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Nanophotonics, Metamaterials, and Plasmonics|100 Article(s)
Perfect absorption and refractive index sensing of an E-shaped hole array metasurface through BICs
Miaomiao Zhang, Kai Yu, Yuanjian Liu, Yatang Dai, Hao Zhang, and Jing Chen
In this Letter, we propose an E-shaped hole metasurface leveraging bound states in the continuum (BICs) for perfect absorption and ultrasensitive refractive index sensing. We can achieve 98.9% optical absorption at 909 nm in the symmetric metasurface through a symmetry-protected BIC mode. It is found that there is a squared relationship between the Q-factor and the asymmetry factor. More importantly, we successfully activate the quasi-BIC (Q-BIC) mode in a symmetry-broken structure at an 8° light incidence angle. Both the symmetry-protected BIC and Q-BIC modes show 1000 nm/RIU (refractive index unit) sensitivity in air, while the latter outperforms in organic solutions with a figure of merit (FOM) of 463.9. This platform offers a versatile solution for ultra-narrowband photonics and high-precision biosensing applications. In this Letter, we propose an E-shaped hole metasurface leveraging bound states in the continuum (BICs) for perfect absorption and ultrasensitive refractive index sensing. We can achieve 98.9% optical absorption at 909 nm in the symmetric metasurface through a symmetry-protected BIC mode. It is found that there is a squared relationship between the Q-factor and the asymmetry factor. More importantly, we successfully activate the quasi-BIC (Q-BIC) mode in a symmetry-broken structure at an 8° light incidence angle. Both the symmetry-protected BIC and Q-BIC modes show 1000 nm/RIU (refractive index unit) sensitivity in air, while the latter outperforms in organic solutions with a figure of merit (FOM) of 463.9. This platform offers a versatile solution for ultra-narrowband photonics and high-precision biosensing applications.
Chinese Optics Letters
- Publication Date: Sep. 08, 2025
- Vol. 23, Issue 9, 093602 (2025)
Flexible manipulation of optical angular momentum using a spherical wavefront
Shuaichao Li, Hongjie Huang, Yili Lu, Pei Wang, and Yonghua Lu
Optical angular momentum (AM), comprising spin angular momentum (SAM) and orbital angular momentum (OAM), is crucial in various applications, yet its flexible control remains challenging. This study proposes, to our knowledge, a novel method for manipulating SAM and OAM using spherical wave illumination and the Λ-shaped spiral aperture. By adjusting the spherical wave’s convergence or divergence, the sign of SAM and OAM can be switched, while the geometric topological charge of the aperture transfers to the optical AM due to AM conservation. The method is theoretically analyzed, simulated, and experimentally validated, offering a compact platform applicable to photonic systems, particle manipulation, and encryption. Optical angular momentum (AM), comprising spin angular momentum (SAM) and orbital angular momentum (OAM), is crucial in various applications, yet its flexible control remains challenging. This study proposes, to our knowledge, a novel method for manipulating SAM and OAM using spherical wave illumination and the Λ-shaped spiral aperture. By adjusting the spherical wave’s convergence or divergence, the sign of SAM and OAM can be switched, while the geometric topological charge of the aperture transfers to the optical AM due to AM conservation. The method is theoretically analyzed, simulated, and experimentally validated, offering a compact platform applicable to photonic systems, particle manipulation, and encryption.
