Researching | GZXB Volume 52 Issue 6,2023

Effect of Zn Diffusion on Avalanche Breakdown Probability of InGaAs/InP Single Photon Avalanche Diodes

Kefei GUO, Fei YIN, Liyu LIU, Kai QIAO, Ming LI, Tao WANG, Mengyan FANG, Chao JI, Youshan QU, Jinshou TIAN, and Xing WANG

Single photon detection technology is a very sensitive photoelectric detection technology that can detect the energy of a single photon. It is a weak signal detection technology widely used in laser ranging, quantum communication, laser radar 3D imaging, and other fields. Single photon avalanche diodes generally operat Single photon detection technology is a very sensitive photoelectric detection technology that can detect the energy of a single photon. It is a weak signal detection technology widely used in laser ranging, quantum communication, laser radar 3D imaging, and other fields. Single photon avalanche diodes generally operate in Geiger mode, that is, the operating voltage is greater than the breakdown voltage. Photon detection efficiency refers to the probability that a photon incident on a device is converted into a macroscopic signal that can be detected. It is an important parameter to measure the detection ability of single photon avalanche diodes. InGaAs/InP single photon avalanche diodes can work in near infrared band, has the characteristics of high photon detection efficiency and good time jitter, in addition to small size, high stability, excellent anti-radiation performance, can realize large array imaging and other advantages, become one of the most promising near infrared single photon detectors. The planar back-illuminated InGaAs/InP single photon avalanche diodes designed in this paper adopt the absorption grading charge multiplication separation structure, in which the charge layer can control the electric field intensity of the multiplier layer to be high enough to produce avalanche breakdown, while the absorption layer electric field intensity is limited to a certain range to reduce the tunneling effect. The grading layer can reduce the accumulation of carriers at the heterogeneous interface. The P+ active region is formed by two Zn diffusion structures, the multiplication region is limited to the area below the deep diffusion. The shallow diffusion can effectively limit the edge electric field of the multiplication region without using the guard ring structure to avoid premature edge breakdown. The structure design and numerical simulation of InGaAs/InP single photon avalanche diodes are carried out by using TCAD software and selecting the appropriate physical model and parameters, and the corresponding electrical and optical parameters are obtained. Then aiming at the effect of avalanche breakdown probability on device photon detection efficiency, the relationship between the avalanche breakdown probability of the device and the difference between the two Zn diffusion depths, the lateral diffusion factor of Zn diffusion, the doping concentration of Zn, and the temperature parameters is emphatically studied. It is found that when the depth of deep diffusion is 2.3 μm, there is an optimal target value corresponding to the shallow diffusion depth. The deeper the shallow diffusion depth, the higher the breakdown probability of avalanche in the center of the multiplication region under the same overbias, and the higher the electric field intensity will also increase. However, when the difference between the two Zn diffusion depths is less than 0.6 μm, non-ideal breakdown will occur outside the multiplication region, resulting in an increase in the dark count of the device. The larger the lateral diffusion factor of Zn diffusion, the higher the breakdown probability of the avalanche at the center of the multiplication region, and the lower the breakdown probability of the avalanche at the edge of the multiplication region. With the same diffusion depth, the shallow diffusion Zn doping concentration has no significant effect on avalanche breakdown probability, but the higher the deep diffusion Zn doping concentration, the lower the avalanche breakdown probability under the same overbias. The study of the influence of temperature on avalanche breakdown probability shows that the device can obtain better performance at low temperature. The research work in this paper can guide the design of InGaAs/InP single photon avalanche diodes with higher photon detection efficiency and lower dark count. Moreover, relevant research can also provide a reference for selecting the optimal working point of the device to ensure the device works in the best state and realize the optimal application of the device..

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0604001 (2023)

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Characteristics of Ternary Organic Photodetectors Based on P3HT∶PC₆₁BM∶ITIC Dual Acceptors

