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Diffraction and Gratings|80 Article(s)
Distortion Correction Method of Interference Projection Based on Convolutional Neural Network
Meng Yan, Qitai Huang, and Jianfeng Ren
In the aspherical surface zero position interference detection, there is a projection distortion between the measurement error distribution and the actual error distribution of the surface to be measured. Aiming at the problems of complex calculation and poor generality of current projection distortion correction methods, a correction method based on a convolutional neural network (CNN) is proposed. In this method, an intersecting parallels flexible occlude is added to the surface, and the interference image is synthesized according to the range of projected distortion coefficient as the data set of CNN. Then the appropriate network structure to train the network based on the data set is selected. Finally, the actual interference image is input into the network to predict the distortion coefficient, and to realize the calibration and correction of the projection distortion. Experimental results show that the theoretical correction error of this method is less than 1 pixel, and the actual error correction accuracy is better than that of the traditional marker method, which proves that the method is efficient and feasible. In the aspherical surface zero position interference detection, there is a projection distortion between the measurement error distribution and the actual error distribution of the surface to be measured. Aiming at the problems of complex calculation and poor generality of current projection distortion correction methods, a correction method based on a convolutional neural network (CNN) is proposed. In this method, an intersecting parallels flexible occlude is added to the surface, and the interference image is synthesized according to the range of projected distortion coefficient as the data set of CNN. Then the appropriate network structure to train the network based on the data set is selected. Finally, the actual interference image is input into the network to predict the distortion coefficient, and to realize the calibration and correction of the projection distortion. Experimental results show that the theoretical correction error of this method is less than 1 pixel, and the actual error correction accuracy is better than that of the traditional marker method, which proves that the method is efficient and feasible.
Laser & Optoelectronics Progress
- Publication Date: Apr. 25, 2024
- Vol. 61, Issue 8, 0805001 (2024)
Error Image Quality Analysis and Experiment of Augmented Reality Display System Based on Grating Waveguide
Zhanhua Huang, Changtai Lu, Cheng Pan, and Yuanjun Wu
In the process of production, processing and assembly of grating waveguide display system, due to the systematic error, cumulative error, and artificial assembly error of micro nano processing equipment, the imaging quality of the system will be affected, resulting in double image, blur, and other problems. In order to solve the above problems, this paper designs a one-dimensional pupil expanding grating waveguide, and uses the ray tracing simulation method to analyze the influence of grating waveguide parallelism error, grating period error, and system assembly error on the imaging quality. The imaging quality of the grating waveguide is processed and adjusted experimentally. By controlling the flatness of the waveguide within 0.3' and the grating period tolerance within 0.2 nm, a one-dimensional exit pupil extended grating waveguide is fabricated. After collimation and alignment, the 30 × 12° field of view angle is reached, good augmented reality display effect and clear imaging quality are achieved, which is of guiding significance for practical mass production. In the process of production, processing and assembly of grating waveguide display system, due to the systematic error, cumulative error, and artificial assembly error of micro nano processing equipment, the imaging quality of the system will be affected, resulting in double image, blur, and other problems. In order to solve the above problems, this paper designs a one-dimensional pupil expanding grating waveguide, and uses the ray tracing simulation method to analyze the influence of grating waveguide parallelism error, grating period error, and system assembly error on the imaging quality. The imaging quality of the grating waveguide is processed and adjusted experimentally. By controlling the flatness of the waveguide within 0.3' and the grating period tolerance within 0.2 nm, a one-dimensional exit pupil extended grating waveguide is fabricated. After collimation and alignment, the 30 × 12° field of view angle is reached, good augmented reality display effect and clear imaging quality are achieved, which is of guiding significance for practical mass production.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2023
- Vol. 60, Issue 9, 0905003 (2023)
Generating Hollow Gaussian Beams with Improved Fresnel Zone Plates
Chaoyue Li, Qing Cao, Changjie Cheng, and Jirui Zhu