Chinese Optics Letters
- Publication Date: Aug. 13, 2025
- Vol. 23, Issue 9, 093601 (2025)
Gradient-descent optimization of metasurfaces based on one deep-enhanced RseNet
Yi Xu, Fu Li, Jianqiang Gu, Quan Xu, Zhen Tian, Jiaguang Han, and Weili Zhang
Metasurfaces have revolutionized planar optics due to their prominent ability in light field manipulation. Recently, the incorporation of machine learning has further improved computational efficiency and reduced the reliance on professionals in designing various metasurfaces. However, the prevalent methods still suffer from configuration complexity and expensive training costs due to more than one model or a combination of rule-driven algorithms. This study proposes a deep learning-based paradigm using only one deep learning model for the end-to-end design of versatile metasurfaces. The adopted deep-enhanced RseNet acts both as the surrogate of the electromagnetic simulator in forward spectrum prediction and as the path for backward gradient descent optimization of the meta-atom structures in the paralleled calculation. Without loss of generality, a polarization-multiplexing holographic and a polarization-independent vortex metasurface were designed by this paradigm and successfully demonstrated in the terahertz range. The extremely simplified framework presented here will not only propel the design and application of metasurfaces in terahertz communication and imaging fields, but its universality will also accelerate the research and development of subwavelength planar optics across various wavelengths through artificial intelligence (AI)-enhanced design for optical devices. Metasurfaces have revolutionized planar optics due to their prominent ability in light field manipulation. Recently, the incorporation of machine learning has further improved computational efficiency and reduced the reliance on professionals in designing various metasurfaces. However, the prevalent methods still suffer from configuration complexity and expensive training costs due to more than one model or a combination of rule-driven algorithms. This study proposes a deep learning-based paradigm using only one deep learning model for the end-to-end design of versatile metasurfaces. The adopted deep-enhanced RseNet acts both as the surrogate of the electromagnetic simulator in forward spectrum prediction and as the path for backward gradient descent optimization of the meta-atom structures in the paralleled calculation. Without loss of generality, a polarization-multiplexing holographic and a polarization-independent vortex metasurface were designed by this paradigm and successfully demonstrated in the terahertz range. The extremely simplified framework presented here will not only propel the design and application of metasurfaces in terahertz communication and imaging fields, but its universality will also accelerate the research and development of subwavelength planar optics across various wavelengths through artificial intelligence (AI)-enhanced design for optical devices.
Chinese Optics Letters
- Publication Date: Jul. 14, 2025
- Vol. 23, Issue 8, 083601 (2025)
Dynamic beam shifts via refractive index tuning in photonic crystal slabs
Mingxuan Gu, Xinghong Chen and Yifei Mao
Light-beam shifts accompanied by propagation between two media show potential in applications such as optical sensing, optical communication, and optical computing. However, existing work tends to focus on the static response of the device, i.e., the beam shift when the structural parameters and incident conditions are fixed. Here, we analyze the dynamics of beam shifting via photonic crystal slabs under refractive index variation. On the one hand, we investigate the trend of cross-polarized phase gradient under small changes in refractive index. Simulation results show that the direction of the beam shift can change by more than 50° for a refractive index change of only 0.06. On the other hand, we study the interaction of incident light with the far-field polarizations of bound states in the continuum in the presence of a refractive index jump in the phase-change material. In this case, simulation results show that the large change in the Pancharatnam–Berry phase gradient causes the beam to move widely, with a change in beam direction of 61.30° and a change in beam displacement of 15 µm. Furthermore, all displacement amounts are comparable to the radius of the incident beam (∼8 µm). Our work provides a new perspective on the study of beam shifts, which can advance practical applications of beam shift in sensing, intelligent detecting, and beam control. Light-beam shifts accompanied by propagation between two media show potential in applications such as optical sensing, optical communication, and optical computing. However, existing work tends to focus on the static response of the device, i.e., the beam shift when the structural parameters and incident conditions are fixed. Here, we analyze the dynamics of beam shifting via photonic crystal slabs under refractive index variation. On the one hand, we investigate the trend of cross-polarized phase gradient under small changes in refractive index. Simulation results show that the direction of the beam shift can change by more than 50° for a refractive index change of only 0.06. On the other hand, we study the interaction of incident light with the far-field polarizations of bound states in the continuum in the presence of a refractive index jump in the phase-change material. In this case, simulation results show that the large change in the Pancharatnam–Berry phase gradient causes the beam to move widely, with a change in beam direction of 61.30° and a change in beam displacement of 15 µm. Furthermore, all displacement amounts are comparable to the radius of the incident beam (∼8 µm). Our work provides a new perspective on the study of beam shifts, which can advance practical applications of beam shift in sensing, intelligent detecting, and beam control.
