arXiv subjects

Shuyuan Xiao

Publications and source records attributed to Shuyuan Xiao.

At least 37 records · Page 2Linked to original sources

arXiv2024

Enhanced third-harmonic generation empowered by doubly degenerate quasi-bound states in the continuum

Recent advancements in nonlinear nanophotonics are driven by the exploration of sharp resonances within high-index dielectric metasurfaces. In this work, we leverage doubly degenerate quasi-bound states in the continuum (quasi-BICs) to demonstrate robust enhancement of third-harmonic generation (THG) in silicon metasurfaces. These quasi-BICs are governed by $C_{4v}$ symmetry and therefore can be equally excited with the pump light regardless of polarization. By tailoring the geometric parameters, we effectively control $Q$-factors and field confinement of quasi-BICs, and thus regulate their resonantly enhanced THG process. A maximum THG conversion efficiency up to $1.03\times10^{-5}$ is recorded under a pump intensity of 5.85 GW/cm$^{2}$. Polarization-independent THG profile is further confirmed by mapping its signal across the polarization directions. This work establishes foundational strategies for the ultracompact design of robust and high-efficiency photon upconversion systems.

physics.optics↗

arXiv2024

Phase-change metasurfaces for reconfigurable image processing

Optical metasurfaces have enabled high-speed, low-power image processing within a compact footprint. However, reconfigurable imaging in such flat devices remains a critical challenge for fully harnessing their potential in practical applications. Here, we propose and demonstrate phase-change metasurfaces capable of dynamically switching between edge detection and bright-field imaging in the visible spectrum. This reconfigurability is achieved through engineering angular dispersion at electric and magnetic Mie-type resonances. The customized metasurface exhibits an angle-dependent transmittance profile in the amorphous state of Sb$_{2}$S$_{3}$ meta-atoms for efficient isotropic edge detection, and an angle-independent profile in the crystalline state for uniform bright-field imaging. The nanostructured Sb$_{2}$S$_{3}$-based reconfigurable image processing metasurfaces hold significant potential for applications in computer vision for autonomous driving systems.

physics.optics↗

arXiv2024

Optoelectronic generative adversarial networks

Artificial intelligence generative content technology has experienced remarkable breakthroughs in recent years and is quietly leading a profound transformation. Diffractive optical networks provide a promising solution for implementing generative model with high-speed and low-power consumption. In this work, we present the implementation of a generative model on the optoelectronic computing architecture, based on generative adversarial network, which is called optoelectronic generative adversarial network. The network strategically distributes the generator and discriminator across the optical and electronic components, which are seamlessly integrated to leverage the unique strengths of each computing paradigm and take advantage of transfer learning. The network can efficiently and high-speed process the complex tasks involved in the training and inference of the generative model. The superior performance of these networks is verified by engaging three types of generative tasks, image generation, conditional generation, and image restoration. By synergistically combining the strengths of optical and electronic computing, the optoelectronic generative adversarial network paves the way for the development of more powerful and accessible artificial intelligence generative content technology that can unlock new creative possibilities across a wide range of applications.

physics.optics↗

arXiv2024

Multiplexed Metasurfaces for Diffractive Optics via Phase Correlation Method

The multiplexing capability of metasurfaces has been successfully demonstrated in applications such as holography and diffractive neural networks. However, identifying a suitable structure that simultaneously satisfies the phase requirements across multiple channels remains a significant challenge in many multiplexing design scenarios. In this study, we propose an innovative phase correlation method for metasurface multiplexing design that utilizes a multi-layer perceptron to establish phase correlations across multiple channels. This approach reduces the difficulty of multi-channel phase training by converting it into a simpler single-channel optimization task, thereby reducing design complexity and computational cost. Using the proposed method, we design a dual-wavelength multiplexed diffractive neural network and a multi-wavelength metasurface color holography under a linear polarization. The designed multiplexed metasurface achieves up to 90% classification accuracy in image recognition and exhibits good performance in color holography.

