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Holography|210 Article(s)
Efficient Encoding Method for Computer-Generated Hologram
chunqi Li, Qitai Huang, and Jianfeng Ren
A computer-generated hologram (CGH) can be used to detect an aspheric surface with high accuracy. To enhance the encoding efficiency of the CGH, this paper proposes an encoding method for the segmented description of engraved stripes with a circular arc as the primitive, dividing the encoding process into two steps: binary encoding and curve description. The binary encoding employs the Newtonian iteration method to discretize the phase contour dividing line. The curve description combines the dichotomy and the minimum root-mean-square criterion of the residual error. Furthermore, by leveraging the circular arc to encode the discrete points of the engraved stripes, the engraved stripes are obtained. In this paper, the CGH is designed, encoded, and generated for an off-axis aspheric surface. To obtain an encoding accuracy higher than λ/1000, the operation time is only 3 h, the encoded file is only 39 MB, and the etching time is only 40 min. This demonstrates that the proposed method can considerably enhance the encoding efficiency compared with the traditional encoding method. Error analysis suggests that the wavefront root-sum square (RSS) error of the CGH is only 0.00255λ, demonstrating that the proposed encoding method is efficient and feasible. A computer-generated hologram (CGH) can be used to detect an aspheric surface with high accuracy. To enhance the encoding efficiency of the CGH, this paper proposes an encoding method for the segmented description of engraved stripes with a circular arc as the primitive, dividing the encoding process into two steps: binary encoding and curve description. The binary encoding employs the Newtonian iteration method to discretize the phase contour dividing line. The curve description combines the dichotomy and the minimum root-mean-square criterion of the residual error. Furthermore, by leveraging the circular arc to encode the discrete points of the engraved stripes, the engraved stripes are obtained. In this paper, the CGH is designed, encoded, and generated for an off-axis aspheric surface. To obtain an encoding accuracy higher than λ/1000, the operation time is only 3 h, the encoded file is only 39 MB, and the etching time is only 40 min. This demonstrates that the proposed method can considerably enhance the encoding efficiency compared with the traditional encoding method. Error analysis suggests that the wavefront root-sum square (RSS) error of the CGH is only 0.00255λ, demonstrating that the proposed encoding method is efficient and feasible.
Laser & Optoelectronics Progress
- Publication Date: Apr. 25, 2024
- Vol. 61, Issue 8, 0809002 (2024)
Color Hologram Reconstruction Based on Deep Learning
Juntong Liu, Jinbin Gui, Aishuai Chen, Xiandong Ma, and Xianfei Hu
This study proposes a deep learning-based color hologram reconstruction method to address the issues of complex reconstruction operations, inaccurate color fusion, and zero-order influence during the reconstruction of large objects. The improved U-Net model is used as the network structure, and the spectrum of color off-axis Fresnel holograms generated by mixing actual photography and simulation is used as training samples to achieve the accurate reconstruction of color holograms. Reconstruction experiments are conducted on simulated holograms and actual digital holograms. Moreover, the results have shown that compared to traditional methods, the proposed method can maintain high resolution and color accuracy of the reconstructed image while achieving improved reconstruction results. The outcomes of the study have potential applications in the reconstruction of color holograms in large-scale inspection fields, and are useful for the application of color holographic detection and deep learning in the field of optical imaging. This study proposes a deep learning-based color hologram reconstruction method to address the issues of complex reconstruction operations, inaccurate color fusion, and zero-order influence during the reconstruction of large objects. The improved U-Net model is used as the network structure, and the spectrum of color off-axis Fresnel holograms generated by mixing actual photography and simulation is used as training samples to achieve the accurate reconstruction of color holograms. Reconstruction experiments are conducted on simulated holograms and actual digital holograms. Moreover, the results have shown that compared to traditional methods, the proposed method can maintain high resolution and color accuracy of the reconstructed image while achieving improved reconstruction results. The outcomes of the study have potential applications in the reconstruction of color holograms in large-scale inspection fields, and are useful for the application of color holographic detection and deep learning in the field of optical imaging.
