Efficient electromagnetic absorption is essential for optical modulation and integrated photonic devices and can be significantly enhanced by interference-assisted resonant nanostructures. Here, we propose a borophene-dielectric nanostructure operating at telecommunication wavelengths to realize tunable coherent perfect absorption (CPA). The structure supports guided-mode resonances (GMRs), which generate strong near-field enhancement near the borophene layer and promote efficient light-matter interaction. Under single-port excitation, resonance-enhanced absorption with directional asymmetry is observed, yielding peak absorption of 42.5% and 57.4% for opposite incidence directions. Under dual-port coherent excitation, CPA with a narrow bandwidth of 0.82 nm occurs at 1549.8 nm when the scattering matrix satisfies the zero-determinant condition. At the CPA wavelength, the absorption can be continuously tuned from below 10% to above 99.9% by adjusting the phase difference between the two incident beams. Electrical tuning of the borophene carrier concentration further enables a resonance shift of 12.4 nm while maintaining absorption above 95%, nearly fifteen times larger than the intrinsic CPA resonance linewidth. Structural asymmetry further leads to unequal external coupling strengths, enabling asymmetric interferometric light-light control under unequal-intensity excitation. These results demonstrate a compact platform for phase-controlled absorption and coherent optical switching in integrated photonic systems.

Dielectric gratings with guided mode resonance (GMR) are integral to narrow-band filtering due to their high resonances, enhancing optical metrics like diffraction efficiency and sensitivity. Recent advancements have introduced polarization-sensitive GMR filters, enabling selective control of TE and TM mode resonances based on polarization. This work presents theoretical and experimental studies on a green filter using polarization-sensitive GMR gratings. These devices are pivotal in applications such as telecommunications, spectroscopy, and imaging. We demonstrate the fabrication of TiO2-coated one-dimensional (1D) GMR gratings with polarizing resonance characteristics at normal incidence. A trapezoidal-profile grating, created via holographic lithography, achieves excellent polarization filtering for green light. Additionally, TiO2-coated photoresist (PR) gratings on SiO2 substrates are fabricated using magnetron sputtering, showcasing high performance and potential for cost-effective mass production. Nanoimprinting these gratings provides a scalable, economical method for producing reproducible GMR filters.Supplementary InformationThe online version contains supplementary material available at 10.1186/s11671-026-04699-z.

Hybrid organic-inorganic metal halides have emerged as versatile materials for optoelectronics due to their outstanding optical properties and solution processability. Among these, chiral bismuth halides combine strong second-order nonlinear susceptibility with improved stability and reduced toxicity, making them attractive for nonlinear nanophotonics. However, efficient second-harmonic generation (SHG) in thin films is limited by weak light-matter interaction. Here, we overcome this limitation by integrating a chiral bismuth iodide (R-MBA)BiI4 with a nonlocal metasurface supporting guided mode resonances in visible and infrared ranges. The metasurface is directly fabricated using a versatile and scalable femtosecond laser ablation technique. We demonstrate that the resonant metasurface enhances SHG in comparison to the unpatterned film. This work establishes a new platform for efficient nonlinear photonic devices based on solution-processed nontoxic and cost-efficient materials.

Infrared detectors are essential for military and civilian applications, yet high-performance mid-infrared (MIR) detection still predominantly relies on cryogenically cooled narrow-bandgap semiconductors, which severely limits portability and scalability, particularly for imaging applications. Although PbSe enables room-temperature operation and is fully compatible with silicon-based processing, the thin-film PbSe active layer suffers from insufficient optical absorption, which fundamentally constrains its achievable performance. Here, we propose and experimentally demonstrate a metasurface-integrated PbSe active layer that overcomes this bottleneck by engineering multi-modal hybridization to realize broadband, high-efficiency light trapping. The metasurface supercell simultaneously excites gap-surface plasmon (GSP), Fabry-Pérot (FP) cavity modes, localized surface plasmon (LSP), magnetic dipole (MD), and guided-mode resonance (GMR), forming a continuous coupled modal landscape that yields a ∼4.5-fold enhancement in PbSe-layer absorption over a bandwidth exceeding 2.5 μm and peak absorption in the PbSe layer approaching 90%. The device further exhibits polarization-insensitive performance (<1% variation from 0-360°) and angular robustness up to 15° incidence. Importantly, strong enhancement persists in compact pixels comprising only a 2×2 metasurface unit-cell footprint (∼9.2 μm), confirming pixel-level scalability compatible with realistic MIR FPAs. These results establish multi-modal metasurface hybridization as a powerful route to overcome fundamental absorption limitations in PbSe films and open a promising pathway toward next-generation high-performance uncooled MIR imaging systems.

