Search Results (149)

In classic all-dielectric one-dimensional photonic crystals, transparent bands exhibit strong angular dispersion. Herein, we realize an angle-dispersion-free near-infrared transparent band in a one-dimensional photonic hypercrystal containing hyperbola-dispersion metamaterials. As the incident angle increases from 0° to 80°, the relative shifts of the wavelengths of four transmittance peaks within the transparent band are smaller than 1.5% and the bandwidth of the transparent band marginally fluctuates from 1098.2 to 1132.5 nm. Particularly, the angle-dispersion-free property of the transparent band is quite robust with respect to the layer thickness disturbance. Our work not only offers a viable method of achieving angle-dispersion-free transparent bands but also facilitates the development of transparency-based optical devices. Full article

Enhancing light absorption in two-dimensional (2D) materials, particularly few-layer structures, is critical for advancing optoelectronic devices such as light sources, photodetectors, and sensors. However, conventional absorption enhancement strategies often suffer from unstable resonant wavelengths and low-quality factors (Q-factors) due to the inherent weak light–matter interactions in 2D materials. To address these limitations, we propose an all-dielectric metasurface graphene-perfect absorber based on toroidal dipole bound state in the continuum (TD-BIC) with an ultra-narrow bandwidth and stable resonant wavelength. The proposed structure achieves tunable absorption linewidths spanning three orders of magnitude (6 nm to 0.0076 nm) through critical coupling modulation. Furthermore, the operational wavelength can be flexibly extended to any near-infrared region by adjusting the grating width. This work establishes a novel paradigm for enhancing the absorption of 2D materials in photonic device applications. Full article

Tunneling modes in all-dielectric one-dimensional photonic crystals can be utilized for multi-channel filtering. However, these tunneling modes generally blue shift upon increasing the incident angle. When hyperbolic metamaterials are introduced into one-dimensional photonic crystals, the competition between the propagation phase shifts in the dielectric materials and hyperbolic metamaterials can result in different angle dependencies, including blue shift, abnormal zero shift, and abnormal red shift. When the reduction in the propagation phase in the dielectric layer exceeds the increment in the propagation phase in the hyperbolic metamaterial, the tunneling modes are blue-shifted; conversely, when the phase increment in the hyperbolic metamaterial exceeds the phase reduction in the dielectric layer, the tunneling modes are abnormally red-shifted. When the phase changes in the two materials are the same, the tunneling modes are angle independent. In this study, we investigated the multiple filtering effects of one-dimensional photonic structures composed of hyperbolic metamaterials. These composed structures exhibited multiple tunneling modes based on one-, two-, or three-angle dependencies and can be applied in novel optical devices with different angle-dependence requirements. Full article

Infrared imaging has gained considerable attention across diverse fields, including security, surveillance, and environmental monitoring. The need to minimize size, weight, power, and cost (SWaP-C) poses challenges for conventional optical systems like refractive lenses. Metalenses with subwavelength surface patterns have emerged as promising solutions to address these limitations. This review provides a comprehensive analysis of all-dielectric metalenses for long-wavelength infrared (LWIR) imaging applications, a critical spectral region for human detection and analytical applications (such as gas analysis). We examine the limitations of conventional infrared (IR) lens materials and highlight the performance advantages of LWIR metalenses. Key design principles, including chromatic and achromatic lens configurations, are discussed alongside their imaging performance. Additionally, we review advanced functionalities such as polarization control, multifocal capabilities, zoom, and reconfigurability. Theoretical performance limits and trade-offs are analyzed to provide insights into design optimization. We identify future challenges related to advanced design methods and fabrication techniques. LWIR metalenses can be expected to overcome the shortcomings of conventional LWIR lenses owing to meta-optics technologies, to achieve SWaP-C and advanced functionalities that cannot be achieved by conventional LWIR lenses. This review will guide researchers in academia and industry to develop LWIR metalenses to advance IR imaging technologies. Full article