Chinese Optics Letters
- Publication Date: Jun. 19, 2025
- Vol. 23, Issue 7, 073602 (2025)
Pixelated Bayer spectral router based on a sparse meta-atom array
Yifan Shao, Rui Chen, Yubo Wang, Shuhan Guo, Junjie Zhan, Pankaj K. Choudhury, and Yungui Ma
It has long been a challenging task to improve the light collection efficiency of conventional image sensors built with color filters that inevitably cause the energy loss of out-of-band photons. Here, we demonstrate a pixelated spectral router based on a sparse meta-atom array, which can efficiently separate incident R (600–700 nm), G (500–600 nm), and B (400–500 nm) band light to the corresponding pixels of a Bayer image sensor, providing over 56% signal enhancement above the traditional color filter scheme. It is enabled by simple compound Si3N4 nanostructures, which are very suitable for massive production. Imaging experiments are conducted to verify the router’s potential for real applications. The complementary metal-oxide-semiconductor (CMOS)-compatible spectral router scheme is also found to be robust and can be freely adapted to image sensors of various pixel sizes, having great potential in building the new generation of high-performance image sensing components. It has long been a challenging task to improve the light collection efficiency of conventional image sensors built with color filters that inevitably cause the energy loss of out-of-band photons. Here, we demonstrate a pixelated spectral router based on a sparse meta-atom array, which can efficiently separate incident R (600–700 nm), G (500–600 nm), and B (400–500 nm) band light to the corresponding pixels of a Bayer image sensor, providing over 56% signal enhancement above the traditional color filter scheme. It is enabled by simple compound Si3N4 nanostructures, which are very suitable for massive production. Imaging experiments are conducted to verify the router’s potential for real applications. The complementary metal-oxide-semiconductor (CMOS)-compatible spectral router scheme is also found to be robust and can be freely adapted to image sensors of various pixel sizes, having great potential in building the new generation of high-performance image sensing components.
Chinese Optics Letters
- Publication Date: Jun. 16, 2025
- Vol. 23, Issue 7, 073601 (2025)
Double-functioned metalens inspired by compound eyes for naked-eye 3D display with high efficiency, high resolution, and large viewing range
Jian Zhu, Qinyue Sun, Zhenhuan Tian, Xuzheng Wang, Feng Li, and Feng Yun
Micro-LED is one of the most promising technologies for naked-eye 3D display. However, due to challenges related to efficiency, resolution, viewing range, and structure integration, the 3D micro-LED display is still at the conceptual stage. In this work, we introduce a double-functioned metalens composed of highly symmetric unit cells into the 3D micro-LED system. The nonpolarized spotlight generated by the micro-LED is collimated and deflected through the designed metalens. Inspired by the compound eyes, metalens modules with varying deflection angles are spliced and penetrated together, enabling a wide viewing angle without sacrificing resolution. Additionally, the viewing position can be dynamically adjusted using adjustable subpixels. The results demonstrate that the proposed metalens and its optical system can reach a viewing angle ranging from -41.5° to 41.5° and an adjustable optimum viewing distance from 25 to 75 cm. The deflection efficiency exceeds 80%, with a resolution of 910 PPI (pixels per inch). Our design shows great potential for naked-eye 3D display. Micro-LED is one of the most promising technologies for naked-eye 3D display. However, due to challenges related to efficiency, resolution, viewing range, and structure integration, the 3D micro-LED display is still at the conceptual stage. In this work, we introduce a double-functioned metalens composed of highly symmetric unit cells into the 3D micro-LED system. The nonpolarized spotlight generated by the micro-LED is collimated and deflected through the designed metalens. Inspired by the compound eyes, metalens modules with varying deflection angles are spliced and penetrated together, enabling a wide viewing angle without sacrificing resolution. Additionally, the viewing position can be dynamically adjusted using adjustable subpixels. The results demonstrate that the proposed metalens and its optical system can reach a viewing angle ranging from -41.5° to 41.5° and an adjustable optimum viewing distance from 25 to 75 cm. The deflection efficiency exceeds 80%, with a resolution of 910 PPI (pixels per inch). Our design shows great potential for naked-eye 3D display.
