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Diffraction, Gratings, and Holography|24 Article(s)
Experimental implementation of phase triplicator gratings in a spatial light modulator
Shang Gao, María del Mar Sánchez-López, and Ignacio Moreno
In this work, we compare different methods for implementing a triplicator, a phase grating that generates three equi-intense diffraction orders. The design with optimal efficiency features a continuous phase profile, which cannot be easily reproduced, and is typically affected by quantization. We compare its performance with binary and sinusoidal phase profiles. We also analyze the effect of quantizing the phase levels. Finally, a random approach is adopted to eliminate the additional harmonic orders. In all cases, a liquid-crystal-on-silicon spatial light modulator is employed to experimentally verify and compare the different approaches. In this work, we compare different methods for implementing a triplicator, a phase grating that generates three equi-intense diffraction orders. The design with optimal efficiency features a continuous phase profile, which cannot be easily reproduced, and is typically affected by quantization. We compare its performance with binary and sinusoidal phase profiles. We also analyze the effect of quantizing the phase levels. Finally, a random approach is adopted to eliminate the additional harmonic orders. In all cases, a liquid-crystal-on-silicon spatial light modulator is employed to experimentally verify and compare the different approaches.
Chinese Optics Letters
- Publication Date: Feb. 21, 2024
- Vol. 22, Issue 2, 020501 (2024)
Femtosecond laser direct written fiber Bragg gratings with narrow bandwidth and high sideband suppression
Wenping Qiu, Shuang Liu, Guanghua Cheng, Huan Zhan, Guodong Zhang, Guanpin Ren, Zhongrui Sun, and Min Zhang
Aiming for suppressing side-mode and spectrum broadening, a slit beam-shaping method and super-Gaussian apodization processing for femtosecond laser point-by-point (PbP) inscription technology of fiber Bragg gratings (FBGs) are reported here. High-quality FBGs, featuring narrow bandwidth of less than 0.3 nm, high reflectivity above 85%, low insertion loss (0.21 dB), and low cladding loss (0.82 dB), were obtained successfully. By a semi-automatic PbP inscription process, an array consisting of six FBGs, exhibiting almost no side-mode peaks with high suppression ability and narrow bandwidth, was fabricated along three independently developed single-mode fibers with an interval of 20 mm. Aiming for suppressing side-mode and spectrum broadening, a slit beam-shaping method and super-Gaussian apodization processing for femtosecond laser point-by-point (PbP) inscription technology of fiber Bragg gratings (FBGs) are reported here. High-quality FBGs, featuring narrow bandwidth of less than 0.3 nm, high reflectivity above 85%, low insertion loss (0.21 dB), and low cladding loss (0.82 dB), were obtained successfully. By a semi-automatic PbP inscription process, an array consisting of six FBGs, exhibiting almost no side-mode peaks with high suppression ability and narrow bandwidth, was fabricated along three independently developed single-mode fibers with an interval of 20 mm.
Chinese Optics Letters
- Publication Date: Jan. 18, 2024
- Vol. 22, Issue 1, 010501 (2024)
Babinet’s meta-apertures for holographic bi-imaging
Syed Yasir Azeem, Dong Zhao, Ruixing Xia, and Kun Huang
Complementary metasurfaces based on Babinet’s principle have shown remarkable performance in optical applications like polarization conversion and split ring resonators by dynamically reversing the properties of light in both transmission and reflection modes. However, complementary diffractive metasurfaces for different holographic images have not yet proven to be effective because Babinet’s principle predicts identical diffraction patterns from complementary surfaces. Here, we report carefully designed complementary metasurfaces consisting of an engineered metallic aluminum layer sitting on a transparent quartz substrate. Upon illumination, both complementary devices output entirely different diffractive intensity profiles from each other, yielding two holographic images at visible wavelengths from 430 nm to 650 nm. It provides experimental evidence for encoding two images into complementary metasurfaces, indicating an exception of Babinet’s principle in the Fresnel region of complementary apertures. Complementary metasurfaces based on Babinet’s principle have shown remarkable performance in optical applications like polarization conversion and split ring resonators by dynamically reversing the properties of light in both transmission and reflection modes. However, complementary diffractive metasurfaces for different holographic images have not yet proven to be effective because Babinet’s principle predicts identical diffraction patterns from complementary surfaces. Here, we report carefully designed complementary metasurfaces consisting of an engineered metallic aluminum layer sitting on a transparent quartz substrate. Upon illumination, both complementary devices output entirely different diffractive intensity profiles from each other, yielding two holographic images at visible wavelengths from 430 nm to 650 nm. It provides experimental evidence for encoding two images into complementary metasurfaces, indicating an exception of Babinet’s principle in the Fresnel region of complementary apertures.