Terahertz (THz) biosensing faces critical challenges in balancing high sensitivity and broadband spectral coverage, particularly under miniaturized device constraints. Conventional quasi-bound states in the continuum (QBIC) metasurfaces achieve high quality factor (Q) but suffer from narrow bandwidth, while angle-scanning strategies for broadband detection require complex large-angle illumination. Here, we propose a symmetry-engineered, all-dielectric metasurface that leverages multipolar interference coupling to overcome this limitation. By introducing angular perturbation, the metasurface transforms the original magnetic dipole (MD)-dominated QBIC resonance into hybridized, multipolar modes. It arises from the interference coupling between MD, toroidal dipole (TD), and magnetic quadrupole (MQ). This mechanism induces dual counter-directional, frequency-shifted, resonance branches within angular variations below 16°, achieving simultaneous 0.42 THz broadband coverage and high Q of 499. Furthermore, a derived analytical model based on Maxwell equations and mode coupling theory rigorously validates the linear relationship between frequency splitting interval and incident angle with the Relative Root Mean Square Error (RRMSE) of 1.4% and the coefficient of determination ($R^2$) of 0.99. This work establishes a paradigm for miniaturized THz biosensors, advancing applications in practical molecular diagnostics and multi-analyte screening. Full article

Optical sensing technologies, particularly refractive index and temperature sensing, are pivotal in biomedical, environmental, and industrial applications. This study introduces a dual-parameter all-dielectric transmissive grating sensor leveraging symmetry-protected bound states in the continuum (BICs). A one-dimensional silicon grating on a silica substrate was designed and analyzed using finite element analysis software. The proposed grating structure enables the excitation of two distinct BICs, both exhibiting high quality factors (Q-factors) of $Q_{\mathrm{I}}=8.03\times {10}^4$ for Mode I and $Q_{\mathrm{I}\mathrm{I}}=4.48\times {10}^4$ for Mode II. These modes demonstrate significantly different sensing characteristics due to their unique field distributions: Mode I predominantly confines its electromagnetic field within the grating slits, achieving an outstanding refractive index (RI) sensitivity of ${S_{\mathrm{R}\mathrm{I}}}^{\mathrm{I}}=406 \mathrm{n}\mathrm{m}/\mathrm{R}\mathrm{I}\mathrm{U}$ with a minor thermal sensitivity of ${S_{\mathrm{T}}}^{\mathrm{I}}=0.052 \mathrm{n}\mathrm{m}/°\mathrm{C}$. In contrast, Mode II concentrates its field energy in the silicon substrate, resulting in enhanced thermal sensitivity of ${S_{\mathrm{T}}}^{\mathrm{I}\mathrm{I}}=0.078 \mathrm{n}\mathrm{m}/°\mathrm{C}$ while maintaining a refractive index sensitivity of ${S_{\mathrm{R}\mathrm{I}}}^{\mathrm{I}\mathrm{I}}=220 \mathrm{n}\mathrm{m}/\mathrm{R}\mathrm{I}\mathrm{U}$. This complementary sensitivity profile between the two modes establishes an ideal platform for developing a dual-parameter sensing system capable of simultaneously monitoring both refractive index variations and temperature changes. These results highlight the correlation between mode field distribution characteristics and sensing sensitivity performance, and enabling high Q-factor dual-parameter sensing with potential applications in lab-on-a-chip systems and real-time biomolecular monitoring. Full article

Accurate real-time temperature measurement under extreme thermal-pressure conditions remains challenging in aerospace. Sapphire fiber Bragg gratings (FBGs), exhibiting temperature measurement capabilities up to 1900 °C, demonstrate suitability for such extreme environments. However, the development of a high-performance demodulation system capable of processing sapphire FBG signals over wide spectral ranges at elevated speeds remains a technical challenge. This study presents a real-time FBG signal demodulation system that incorporates an all-dielectric subwavelength grating edge filter. The designed grating, comprising a TiO₂/Si₃N₄ subwavelength unit array, modulates Mie-type electric and magnetic multipole resonances to achieve precisely tailored transmission and reflection spectra. Simulation results indicate that the grating exhibits low ohmic loss, excellent linearity, complementary transmission/reflection characteristics, a wide linear range, and angular-dependent tunability. The designed edge-filter-based demodulation system incorporates dual single-point detectors to simultaneously monitor the transmitted and reflected signals. Leveraging the functional relationship between the center wavelength of the FBG and the detected signals, this system enables high-speed, wide-range interrogation of the center wavelength, thus facilitating real-time demodulation for wide-range temperature sensing. The proposed method and system are validated through theoretical modeling, offering an innovative approach for sapphire FBG signal demodulation under extreme thermal-pressure conditions. Full article