physics.optics↗

arXiv2024

Continuous Varifocal Metalens Based on Phase-Change Material

Metasurfaces have provided new opportunities for the realization of flat lenses, among which tunable metalenses have garnered considerable attention due to their flexible functionalities. In this paper, we present a continuously tunable metalens based on the phase-change material Sb$_{2}$S$_{3}$, which enables precise and continuous focal length control through the transition of states. Under the excitation of linearly polarized light at 1550 nm, phase compensation is provided by changing the crystallization state of the Sb$_{2}$S$_{3}$ nanopillars, allowing the focal length to continuously shift between 36 $μ$m and 48 $μ$m. At the same time, the metalens maintains a high focusing efficiency over 75%. This approach provides greater design flexibility and broader applicability across diverse applications. By reducing the reliance on polarized light sources, it enhances device integration and tunability, paving the way for new opportunities in the practical implementation of metalenses in advanced optical imaging and nanophotonics.

physics.optics↗

arXiv2024

Enhanced third-harmonic generation and degenerate four-wave mixing in an all-dielectric metasurfaces via Brillouin zone folding-induced bound states in the continuum

Bound states in the continuum (BICs) exhibit significant electric field confinement capabilities and have recently been employed to enhance nonlinear optics response at the nanoscale. In this study, we achieve substantial enhancement of third-harmonic generation (THG) and degenerate four-wave mixing (dFWM) by implementing Brillouin zone folding-induced BICs (BZF-BICs) in an air-hole type nonlinear metasurface. By introducing gap perturbations within the metasurface, guided modes below the light line can be folded into the light cone, resulting in three resonant modes: guided resonances (GRs), $Γ$-BICs, and BZF-BICs. Through the eigenvalue analysis and multipole decompositions, we establish their excitation conditions. With their resonantly enhanced local field, we successfully boost both THG and dFWM under $x$- and $y$- polarizations within the same metasurfaces. The simulated results indicate that the BZF-BICs provide the most significant enhancement of third-order nonlinear optical responses, with the output power of THG to 10$^{-4}$ W and dFWM output power of 10$^{-2}$ W under a moderate input power density of 1 MW/cm$^{2}$. These findings demonstrate that the BZF-BICs can offer an effective pathway for chip-scale nonlinear optical applications.

physics.optics↗

arXiv2024

Giant enhancement of the transverse magneto-optical Kerr effect in etchless bismuth-substituted yttrium iron garnet empowered by quasi-bound states in the continuum

Here, we propose an etchless bismuth-substituted yttrium iron garnet layer assisted by a one-dimensional resonant grating waveguide to enhance transverse magneto-optical Kerr effect (TMOKE) via the excitation of quasi-bound state in the continuum. The TMOKE amplitude can be tailored by manipulating the perturbation parameter, and it can reach as high as 1.978, approaching the theoretical maximum value of 2. Additionally, a single-mode temporal coupled-mode theory is employed to further reveal the underlying physical mechanism. It is found that TMOKE is strongly related to the line width of the quasi-BIC resonance and local field enhancement, which are pivotal factors in the design and optimization of photonic devices. As a potential application, we design and numerically demonstrate a refractive index sensor based on the resonantly enhanced TMOKE, with the optimal sensitivity of 110.66 nm/RIU and the corresponding maximum figure of merit of 299.3 RIU$^{-1}$. Our work provides a simple and efficient approach for enhancing TMOKE based on an easy-to-fabricate platform, laying the groundwork for exploring and developing magneto-optical devices such as sensors, magnetic storage devices, and nonreciprocal photonic devices.

physics.optics↗

arXiv2024

Edge detection imaging by quasi-bound states in the continuum

Optical metasurfaces have revolutionized analog computing and image processing at sub-wavelength scales with faster speed and lower power consumption. They typically involve spatial differentiation with engineered angular dispersion. Quasi-bound states in the continuum (quasi-BICs) have recently emerged as a powerful tool for tailoring properties of optical resonances. While quasi-BICs have been explored in various applications that require high $Q$-factors and enhanced field confinement, their full potential in image processing remains unexplored. Here, we demonstrate edge detection imaging by leveraging a quasi-BIC in an all-dielectric metasurface. This metasurface, composed of four nanodisks per unit cell, supports a polarization-independent quasi-BIC through structural perturbations, allowing simultaneously engineering $Q$-factor and angular dispersion. Importantly, we find that with suitable parameters, this quasi-BIC metasurface can perform isotropic two-dimensional spatial differentiation, which is the core element for realizing edge detection. Following the theoretical design, we fabricate the metasurfaces on the silicon-on-insulator platform and experimentally validate their capability of high-quality, efficient, and uniform edge detection imaging under different incident polarizations. Our results illuminate the mechanisms of edge detection with quasi-BIC metasurfaces and highlight new opportunities for their application in ultra-compact, low-power optical computing devices.

