Journals > > Topics > Nanophotonics and Photonic Crystals
Nanophotonics and Photonic Crystals|106 Article(s)
Giantly enhancing harmonic generations by a moiré superlattice nanocavity
Yingke Ji, Liang Fang, Jianguo Wang, Yanyan Zhang, Chenyang Zhao, Jie Wang, Xianghu Wu, Yu Zhang, Mingwen Zhang, Jianlin Zhao, and Xuetao Gan
We demonstrate that a moiré superlattice nanocavity constructed in a photonic crystal slab promises strongly enhanced nonlinear optics, which is beneficial from the high-quality factor and high coupling efficiency of the flat-band mode with zero group velocity. From a silicon moiré superlattice nanocavity integrated with few-layer gallium selenide (GaSe), the second-harmonic generation (SHG) of GaSe is enhanced by over 10,000 times, and the third-harmonic generation (THG) is enhanced by 8500 times. Our results suggest the moiré superlattice nanocavity could be considered as a promising platform for developing high-efficiency nonlinear photonic devices. We demonstrate that a moiré superlattice nanocavity constructed in a photonic crystal slab promises strongly enhanced nonlinear optics, which is beneficial from the high-quality factor and high coupling efficiency of the flat-band mode with zero group velocity. From a silicon moiré superlattice nanocavity integrated with few-layer gallium selenide (GaSe), the second-harmonic generation (SHG) of GaSe is enhanced by over 10,000 times, and the third-harmonic generation (THG) is enhanced by 8500 times. Our results suggest the moiré superlattice nanocavity could be considered as a promising platform for developing high-efficiency nonlinear photonic devices.
Photonics Research
- Publication Date: Aug. 29, 2025
- Vol. 13, Issue 9, 2697 (2025)
Chiral and antichiral edge states in gyromagnetic photonic crystals under magnetic and pseudomagnetic fields
Shiyu Liu, Yuting Yang, Liwei Shi, Enyuan Wang, and Zhi Hong Hang
Inhomogeneous uniaxial strain-induced lattice deformations result in the Dirac point shift, leading to a strong synthetic pseudomagnetic field. The chiral edge state in the Haldane model and the antichiral edge state in the modified Haldane model can be realized in gyromagnetic photonic crystals, immersed in external real magnetic fields. Here, the interplay of the real- and pseudo-magnetic fields is investigated based on the onsite magnetization modulation and the uniaxial strain within gyromagnetic photonic crystals, thereby resulting in photonic band deformations including the shift of the chiral edge states and the lift of the degenerate antichiral edge states. The experiment is further performed to observe the imbalanced transport of these edge states on two opposite sides. Our findings can help to deeply explore rich and significant physics of synthetic gauge fields, and facilitate designs of photonic functional devices, such as the proposed unidirectional multichannel waveguide. Inhomogeneous uniaxial strain-induced lattice deformations result in the Dirac point shift, leading to a strong synthetic pseudomagnetic field. The chiral edge state in the Haldane model and the antichiral edge state in the modified Haldane model can be realized in gyromagnetic photonic crystals, immersed in external real magnetic fields. Here, the interplay of the real- and pseudo-magnetic fields is investigated based on the onsite magnetization modulation and the uniaxial strain within gyromagnetic photonic crystals, thereby resulting in photonic band deformations including the shift of the chiral edge states and the lift of the degenerate antichiral edge states. The experiment is further performed to observe the imbalanced transport of these edge states on two opposite sides. Our findings can help to deeply explore rich and significant physics of synthetic gauge fields, and facilitate designs of photonic functional devices, such as the proposed unidirectional multichannel waveguide.