Electromagnetically induced transparency based on bound states in the continuum (EIT-BIC) has emerged as a significant research focus in photonics due to its exceptionally high quality factor (Q-factor). This study investigates a periodic dielectric metasurface composed of silicon bar–square ring resonators, with a comparative analysis of both monolayer and bilayer configurations. Through systematic examination of transmission spectra, electric field distributions, and Q-factors, we have identified the existence of EIT-BIC and quasi-BIC phenomena in these structures. The experimental results demonstrate distinct characteristics between monolayer and bilayer systems. In the monolayer configuration, a single BIC is observed in the low-frequency region, with its quasi-BIC state generating an EIT window. In contrast, the bilayer structure exhibits dual BICs and dual EIT phenomena in the same spectral range, demonstrating enhanced spectral modulation capabilities. Notably, in the high-frequency region, both configurations maintain a single BIC, with the number remaining independent of structural layer count. The number and spectral positions of BICs can be effectively modulated through variations in incident angle and structural symmetry. In particular, the bilayer configuration demonstrates superior modulation characteristics under oblique incidence conditions, where the quasi-BIC linewidth broadens with increasing incident angle, forming a broader high-Q transparency window. This comparative study between monolayer and bilayer systems not only elucidates the influence of structural layers on BIC characteristics but also provides new insights for flexible spectral control. These findings hold significant implications for artificial linear modulation and play a crucial role in the design of future ultra-high-sensitivity sensors, particularly in optimizing performance through structural layer engineering. Full article

The use of bound states in the continuum (BICs) has emerged as an effective tool to trap light at the nanoscale and has many potential applications in photonics. Breaking the structural symmetry is regarded as an effective way to excite quasi-BICs (QBICs) and generate high-Q resonances. However, this approach may impact the resonance polarization sensitivity, consequently limiting its practicality in multi-wavelength polarization-dependent applications. Furthermore, the introduction of different types of structural perturbations into the design to form BICs has yet to be explored in depth. In this study, we present an optical sensor consisting of an L-shaped metasurface that supports three quasi-BIC modes in the terahertz band, where specific displacements, collective perturbations, or both occur. Furthermore, we analyze the field distributions in detail and combine them with multipolar decomposition to reveal the underlying mechanisms of the different resonant modes. Multiple asymmetric perturbations are found to affect the sensitivity of the metasurface in refractive index sensing, thus allowing for a comparison of different resonant modes. The quasi-BIC mode can attain a Q-factor of 1067.6, a sensitivity (S) of 300 GHz/RIU, and a figure of merit (FOM) of 5367.8 RIU⁻¹ for vertical light incidence. These three quasi-BIC modes are polarization-independent, and their properties are maintained even for circularly polarized light. The results reveal a novel design strategy for metasurface-based sensors with promising application potential in biosensing, filtering, and lasers. Full article

In this article, a chip-fed millimeter-wave high-gain antenna system with in-antenna power combining capability is presented. A low-profile resonant cavity antenna (RCA) array is fed by multiple spherical dielectric resonators (DRs), demonstrating its multi-feed capabilities. Each of the DRs is fed by two microstrip resonators on a planar circuit board. A printed superstrate is used in the proposed RCA as the partially reflecting superstrate (PRS), which makes the antenna profile small. To increase the directivity and gain, a 2 × 2 RCA array is developed. The demonstrated design shows a prominent peak gain of 25.03 dBi, a radiation efficiency of more than 80% and 3.38 GHz 3 db gain-bandwidth while maintaining a low profile. To steer the beam of the demonstrated 2 × 2 RCA array in a wide angular range with a low side-lobe-level, two planar all-dielectric passive beam steering metasurfaces have been designed and optimized. A detailed analysis of the optimization procedure is presented in this article. This numerical investigation is vitally important for realizing beam steering metasurfaces with suppressed side-lobe-level, wide bandwidth, excellent efficiency and less complexity. Full article

Terahertz (THz) spectroscopy, an advanced label-free sensing method, offers significant potential for biomolecular detection and quantitative analysis in biological samples. Although broadband fingerprint enhancement compensates for limitations in detection capability and sensitivity, the complex optical path design in operation restricts its broader adoption. This paper proposes a multi-degree-of-freedom stretchable metasurface that supports magnetic dipole resonance to enhance the broadband THz fingerprint detection of trace analytes. The metasurface substrate and unit cell structures are constructed using polydimethylsiloxane. By adjusting the sensor’s geometric dimensions or varying the incident angle within a narrow range, the practical optical path is significantly simplified. Simultaneously, the resonance frequency of the transmission curve is tuned, achieving high sensitivity for effectively detecting cinnamoylglycine. The results demonstrate that the metasurface achieves a high-quality factor of 770.6 and an excellent figure of merit of 777.2, significantly enhancing the THz sensing capability. Consequently, the detection sensitivity for cinnamoylglycine can reach 24.6 µg·cm⁻². This study offers critical foundations for applying THz technology to biomedical fields, particularly detecting urinary biomarkers for diseases like gestational diabetes. Full article