Laser & Optoelectronics Progress
- Publication Date: Apr. 25, 2024
- Vol. 61, Issue 8, 0809001 (2024)
Effect of Stereo Video Acquisition Distortion on Visually Induced Motion Sickness
Yi Bai, Zhenping Xia, Bowen Zhang, Zixiong Peng, and Yuanshen Zhang
Visually induced motion sickness has become a serious problem for users of virtual reality technology. Users immersed in a virtual reality environment generally suffer from dizziness, vomiting, and other symptoms. The distortion in stereoscopic image acquisition leads to virtual space distortion in human perception, which may be an important factor inducing and enhancing visually induced motion sickness. To study the effect of the distortion of stereoscopic video acquisition on visually induced motion sickness, a virtual spatial distortion model is constructed based on the theory of stereoscopic video acquisition. In addition, different levels of stereoscopic spatially distorted videos are obtained from lenses with three focal length parameters. Visual perception experiments were conducted to objectively and subjectively evaluate visually induced motion sickness under different spatial aberrations. The results show that when the angle of view of the acquired stereoscopic video does not match the stereoscopic visual angle of human eyes, the distortion of the video significantly affects the visually induced motion sickness, and the distortion of the stereoscopic video acquisition results in a more intense visually induced motion sickness. This paper presents a novel and systematic method to experimentally verify that distortions in virtual space caused by the mismatch between acquisition and perception parameters enhance visually induced motion sickness. The findings of this study can help put forward practical mitigation methods. Visually induced motion sickness has become a serious problem for users of virtual reality technology. Users immersed in a virtual reality environment generally suffer from dizziness, vomiting, and other symptoms. The distortion in stereoscopic image acquisition leads to virtual space distortion in human perception, which may be an important factor inducing and enhancing visually induced motion sickness. To study the effect of the distortion of stereoscopic video acquisition on visually induced motion sickness, a virtual spatial distortion model is constructed based on the theory of stereoscopic video acquisition. In addition, different levels of stereoscopic spatially distorted videos are obtained from lenses with three focal length parameters. Visual perception experiments were conducted to objectively and subjectively evaluate visually induced motion sickness under different spatial aberrations. The results show that when the angle of view of the acquired stereoscopic video does not match the stereoscopic visual angle of human eyes, the distortion of the video significantly affects the visually induced motion sickness, and the distortion of the stereoscopic video acquisition results in a more intense visually induced motion sickness. This paper presents a novel and systematic method to experimentally verify that distortions in virtual space caused by the mismatch between acquisition and perception parameters enhance visually induced motion sickness. The findings of this study can help put forward practical mitigation methods.
Laser & Optoelectronics Progress
- Publication Date: Feb. 25, 2024
- Vol. 61, Issue 4, 0409001 (2024)
Comparative Study of Phase-Only Hologram Generation Algorithms Based on Iteration
Xiaoshi Wang, Jinbin Gui, Junchang Li, and Qinghe Song
Phase-only holograms are used widely in holographic three-dimensional display owing to their high diffraction efficiency and no conjugate image. An iterative algorithm plays an important role in generating phase-only holograms because of its flexible calculation and high-quality image reconstruction. This study introduced a comparative study on the latest iterative algorithms for generating phase-only holograms. The basic principle of generating phase-only holograms by iterative algorithm was introduced, and representative and innovative algorithms were realized by programming. Experiments were performed to analyze the characteristics, advantages, and disadvantages of various methods by comparing the image reconstruction quality and computation time. The results show that the histogram compensation algorithm can obtain better results for images with large pixel differences, the adaptive weighted Gerchberg-Saxton algorithm can be used for images with high reconstruction quality. Phase-only holograms are used widely in holographic three-dimensional display owing to their high diffraction efficiency and no conjugate image. An iterative algorithm plays an important role in generating phase-only holograms because of its flexible calculation and high-quality image reconstruction. This study introduced a comparative study on the latest iterative algorithms for generating phase-only holograms. The basic principle of generating phase-only holograms by iterative algorithm was introduced, and representative and innovative algorithms were realized by programming. Experiments were performed to analyze the characteristics, advantages, and disadvantages of various methods by comparing the image reconstruction quality and computation time. The results show that the histogram compensation algorithm can obtain better results for images with large pixel differences, the adaptive weighted Gerchberg-Saxton algorithm can be used for images with high reconstruction quality.
Laser & Optoelectronics Progress
- Publication Date: Mar. 25, 2023
- Vol. 60, Issue 6, 0609001 (2023)
Production of Three-Parameter Lommel Beams Using Lohmann-Type Detour Phase-Coding Method
Jingyu Yang, Yile Shi, Run Zhou, Zimo Liu, Ning Gong, Rijian Chen, and Zhijun Ren
Lommel beams are a type of complex-structure nondiffractive beams expressed by the Lommel function. Their optical features can be adjusted using three parameters: order n, asymmetry c0, and rotation angle ?0. However, the optical structure of a Lommel beam is complex, making it challenging to be produced experimentally. In this study, we introduce a complex amplitude modulation technique to generate nondiffractive Lommel beams. The amplitude and phase of complex wavefronts are simultaneously encoded using the Lohmann-type detour phase-coding method. High-quality Lommel beams are produced by processing the computer-generated hologram into a real amplitude mask using the holographic direct-writing printing system. In the experiments, the mask plate reaches 35000 pixel×35000 pixel. Furthermore, this study provides a general approach for producing nondiffractive beams with other different complex structures. Lommel beams are a type of complex-structure nondiffractive beams expressed by the Lommel function. Their optical features can be adjusted using three parameters: order n, asymmetry c0, and rotation angle ?0. However, the optical structure of a Lommel beam is complex, making it challenging to be produced experimentally. In this study, we introduce a complex amplitude modulation technique to generate nondiffractive Lommel beams. The amplitude and phase of complex wavefronts are simultaneously encoded using the Lohmann-type detour phase-coding method. High-quality Lommel beams are produced by processing the computer-generated hologram into a real amplitude mask using the holographic direct-writing printing system. In the experiments, the mask plate reaches 35000 pixel×35000 pixel. Furthermore, this study provides a general approach for producing nondiffractive beams with other different complex structures.