physics.optics↗

arXiv2024

High-efficiency broadband achromatic metalens in the visible

The metalenses have been extensively studied for their compact and flexible characteristics in focusing and imaging applications. However, it remains a significant challenge to design a broadband achromatic metalens that maintains high efficiency under arbitrary polarization incidence. In this work, we design a broadband achromatic metalens that achieves polarization-independent, high-efficiency focusing by effectively utilizing both co-polarization and cross-polarization components of the transmitted light. Using a minimalist anisotropic nanofin library, we optimize the phase distribution of the metalens at each designed wavelength with the particle swarm algorithm. Numerical simulations demonstrate a stable focal length with a deviation of less than 4$\%$ and an average focusing efficiency of 80.5$\%$ in the visible wavelength range of 450 to 650 nm. Moreover, we design a multi-wavelength off-axis bi-focal metalens to demonstrate the flexible control of output light phase and dispersion achieved by this method. The generality of this design enables its implementation in various metasurface devices, accelerating applications in broadband imaging and virtual/augmented reality.

physics.optics↗

arXiv2024

Enhanced second harmonic generation in high-$Q$ all-dielectric metasurfaces with backward frequency conversion

Here we employ the quasi-bound state in the continuum (quasi-BIC) resonance in all-dielectric metasurfaces for efficient nonlinear processes in consideration of the backward frequency conversion. We theoretically study the second-harmonic generation (SHG) from symmetry-broken AlGaAs metasurfaces and reveal the efficiency enhancement empowered by high-$Q$ quasi-BIC resonances. By introducing the correction term of nonlinear polarization at the fundamental wave field to the conventional undepleted approximation, we uncover the effect of backward frequency conversion on the nonlinear conversation efficiency. The SHG efficiency as $2.45\times10^{-2}$ with the developed depleted model, shows a $14.3\%$ decrease compared with $2.86\times10^{-2}$ in conventional undepleted approximation, under the incident intensity of 10 MW/cm$^{2}$. Our results are of significant importance for designing efficient nonlinear metasurfaces supporting high-$Q$ resonances.

physics.optics↗

arXiv2024

Extremely intrinsic chirality in two-dimensional planar waveguide grating induced by quasi-bound states in the continuum

The strong chiral light-matter interaction is crucial for various important fields such as chiral optics, quantum optics, and biomedical optics, driving a quest for the extreme intrinsic chirality assisted by ultrahigh quality ($Q$-) factor resonances. In this quest, we propose a straightforward method to achieve extreme intrinsic chirality in lossless planar structures by manipulating the quasi-BIC through in-plane perturbation. The temporal coupled-mode theory is employed to derive the conditions necessary for achieving maximal intrinsic chirality. The quasi-BIC should be excited within the transparent spectral range of the structure and couple with $x$- and $y$-polarized waves with the same intensity but a phase difference of $π$/2. For an illustration, a planar chiral dielectric dimeric waveguide grating is designed that strong interacts with left circularly polarized (LCP) light while decouples from right circularly polarized (RCP) light through in-plane symmetry engineering. Furthermore, by adjusting the magnitude of the in-plane asymmetry, we can independently manipulate the $Q$-factors of the chiral quasi-BIC while maintaining nearly unity circular dichroism. Our results provide a simple yet powerful paradigm for achieving extreme intrinsic chirality on an easily manufacturable platform, which may have potential applications in chiral emission, chiral sensing, and enantiomer separation.

physics.optics↗

arXiv2024

Single-sized phase-change metasurfaces for dynamic information multiplexing and encryption