Photonics Research
- Publication Date: Aug. 28, 2025
- Vol. 13, Issue 9, 2688 (2025)
Anisotropy-induced flattened dispersion and higher-order topology in C2v symmetry triangular photonic crystals
Liyun Tao, Yahong Liu, Yue He, Lianlian Du, Shaojie Ma, Xiaoyong Yang, Shengzhe Xia, Chen Zhang, Kun Song, Zhenfei Li, and Xiaopeng Zhao
Symmetry plays a fundamental role in topological photonic crystals, and topological phase transitions induced by disorder have also been extensively explored in recent years. However, in this work, we find anisotropy can be induced by reducing symmetry in a C2v symmetry triangular photonic crystal. We investigate that anisotropy-induced interfaces profoundly affect edge states and enable the realization of slow light dispersion. Numerical simulations reveal a transition from gapless chiral edge modes to gapped flat band dispersion. Furthermore, we observe higher-order corner states in corner structures constructed by anisotropic interfaces. The corner states can be induced and localized at different lattice positions, thereby realizing multiple types of higher-order topological states. We demonstrate the significance of anisotropic geometry in topological photonics. These findings open new possibilities for steering wave transport in multiple dimensions and offer, to our knowledge, a novel research perspective on the transformation of topological states induced by anisotropic lattices. Symmetry plays a fundamental role in topological photonic crystals, and topological phase transitions induced by disorder have also been extensively explored in recent years. However, in this work, we find anisotropy can be induced by reducing symmetry in a C2v symmetry triangular photonic crystal. We investigate that anisotropy-induced interfaces profoundly affect edge states and enable the realization of slow light dispersion. Numerical simulations reveal a transition from gapless chiral edge modes to gapped flat band dispersion. Furthermore, we observe higher-order corner states in corner structures constructed by anisotropic interfaces. The corner states can be induced and localized at different lattice positions, thereby realizing multiple types of higher-order topological states. We demonstrate the significance of anisotropic geometry in topological photonics. These findings open new possibilities for steering wave transport in multiple dimensions and offer, to our knowledge, a novel research perspective on the transformation of topological states induced by anisotropic lattices.
Photonics Research
- Publication Date: Aug. 28, 2025
- Vol. 13, Issue 9, 2574 (2025)
Numerical aperture customized differentiation metasurfaces via the spatial-frequency Trust-Region algorithm
Weiji Yang, Jianyao Li, Zhiguang Lin, Dongmei Lu, and Xiaoxu Deng
Two-dimensional second-order spatial differentiation metasurfaces with different numerical apertures (NAs) were designed by the spatial-frequency Trust-Region algorithm, which can be directly embedded into existing optical imaging systems to efficiently extract edge information of the observed targets. The spatial-frequency Trust-Region algorithm was implemented by integrating the Fourier modal method (FMM) with the Trust-Region algorithm to perform inverse optimization of the metasurface nanostructure. The fabricated metasurface with high-resolution functionality achieved a resolution of 1.2 μm and numerical aperture of 0.87, while the high-contrast one obtained a root-mean-square (RMS) contrast higher than that of the first with a numerical aperture of 0.26. Embedded in an optical microscope, the high-resolution differentiation metasurface, with more high-spatial-frequency components in the transfer function, was utilized to extract fine structures of unstained, even transparent, cell images, providing a new avenue for image segmentation, such as in magnetic resonance imaging. The high-contrast counterpart, due to its high transmission efficiency, was employed to detect edges in dynamic images of paramecia and Brachionus without motion smear, offering potential for application in microsurgical procedures involving real-time image analysis. Two-dimensional second-order spatial differentiation metasurfaces with different numerical apertures (NAs) were designed by the spatial-frequency Trust-Region algorithm, which can be directly embedded into existing optical imaging systems to efficiently extract edge information of the observed targets. The spatial-frequency Trust-Region algorithm was implemented by integrating the Fourier modal method (FMM) with the Trust-Region algorithm to perform inverse optimization of the metasurface nanostructure. The fabricated metasurface with high-resolution functionality achieved a resolution of 1.2 μm and numerical aperture of 0.87, while the high-contrast one obtained a root-mean-square (RMS) contrast higher than that of the first with a numerical aperture of 0.26. Embedded in an optical microscope, the high-resolution differentiation metasurface, with more high-spatial-frequency components in the transfer function, was utilized to extract fine structures of unstained, even transparent, cell images, providing a new avenue for image segmentation, such as in magnetic resonance imaging. The high-contrast counterpart, due to its high transmission efficiency, was employed to detect edges in dynamic images of paramecia and Brachionus without motion smear, offering potential for application in microsurgical procedures involving real-time image analysis.