Ruliang ZHANG, Mingchao PI, Tao AN, Gang LU, and Qian WANG

Traditional Organ Photodetectors (OPDs) respond not enough in long-wave region, and it is difficult to support panchromatic detection from ultraviolet to infrared regions. In order to overcome the weak absorption ability, researchers adopted a ternary heterojunction structure and the material of complementary absorptio Traditional Organ Photodetectors (OPDs) respond not enough in long-wave region, and it is difficult to support panchromatic detection from ultraviolet to infrared regions. In order to overcome the weak absorption ability, researchers adopted a ternary heterojunction structure and the material of complementary absorption spectra. Ternary polymer high-performance OPDs, with ultra-broad spectral response, in panchromatic range, have been reported by mixing the third component. However, there are still problems existing, such as low detection rate, insufficient photoelectric characteristics, and low spectral response uniformity, which are the current research focuses in OPDs.In order to realize panchromatic response to three primary colors, a ternary active layer with heterojunction structure was introduced to broaden spectra by mixing non-fullerene receptor ITIC in P3HT∶PCBM, which can improve detection performance by achieving mobility balance and surface morphology of active layer. In the proposed ternary active layer, polymer P3HT was used as the donor, while fullerene PC61BM and non-fullerene ITIC were adopted as acceptors. The influence of ITIC acceptor mass ratio on photoelectric performance of the detector was mainly studied.The optical characteristic analysis of proposed ternary OPDs indicates that the main material P3HT∶PC61BM film has good light absorption ability from 400 to 600 nm. Moreover, ITIC molecules have stronger absorption abilty in red light region, and main absorption peak is located at 702 nm. Ternary blend film produces a new absorption peak in the range of 600 nm to 750 nm. With gradual increase of ITIC ratio, the absorption ability of blend film in long-wave region enhances. By changing the ratio of PC61BM and ITIC, the absorption intensity of long-wave region can be effectively adjusted.In electrical characteristic, the J-V tests show that dark current density gradually reduces as dual acceptors increase Under red light, the bright current density increases first and then decreases with increasing of the mass ratio of ITIC. As the mass ratio of the active layer was 10∶8∶2, the red current density reached a maximum of 1.91×10^-4 A·cm^-2. Mixing ITIC into an active layer enhances photocurrent absorption in red light and carriers transport.ITIC influence on the electrical characteristics in the full spectrum was analyzed with External Quantum Efficiency (EQE) spectroscopy at different mass ratios. The EQE of ternary OPDs with ITIC extends to 800 nm, which is attributed to mixing ITIC to promote absorption in long-wave band. The effect on the charge dynamics process in active layer was investigated by fluorescence quenching experiment, to analyze charge transfer inside different mass ratios blend. Photoluminescence spectroscopy (PL) intensity of P3HT is greatly quenched in blended film, which indicates charge transfer existing between P3HT and ITIC. It improves the internal exciton dissociation efficiency and significantly increases photocurrent. By interaction experiments between dual acceptors PC61BM and ITIC, the photocurrent density of mixture is larger than that of single. Charge transfer can improve photocurrent introduction, which enhances light absorption ability and forms more efficient exciton dissociation surfaces.In summary, an appropriate ratio of non-fullerene ITIC mixed into P3HT:PC61BM bulk heterojunction structure can widen OPDs spectrum to 400~800 nm. As a mass ratio of P3HT:PC61BM:ITIC is 10∶8∶2, the EQE of ternary OPDs in three primary colors is up to 56%, 68% and 52%, respectively, and specific detection rate (D*) of three components are up to 10¹² Jones in the range of 400~700 nm. Response spectra range is broadened from 600 nm to 800 nm. ITIC compensates absorption of binary blend film in long-wave range, achieves high and balanced carrier mobility ability. ITIC dissociates with original donor and acceptor, which improves light current. Moreover, ITIC also reduces dark current by promoting thin film crystallization and weakening bimolecular recombination.In conclusion, the proposed dual acceptors ternary organic photodetector with complementary absorption ranges, has high mobility of fullerene in active layer film and strong absorption non-fullerene in red and near-infrared light, which contributes to wide spectrum and high sensitivity OPDs..

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0604002 (2023)

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A Pupil Position Extraction Method of Unstable Cavity Laser

Ruihao MA, Yongdong GAN, Xinyang LI, Yue MEI, Sinazhuoma, Feng ZHU, Qiwang JIA, and Tianyi WU

The confocal unstable cavity has been widely used in chemical laser systems due to its large controllable mode volume, high transverse mode discrimination, near-diffraction limit plane wave output, and high power and high quality far-field spots. The guiding light emitted by the laser is reflected back and forth betwee The confocal unstable cavity has been widely used in chemical laser systems due to its large controllable mode volume, high transverse mode discrimination, near-diffraction limit plane wave output, and high power and high quality far-field spots. The guiding light emitted by the laser is reflected back and forth between the two mirrors of the confocal unstable cavity and interferes with each other. In theory, the beam that output from the confocal unstable cavity is multiple concentric rings. However, due to the influence of air disturbance, platform vibration and other factors, the gray level of the output interference concentric rings fluctuates, the light intensity is gradually weakened from inside to outside, and is in rapid dynamic change. These factors increase the difficulty of extracting the optical pupil position of the guiding light in the automatic optical path collimation. In order to solve the difficult problem of optical pupil position extraction in automatic optical path collimation, a method for optical pupil position extraction of unstable cavity laser is proposed in this paper. First, the original image is preprocessed using the bilateral filtering algorithm. After image preprocessing, calculate the image threshold. Multiplying the coefficient by the image threshold of the Otsu algorithm to get the final threshold of the image. After calculating the threshold, performing threshold segmentation on the image. After the binary image is obtained, the median filter is applied to the binary image to reduce the noise in the binary image and fill the small holes in the binary image. Each contour in the binary image is regarded as a separate connected region, and the contours of the binary image are extracted by using the idea of connected region detection. Then, the inner contour of the optical pupil image can be found from many contours by using the two contour attributes of the contour center and the number of points that make up the contour. After finding the inner contour of the optical pupil image, the Random sample consensus (RANSAC) ellipse fitting algorithm is used to fit the inner contour, which reduces the influence of the internal contour noise on the ellipse fitting results, so as to improve the robustness and accuracy of the optical pupil position extraction results. Since the RANSAC ellipse fitting algorithm needs to fit multiple ellipses, NVIDIA GPU is used to speed up the RANSAC ellipse fitting algorithm, and thousands of ellipses are fitted in the GPU core at the same time to improve the real-time performance of the algorithm. The optical pupil position extraction method proposed in this paper can meet the requirements of real-time, reduce the impact of internal contour noise on ellipse fitting, and improve the accuracy and robustness of optical pupil position extraction results. MATLAB is used to generate 100 frames of simulated optical pupil images with the known position, and then 40% random noise points with amplitude 0~13 are added to the inner contour of the simulated optical pupil image. The proposed method and the direct ellipse fitting method are used to fit the inner contour, to extract the position of the optical pupil image. The simulation results show that the proposed method has higher accuracy and robustness than the direct ellipse fitting method. Compared with the results of direct ellipse fitting, the average value of the extracted position deviation is 0.283 pixels smaller, the maximum value of the position deviation is 0.660 pixels smaller, and the root mean square value of the position deviation is 0.136 pixels smaller..