Chinese Optics Letters
- Publication Date: Aug. 14, 2023
- Vol. 21, Issue 9, 090501 (2023)
Suppressing defocus noise with U-net in optical scanning holography
Haiyan Ou, Yong Wu, Kun Zhu, Edmund Y. Lam, and Bing-Zhong Wang
Optical scanning holography (OSH) records both the amplitude and phase information of a 3D object by a 2D scan. To reconstruct a 3D volumetric image from an OSH hologram is difficult, as it suffers from the defocus noise from the other sections. The use of a random phase pupil can convert defocus noise into speckle-like noise, which may require further processing in sectional image reconstruction. In this paper, we propose a U-shaped neural network to reduce this speckle haze. Simulation results show that the proposed method works effectively and efficiently both in simple and complex graphics. Optical scanning holography (OSH) records both the amplitude and phase information of a 3D object by a 2D scan. To reconstruct a 3D volumetric image from an OSH hologram is difficult, as it suffers from the defocus noise from the other sections. The use of a random phase pupil can convert defocus noise into speckle-like noise, which may require further processing in sectional image reconstruction. In this paper, we propose a U-shaped neural network to reduce this speckle haze. Simulation results show that the proposed method works effectively and efficiently both in simple and complex graphics.
Chinese Optics Letters
- Publication Date: Aug. 07, 2023
- Vol. 21, Issue 8, 080501 (2023)
Self-healing of holographically generated moiré lattice wave fields|Editors' Pick
Siwei Tang, Chunlei Shang, Zhaofeng Liu, Chengzhen Lu, Yangjian Cai, Yuanmei Gao, and Zengrun Wen
Self-healing in optics generally refers to the ability to reconstruct itself and restore the original state after encountering obstacles in the propagation of the light field. In this research, we observe the processes of the wave fields from perfect to defect in front of the focal plane of the 4f system, finally returning to an intact situation after the plane. According to simulations and experimental results, there is a minimum self-healing distance for the moiré lattice field that positively associates with the radius of the defect (obstacle) in the nondiffracting transmission range. Furthermore, it is observed that the defect self-healing is a process of “repairing the center and then repairing the edges.” These findings can be applied in areas such as optical imaging, capture, and information processing. Self-healing in optics generally refers to the ability to reconstruct itself and restore the original state after encountering obstacles in the propagation of the light field. In this research, we observe the processes of the wave fields from perfect to defect in front of the focal plane of the 4f system, finally returning to an intact situation after the plane. According to simulations and experimental results, there is a minimum self-healing distance for the moiré lattice field that positively associates with the radius of the defect (obstacle) in the nondiffracting transmission range. Furthermore, it is observed that the defect self-healing is a process of “repairing the center and then repairing the edges.” These findings can be applied in areas such as optical imaging, capture, and information processing.
Chinese Optics Letters
- Publication Date: Oct. 12, 2022
- Vol. 21, Issue 3, 030502 (2023)
Binary diffractive lens with subwavelength focusing for terahertz imaging
Ran Ning, Dayong Wang, Lu Rong, Jie Zhao, Yunxin Wang, and Shufeng Lin
The converging lens is one of the key components in high-resolution terahertz imaging. In this Letter, a binary diffractive lens is proposed for the scanning imaging system working at 278.6 GHz, in which a convergent beam with a waist diameter of 0.65 mm is generated, and 1 mm lateral imaging resolution is realized. This low-cost terahertz lens, constituted by concentric rings with different radii, is optimized by stimulated annealing algorithm and fabricated by three-dimensional printing. Compared with the conventional transmissive convex lens, higher resolution and enhanced imaging quality are achieved via smaller focal spot of the illumination beam. This type of lens would promote terahertz imaging closer to practical applications such as nondestructive testing and other scenarios. The converging lens is one of the key components in high-resolution terahertz imaging. In this Letter, a binary diffractive lens is proposed for the scanning imaging system working at 278.6 GHz, in which a convergent beam with a waist diameter of 0.65 mm is generated, and 1 mm lateral imaging resolution is realized. This low-cost terahertz lens, constituted by concentric rings with different radii, is optimized by stimulated annealing algorithm and fabricated by three-dimensional printing. Compared with the conventional transmissive convex lens, higher resolution and enhanced imaging quality are achieved via smaller focal spot of the illumination beam. This type of lens would promote terahertz imaging closer to practical applications such as nondestructive testing and other scenarios.