Photonics Research
- Publication Date: Aug. 28, 2025
- Vol. 13, Issue 9, 2566 (2025)
Toroidal dipole Fabry–Perot bound states in the continuum metasurfaces for ultrasensitive chiral detection
Chengfeng Li, Tao He, Xiaofeng Rao, Chao Feng, Jingyuan Zhu, Siyu Dong, Zeyong Wei, Hongfei Jiao, Yuzhi Shi, Zhanshan Wang, and Xinbin Cheng
Circular dichroism (CD) spectroscopy, widely used for chiral sensing, has been limited by the detection sensitivity. Enhancing optical chirality in the light fields interacting with chiral molecules is crucial for achieving ultrasensitive chiral detection. Here, we present a new paradigm for ultrasensitive chiral detection by creating accessible chiral hotspots using a toroidal dipole Fabry–Perot bound state in the continuum (TD FP-BIC) metasurface. BIC resonance is achieved by controlling the coupling between the TD resonance and its multilayer reflector-induced perfect mirror image. This method enables unprecedented local maximum and average optical chirality enhancements of up to 6×104-fold and 2×103-fold, respectively, within non-structured regions, resulting in an 866-fold increase in CD signals compared to chiral molecules alone without nanostructures. Our results pave the way for enhanced light–matter interactions and ultrasensitive enantiomeric operation. Circular dichroism (CD) spectroscopy, widely used for chiral sensing, has been limited by the detection sensitivity. Enhancing optical chirality in the light fields interacting with chiral molecules is crucial for achieving ultrasensitive chiral detection. Here, we present a new paradigm for ultrasensitive chiral detection by creating accessible chiral hotspots using a toroidal dipole Fabry–Perot bound state in the continuum (TD FP-BIC) metasurface. BIC resonance is achieved by controlling the coupling between the TD resonance and its multilayer reflector-induced perfect mirror image. This method enables unprecedented local maximum and average optical chirality enhancements of up to 6×104-fold and 2×103-fold, respectively, within non-structured regions, resulting in an 866-fold increase in CD signals compared to chiral molecules alone without nanostructures. Our results pave the way for enhanced light–matter interactions and ultrasensitive enantiomeric operation.
Photonics Research
- Publication Date: Aug. 26, 2025
- Vol. 13, Issue 9, 2497 (2025)
High-accuracy and broadband polarization detection via metasurface vector beam modulation
Han Hao, Yao Fang, Zhihuai Diao, Xiong Li, Lianwei Chen, Qingsong Wang, Xiaoliang Ma, Yanqin Wang, and Xiangang Luo
Polarization detection is essential for various applications, ranging from biological diagnostics to quantum optics. Although various metasurface-based polarimeters have emerged, these platforms are commonly realized through spatial-division designs, which restrict detection accuracy due to inherent factors such as crosstalk. Here, we propose, to our knowledge, a novel strategy for high-accuracy, broadband full-Stokes polarization detection based on the analysis of a single vector beam, whose polarization profile varies sensitively and exhibits a one-to-one correspondence with the incident polarization. Based on this, the incident polarization is completely encoded into the field profile of the vector beam, which avoids crosstalk in principle, and results in high-accuracy polarization detection without any calibration process. As a proof of concept, a geometric-phase metasurface-based grafted perfect vector vortex beam (GPVVB) generator was designed and fabricated. Experimental results demonstrate that our method achieves polarization detection with an average relative error of 2.25%. Benefiting from the broadband high transmittance exceeding 95% of the metasurface due to the femtosecond laser-induced birefringence process, our method operates across a wavelength range of 450–1100 nm. Furthermore, the detection capability of the vector beam polarization profile was validated using a GPVVB-generating array. These results highlight the potential of our approach for transformative applications in polarization detection, including optical communication and machine vision. Polarization detection is essential for various applications, ranging from biological diagnostics to quantum optics. Although various metasurface-based polarimeters have emerged, these platforms are commonly realized through spatial-division designs, which restrict detection accuracy due to inherent factors such as crosstalk. Here, we propose, to our knowledge, a novel strategy for high-accuracy, broadband full-Stokes polarization detection based on the analysis of a single vector beam, whose polarization profile varies sensitively and exhibits a one-to-one correspondence with the incident polarization. Based on this, the incident polarization is completely encoded into the field profile of the vector beam, which avoids crosstalk in principle, and results in high-accuracy polarization detection without any calibration process. As a proof of concept, a geometric-phase metasurface-based grafted perfect vector vortex beam (GPVVB) generator was designed and fabricated. Experimental results demonstrate that our method achieves polarization detection with an average relative error of 2.25%. Benefiting from the broadband high transmittance exceeding 95% of the metasurface due to the femtosecond laser-induced birefringence process, our method operates across a wavelength range of 450–1100 nm. Furthermore, the detection capability of the vector beam polarization profile was validated using a GPVVB-generating array. These results highlight the potential of our approach for transformative applications in polarization detection, including optical communication and machine vision.