Hollow Gaussian beam is a hollow beam class that does not carry orbital angular momentum, its dark spot size is small and has a simple function formula. Hollow Gaussian beam has potential application in the fields of atomic guiding, particle manipulation, and optical communication. Meanwhile, zone plates, also known as Fresnel zone plates, focus light waves through diffraction onto a receiving object. Therefore, this relationship can be applied to design zone plates which generate hollow Gaussian beams. This study demonstrates that the zone plate focal plane complex amplitude distribution function is proportional to the Fourier-Bessel transform of the equivalent pupil function which describes the effects of transmission on waves. The zone plate equivalent pupil functions were calculated to produce the 1st, 3rd, and 6th order hollow Gaussian beams. Subsequently, the structural parameters of these three zone plates were designed. The wavelength and focal length of the zone plates were also changed to determine their influence on the structure parameters and dark spot size. Next, the focal plane light fields of these three modified zone plates were simulated using the Rayleigh-Sommerfeld diffraction integral. The simulation results are consistent with expectations which verifies the reliability and accuracy of the equivalent pupil function method to design Fresnel zone plates. Hollow Gaussian beam is a hollow beam class that does not carry orbital angular momentum, its dark spot size is small and has a simple function formula. Hollow Gaussian beam has potential application in the fields of atomic guiding, particle manipulation, and optical communication. Meanwhile, zone plates, also known as Fresnel zone plates, focus light waves through diffraction onto a receiving object. Therefore, this relationship can be applied to design zone plates which generate hollow Gaussian beams. This study demonstrates that the zone plate focal plane complex amplitude distribution function is proportional to the Fourier-Bessel transform of the equivalent pupil function which describes the effects of transmission on waves. The zone plate equivalent pupil functions were calculated to produce the 1st, 3rd, and 6th order hollow Gaussian beams. Subsequently, the structural parameters of these three zone plates were designed. The wavelength and focal length of the zone plates were also changed to determine their influence on the structure parameters and dark spot size. Next, the focal plane light fields of these three modified zone plates were simulated using the Rayleigh-Sommerfeld diffraction integral. The simulation results are consistent with expectations which verifies the reliability and accuracy of the equivalent pupil function method to design Fresnel zone plates.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2023
- Vol. 60, Issue 9, 0905002 (2023)
Preparation of Two-Dimensional Photonic Crystals of Polytetrafluoroethylene Based on Ultrafast Laser
Zhengbo Wang, Chao Wu, Li Cheng, and Zhaolei Diao
Polytetrafluoroethylene has broad application prospects and great potential value in the field of photonic crystal substrate materials because of its low dielectric constant and low loss of light transmission at 0.7-2.5 THz. This paper describes the use of femtosecond laser, with a pulse duration of 388 fs and repetition frequency of 100 kHz, to research the preparation of two-dimensional photonic crystal from polytetrafluoroethylene sheet. By fitting the experimental results, the calculated radiation exposure was found to be 840 mJ/cm2 at wavelength of 1040 nm. In addition, it was revealed that laser parameters affected the quality of the two-dimensional photonic crystal and the single-layer micropore processing quality under the multi-pulse tapping path were the best. Further, the effects of laser power, scanning speed, and scanning times on the periodic cylindrical structure were investigated. Desirable preparing results were obtained at an average laser power of 9 W, scanning speed of 100 mm/s, and scanning times of 9. The results of this study can be useful for preparing two-dimensional photonic crystal of polytetrafluoroethylene by ultrafast laser. Polytetrafluoroethylene has broad application prospects and great potential value in the field of photonic crystal substrate materials because of its low dielectric constant and low loss of light transmission at 0.7-2.5 THz. This paper describes the use of femtosecond laser, with a pulse duration of 388 fs and repetition frequency of 100 kHz, to research the preparation of two-dimensional photonic crystal from polytetrafluoroethylene sheet. By fitting the experimental results, the calculated radiation exposure was found to be 840 mJ/cm2 at wavelength of 1040 nm. In addition, it was revealed that laser parameters affected the quality of the two-dimensional photonic crystal and the single-layer micropore processing quality under the multi-pulse tapping path were the best. Further, the effects of laser power, scanning speed, and scanning times on the periodic cylindrical structure were investigated. Desirable preparing results were obtained at an average laser power of 9 W, scanning speed of 100 mm/s, and scanning times of 9. The results of this study can be useful for preparing two-dimensional photonic crystal of polytetrafluoroethylene by ultrafast laser.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2023