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0610001 (2023)

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Low-light Image Enhancement via Extend Atmospheric Scattering Model

Manli WANG, Bingbing CHEN, and Changsen ZHANG

Low contrast and weak detail features of images collected in a low-light environment will seriously affect the accuracy and stability of machine vision detection. In recent years, the low-light image enhancement technology has made remarkable progress. However, the existing low-light image enhancement algorithms have s Low contrast and weak detail features of images collected in a low-light environment will seriously affect the accuracy and stability of machine vision detection. In recent years, the low-light image enhancement technology has made remarkable progress. However, the existing low-light image enhancement algorithms have some problems, such as image detail loss, low brightness, local exposure, insufficient visual naturalness, complex algorithm and high resource overhead. To solve the above problems, a low-light image enhancement algorithm based on extended atmospheric scattering model is proposed. Firstly, the maximum value of R, G and B color channels is calculated and the initial transmission map is obtained by gamma correction. Secondly, the main structure and fine structure of the initial transmission map were extracted, PCA (Principal Component Analysis) method was used to fuse the main structure transmission map and fine structure transmission map to obtain the optimized local consistency transmission map of texture detail removal. Then, the inverse atmospheric light value is calculated using the dark pixel of the bright channel. Finally, the LIEAS (Low-light Image Enhancement via Extend Atmospheric Scattering Model) model is solved to obtain the final enhanced image with natural color and good contrast. The enhanced model derived by the algorithm is similar to the Retinex enhanced model in form, but the difference is that there is an additional correction term in the LIEAS model, which can better suppress the excessive enhancement and detail loss in the image. The algorithm uses the image fusion method to optimize the transmission image and can reproduce the contour and texture details well. In order to evaluate the algorithm objectively, spatial frequency, average gradient, edge intensity and natural image quality evaluation are used as the image quality evaluation metrics. In order to verify the effectiveness of the algorithm, the parameter analysis experiment, model analysis experiment and performance comparison experiment are carried out respectively. In the parameter analysis experiment, firstly, the influence of the selection of gamma parameters on the enhanced image is analyzed. The subjective visual analysis and objective data analysis are carried out on the test results under different parameters, and a good gamma parameter value is obtained. Secondly, the influence of the selection of the maximum filtering window size of the bright channel on the solution of the inverse atmospheric light value and the enhanced image is analyzed. The test results under different window sizes are analyzed to obtain an appropriate window size. Then, the darkest pixel proportion of the bright channel in the solution of the inverse atmospheric light value is selected and analyzed. Finally, this paper verifies the advantages of the transmission map optimization method based on fusion technology. In the model analysis experiment, compared with Retinex model, spatial frequency and average gradient of the proposed algorithm are significantly improved, which also has prominent visual advantages, indicating that the correction term in the proposed algorithm can better suppress the excessive enhancement and detail loss of the enhanced image, and has good enhancement ability. At the same time, by changing the atmospheric light value in the model, the proposed algorithm can also be used in image dehazing, and the image dehazing can get a good effect from both subjective and objective aspects. In the performance verification experiment, three low-light image datasets were selected to test, and the performance of the proposed enhancement algorithm was compared with that of other eight algorithms from both subjective and objective aspects. Compared with the other eight algorithms, this algorithm has the advantages of bright background, high contrast, complete edge details, natural, vivid image, avoiding local overexposure and so on. The algorithm has more advantages in spatial frequency, average gradient, and edge intensity, which indicates that the algorithm has better performance in the aspects of image color richness and image sharpness. Both for the metric analysis of the whole image of the dataset and for the metric analysis of a single image, the proposed algorithm is very advantageous, and the model is simple and low complexity. Compared with the existing enhancement algorithms, the proposed algorithm has some advantages in detail information retention, contrast enhancement, image naturalness and local overexposure suppression..

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0610002 (2023)

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Current Status and Development Tendency of Image Motion and Compensation About Space Based on Optical Imaging System（Invited）

Wei HAO, Peipei YAN, Zhiguo LI, Zhiyuan CHENG, and Wenji SHE

Along with the development and progress of science and technology, the image quality will be affected by variation of orbit, attitude angle and other factors, as well as tracking speed errors, platform and moving parts jitter. All of these factors will cause image motion, which will lead to image resolution reduction, Along with the development and progress of science and technology, the image quality will be affected by variation of orbit, attitude angle and other factors, as well as tracking speed errors, platform and moving parts jitter. All of these factors will cause image motion, which will lead to image resolution reduction, image blurring and image quality declined. Therefore, how to suppress the impact of dynamic image motion becomes the bottleneck of obtaining high-resolution images. At present, the existed researches basically analyze the factors of image motion from a separate application field. They do not present the generation and compensation technology of image motion of space-based optical system systematically and comprehensively. How to suppress the influence of dynamic image shift gradually has become the bottleneck of obtaining high-resolution and clear images. Compared to the conventional ground-based telescope, the space one can get away from the distortions of the Earth’s atmosphere. So less background noise, wider optical wavebands and higher imaging precision to the diffraction limit can be achieved. This paper analyzes the various factors that produce image shifts during the imaging process of the space-based space target optical system and on this basis, comprehensively analyzes and locates the factors that affect the quality of dynamic imaging. Aiming at the problem of unclear imaging caused by dynamic image movement in the process of space high-speed moving target tracking, the degradation mechanism is analyzed, and the satellite platform disturbance, moving base tracking stability, stray light, defocusing, and imaging distance within the integration time are analyzed in detail. The influence of factors such as changes on the dynamic MTF is given, and the mathematical model corresponding to each influencing factor is given. An image motion compensation scheme based on FSM is given, which has been verified by laboratory tests and can effectively reduce the impact of image motion. During the space camera's on-orbit working process, vibration caused by reaction wheel assembles; solar panels and lower frequency can be compensated and suppressed by attitude controllers. While vibration with a smaller amplitude and higher frequency will still convey through the platform to the sensor, resulting in subtle jitter and weakened attitude stability of the sensor. Due to the tiny unit pixel view angle of high resolution sensor, jitter will lead to the image point of the ground scene indistinct and imaging quality declined in exposure time. With the development of spacecraft attitude control method, sensing, optical system design and manufacturing level, how to suppress the influence of dynamic image shift gradually It has become the bottleneck of obtaining high-resolution and clear images. In order to realize high resolution imaging, the space-based space target optical imaging system has higher and higher requirements for the spatial resolution of the payload, and a wider and wider range of motion adaptation of the space moving target. This paper sketches the mechanism of image motion influence and image motion compensation technologies. On the basis of that, this paper classifies space-based imaging according to the applications, such as remote sensing, space astronomical observation, Mars exploration and space target detection. Furthermore, we introduce in detail the research progress of image motion influence and compensation in the fields of remote sensing, space astronomical observation, Mars exploration and space target detection. This paper provides the research progress of image motion influence and compensation in the fields of domestic and international in recent years. Through analyzing the research, we can further improve our understanding of the development direction of space optical technology, and provide new methods and approaches for the development of space optical technology and equipment..