Chinese Optics Letters
- Publication Date: May. 30, 2025
- Vol. 23, Issue 6, 063604 (2025)
Generation of arbitrary vector vortex beams on the hybrid-order Poincaré sphere from cholesteric liquid crystals
Tiegang Lin, Ben Niu, Furong Liu, Xianglin Ye, Fan Fan, and Yufang Liu
In this Letter, by exploiting the spin-to-orbital angular momentum conversion capability and the polarization selectivity characteristic of cholesteric liquid crystal planar optical elements, an approach of combing two cholesteric liquid crystal layers with opposite handedness and independent surface patterns is proposed and investigated for generating arbitrary vector vortex beams on the hybrid-order Poincaré sphere. Furthermore, the intensity profiles and polarization distributions of typical vector vortex beams are experimentally demonstrated and analyzed, which shows good agreement with the theoretical prediction. The approach also suggests its advantages of operating light in the polychromatic spectral region of Bragg reflection. Our method presents a simple and direct way of phase and polarization manipulation, which also provides promising opportunities for developing advanced applications in structured light, high-resolution imaging, and information processing. In this Letter, by exploiting the spin-to-orbital angular momentum conversion capability and the polarization selectivity characteristic of cholesteric liquid crystal planar optical elements, an approach of combing two cholesteric liquid crystal layers with opposite handedness and independent surface patterns is proposed and investigated for generating arbitrary vector vortex beams on the hybrid-order Poincaré sphere. Furthermore, the intensity profiles and polarization distributions of typical vector vortex beams are experimentally demonstrated and analyzed, which shows good agreement with the theoretical prediction. The approach also suggests its advantages of operating light in the polychromatic spectral region of Bragg reflection. Our method presents a simple and direct way of phase and polarization manipulation, which also provides promising opportunities for developing advanced applications in structured light, high-resolution imaging, and information processing.
Chinese Optics Letters
- Publication Date: May. 30, 2025
- Vol. 23, Issue 6, 063603 (2025)
Optical performances of near-infrared metalenses with process-induced defects
Xiaofei Liu, Ruohui Chen, Yilin Lu, Chenxu Zhu, Yang Qiu, Xingyan Zhao, Shaonan Zheng, Qize Zhong, Bo Cui, Yuan Dong, and Ting Hu
Defects are inevitably induced during the fabrication process of a metalens, which will affect the metalens’s yield and optical performances. Thus, investigations on the fabrication defects are becoming increasingly important for the mass production of metalenses. In this Letter, the optical performances of near-infrared metalenses with four types of fabrication defects are investigated. The results show that the process-induced defects obviously affect the focusing efficiency at λ = 940 nm, but they have less impact on the quality of the focal spot. This work provides fabrication guidance for large-scale manufacturing of metalenses in the future. Defects are inevitably induced during the fabrication process of a metalens, which will affect the metalens’s yield and optical performances. Thus, investigations on the fabrication defects are becoming increasingly important for the mass production of metalenses. In this Letter, the optical performances of near-infrared metalenses with four types of fabrication defects are investigated. The results show that the process-induced defects obviously affect the focusing efficiency at λ = 940 nm, but they have less impact on the quality of the focal spot. This work provides fabrication guidance for large-scale manufacturing of metalenses in the future.
