (FD-CDs) was designed and synthesized by doping nitrogen and sulfur elements. Dithiosalicylic acid and formamide were used as raw materials, and acetic acid was used as solvent. The dual emission peak and aggregation induced emission characteristics of FD-CDs make it suitable for fingerprint detection, ink printing and anti-counterfeiting applications. The structural analysis shows that FD-CDs is spherical and evenly distributed. It is composed of surface functional groups containing nitrogen, sulfur and other elements as well as carbon graphite nuclei. FD-CDs exhibit blue emission in the dispersed state and red emission in the aggregated or powder state. FD-CDs solution has only one emission peak at 367 nm, while FD-CDs powder has double emission peaks at 482 nm and 612 nm. The fluorescence quantum yield of FD-CDs in solid state is as high as 41.01%, while that in solution state is only 17.68%, showing a typical phenomenon of aggregation induced enhanced emission. The structure and optical characterization indicate that the double emission of FD-CDs has different luminescence centers. In low concentration or dispersed state, FD-CDs only has short wavelength emission, which may be caused by carbon nucleus emission. With the increase of concentration, FD-CDs agglomerates, π-π accumulation occurs in carbon nuclei with large conjugated structure, and short-wavelength fluorescence is quenched, therefore blue emission is inhibited. When FD-CDs aggregates, the symmetric heterocycles induced by S-S bonds limit the intramolecular rotation, and the main surface energy transition will be converted to fluorescence, resulting in red emission. By further calculating the ratio of radiative and non-radiative transitions, the non-radiative transition channels of FD-CDs in powder state are significantly reduced. It is inferred that aggregation can inhibit the movement of surface groups, prevent the dissipation of energy, inhibit the non-radiative transition process, and significantly improve the fluorescence emission efficiency of FD-CDs. According to the unique double emission and aggregation induced emission effect, a double switch ink based on FD-CDs was designed. Apply the prepared FD-CDs solution to the“butterfly”filter paper with a glue head dropper. After the water evaporates, the overall “butterfly”appears red. The filter paper emits strong red fluorescence under ultraviolet irradiation at 365 nm. Then the surface of the“butterfly”was coated with anhydrous ethanol, and the red fluorescence disappeared and showed blue fluorescence. After the anhydrous ethanol volatilized, the water was coated again, the blue fluorescence disappeared, and the red fluorescence appeared again. The use of anti-counterfeiting ink to print a pattern“two-dimensional code”on acid-free paper, in visible light, acid-free paper without any trace, and in 365 nm ultraviolet irradiation can see a red two-dimensional code pattern, with a smart phone scanning the two-dimensional code can be swept out of the official website of “Shaanxi University of Technology”. The excellent long wavelength red emission can also be used as fingerprint recognition, and the finger containing FD-CDs can be printed on the tape with a fingerprint pattern. Under 365 nm ultraviolet irradiation, the bifurcation, termination, island, eye, nucleus, cross and scar information on the fingerprint were clearly presented..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753312 (2024)
Special Issue for Ultrafast Optics
Polarization Photodetector Based on van der Waals Materials and Performance Enhancement Strategies （Invited）
Jing WANG, Hanxue JIAO, Yan CHEN, Shuaiqin WU, Xudong WANG, Shukui ZHANG, Junhao CHU, and Jianlu WANG
With the growing demand for precision and efficiency in photodetection from advanced technologies such as high-resolution imaging, information communication, and quantum computing, polarization detection, as a crucial branch of photonic technology, is facing unprecedented challenges and opportunities. In response, thisWith the growing demand for precision and efficiency in photodetection from advanced technologies such as high-resolution imaging, information communication, and quantum computing, polarization detection, as a crucial branch of photonic technology, is facing unprecedented challenges and opportunities. In response, this document provides a comprehensive review of the latest advancements in polarization photodetection technologies that harness the unique properties of two-dimensional van der Waals materials. Particularly, it focuses on innovative methods that substantially enhance the performance of polarization detectors through three advanced strategies: surface plasmons, ferroelectric field control, and twist-angle materials. These techniques not only represent the forefront of research but also hold significant potential to revolutionize the way polarization is detected, offering deeper insights and broader applications across a spectrum of scientific fields. The review aims to bridge the current technological gaps by integrating these sophisticated materials and strategies, setting a new benchmark for the capabilities of polarization photodetection systems.Surface plasmons are emphasized as a core method to enhance light-material interactions within the realm of polarization photodetection. The strategy utilizes the phenomenon of localized and propagating plasmon resonances to amplify the interaction between light and the material surface, thus significantly boosting the sensitivity and selectivity of detectors. By intricately engineering nano-scale metallic structures, such as nano-wires or gratings, it is possible to localize these plasmons, which in turn magnify the electromagnetic fields at the material's surface. This intensification allows for the more effective detection of subtle polarization changes in light, enhancing the detector's ability to discern complex light patterns with greater accuracy and reliability.This review further discusses the innovative approach of ferroelectric field control, which harnesses the spontaneous polarization and localized electric fields inherent to ferroelectric materials. This method manipulates the carrier concentration and photovoltaic performance of polarization detectors, offering a significant enhancement in efficiency and energy utilization. By leveraging the persistent internal electric fields provided by ferroelectric materials, the technology enables detectors to operate efficiently with reduced energy input. This optimization not only enhances the operational efficiency of the devices but also contributes to a reduction in operational costs and energy consumption, making it a sustainable option for long-term applications in various technological fields.Another notable strategy explored is the utilization of twist-angle materials, where adjusting the relative angle between layers of two-dimensional materials introduces customizable electronic structures and optical properties. This adjustment allows for a tunable response to polarized light, which can be meticulously controlled to suit specific detection needs. The flexibility offered by twist-angle materials opens up new domains for polarization detection, making it possible to adapt and tailor photodetectors for a wide range of scientific and industrial applications. The ability to modify the twist angle provides a powerful tool for researchers and engineers to develop highly adaptable and efficient photodetectors that can respond dynamically to different polarization states of light.The integration of these cutting-edge strategies into existing detector technologies marks a significant advancement towards developing high-performance, polarization-sensitive photodetectors. This review underscores the critical role of a synergistic approach that blends advanced material science with sophisticated micro-nano manufacturing techniques. This combination is essential for pushing the boundaries of current polarization detection technologies, facilitating the development of devices that are not only more effective but also more versatile and energy-efficient. By fostering innovation in material manipulation and device engineering, the field is poised for transformative breakthroughs that will enhance the capabilities of photonic technologies.Looking ahead, this review outlines the broad potential applications for these enhanced detectors in critical areas of modern technology. The advancements in polarization detection are not merely about keeping pace with technological demands—they also set the stage for pioneering new applications in photonics and related fields. The conclusion offers a visionary perspective on the future trajectory of polarization photodetection technology, highlighting the ongoing research and potential innovations that could continue to revolutionize the landscape of optical detection technologies. This continued evolution is expected to yield substantial scientific breakthroughs and propel industrial advancements, significantly impacting various sectors reliant on sophisticated optical detection systems..
Acta Photonica Sinica
- Publication Date: Jul. 25, 2024
- Vol. 53, Issue 7, 0753301 (2024)
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