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0611001 (2023)

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3D Retina Projection Display Using Doublet Holographic Optical Elements

Hongwei LIU, Yimin LOU, Juanmei HU, and Fengmin WU

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0611002 (2023)

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Underwater Frequency Modulated Continuous Wave Laser Ranging Based on Blue External Cavity Diode Laser

Chaofeng MA, Qi JIANG, Ying WU, and Wei LIANG

Underwater lidar technology has become an important tool for ocean exploration and underwater operations. So far, all of the reported underwater lidars are based on the pulsed Time-Of-Flight(TOF) method for ranging, which is characterized by high pulse peak power and relatively long detection distance. However, TOF lid Underwater lidar technology has become an important tool for ocean exploration and underwater operations. So far, all of the reported underwater lidars are based on the pulsed Time-Of-Flight(TOF) method for ranging, which is characterized by high pulse peak power and relatively long detection distance. However, TOF lidar is large in size, high in power consumption, and small in dynamic range, and there will be interference between different TOF lidars. Hence they are not suitable for compact platforms such as Autonomous Underwater Vehicles(AUV) swarms. In addition, back scattering presents a great challenge to underwater pulsed lidar, which limits the sensitivity and dynamic range of the detector. Strong back scattering of suspended solids in water can completely submerge the real signal, leading to false target detection. Underwater Frequency Modulated Continuous Wave (FMCW) lidar has a greater dynamic range than TOF radar and can output a continuous spectral signal proportional to distance. Because the signal of the coherent detection is amplified by the local oscillator, FMCW lidar requires low laser output power and can be realized with low power diode laser, which can significantly reduce the size, weight and power of the lidar system. So far most reported studies on FMCW lidar are concentrated on near-infared wavelength such as 1 μm, 1.55 μm. However, there have been no reports of underwater FMCW lidar using blue or green lasers so far.The implementation of FMCW lidar is faced with two challenges, one is to obtain a single-mode tunable narrow linewidth laser, the other is to eliminate the nonlinear effect of laser frequency modulation. Because the light absorption loss of water will lead to the signal attenuation and shorten the detection distance, it is necessary to select the blue-green laser located in the seawater “transmission window” with a small attenuation coefficient. A commercial 405 nm Blue FP laser diode and a 30% reflector are used to construct an External Cavity Diode Laser(ECDL). The blue ECDL exhibits a coherence much longer than 10 meters in fiber, and a continuous frequency sweep range of 1.5 GHz by direct modulation of the injection current. Modulation nonlinearity of the FMCW laser can broaden the FFT spectrum of the measured signal and reduce the ranging accuracy. To overcome this problem, an FMCW ranging method based on equal optical frequency resampling is adopted. The system consists of both a fiber interferometer and a free space interferometer. The optical fiber interferometer uses 10 m delay optical fiber to monitor the frequency change with time, and the free space interferometer is used to obtain the beat frequency signal containing the distance information of the target to be measured. Theoretical analysis and experimental verification were carried out. The underwater ranging was conducted by adding Mg(OH)₂ powder in the water tank to adjust the attenuation coefficient to simulate the seawater environment. An FMCW laser ranging system with dual interferometers is built, and the extremum point of the beat signal of the fiber optic interferometer is extracted to sample the beat signal of the free space Interferometer. It is verified that the beat signal spectrum broadening problem due to the laser′s frequency modulation nonlinearity is well corrected. Using the resampling method, the distance is measured at eight equally spaced positions, and a reflector is placed at these positions in turn as the detection target. The results show that the measurement range of the target is linear with the actual range, and a detection range of 5 meters is realized with only 9.5 mW laser output power, and the maximum error is 0.051 m. In order to obtain the measurement error of the FMCW ranging system, ten groups of data are measured at the same position. Through calculation, the average measurement error of the ranging system is 0.027 m. Our work demonstrates that a low power commercial blue laser diode can be used to construct a single frequency ECDL laser, and it can be directly frequency modulated to perform accurate underwater FMCW laser ranging. This lidar architecture characterizes by small size, low power and weight, which promises an effective laser ranging sensor for compact AUV swarm..