- Vol. 60, Issue 9, 0905001 (2023)
Scalar Analysis of Conical Diffraction of Blazed Grating
Yuning Ye, and Changshun Wang
Based on the extended scalar diffraction theory, the relative diffraction efficiency of any diffraction order is deduced considering the azimuth of incident light (conical diffraction) for transmission and reflection. It is proved that the relative diffraction efficiency formulas are different when using the extended scalar theory for a blazed grating bounded by the plane and medium interface, respectively. However, the optimized depth and blaze wavelength are the same, with corresponding explicit expressions provided. The two relative diffraction efficiency formulas are applied to a blazed grating with specific parameters to compare with rigorous coupled-wave analysis. The results show that the difference between the two formulas is minimal, and both are consistent with the rigorous coupled-wave analysis. Based on the extended scalar diffraction theory, the relative diffraction efficiency of any diffraction order is deduced considering the azimuth of incident light (conical diffraction) for transmission and reflection. It is proved that the relative diffraction efficiency formulas are different when using the extended scalar theory for a blazed grating bounded by the plane and medium interface, respectively. However, the optimized depth and blaze wavelength are the same, with corresponding explicit expressions provided. The two relative diffraction efficiency formulas are applied to a blazed grating with specific parameters to compare with rigorous coupled-wave analysis. The results show that the difference between the two formulas is minimal, and both are consistent with the rigorous coupled-wave analysis.
Laser & Optoelectronics Progress
- Publication Date: Oct. 10, 2023
- Vol. 60, Issue 19, 1905001 (2023)
Research on Single Grating Semi-Coated Temperature and Humidity Sensing Technology
Lin Zhao, Jinlai Feng, Zeyu Zou, Fengjun Guo, Changfeng Zhang, Jinyu Wang, and Jiqiang Wang
Optical fiber sensors have the advantages of high sensitivity, high-inherent insulation, and good anti-electromagnetic interference ability compared to standard monitoring technologies. However, humidity sensors based on fiber Bragg gratings are easily affected by temperature and stress, resulting in issues such as significant humidity measurement errors and low stability. This paper proposes a fabrication method based on a single grating half-coated temperature and humidity sensor to solve these problems. First, a moisture-sensitive material is coated on half of the grating, and the other half is a bare grating area. Then, the bare grating reflection spectrum peak curve is then Gaussian fitted to establish the functional relationship between ambient temperature and center wavelength λ. Finally, the relationship between the area S enclosed by the grating reflection spectrum curve and the peak power under various environmental humidity conditions is analyzed. The function model of the area S and the relative humidity of the environment is established. The sensor is tested by a temperature and humidity generator. The experimental result shows that the sensor has good repeatability in the range of 10%‒90%RH (%RH is relative humidity). The humidity monitoring sensitivity is 2.95/%RH, and the response time is 6.6 min, which matches the temperature and humidity monitoring requirements in storage and other fields while also providing a new solution for temperature and humidity monitoring in related fields. Optical fiber sensors have the advantages of high sensitivity, high-inherent insulation, and good anti-electromagnetic interference ability compared to standard monitoring technologies. However, humidity sensors based on fiber Bragg gratings are easily affected by temperature and stress, resulting in issues such as significant humidity measurement errors and low stability. This paper proposes a fabrication method based on a single grating half-coated temperature and humidity sensor to solve these problems. First, a moisture-sensitive material is coated on half of the grating, and the other half is a bare grating area. Then, the bare grating reflection spectrum peak curve is then Gaussian fitted to establish the functional relationship between ambient temperature and center wavelength λ. Finally, the relationship between the area S enclosed by the grating reflection spectrum curve and the peak power under various environmental humidity conditions is analyzed. The function model of the area S and the relative humidity of the environment is established. The sensor is tested by a temperature and humidity generator. The experimental result shows that the sensor has good repeatability in the range of 10%‒90%RH (%RH is relative humidity). The humidity monitoring sensitivity is 2.95/%RH, and the response time is 6.6 min, which matches the temperature and humidity monitoring requirements in storage and other fields while also providing a new solution for temperature and humidity monitoring in related fields.