This work proposes a gap-opening double-elliptical cylinder metamaterial that achieves dual polarization multi-resonance mode synergistic excitation by introducing out-of-plane symmetric breaking. Under TE polarization, an exceptionally high Q-factor (4.27 × 105) of quasi-BIC (Mode 1) is realized, with excellent sensing sensitivity of 750 GHz/RIU, whereas two different quasi-BIC modes (called Mode 2 and Mode 3) are gained under TM polarization. In particular, the near-field coupling of Mode 2 and guided-mode resonance (GMR) gives rise to an electromagnetically induced transparency (EIT), whose performance could be flexibly controlled by precisely tuning the structural asymmetry and other relevant parameters, thereby offering versatile spectral tunability. Multipole decomposition and near-field analysis reveal the formation mechanisms of dual-polarization multi-resonance modes. Our results could have application prospects in fields such as beamforming and biomedical sensing.

This study investigated exciton-photon coupling in monolayer MoS2integrated with a nanocorrugated SiN dielectric cavity, which supports tunable guided-mode resonances near a quasi-bound state in the continuum. The cavity exhibited a high quality-factor (Q-factor) of up to 6300 and near-field enhancement of approximately 220-2. By engineering the SiN thickness and corrugation geometry, the cavity resonance was tuned across the MoS2A-exciton, enabling a transition from weak-coupling regime to a pronounced polaritonic regime, as indicated by the emergence of two strong transmission dips. Full-wave finite-element simulations combined with Lorentz oscillator dispersion modeling revealed clear anti-crossing behavior and narrow spectral features with a highQ-factor of approximately 340. Depending on the corrugation amplitude, a Rabi splitting of approximately 27 meV was achieved in conjunction with high-Qpolariton modes, confirming a strong coupling regime. Furthermore, the curvature-induced strain introduced an additional tuning mechanism by modulating the exciton energy and detuning, thereby enabling controllable polariton dispersion while maintaining robust coupling strength. Results revealed that a nanocorrugated dielectric cavity with a facile configuration can serve as a scalable platform for strong light-matter interactions in two-dimensional materials and for designing high-Qexciton-polariton quantum devices.

We investigate the laser induced damage threshold (LIDT) of a sapphire-substrate-based resonant waveguide grating (RWG) at a pulse duration of 500 fs and a wavelength of 1 µm. The RWG structure consists of a single-layer waveguide of Tantalum Pentoxide (Ta2O5)deposited on a micro-structured c-cut sapphire (α - Al2O3) substrate. The study examines the influence of the spectrum and the polarization of the laser pulses on the resistance of the RWG on laser-induced damage. The measurements were conducted at an angle of incidence of 10.8°, where TE-polarized radiation experiences a guided-mode resonance, while for TM polarized radiation it corresponds to an off-resonance condition. At the resonance, the LIDT for single-shot test was measured to be (101.5 ± 9) mJ⁄cm2, whereas off-resonance, the LIDT was measured to be (580 ± 52) mJ⁄cm2. Moreover, a comprehensive and simple model, supported by numerical simulations of the electric-field distribution within the RWG, is proposed to interpret the measured LIDT values. The close agreement observed between experimental and simulation results confirms the reliability of the proposed model and demonstrates its capability to predict the LIDT of RWG with a relatively good accuracy. To the best our knowledge, this is the first study highlighting the effect of the energy spectral density of sub-picosecond laser pulses on the analysis and interpretation of LIDT measurements, particularly related to resonant optical components.