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0614001 (2023)

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Theoretical Study of Near Single-cycle Post Compression for Yb Dopped Lasers

Qi CHENG, Hao YUAN, Huabao CAO, and Yuxi FU

The attosecond light source can reveal the macroscopic properties of matter from the microscopic field, so it is widely used in the fields of materials, medicine, atomic and molecular physics, and quantum physics. The common laser for generating attosecond light sources is the Ti∶Sapphire laser with a central wavelengt The attosecond light source can reveal the macroscopic properties of matter from the microscopic field, so it is widely used in the fields of materials, medicine, atomic and molecular physics, and quantum physics. The common laser for generating attosecond light sources is the Ti∶Sapphire laser with a central wavelength of 800 nm. However, the average power is limited due to the thermal effect limitation. With the deepening of the application of attosecond light sources, high power with a high repetition rate driving laser if highly demanded. In order to achieve the driving laser with short pulse duration, high repetition rate and high pulse energy, Yb-doped lasers, such as Yb∶KGW, Yb∶YAG have been developed rapidly in recent years. However, the pulse duration of the Yb-doped laser is much longer, and it needs to be compressed by a post-compression method in order to obtain few-cycle laser pulses. Noble gas filled hollow core fibers are widely employed for pulse compression, but it is difficult to compress the 515 nm pulses obtained by frequency doubling to a nearly single cycle. Therefore, this paper simulates the compression obtaining few cycle pulses based on the time-domain generalized nonlinear Schr?dinger equation satisfied when the pulses are transmitted in a hollow core fiber. The light source in the calculation process refers to the PH2-2mJ-SP laser of Light Conversion Company, the center wavelength is 1 030 nm, the repetition rate is 10 kHz, and the pulse energy is 2mJ. In the simulation, the input pulse with a center wavelength of 515 nm, a pulse energy of 1 mJ, and a pulse duration of 250 fs is employed, which peak power is 4×10⁹ W. In order to achieve controlled spectral broadening with minimum loss in the hollow core fiber, the peak power of the pulse should first be less than the photoionization threshold intensity of the noble gas, which limits the minimum core radius to 50 μm. Besides, the peak power should be lower than the self-focusing threshold in order to avoid self-focusing when the pulse is transmitted in a hollow core fiber, which limits the maximum pressure of the noble gas. For the argon and krypton to be investigated, the maximum pressures are 10 bar and 3.5 bar, respectively. Considering the loss coefficient when the pulse is transmitted in the hollow core fiber, and the broadening factor required to broaden the pulse spectrum to an octave, a preliminary length of 2.5 m and a core radius of 125 um can be determined for the hollow core fiber. On this basis, the frequency spectrum and time domain broadening of the pulses under various gas pressure and propagation length are simulated. Finally, the pulse spectrum can be broadened to an octave. Considering the influence of the broadening factor and transmission efficiency, the length of the hollow core fiber is finally selected as 2.5 m when the argon and krypton are filled at their maximum pressures. After compensating the dispersions, the pulses of 2.91 fs and 2.62 fs can be obtained in argon and krypton, respectively, which are less than two optical cycles. But at this time, the compressed pulses still have some high-order dispersion that cannot be compensated. Thus, we employed the multi-stage compression method, which avoids introducing too much high-order dispersion. The first stage compression is referenced to the work of HARITON V et al., who successfully compressed a 515 nm, 250 fs pulse to 38 fs in their experiments using a multi-pass cavity. The second stage uses a hollow core fiber. Under the appropriate gas pressure, transmission length, and dispersion compensation, the pulse is compressed to ~ 2 fs, which is close to a single cycle, with significantly reduced high-order dispersion than that from single stage compression..

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0614002 (2023)

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Dual Wavelength Laser Road Meteorological Sensing Method

Junyu LONG, Decao WU, Binbin LUO, Ying ZHANG, Yufeng GUO, Sheng CAO, Lei DENG, and Mingfu ZHAO

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0614003 (2023)

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Preparation and Photocatalytic Properties of Highly Stable Mn：ZnO/Mn₂O₃ Nanocomposite Photocatalysts

Minghui BAI, Xian LIU, Qiuping ZHANG, Man SONG, Jianhong LI, Yifei SUN, Fei YU, Huan YUAN, Yuanjie SU, and Ming XU