Laser & Optoelectronics Progress
- Publication Date: Apr. 10, 2022
- Vol. 59, Issue 7, 0705001 (2022)
Application of Fiber Bragg Grating Sensing Technology in the Health Monitoring of Special-Shaped Structures
Dingbo Zhang, Jun Li, Wei Zhang, Xingchao Duan, Xinwei Zhang, Tian Ma, and Weifeng Wang
The current technological development has a certain field of exploration and application for the health monitoring of building structures. As a sensor with good performance, the fiber grating sensor is widely used in civil structures. The fiber Bragg grating (FBG) Internet of Things sensing is applied in the health monitoring of special-shaped structure based on the technology. The structure principal and performance advantage of fiber gratings are mainly introduced. Combined with engineering project examples, the relevant application methods of FBG in the health monitoring of special-shaped structures is studied. and data analysis is carried out. The research shows that FBG sensors can be used in the health monitoring of special-shaped structures, and there are also certain promotion and application values for other related civil infrastructure structures. The current technological development has a certain field of exploration and application for the health monitoring of building structures. As a sensor with good performance, the fiber grating sensor is widely used in civil structures. The fiber Bragg grating (FBG) Internet of Things sensing is applied in the health monitoring of special-shaped structure based on the technology. The structure principal and performance advantage of fiber gratings are mainly introduced. Combined with engineering project examples, the relevant application methods of FBG in the health monitoring of special-shaped structures is studied. and data analysis is carried out. The research shows that FBG sensors can be used in the health monitoring of special-shaped structures, and there are also certain promotion and application values for other related civil infrastructure structures.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2022
- Vol. 59, Issue 5, 0505001 (2022)
ITO-Based Active Metasurfaces with Phase Tunability
Feng Gao, Chenyue Zhu, Jingyue Li, Chunyan Wu, and Linbao Luo
Transparent conductive oxides have been widely used in optoelectronic devices owing to their special optical property. In near-infrared wavelength region, the real part of the dielectric constant will decrease from positive to negative. Within epsilon-near-zero (ENZ) region, strong interaction will occur between light and matter, and wide phase modulation will be achieved. Herein, using a bias voltage of 0-5 V, the carrier concentration within a region (thickness: 1 nm) near the interface of an ITO-based MOS structure was adjusted, and a phase modulation close to 265° in a 1470-nm wavelength was achieved. Based on this modulation, the practical applications of the proposed structure in the fields of beam deflection and focusing have been explored. Furthermore, a dual-gated MOS structure, which further expanded the phase coverage region, was designed. Transparent conductive oxides have been widely used in optoelectronic devices owing to their special optical property. In near-infrared wavelength region, the real part of the dielectric constant will decrease from positive to negative. Within epsilon-near-zero (ENZ) region, strong interaction will occur between light and matter, and wide phase modulation will be achieved. Herein, using a bias voltage of 0-5 V, the carrier concentration within a region (thickness: 1 nm) near the interface of an ITO-based MOS structure was adjusted, and a phase modulation close to 265° in a 1470-nm wavelength was achieved. Based on this modulation, the practical applications of the proposed structure in the fields of beam deflection and focusing have been explored. Furthermore, a dual-gated MOS structure, which further expanded the phase coverage region, was designed.