Photonics Research
- Publication Date: Aug. 26, 2025
- Vol. 13, Issue 9, 2487 (2025)
On-chip ultra-high-Q optical microresonators approaching the material absorption limit|Spotlight on Optics
Qi Shi, Jianxiong Tian, Shulin Ding, Yunan Wang, Shujian Lei, Menghua Zhang, Wenjie Wan, Xingchen Ji, Bing He, Min Xiao, and Xiaoshun Jiang
Chip-based optical microresonators with ultra-high Q-factors are becoming increasingly important to a variety of applications. However, the losses of on-chip microresonators with the highest Q-factor reported in the past are still far from their material absorption limits. Here, we demonstrate an on-chip silica microresonator that has approached the absorption limit of the state-of-the-art material on chip, realizing, to our knowledge, record intrinsic Q-factors exceeding 3 billion at both 1560 nm and 1064 nm. This fact is corroborated by photo-thermal spectroscopy measurements. Especially, compared with the standard optical fibers, its corresponding optical losses are only 38.4 times and 7.7 times higher at the wavelengths of 1560 nm and 1064 nm, respectively. To exhibit the performance of such fabricated microresonator, we achieve a record-low optical parametric oscillation threshold (31.9 μW) for millimeter-sized microresonators and generate a single-soliton microcomb with a record-low pump power of 220.2 μW for all soliton microcombs realized thus far. Chip-based optical microresonators with ultra-high Q-factors are becoming increasingly important to a variety of applications. However, the losses of on-chip microresonators with the highest Q-factor reported in the past are still far from their material absorption limits. Here, we demonstrate an on-chip silica microresonator that has approached the absorption limit of the state-of-the-art material on chip, realizing, to our knowledge, record intrinsic Q-factors exceeding 3 billion at both 1560 nm and 1064 nm. This fact is corroborated by photo-thermal spectroscopy measurements. Especially, compared with the standard optical fibers, its corresponding optical losses are only 38.4 times and 7.7 times higher at the wavelengths of 1560 nm and 1064 nm, respectively. To exhibit the performance of such fabricated microresonator, we achieve a record-low optical parametric oscillation threshold (31.9 μW) for millimeter-sized microresonators and generate a single-soliton microcomb with a record-low pump power of 220.2 μW for all soliton microcombs realized thus far.
Photonics Research
- Publication Date: Aug. 01, 2025
- Vol. 13, Issue 8, 2409 (2025)
Inherent non-Hermitian Chern insulators with PT-symmetry and synthetic translation dimension
Ke-Xin Sun, Jian-Wen Dong and Wen-Jie Chen
The introduction of non-Hermiticity provides photonic systems with more design degrees of freedom, along with unique properties, which have aroused widespread interest. On the other hand, the concept of synthetic dimensions has also been introduced into non-Hermitian topological physics. In this work, we theoretically investigate the two-dimensional (2D) band structure of a 1D non-Hermitian photonic crystal (PC) by introducing globally a translation deformation as a synthetic dimension. The resulting two-dimensional photonic crystal is a Chern insulator, which is numerically verified by calculated Chern numbers and edge dispersions. We find that this property stems from the inherent topology of synthetic space (kx,Δx), which does not depend on the crystal’s structural and material parameters. It guarantees robust edge states traversing the gap along the synthetic dimension. To provide deeper insight, we derive the reflection phase of a 1D crystal using the plane wave expansion method and give a clear physical picture of the topological edge states generated by translation deformation. These findings may pave the way for translation-based photonic devices, including topological filters and lasers. The introduction of non-Hermiticity provides photonic systems with more design degrees of freedom, along with unique properties, which have aroused widespread interest. On the other hand, the concept of synthetic dimensions has also been introduced into non-Hermitian topological physics. In this work, we theoretically investigate the two-dimensional (2D) band structure of a 1D non-Hermitian photonic crystal (PC) by introducing globally a translation deformation as a synthetic dimension. The resulting two-dimensional photonic crystal is a Chern insulator, which is numerically verified by calculated Chern numbers and edge dispersions. We find that this property stems from the inherent topology of synthetic space (kx,Δx), which does not depend on the crystal’s structural and material parameters. It guarantees robust edge states traversing the gap along the synthetic dimension. To provide deeper insight, we derive the reflection phase of a 1D crystal using the plane wave expansion method and give a clear physical picture of the topological edge states generated by translation deformation. These findings may pave the way for translation-based photonic devices, including topological filters and lasers.