Laser & Optoelectronics Progress
- Publication Date: Oct. 10, 2023
- Vol. 60, Issue 19, 1909001 (2023)
Holographic Double-Sided Photolithography Based on Improved Gerchberg-Saxton Algorithm
Huabin Wang, Yu He, and Lixin Zhao
Given the problems of cumbersome steps and low effectiveness of the present double-sided microdevice processing technique, a holographic double-sided photolithography based on the enhanced Gerchberg-Saxton (GS) algorithm is proposed, which employs a single light source to achieve a double-sided pattern produced by single exposure on the upper and lower surfaces of the glass substrate. This approach realizes double-sided pattern reproduction in the target space by determining the combined holograms corresponding to various axial position patterns and loading them onto a spatial light modulator (LCOS-SLM) to regulate the incident light field. The holographic reconstruction of patterns A and B at distances of 2 mm and 4.06 mm from the focal plane, respectively, is calculated and simulated using the modified GS method. The experimental device was set up to achieve the simultaneous exposure of the upper and lower surfaces of the 3-mm thick transparent quartz glass substrate, and the problems of speckle, stray light, and crosstalk in the process of light field generation were examined and solutions were proposed, and finally 60-μm linewidth double-layer pattern exposure was realized, which confirm the feasibility of the proposed method for double-sided lithography. A single hologram and a single light source are used in the technique described in this research to create numerous layers of arbitrary images in the target volume during a single exposure, considerably simplifying the processes involved in producing double-sided pictures. Given the problems of cumbersome steps and low effectiveness of the present double-sided microdevice processing technique, a holographic double-sided photolithography based on the enhanced Gerchberg-Saxton (GS) algorithm is proposed, which employs a single light source to achieve a double-sided pattern produced by single exposure on the upper and lower surfaces of the glass substrate. This approach realizes double-sided pattern reproduction in the target space by determining the combined holograms corresponding to various axial position patterns and loading them onto a spatial light modulator (LCOS-SLM) to regulate the incident light field. The holographic reconstruction of patterns A and B at distances of 2 mm and 4.06 mm from the focal plane, respectively, is calculated and simulated using the modified GS method. The experimental device was set up to achieve the simultaneous exposure of the upper and lower surfaces of the 3-mm thick transparent quartz glass substrate, and the problems of speckle, stray light, and crosstalk in the process of light field generation were examined and solutions were proposed, and finally 60-μm linewidth double-layer pattern exposure was realized, which confirm the feasibility of the proposed method for double-sided lithography. A single hologram and a single light source are used in the technique described in this research to create numerous layers of arbitrary images in the target volume during a single exposure, considerably simplifying the processes involved in producing double-sided pictures.
Laser & Optoelectronics Progress
- Publication Date: Aug. 25, 2023
- Vol. 60, Issue 16, 1609001 (2023)
Three-Dimensional Phase-Only Holographic Display Based on Deep Learning and Angular-Spectrum Layer-Oriented
Xiao Sun, and Chao Han
Traditional phase-only holographic imaging methods rely on high-intensity iteration, which is time-consuming, and the imaging quality is not high. To address this issue, a phase-only hologram generation algorithm based on depth learning and angular-spectrum layer-oriented, which can generate holograms quickly and improve the quality of hologram reconstruction, is proposed. The LeNet network structure predicts the complex amplitude information of three-dimensional objects, which reduces the amount of calculation. The accurate angular-spectrum algorithm creates a high-quality phase-only hologram of a three-dimensional object. The simulation results show that the algorithm is feasible and the quality of the reconstructed image is effectively improved. Traditional phase-only holographic imaging methods rely on high-intensity iteration, which is time-consuming, and the imaging quality is not high. To address this issue, a phase-only hologram generation algorithm based on depth learning and angular-spectrum layer-oriented, which can generate holograms quickly and improve the quality of hologram reconstruction, is proposed. The LeNet network structure predicts the complex amplitude information of three-dimensional objects, which reduces the amount of calculation. The accurate angular-spectrum algorithm creates a high-quality phase-only hologram of a three-dimensional object. The simulation results show that the algorithm is feasible and the quality of the reconstructed image is effectively improved.