Chinese Optics Letters
- Publication Date: May. 26, 2025
- Vol. 23, Issue 6, 063602 (2025)
Compact nanohole/disk array-based plasmonic fiber-optic end-facet sensing probe: batch preparation and performance determination
Yijin He, Yuzhang Liang, Xinran Wei, Yuqi Du, Lanlan Shen, Jingyuan Zhao, Cheng Yang, Yurui Fang, and Wei Peng
A gold nanohole/disk array-based plasmonic fiber end-facet sensing probe is proposed and demonstrated experimentally, where the hybrid plasmon mode on the top surface used for sensing is excited by the cooperative effect of the near-field coupling between the nanohole and the nanodisk, as well as the localized surface plasmon of the nanodisk. The high-quality integration of the nanohole/disk array on the fiber end facet is achieved by combining nanoimprint lithography on a planar substrate with fiber ultraviolet (UV)-curable adhesive transfer techniques. As a result, the fabricated fiber probe experimentally exhibits a moderately high bulk refractive index sensitivity of ∼196.91 nm/RIU and excellent surface sensitivity. Furthermore, the specific identification and determination of protein molecules verify their sensitivity analysis capabilities for future bioassays. This work provides a feasible plasmonic excitation strategy and enables batch-manufactured technology for nanostructure-based fiber probes to break through the current bottlenecks in biosensing applications. A gold nanohole/disk array-based plasmonic fiber end-facet sensing probe is proposed and demonstrated experimentally, where the hybrid plasmon mode on the top surface used for sensing is excited by the cooperative effect of the near-field coupling between the nanohole and the nanodisk, as well as the localized surface plasmon of the nanodisk. The high-quality integration of the nanohole/disk array on the fiber end facet is achieved by combining nanoimprint lithography on a planar substrate with fiber ultraviolet (UV)-curable adhesive transfer techniques. As a result, the fabricated fiber probe experimentally exhibits a moderately high bulk refractive index sensitivity of ∼196.91 nm/RIU and excellent surface sensitivity. Furthermore, the specific identification and determination of protein molecules verify their sensitivity analysis capabilities for future bioassays. This work provides a feasible plasmonic excitation strategy and enables batch-manufactured technology for nanostructure-based fiber probes to break through the current bottlenecks in biosensing applications.
Chinese Optics Letters
- Publication Date: May. 16, 2025
- Vol. 23, Issue 6, 063601 (2025)
Ultrafast polarization modulation with high-purity chiral quasi-BIC metasurfaces|Fast Track
Fangxing Lai, Yubin Fan, Xinbo Sha, Huachun Deng, Xiong Jiang, Shumin Xiao, Can Huang, and Qinghai Song
Precise control of the polarization state of light on ultrafast time scales plays a key role in revealing the inherent chiral or anisotropic optical responses in various material systems, and it is crucial for applications that require complex polarization encoding. Here, we explore ultrafast polarization control enabled by silicon-based chiral bound state in the continuum (BIC) metasurfaces. By utilizing the intrinsic chiral mode, we achieve high-purity chiral reflection light (S3 ∼ -0.92) and rapid modulation (∼0.4 ps) of polarization states through all-optical methods. Unlike traditional polarization modulation techniques, our approach leverages the unique advantages of slanted etching dielectric chiral BIC metasurfaces, which facilitate high-Q resonance and exhibit narrow linewidths. These advantages allow swift alterations in polarization states with minimal modulation energy consumption, which should help for greater control of light in integrated photonic applications. Precise control of the polarization state of light on ultrafast time scales plays a key role in revealing the inherent chiral or anisotropic optical responses in various material systems, and it is crucial for applications that require complex polarization encoding. Here, we explore ultrafast polarization control enabled by silicon-based chiral bound state in the continuum (BIC) metasurfaces. By utilizing the intrinsic chiral mode, we achieve high-purity chiral reflection light (S3 ∼ -0.92) and rapid modulation (∼0.4 ps) of polarization states through all-optical methods. Unlike traditional polarization modulation techniques, our approach leverages the unique advantages of slanted etching dielectric chiral BIC metasurfaces, which facilitate high-Q resonance and exhibit narrow linewidths. These advantages allow swift alterations in polarization states with minimal modulation energy consumption, which should help for greater control of light in integrated photonic applications.
Chinese Optics Letters
- Publication Date: May. 06, 2025
- Vol. 23, Issue 5, 053605 (2025)
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