Chinese Optics Letters
- Publication Date: Nov. 03, 2022
- Vol. 21, Issue 3, 030501 (2023)
Wavelength and polarization dual-multiplexed imaging based on holographic metasurfaces
Jilian Xu, Zhiyuan Yue, Peiyao Lu, Rui Wu, Kun Jiang, Xiquan Jiang, and Shuyun Teng
In light of the powerful light manipulation ability of holographic metasurfaces, optical imaging with wavelength multiplexing and polarization multiplexing is performed in this paper. The metasurface is composed of identical rectangular nanoholes etched in silver film. Three imaging effects, including the in-plane color imaging, three-dimensional wavelength-encrypted imaging, and polarization-multiplexing wavelength-encrypted imaging, are realized. The designed metasurface has compact structure, and the obtained image has lower noise. The simulation and experiment results give the verification. Multiple images, including spatial multiplexing, wavelength multiplexing, and polarization multiplexing, exhibit immense potentialities of metasurfaces, and this work is helpful for expanding the applications of metasurfaces. In light of the powerful light manipulation ability of holographic metasurfaces, optical imaging with wavelength multiplexing and polarization multiplexing is performed in this paper. The metasurface is composed of identical rectangular nanoholes etched in silver film. Three imaging effects, including the in-plane color imaging, three-dimensional wavelength-encrypted imaging, and polarization-multiplexing wavelength-encrypted imaging, are realized. The designed metasurface has compact structure, and the obtained image has lower noise. The simulation and experiment results give the verification. Multiple images, including spatial multiplexing, wavelength multiplexing, and polarization multiplexing, exhibit immense potentialities of metasurfaces, and this work is helpful for expanding the applications of metasurfaces.
Chinese Optics Letters
- Publication Date: Oct. 03, 2023
- Vol. 21, Issue 10, 100501 (2023)
Electrically switchable structural patterns and diffractions in a dual frequency nematic liquid crystal
Zhenpeng Song, Ziyang Li, Xiaohu Shang, Chaoyi Li, Lingling Ma, Yanqing Lu, and Bingxiang Li
Electrically driven structural patterns in liquid crystals (LCs) have attracted considerable attention due to their electro-optical applications. Here, we disclose various appealing reconfigurable LC microstructures in a dual frequency nematic LC (DFNLC) owing to the electroconvection-induced distortion of the LC director, including one-dimensional rolls, chevron pattern, two-dimensional grids, and unstable chaos. These patterns can be switched among each other, and the lattice constants are modulated by tuning the amplitude and frequency of the applied electric field. The electrically switchable self-assembled microstructures and their beam steering capabilities thus provide a feasible way to tune the functions of DFNLC-based optical devices. Electrically driven structural patterns in liquid crystals (LCs) have attracted considerable attention due to their electro-optical applications. Here, we disclose various appealing reconfigurable LC microstructures in a dual frequency nematic LC (DFNLC) owing to the electroconvection-induced distortion of the LC director, including one-dimensional rolls, chevron pattern, two-dimensional grids, and unstable chaos. These patterns can be switched among each other, and the lattice constants are modulated by tuning the amplitude and frequency of the applied electric field. The electrically switchable self-assembled microstructures and their beam steering capabilities thus provide a feasible way to tune the functions of DFNLC-based optical devices.