Recently, with the growing problem of environmental pollution, a large number of emerging environmental purification technologies, especially the photocatalytic oxidation technique based on semiconducting metal oxide nanostructures, have been rapidly developed for the applications in degradation of organic pollutants f Recently, with the growing problem of environmental pollution, a large number of emerging environmental purification technologies, especially the photocatalytic oxidation technique based on semiconducting metal oxide nanostructures, have been rapidly developed for the applications in degradation of organic pollutants from water and atmospheric environments. In the process of development, scientists around the world have recognized that the improvement in the visible light response, the separation efficiency of photogenerated charge carriers and the light stability of the catalysts are the key factors to promote the large-scale application of the photocatalytic oxidation technique. For this purpose, a series of new high-performance nanostructured composite photocatalysts have been continuously developed and investigated, but the process complexity and synthesis cost are gradually increasing. Also, it is difficult to realize the band structure regulation of the semiconductors and well-match energy levels between different semiconductors. These problems need to be solved urgently. At the same time, with the future demand for high selectivity of new technologies (such as selective sensing, selective gas separation, selective carbon dioxide reduction), the selective photocatalytic degradation of organic pollutants will also become a development direction in this field. In this study, a series of photocatalysts including pure ZnO, Mn-doped ZnO (Mn:ZnO), Mn₂O₃ coupled ZnO (ZnO/Mn₂O₃) and Mn₂O₃ coupled Mn-doped ZnO (Mn:ZnO/Mn₂O₃) are successfully prepared by a modified polymer network gel method, and the characteristics of the catalysts for photocatalytic degradation of Rhodamine B (RhB) and Methylene Blue (MB) dyes under simulated sunlight irradiation are investigated. The phase compositions, microstructures, surface chemical states as well as optical and optoelectronic properties are analyzed through some material characterization approaches in detail. The results of X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Brunauer-emmett-teller (BET) specific surface area shows that the particle sizes of Mn:ZnO and Mn:ZnO/Mn₂O₃ are decreased and the particle dispersibility are improved after trace (0.1 mol%) Mn doping and then coupling trace (0.2 mol%) Mn₂O₃,_{increasing BET specific surface area. Correspondingly, this results in the decrease of crystalline quality and the increase of crystal defects. Ultraviolet-visible (UV-vis) light absorption spectra indicates that the light absorption capacities of the composite photocatalysts in the visible region are significantly improved compared with pure ZnO and doped ZnO samples. Photoluminescence (PL) spectra suggests that trace Mn doping and trace Mn₂O₃ coupling jointly facilitate the separation of photogenerated electron-hole pairs. Combined with X-ray photoelectron spectroscopy (XPS), it is found that the enhanced visible light absorption capability and photogenerated electron-hole pair separation rate originates from the increase of oxygen vacancies on the catalyst surface and the formation of type II heterojunction structure between Mn:ZnO and Mn₂O₃. Therefore, Mn:ZnO/Mn₂O₃ exhibits the robust and superior photocatalytic activity for degradation of RhB dye under simulated sunlight irradiation. However, because of the narrow band gap (E_g ≈ 1.4 eV) of Mn₂O₃ and its higher valence band position than the redox potential of hydroxyl radical (·OH), the oxidation potential of photogenerated holes is too low to generate ·OH with the stronger oxidizing power. This results in the lower RhB and MB dyes photodegradation efficiencies of the ZnO/Mn₂O₃ photocatalysts. In addition, Mn:ZnO/Mn₂O₃ exhibits a selective photodegradation behavior towards RhB and MB dyes, that is, a significantly lower photodegradation efficiency for the easily degradable MB. Such a selective photocatalytic property is attributed to the difference between active species during the photocatalytic reactions and the relationship between the Zero Charge Point (ZPC) of the catalyst and the pH of the initial dye solution. In the photocatalytic processes, the strong oxidizing species (·O₂^-, ·OH and h⁺) on the surfaces of the catalysts for the photodegradation of RhB dye are more than those (·OH and h⁺) for the photodegradation of MB dye. The ZPC value of Mn:ZnO/Mn₂O₃ closes to the pH value of the weakly acidic RhB (pH=6.3~6.6) rather than MB (pH=6.0) dye aqueous solution, resulting in a higher adsorption ratio of cationic RhB dye molecules on the catalyst surface..showLess}

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0616001 (2023)

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Research and Design of Bacterial Autofluorescence Detection Device

Jiayun ZHENG, Yikun WANG, Jingshu NI, Yang ZHANG, Yao HUANG, Yuanzhi ZHANG, Quanfu WANG, Xia WANG, Yong LUI, Jinhua ZHOU, and Meili DONG

Excessive bacterial load will not only cause delayed wound healing and local or systemic inflammatory reaction, but also threaten the life safety of patients in severe cases. Therefore, a new method that can detect wound bacteria quickly and directly is needed. Traditional bacterial detection methods are mainly visual Excessive bacterial load will not only cause delayed wound healing and local or systemic inflammatory reaction, but also threaten the life safety of patients in severe cases. Therefore, a new method that can detect wound bacteria quickly and directly is needed. Traditional bacterial detection methods are mainly visual observation of clinical symptoms (including fever, redness and swelling, pus exudate, etc.) and microbial swab sampling, but these two methods are usually subjective and time-consuming. The results of the same clinical symptom observed by doctors with different experiences may be different, and in some cases the infection may not show obvious symptoms. Therefore, it is often subjective to judge the infection by observing the clinical symptoms with naked eyes and may cause misdiagnosis. Swab sampling is often plagued by false negative, and different sampling methods and selection of sampling areas will affect the results of sampling and culture. False negative areas or missed areas may contain a large number of bacteria. The missing of a large number of bacteria in these areas may lead to repeated wound healing, causing great pain to patients and great burden on the medical and health system. In addition, longer culture time is also a pain point for swab sampling, because it may cause inaccurate culture results and miss the best treatment opportunity. Relevant studies have found that bacteria can emit fluorescence by themselves under the excitation of 405 nm light source, without using contrast agents. The purpose of this study is to design a fluorescence detection imaging device based on the principle of spontaneous fluorescence of bacteria, which provides a fast and direct new method for wound bacteria detection. In this study, a bacterial fluorescence imaging system is developed. The light source module of the system consists of two LED with a central wavelength of 405 nm and LED driver modules. After calibration and parameter setting, the light source driver works in constant current mode to ensure stable operation of the light source. When the light source shines on the wound bacteria, it can stimulate the spontaneous fluorescence of bacteria almost in a moment. The customized dual band filter is used to receive bacterial fluorescence and filter out the interference of reflected light from the light source. The transmission band of the filter is selected according to the results of the three-dimensional fluorescence spectrum of bacteria. In the dark environment, the smartphone imaging mode is set to night mode, the shutter speed is set to 3 s, the automatic white balance is set, and each sample is collected five times to reduce experimental error. Porphyrin fluorescence images are converted into three-dimensional intensity images to verify the imaging uniformity of the device. The fluorescence region is detected by region extraction algorithm, and the bacterial fluorescence is quantified. The signal area is extracted by using the Hough circle detection and edge contour extraction method as well as the mask method obtained by using the binary function. The gray value of all pixels in the signal area is traversed and the average value is calculated, which is taken as the quantitative result of the relative fluorescence intensity of bacteria. Finally, a linear rule between the fluorescence intensity and the concentration is obtained by linear fitting of the quantitative result. The experimental results of three-dimensional fluorescence spectrum of bacteria provide an important basis for the selection of excitation and emission bands in this study. It can be seen from the porphyrin three-dimensional intensity map that, except for the projection points of the two light sources, the uniformity of the signal area is good. This indicates that the two LED light sources used in the device can uniformly excite the fluorescent signal area, and the fluorescent image with good quality can be obtained without using the whole row of ring LEDs as light, which greatly reduces the power consumption and heat generation of the system. The result of image processing proves that regular and irregular signal regions can be extracted with the device. The regular region extraction algorithm can accurately extract the fluorescent signal region, avoid the fluorescent interference of the culture dish wall, and effectively improve the calculation accuracy of the relative signal strength. The gradient concentration of Escherichia coli and Staphylococcus aureus shows that there is a good linear relationship between the bacterial fluorescence intensity and the bacterial quantity under the experimental bacterial concentration. Combined with the bacterial plate counting experiment, the minimum detection limit of the system is 10⁵ CFU/mL, which indicates that the system can effectively detect the infection of wounds. Through linear fitting of the calculation results, it can be obtained that there is a linear relationship between bacterial fluorescence intensity and concentration, and the minimum detection limit of the system can be calculated according to the linear relationship. The device provides a new means for the bacterial detection of the wound, with high detection sensitivity to meet the bacterial load identification of the infected wound. There is no need for swab sampling and fluorescent labeling, and the detection procedure is simple and easy to operate. The extraction of signal region can clearly and intuitively show the location of bacteria, which can provide effective reference information for wound debridement and targeted drug administration. This study only conducts quantitative detection of bacteria in vitro, and further measurement of bacteria in vivo is needed. In addition, future efforts should include the development of a smartphone app that integrates existing processing algorithms to further simplify the process and enable rapid in vivo detection of wound bacteria..