Optical metasurfaces empower us to manipulate the electromagnetic space and control light propagation at the nanoscale, offering a powerful tool to achieve modulation of light for information processing and storage. In this work, we propose a phase-change metasurface to realize dynamic multiplexing and encryption of near-field information. Based on the orientation degeneracy and polarization control governed by Malus's law, we elaborately design the orientation distribution of Sb$_2$S$_3$ meta-atoms with the same dimension to simultaneously satisfy the amplitude modulation requirements of different channels. Using the corresponding polarization control as decoding keys, three different nanoprinting images can be displayed, and these multiplexed images can be switched on and off by leveraging the reversible tunability of the Sb$_2$S$_3$ meta-atoms between the amorphous and crystalline states. With the unparalleled advantages of ultra-compactness, simple design strategy, high information density and security, the proposed metasurfaces afford promising prospects for high-end applications in ultracompact and intelligent dynamic display, high-dense optical data storage, optical information encryption, etc.

physics.optics↗

arXiv2024

Efficient photon-pair generation empowered by dual quasi-bound states in the continuum

Here we demonstrate the efficient photon-pair generation via spontaneous parametric down conversion from a semiconductor metasurface supporting dual quasi-bound states in the continuum (quasi-BICs). In a simple metasurface design composed of AlGaAs ellipse nano-cyclinders, the two high-$Q$ quasi-BIC resonances that coincide with the generated signal and idler frequencies significantly boost the local electric field. This leads to a substantial enhancement in the reverse classical nonlinear process of sum frequency generation and subsequently the remarkable high generation rate of photon pairs under the quantum-classical correspondence principle. Within a narrowband wavelength regime around the quasi-BIC resonances, the rate of pair production is enhanced up to $\sim10^{4}$ Hz, two orders of magnitude larger than that in the Mie resonant AlGaAs nanoantennas. Moreover, the photon pair emission is mainly concentrated in the normal direction with respect to the metasurface, and shows tunable rate with the $Q$ factor by engineering the rotation angle of nano-cylinders. The presented work enables nanoscale sources of high-quality entangled photons which will find applications in advanced quantum imaging and communications.

physics.optics↗

arXiv2023

Decision-making and control with diffractive optical networks

The ultimate goal of artificial intelligence is to mimic the human brain to perform decision-making and control directly from high-dimensional sensory input. Diffractive optical networks provide a promising solution for implementing artificial intelligence with high-speed and low-power consumption. Most of the reported diffractive optical networks focus on single or multiple tasks that do not involve environmental interaction, such as object recognition and image classification. In contrast, the networks capable of performing decision-making and control have not yet been developed to our knowledge. Here, we propose using deep reinforcement learning to implement diffractive optical networks that imitate human-level decision-making and control capability. Such networks taking advantage of a residual architecture, allow for finding optimal control policies through interaction with the environment and can be readily implemented with existing optical devices. The superior performance of these networks is verified by engaging three types of classic games, Tic-Tac-Toe, Super Mario Bros., and Car Racing. Finally, we present an experimental demonstration of playing Tic-Tac-Toe by leveraging diffractive optical networks based on a spatial light modulator. Our work represents a solid step forward in advancing diffractive optical networks, which promises a fundamental shift from the target-driven control of a pre-designed state for simple recognition or classification tasks to the high-level sensory capability of artificial intelligence. It may find exciting applications in autonomous driving, intelligent robots, and intelligent manufacturing.

cs.LG↗

arXiv2023

Phase-change nonlocal metasurfaces for dynamic wavefront manipulation

Recent advances in nonlocal metasurfaces have enabled unprecedented success in shaping the wavefront of light with spectral selectivity, offering new solutions for many emerging nanophotonics applications. The ability to tune both the spectral and spatial properties of such a novel class of metasurfaces is highly desirable, but the dynamic nonvolatile control remains elusive. Here, we demonstrate active narrowband wavefront manipulation by harnessing quasi-bound states in the continuum (quasi-BICs) in phase-change nonlocal metasurfaces. The proof-of-principle metasurfaces made of Sb$_2$S$_3$ allow for nonvolatile, reversible, and tunable spectral control over wavefront and switchable spatial response at a given wavelength. The design principle mainly builds upon the combination of the geometry phase of quasi-BICs and the dynamic tunability of phase-change meta-atoms to tailor the spatial response of light at distinct resonant wavelengths. By tuning the crystallization level of Sb$_2$S$_3$ meta-atoms, the dynamic nonlocal wavefront-shaping functionalities of beam steering, 1D, and 2D focusing are achieved. Furthermore, we demonstrate tunable holographic imaging with active spectral selectivity using our phase-change nonlocal metasurface. This work represents a critical advance towards developing integrated dynamic nonlocal metasurface for future augmented and virtual reality wearables.