Laser & Optoelectronics Progress
- Publication Date: Feb. 20, 2022
- Vol. 59, Issue 4, 0405001 (2022)
Demodulation of Temperature Stabilized Fiber Bragg Grating Sensor Based on Optimized Least Square Support Vector Machine
Wenjuan Sheng, Zhengbin Hu, Ning Yang, and Gangding Peng
Fiber Fabry-Perot tunable filter (FFP-TF) is one of the core components of the fiber Bragg grating sensor demodulation system. Its stability is very important to the demodulation accuracy, and the temperature drift is the influence one of the key factors of its stability. The nonlinear mapping ability of the least squares support vector machine (LSSVM) can effectively compensate for drift. In this paper, aiming at the problem that the traditional LSSVM model parameter selection is easy to fall into the local optimum, based on the improved beetle search particle swarm optimization algorithm to find the optimal penalty factor and kernel parameters of the LSSVM model in the global scope. The experimental results show that using the optimized LSSVM to compensate the temperature drift of FFP-TF can reduce the temperature drift error from the maximum amplitude of 1025.21 pm to ±3.03 pm, and improve the temperature stability of FFP-TF demodulation in a variable temperature environment. Fiber Fabry-Perot tunable filter (FFP-TF) is one of the core components of the fiber Bragg grating sensor demodulation system. Its stability is very important to the demodulation accuracy, and the temperature drift is the influence one of the key factors of its stability. The nonlinear mapping ability of the least squares support vector machine (LSSVM) can effectively compensate for drift. In this paper, aiming at the problem that the traditional LSSVM model parameter selection is easy to fall into the local optimum, based on the improved beetle search particle swarm optimization algorithm to find the optimal penalty factor and kernel parameters of the LSSVM model in the global scope. The experimental results show that using the optimized LSSVM to compensate the temperature drift of FFP-TF can reduce the temperature drift error from the maximum amplitude of 1025.21 pm to ±3.03 pm, and improve the temperature stability of FFP-TF demodulation in a variable temperature environment.
Laser & Optoelectronics Progress
- Publication Date: Feb. 10, 2022
- Vol. 59, Issue 3, 0305002 (2022)
Preparation of Reflective Volume Holographic Grating for Plate Waveguide Display
Liu Yang, Shilei Jiang, Xuesong Ji, Jin Zhang, Yujin Wang, and Guobin Sun
By studying the core holographic optical elements in the holographic plate waveguide display system, we prepare a reflective volume holographic grating with refractive index modulation on a holographic plate with quartz glass as substrate and dichromate gelatin as recording medium. The effects of different exposure intensity, refractive index modulation and water washing time on diffraction efficiency of grating are researched. Experimental results show that the diffraction efficiency of reflective volume holographic gratings can be improved by using 441.6 nm He-Cd laser light source and complex post-treatment process. The diffraction efficiency of reflective volume gratings can reach 61.8%. Under the condition of visible light incident, a remarkable light splitting effect is produced. The prepared holographic experimental sample can be transmitted by waveguide under the condition of total reflection, which provides a method to improve the diffraction efficiency of display devices such as head mounted display device and augmented reality during transmission. By studying the core holographic optical elements in the holographic plate waveguide display system, we prepare a reflective volume holographic grating with refractive index modulation on a holographic plate with quartz glass as substrate and dichromate gelatin as recording medium. The effects of different exposure intensity, refractive index modulation and water washing time on diffraction efficiency of grating are researched. Experimental results show that the diffraction efficiency of reflective volume holographic gratings can be improved by using 441.6 nm He-Cd laser light source and complex post-treatment process. The diffraction efficiency of reflective volume gratings can reach 61.8%. Under the condition of visible light incident, a remarkable light splitting effect is produced. The prepared holographic experimental sample can be transmitted by waveguide under the condition of total reflection, which provides a method to improve the diffraction efficiency of display devices such as head mounted display device and augmented reality during transmission.
Laser & Optoelectronics Progress
- Publication Date: Feb. 10, 2022
- Vol. 59, Issue 3, 0305001 (2022)
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