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0617001 (2023)

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Transmission and Control of Solitons with Saturable Nonlinear in Linear Defocusing PT-symmetric Waveguide

Qi WU, Juanfen WANG, Chenrui DU, Lingzhen YANG, Pingping XUE, and Linlin FAN

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0619001 (2023)

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Optimal Selection of Correlation Function Fitting Window in Bimodal Particle Size Inversion by Dynamic Light Scattering

Yuexin LIU, Wei LIU, Hongyan JIA, Jizhou CHEN, Yajin WANG, and Jin SHEN

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0629001 (2023)

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Universal and Improved Mutation Strategy for Feedback-based Wavefront Shaping Optimization Algorithm

Hui LIU, Xiangyu ZHU, Xiaoxue ZHANG, Xudong CHEN, and Zhili LIN

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0629002 (2023)

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Study on Thickness Uniformity of Double-sided Sputtering Film on Large-diameter Ultra-thin Substrates

Xiuhua FU, Junqi LIU, Zhuolin LI, Haicheng LIU, Haifeng REN, Yibo WANG, and Kexu HAN

As an important part of the original fingerprint identification under the optical screen, the infrared cut-off filter needs to be plated on a large-diameter and ultra-thin substrate in order to connect the subsequent processing process and facilitate mass production. The substrate surface type has very high requirement As an important part of the original fingerprint identification under the optical screen, the infrared cut-off filter needs to be plated on a large-diameter and ultra-thin substrate in order to connect the subsequent processing process and facilitate mass production. The substrate surface type has very high requirements. In recent years, many scholars have done a lot of experimental research on the issues related to the uniformity of sputtering coating film thickness, but there are few references on the related research on the uniformity control of ultra-thin and large-area substrates. In the traditional method of coating double-sided film layers, in the process of using ultra-thin and large-diameter substrates, only one side can be plated first, and then the substrate can be taken out and turned over to coat the other side. This operation is inefficient and the risk of substrate chipping is high and the film uniformity is poor, which will cause uneven stress distribution in the film layer, resulting in the bending of the substrate, which can not meet the actual use requirements. In this paper, two materials, SiO₂ and Nb₂O₅, are used as the research objects, and the influence on the film thickness uniformity is analyzed from three aspects: the distribution of the magnetic field intensity of the target material, the public-rotation system, and the shielding angle of the substrate fixture. According to the experimental results, the relative strength of the target magnetic field has a certain relationship with the uniform distribution of the relative thickness of the film, and the relative thickness of the film will also increase when the relative strength of the magnetic field is larger. The revolution system can greatly improve the film thickness uniformity. In this paper, the film thickness uniformity under three rotational speed ratios of 1∶2, 2∶1, and 5∶4 is studied. When the rotational speed ratio is 5∶4, the film thickness is uniform,and the uniformity is the best. The film uniformity of SiO₂ increases from 17.31% when only rotating to 3.86%, and the film uniformity of Nb₂O₅increases from 15.99% when only rotating to 3.41%. After calculation, the coating efficiency and target utilization rate increase by 12.3% and 17.6% respectively. Since the equipment has a public rotation system, the edge of the substrate fixture will block the effective coating area. In this paper, five blocking angles of 0°, 20°, 35°, 55°, and 70° are studied. Among them, SiO₂ single-layer film is thin at a 20° blocking angle, and has the best thickness uniformity, which is 0.62%. The uniformity of 0°, 35°, 55°, and 70° is 1.42%, 5.43%, 7.52%, and 8.58%, respectively. The thickness of Nb₂O₅ single-layer film is uniform at 20° blocking angle, and the best performance is 0.71%. The uniformity of 0°, 35°, 55°, and 70° is 1.55%, 3.64%, 7.56%, and 10.81%, respectively. Considering factors such as substrate loading and uniformity, a 20° blocking angle is selected for the preparation of the infrared cut-off filter. The filter is made of D263T substrate with a diameter of 20.32 cm and a thickness of 0.07 mm. In order to balance the influence of the film stress on the upper and lower surfaces on the surface shape of the substrate as much as possible, the Essential Meclord software is used to adopt the design of a symmetrical film system. The physical thicknesses of the upper and lower surfaces are 3 944.27 nm and 4 366.19 nm, respectively. After measurement of the prepared samples, the wavelengths at the transmittance of 50% are 572.6 nm and 572.5 nm, the transmittance at the 450~550 nm band are 97.59%, 98.14%, and the transmittance at the 590~1 100 nm band is 0.042%, 0.048%, which all meet the design and practical application requirements. The sample uniformity can reach 0.13% and 0.142%, and the warpage degree of the substrate is 0.085 mm, which meets the requirements. How to obtain a film with a larger effective coating area and better film thickness uniformity on the magnetron sputtering equipment is the key research direction for the next step..