Laser & Optoelectronics Progress
- Publication Date: Feb. 20, 2022
- Vol. 59, Issue 4, 0409001 (2022)
Digital Holographic Phase Unwrapping Based on Transport Intensity Equation Solved with Discrete Cosine Transform
Jieyu Wang, Huaying Wang, Xue Wang, Gaofu Men, Wenjian Wang, Zijian Zhang, Jialiang Lei, and Zhao Dong
This paper proposes a digital holographic phase demodulation approach based on the transport intensity equation (TIE), which is solved with a discrete cosine transform. Simulative and experimental findings reveal that the new approach successfully accelerates the unwrapping process with no loss of accuracy compared with the traditional approach based on fast Fourier transform. The new approaches' efficiency can still be enhanced after choosing a suitable extending scheme for the computation of the axis derivative of intensity. The proposed new TIE-based phase unwrapping approaches can lead to the real-time uses of the phase measurement with high processing speed and precision. This paper proposes a digital holographic phase demodulation approach based on the transport intensity equation (TIE), which is solved with a discrete cosine transform. Simulative and experimental findings reveal that the new approach successfully accelerates the unwrapping process with no loss of accuracy compared with the traditional approach based on fast Fourier transform. The new approaches' efficiency can still be enhanced after choosing a suitable extending scheme for the computation of the axis derivative of intensity. The proposed new TIE-based phase unwrapping approaches can lead to the real-time uses of the phase measurement with high processing speed and precision.
Laser & Optoelectronics Progress
- Publication Date: Nov. 10, 2022
- Vol. 59, Issue 21, 2109001 (2022)
Multiscale Digital Hologram Reconstruction Based on Deep Learning
Jian Pu, Jinbin Gui, and Kai Zhang
To address the problem of a single deep-learning model being unable to reconstruct the wavefront of digital holograms with multiple scales, an improved network structure based on the U-Net model is proposed to simulate the digital holographic imaging process and generate holographic images with different scales as data sets. Digital holograms with different scales are used in different parts of the training network, and a depth learning model is obtained, which can reconstruct the wavefront information of digital holograms with three different scales. The experimental results show that the proposed network structure can reconstruct digital holograms with various scales and obtain accurate wavefront information of digital holograms. The research content solves the problem of using a single deep-learning model to deal with digital holograms with varying scales. To address the problem of a single deep-learning model being unable to reconstruct the wavefront of digital holograms with multiple scales, an improved network structure based on the U-Net model is proposed to simulate the digital holographic imaging process and generate holographic images with different scales as data sets. Digital holograms with different scales are used in different parts of the training network, and a depth learning model is obtained, which can reconstruct the wavefront information of digital holograms with three different scales. The experimental results show that the proposed network structure can reconstruct digital holograms with various scales and obtain accurate wavefront information of digital holograms. The research content solves the problem of using a single deep-learning model to deal with digital holograms with varying scales.
Laser & Optoelectronics Progress
- Publication Date: Jan. 20, 2022
- Vol. 59, Issue 2, 0209001 (2022)
Study on Focusing Characteristics of Double-Period Graded Photonic Crystal Lens Based on Biconical Interferometry
Xiaorong Zhang, He Yang, and Xiaohong Sun
As a biconical interference model is constructed to design a double-period graded photonic crystal (GPC) structure, we design a GPC lens with graded dielectric column size based on the graded light intensity distribution of the GPC structure, and study the influence of the inner and outer cone interference angle on the GPC period and the focusing characteristics of the lens. It is found that the sine difference of the inner and outer cone angles of the interference beam determines the large period of the lens, while the outer cone angle directly affects the small period. When the large period of the lens is fixed, the smaller the small period is, the better the focusing effect will be. What’s more, when the small period is fixed, the smaller the large period is, the larger the numerical aperture of the lens will be. The designed lens can achieve sub-diffraction-limit focusing. This research is helpful for the application of lenses in optical coupling, optical integration, optical display, and imaging. As a biconical interference model is constructed to design a double-period graded photonic crystal (GPC) structure, we design a GPC lens with graded dielectric column size based on the graded light intensity distribution of the GPC structure, and study the influence of the inner and outer cone interference angle on the GPC period and the focusing characteristics of the lens. It is found that the sine difference of the inner and outer cone angles of the interference beam determines the large period of the lens, while the outer cone angle directly affects the small period. When the large period of the lens is fixed, the smaller the small period is, the better the focusing effect will be. What’s more, when the small period is fixed, the smaller the large period is, the larger the numerical aperture of the lens will be. The designed lens can achieve sub-diffraction-limit focusing. This research is helpful for the application of lenses in optical coupling, optical integration, optical display, and imaging.
Laser & Optoelectronics Progress
- Publication Date: Sep. 10, 2022
- Vol. 59, Issue 17, 1709001 (2022)
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