physics.optics↗

arXiv2023

Enhanced sum-frequency generation from etchless lithium niobate empowered by dual quasi-bound states in the continuum

The miniaturization of nonlinear light sources is central to the integrated photonic platform, driving a quest for high-efficiency frequency generation and mixing at the nanoscale. In this quest, the high-quality ($Q$) resonant dielectric nanostructures hold great promise, as they enhance nonlinear effects through the resonantly local electromagnetic fields overlapping the chosen nonlinear materials. Here, we propose a method for the enhanced sum-frequency generation (SFG) from etcheless lithium niobate (LiNbO$_{3}$) by utilizing the dual quasi-bound states in the continuum (quasi-BICs) in a one-dimensional resonant grating waveguide structure. Two high-$Q$ guided mode resonances corresponding to the dual quasi-BICs are respectively excited by two near-infrared input beams, generating a strong visible SFG signal with a remarkably high conversion efficiency of $3.66\times10^{-2}$ (five orders of magnitude higher than that of LiNbO$_{3}$ films of the same thickness) and a small full-width at half-maximum less than 0.2 nm. The SFG efficiency can be tuned via adjusting the grating geometry parameter or choosing the input beam polarization combination. Furthermore, the generated SFG signal can be maintained at a fixed wavelength without the appreciable loss of efficiency by selectively exciting the angle-dependent quasi-BICs, even if the wavelengths of input beams are tuned within a broad spectral range. Our results provide a simple but robust paradigm of high-efficiency frequency conversion on an easy-fabricated platform, which may find applications in nonlinear light sources and quantum photonics.

physics.optics↗

arXiv2023

Enhancing Faraday and Kerr rotations based on toroidal dipole mode in an all-dielectric magneto-optical metasurface

The magneto-optical Faraday and Kerr effects are widely used in modern optical devices. In this letter, we propose an all-dielectric metasurface composed of perforated magneto-optical thin films, which can support the highly confined toroidal dipole resonance and provide full overlap between the localized electromagnetic field and the thin film, and consequently enhance the magneto-optical effects to an unprecedented degree. The numerical results based on finite element method show that the Faraday and Kerr rotations can reach -13.59$°$ and 8.19$°$ in the vicinity of toroidal dipole resonance, which are 21.2 and 32.8 times stronger than those in the equivalent thickness of thin films, respectively. In addition, we design an environment refractive index sensor based on the resonantly enhanced Faraday and Kerr rotations, with sensitivities of 62.96 nm/RIU and 73.16 nm/RIU, and the corresponding maximum figures of merit 132.22$°$/RIU and 429.45$°$/RIU, respectively. This work provides a new strategy for enhancing the magneto-optical effects at nanoscale, and paves the way for the research and development of magneto-optical metadevices such as sensors, memories, and circuits.

physics.optics↗

arXiv2023

High-efficiency optical frequency mixing in an all-dielectric metasurface enabled by multiple bound states in the continuum

We present nonlinear optical four-wave mixing in a silicon nanodisk dimer metasurface. Under the oblique incident plane waves, the designed metasurface exhibits a multi-resonant feature with simultaneous excitations of three quasi-bound states in the continuum (BIC). Through employing these quasi-BICs with maximizing electric field energy at the input bump wavelengths, significant enhancement of third-order nonlinear processes including third-harmonic generation, degenerate and non-degenerate four-wave mixing are demonstrated, giving rise to ten new frequencies in the visible wavelengths. This work may lead to a new frontier of ultracompact optical mixer for applications in optical circuitry, ultrasensitive sensing, and quantum nanophotonics.

physics.optics↗