The computer-assisted inverse design of photonic computing, especially by leveraging artificial intelligence algorithms, offers great convenience to accelerate the speed of development and improve calculation accuracy. However, traditional thickness-based modulation methods are hindered by large volume and difficult fabrication process, making it hard to meet the data-driven requirements of flexible light modulation. Here, we propose a diffractive deep neural network (D²NN) framework based on a three-layer all-dielectric phased transmitarray as hidden layers, which can perform the classification of handwritten digits. By tailoring the radius of a silicon nanodisk of a meta-atom, the metasurface can realize the phase profile calculated by D²NN and maintain a relative high transmittance of 0.9 at a wavelength of 600 nm. The designed image classifier consists of three layers of phase-only metasurfaces, each of which contains 1024 units, mimicking a fully connected neural network through the diffraction of light fields. The classification task of handwriting digits from the ‘0’ to ‘5’ dataset is verified, with an accuracy of over 90% on the blind test dataset, as well as demonstrated by the full-wave simulation. Furthermore, the performance of the more complex animal image classification task is also validated by increasing the number of neurons to enhance the connectivity of the neural network. This study may provide a possible solution for practical applications such as biomedical detection, image processing, and machine vision based on all-optical computing. Full article

Metasurfaces composed of silicon nanogap units have a variety of optical resonances, including bound states in the continuum (BIC). We show comprehensive numerical results on metasurfaces of Si-nanogap units, analyze the optical resonances, and clarify optically prominent resonances as well as symmetry-forbidding resonances that are the BIC, based on the numerical analyses of optical spectra and resonant electromagnetic field distributions. Introducing asymmetry in the unit cell, the BIC become optically allowed, being identified as magnetic dipole, electric quadrupole, and magnetic quadrupole resonances. Moreover, the optical resonances are examined in terms of refractive index sensing performance. A pair of the resonances associated with electric field localization at the nanogap was found to be sensitive to the refractive index in contact with the metasurfaces. Consequently, the gap mode resonances are shown to be suitable for a wide range of refractive index sensing over 1.0–2.0. Full article

Zero-index materials, characterized by near-zero permittivity and/or permeability, represent a distinctive class of materials that exhibit a range of novel physical phenomena and have potential for various advanced applications. However, conventional zero-index materials are often hindered by constraints such as narrow bandwidth and significant material loss at high frequencies. Here, we numerically demonstrate a scheme for realizing low-loss all-dielectric dual-band anisotropic zero-index materials utilizing three-dimensional terahertz silicon photonic crystals. The designed silicon photonic crystal supports dual semi-Dirac cones with linear-parabolic dispersions at two distinct frequencies, functioning as an effective double-zero material along two specific propagation directions and as an impedance-mismatched single-zero material along the orthogonal direction at the two frequencies. Highly anisotropic wave transport properties arising from the unique dispersion and extreme anisotropy are further demonstrated. Our findings not only show a novel methodology for achieving low-loss zero-index materials with expanded operational frequencies but also open up promising avenues for advanced electromagnetic wave manipulation. Full article

All-dielectric metasurfaces offer a low-loss alternative to plasmonic metasurfaces. We proposed the configuration for high-reflectivity all-dielectric metasurfaces based on single-crystal diamond (SCD) resonators on fused silica substrate and conducted simulations to optimize and analyze such a configuration via the FDTD solver. We utilized GMR as the design principle to select the configuration and the substrate material, and analyzed the scattering properties of a single SCD resonator by multipole decomposition. Then, we demonstrated that both the cylindrical resonators in square lattice and frustum-shaped resonators in hexagonal lattice can achieve near-unity reflectivity (>99.99%) and ultra-low absorption (<0.001%) at 795 nm, the typical alkali-metal laser wavelength. Additionally, we demonstrated that such a design is quite tolerant of fabrication errors and further supports its potential for realistic applications. To expand the functionality of such devices across multiple wavelengths, dual-band high-reflectivity metasurfaces at 744 nm and 828 nm were also designed. Our work is quite useful for designing diamond-based highly reflective mirrors, paving the way for low-loss all-dielectric reflective metasurfaces in high-power laser applications. Full article