Photonics Research
- Publication Date: Aug. 01, 2025
- Vol. 13, Issue 8, 2400 (2025)
Rapid imaging of chaotic modes in optical microcavities
Zi Wang, Ziyu Li, Ziheng Ji, Shumin Xiao, and Qinghai Song
Identifying optical modes in chaotic cavities is crucial for exploring and understanding the physical mechanisms inside them. Compared with free spectral range estimation, the direct imaging technique has the capability of providing more precise mode information, but it is extremely time-consuming and susceptible to environmental perturbations. Here we report a high-speed imaging technique for visualizing field distributions in chaotic microcavities. When a silicon microdisk is excited by a femtosecond laser, free carriers are locally generated, thereby reducing the refractive index. Under a constant laser power, the spatial distribution of mode inside the silicon microdisk is proportional to its wavelength shift and can be precisely identified by comparing it with numerical simulation. With the assistance of a galvanometer, imaging a mode profile only takes a few hundred milliseconds to a few seconds, orders of magnitude faster than previous reports. The impacts of slight fabrication deviations on spectra have also been identified. Identifying optical modes in chaotic cavities is crucial for exploring and understanding the physical mechanisms inside them. Compared with free spectral range estimation, the direct imaging technique has the capability of providing more precise mode information, but it is extremely time-consuming and susceptible to environmental perturbations. Here we report a high-speed imaging technique for visualizing field distributions in chaotic microcavities. When a silicon microdisk is excited by a femtosecond laser, free carriers are locally generated, thereby reducing the refractive index. Under a constant laser power, the spatial distribution of mode inside the silicon microdisk is proportional to its wavelength shift and can be precisely identified by comparing it with numerical simulation. With the assistance of a galvanometer, imaging a mode profile only takes a few hundred milliseconds to a few seconds, orders of magnitude faster than previous reports. The impacts of slight fabrication deviations on spectra have also been identified.
Photonics Research
- Publication Date: Aug. 01, 2025
- Vol. 13, Issue 8, 2393 (2025)
Dielectric quarter-waveplate metasurfaces for longitudinally tunable manipulation of high-order Poincaré beams
Teng Ma, Kaixin Zhao, Chuanfu Cheng, Manna Gu, Qingrui Dong, Haoyan Zhou, Song Gao, Duk-Yong Choi, Chunxiang Liu, and Chen Cheng
The dynamic tunability of vector beams (VBs) with metasurfaces plays an important role in the discovery of exotic optical phenomena and development of classic and quantum applications. Using the tunability with longitudinal propagation distance and multifunctional capability of the quarter-waveplate (QWP) meta-atoms, dielectric metasurfaces were designed to generate high-order Poincaré (HOP) beams with tunable elliptical polarization states at arbitrary latitudes. The metasurface contained two interleaved sub-metasurfaces of QWP meta-atoms, each configured with helical, hyperbolic, and primary and secondary axicon-phase profiles to generate a vortex, beam focus, and beam deflection, respectively. Importantly, the axicons were suitably designed by combining the propagation and geometric phases to introduce differences in the z-component wavevectors, and the amplitudes of the co- and cross-polarized vortices were tuned by the longitudinal distance. The method broke through the limitation of previously generating only the linear polarization states on the equator of the HOP sphere, and it also circumvented the traditional tunability using the troublesome waveplate-polarizer combination. This study is of great significance for the miniaturization and integration of optical systems for applications such as optical communications, micromanipulation, and high-precision detection. The dynamic tunability of vector beams (VBs) with metasurfaces plays an important role in the discovery of exotic optical phenomena and development of classic and quantum applications. Using the tunability with longitudinal propagation distance and multifunctional capability of the quarter-waveplate (QWP) meta-atoms, dielectric metasurfaces were designed to generate high-order Poincaré (HOP) beams with tunable elliptical polarization states at arbitrary latitudes. The metasurface contained two interleaved sub-metasurfaces of QWP meta-atoms, each configured with helical, hyperbolic, and primary and secondary axicon-phase profiles to generate a vortex, beam focus, and beam deflection, respectively. Importantly, the axicons were suitably designed by combining the propagation and geometric phases to introduce differences in the z-component wavevectors, and the amplitudes of the co- and cross-polarized vortices were tuned by the longitudinal distance. The method broke through the limitation of previously generating only the linear polarization states on the equator of the HOP sphere, and it also circumvented the traditional tunability using the troublesome waveplate-polarizer combination. This study is of great significance for the miniaturization and integration of optical systems for applications such as optical communications, micromanipulation, and high-precision detection.
Photonics Research
- Publication Date: Aug. 01, 2025
- Vol. 13, Issue 8, 2257 (2025)
Topics
© Copyright 2018-2021 | Chinese Laser Press. All Rights Reserved 沪ICP备15018463号-20