Chinese Optics Letters
- Publication Date: Sep. 07, 2022
- Vol. 21, Issue 1, 010501 (2023)
Double-groove rectangular gratings for high-efficiency wideband vertical coupling in planar-integrated optical systems
Guoqing Ma, Changhe Zhou, Yongfang Xie, Ge Jin, Rongwei Zhu, Jin Zhang, Junjie Yu, and Guohai Situ
A planar-integrated optical system (PIOS) represents powerful optical imaging and information processing techniques and is a potential candidate for the realization of a three-dimensional (3D) integrated optoelectronic intelligent system. Coupling the optical wave carrying information into a planar transparent substrate (typically fused silica) is an essential prerequisite for the realization of such a PIOS. Unlike conventional grating couplers for nano-waveguides on the silicon-on-insulator platform, the grating couplers for PIOS enable to obtain a higher design freedom and to achieve much higher coupling efficiency. By combining the rigorous coupled wave algorithm and simulated annealing optimization algorithm, a high-efficiency asymmetric double-groove grating coupler is designed for PIOS. It is indicated that, under the condition of the normal incidence of TE polarization, the diffraction efficiency of the -1st order is over 95%, and its average value is 97.3% and 92.8% in the C and C+L bands. The simulation results indicate that this type of grating coupler has good tolerance and is expected to be applied in optical interconnections, waveguide-based augmented reality glasses, and planar-integrated 3D interconnection optical computing systems. A planar-integrated optical system (PIOS) represents powerful optical imaging and information processing techniques and is a potential candidate for the realization of a three-dimensional (3D) integrated optoelectronic intelligent system. Coupling the optical wave carrying information into a planar transparent substrate (typically fused silica) is an essential prerequisite for the realization of such a PIOS. Unlike conventional grating couplers for nano-waveguides on the silicon-on-insulator platform, the grating couplers for PIOS enable to obtain a higher design freedom and to achieve much higher coupling efficiency. By combining the rigorous coupled wave algorithm and simulated annealing optimization algorithm, a high-efficiency asymmetric double-groove grating coupler is designed for PIOS. It is indicated that, under the condition of the normal incidence of TE polarization, the diffraction efficiency of the -1st order is over 95%, and its average value is 97.3% and 92.8% in the C and C+L bands. The simulation results indicate that this type of grating coupler has good tolerance and is expected to be applied in optical interconnections, waveguide-based augmented reality glasses, and planar-integrated 3D interconnection optical computing systems.
Chinese Optics Letters
- Publication Date: Jun. 14, 2022
- Vol. 20, Issue 9, 090501 (2022)
Machine-learning-based high-speed lensless large-field holographic projection using double-sampling Fresnel diffraction method
Chentianfei Shen, Tong Shen, Qi Chen, Qinghan Zhang, and Jihong Zheng
Machine learning can effectively accelerate the runtime of a computer-generated hologram. However, the angular spectrum method and single fast Fresnel transform-based machine learning acceleration algorithms are still limited in the field-of-view angle of projection. In this paper, we propose an efficient method for the fast generation of large field-of-view holograms combining stochastic gradient descent (SGD), neural networks, and double-sampling Fresnel diffraction (DSFD). Compared with the traditional Gerchberg–Saxton (GS) algorithm, the DSFD-SGD algorithm has better reconstruction quality. Our neural network can be automatically trained in an unsupervised manner with a training set of target images without labels, and its combination with the DSFD can improve the optimization speed significantly. The proposed DSFD-Net method can generate 2000-resolution holograms in 0.05 s. The feasibility of the proposed method is demonstrated with simulations and experiments. Machine learning can effectively accelerate the runtime of a computer-generated hologram. However, the angular spectrum method and single fast Fresnel transform-based machine learning acceleration algorithms are still limited in the field-of-view angle of projection. In this paper, we propose an efficient method for the fast generation of large field-of-view holograms combining stochastic gradient descent (SGD), neural networks, and double-sampling Fresnel diffraction (DSFD). Compared with the traditional Gerchberg–Saxton (GS) algorithm, the DSFD-SGD algorithm has better reconstruction quality. Our neural network can be automatically trained in an unsupervised manner with a training set of target images without labels, and its combination with the DSFD can improve the optimization speed significantly. The proposed DSFD-Net method can generate 2000-resolution holograms in 0.05 s. The feasibility of the proposed method is demonstrated with simulations and experiments.
Chinese Optics Letters
- Publication Date: Mar. 25, 2022
- Vol. 20, Issue 5, 050502 (2022)
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