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0631001 (2023)

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Optical Properties of Titanium-doped Gallium Oxide Thin Films by Thermal Atomic Layer Deposition

Cunyu LI, Xiangping ZHU, Wei ZHAO, Jichao LI, and Jingpeng HU

Gallium oxide (Ga2O3) is a wide bandgap (4.8 eV) semiconductor oxide with the advantages of high transparency and excellent chemical and thermal stability. Therefore, Ga2O3 thin film has a wide range of applications in metal oxide field effect transistors, photodetectors and so on. However, the large bandgap of Ga2O3 i Gallium oxide (Ga₂O₃) is a wide bandgap (4.8 eV) semiconductor oxide with the advantages of high transparency and excellent chemical and thermal stability. Therefore, Ga₂O₃ thin film has a wide range of applications in metal oxide field effect transistors, photodetectors and so on. However, the large bandgap of Ga₂O₃ is unfavorable to the conductivity, which limits the application of Ga₂O₃ film in optoelectronic devices. The optical and electrical properties of Ga₂O₃ can be significantly improved by elemental doping, thereby enhancing device performance. The lattice deformation of Ti-doped Ga₂O₃ (TGO) is small due to the close matching of the Shannon ion radii (0.060 5 nm, 0.042 nm) of Ti⁴⁺ in octahedral and tetrahedral coordination with Ga³⁺ (0.062 nm, 0.047 nm). The reported plasma-enhanced atomic layer deposition at 120 ℃ for the preparation of TGO films requires four precursors: triethyl gallium, oxygen plasma, titanium tetraisopropoxide (TTIP) and H₂O. Using H2O as an oxidizer requires long purging times after water vapor exposure and brings in hydroxyl (-OH) impurities at deposition temperatures below 150 ℃. Compared with H₂O, O₃ has stronger oxidability and higher volatility and does not introduce impurities. In order to avoid the problems caused by using H₂O as precursor. TiO₂, Ga₂O₃ and TGO films are prepared by thermal atomic layer deposition using Trimethylgallium (TMG) and Tetrakis-dimethyl-amido Titanium (TDMAT) as precursor sources and O₃ as reaction gas at 250 ℃. The Ti-doped Ga₂O₃ concentration is adjusted by designing the Ga₂O₃/TiO₂ cycle ratio. TGO thin films form sandwich structure through different cycles (9, 6 and 3) of Ga₂O₃ and 1 cycle of TiO₂. The growth rates of Ga₂O₃ and TiO₂ measured by spectroscopic ellipsometry are 0.037 nm/cycle and 0.08 nm/cycle, respectively. The growth rate of TGO film is lower than the theoretical calculated value due to the delayed growth of Ga₂O₃ nucleation caused by the decrease of surface reactive site density after TiO₂ growth. The results of X-ray photoelectron spectroscopy show that the concentration of Ti in the film increases with the decrease of Ga₂O₃/TiO₂ cycle ratio, the binding energy of O 1s, Ga 2p and Ti 2p shifts to the lower, which is attributed to the replacement of some sites of Ga by Ti atoms, indicating that Ti elements are successfully doped into Ga₂O₃ films. The core level spectra of TiO₂ and Ga₂O₃ show the presence of Ti⁴⁺ and Ga³⁺ ions in the films. In the O 1s core level spectra of TGO films, Ga-O bonding decreases with increasing Ti-O bonding content, indicating the formation of Ga₂O₃-TiO₂ composites in the TGO films. The absence of diffraction peaks in the grazing incidence X-ray diffraction spectra indicates that the deposited Ga₂O₃ and TGO films are amorphous. The surface root mean square roughness of 0.377 nm is observed by atomic force microscopy, indicating that the surface of the film is flat and smooth. This is attributed to the layer-by-layer growth of atomic layer deposition with the advantage of atomic-level thickness control. The TGO films exhibit high transparency in the visible region and strongly absorb ultraviolet light. With the increase of Ti doping concentration, the refractive index of TGO films increases from 1.75 to 1.99 due to chemical changes, the transmittance decreases due to the increase of extinction coefficient in the ultraviolet region, the absorption edge appears red-shifted and the optical bandgap decreases from 4.9 eV to 4.3 eV. The reduced band gap of TGO films can extend the sensitive region of optoelectronic devices to longer wavelengths. The optical band gap of thin films measured by spectrophotometric and X-ray photoelectron spectroscopy shows consistent results. The comprehensive analysis shows that Ti doping has a significant impact on the optical properties of Ga₂O₃..

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0631002 (2023)

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Investigation on the Preparation of TiO₂∶Al₂O₃ Nanocomposite Film Applied to the Conductive Layer of Microchannel Plate

Jichao LI, Xiangping ZHU, Xiangxin LI, Jingpeng HU, Cunyu LI, and Wei ZHAO

Acta Photonica Sinica

Publication Date: Jun. 25, 2023
Vol. 52, Issue 6, 0631003 (2023)

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