Angle sensitivity to incident light remains a fundamental limitation in conventional Fabry-Pérot (F-P) and guided-mode resonance (GMR) filters due to the angular dependence of the transverse wave vector. In this work, we propose a compact planar notch filter based on localized guided-mode resonance (LGMR) by embedding a metallic grating within a tri-layer SiO2-Si-SiO2 structure. The design achieves three-dimensional (3D) confinement of the transverse wave vector, effectively suppressing angular dispersion and stabilizing the resonance condition. Numerical simulations based on the finite-difference time-domain (FDTD) method demonstrate a flat stop band near 1.55 µm with a minimal wavelength shift of only 7.4 nm over a broad angular range of 0°-70°. Spectral tunability in the near-infrared (NIR) region is realized through controlled adjustment of the grating period. The proposed LGMR notch filter provides a robust and integrable solution for angle-insensitive spectral filtering in applications such as Raman spectroscopy and optical communication.

Efficient operations of hot-electron photodetectors (HE PDs) require strong energy depositions in metals assisted by device-dependent optical resonances whose spectral properties are fundamental to electrical performances, particularly with the linewidths of responsivity spectra. However, ultra-narrowband HE PDs based on thin, planar structures remain scarce due to the difficulty of achieving sufficiently narrow resonance linewidths. Here, we propose a design of HE PDs that exhibits ultra-narrowband photoelectric conversions through Friedrich-Wintgen bound states in the continuum (BIC). Optical studies based on modal analysis reveal that the phase reversal of the guided mode resonance enable the HE PD support dual Friedrich-Wintgen BICs, arising from the coupling between optical Tamm states and guided mode resonance. Probability-based electrical calculations show that, when suitable structural parameters are chosen for quasi-BIC excitations, the designed device exhibits high absorption efficiencies (> 0.97) and enhanced responsivities (> 1 mA/W), together with ultra-narrowband responsivity spectra with extremely small linewidths (∼ 1 nm). Furthermore, the analysis on external and internal quantum efficiencies indicates that the role of BIC excitations is primarily associated with optical responses. The proposed BIC-assisted HE PDs are expected to open the pathway for highly selective photoelectric conversion.

Abstract The high-order diffraction of the high-order surface grating laser leads to large radiation loss and low output power. The optical bound state in the continuum (BIC) has been proved to be a novel tool to suppress cavity radiative loss and increase quality factor. Here, by adjusting the surface grating parameters to realize the destructive interference between high-order guide mode resonances, we construct high-band quasi-BIC in the electrically pumped edge-emitting laser. Distinguished from previous wavelength-scale BIC structures, our laser with multiwavelength-scale microsturctures reduces process complexity while mitigating out-of-plane radiative loss. Compared with the conventional 20th-order and 24th-order grating lasers prepared on the same epiwafer, the BIC laser has lower threshold current, higher output power, better side mode suppression ratio and narrower intrinsic linewidth.

To effectively address the passivity and field distribution limitations inherent in conventional refractive index (RI) sensors, we present an active laser sensor that employs a single-layer guided-mode resonance (GMR) grating with slant ridges, which simultaneously functions as both an optical cavity and a gain layer. Specifically, by leveraging slant ridges, a quasi-bound state in the continuum is excited, which destructively interferes with the inherent GMR mode featuring a broadband spectrum, resulting in a transmissive resonance mode. By exploiting its unique field distribution concentrated within the gap regions and aligning its resonance wavelength with the gain medium, our design achieves active, high-performance sensing. This work presents a promising approach for RI sensing in compact systems, such as the end facet of an optical fiber, demonstrating a pathway for high-precision and integrated laser sensor applications.

Nonlocal metasurfaces extend the capabilities of flat optics by exploiting collective, spatially extended electromagnetic modes that enable momentum-dependent control of light within an ultrathin platform. When combined with electrical tunability, such metasurfaces move beyond static wavefront shaping toward dynamic, programmable manipulation of optical fields. In this Focus Article, we review recent advances in electrically controlled nonlocal metasurfaces, highlighting the physical mechanisms that underpin nonlocal responses, including coupled-resonator networks, guided-mode resonances, and surface lattice resonances. We discuss how electrical control based on carrier modulation, phase-change materials, and electro-optic effects enables dynamic tuning of phase, amplitude, and wavevector, and how resonant nonlocal architectures enhance otherwise weak modulation strengths. Finally, we examine emerging spatiotemporal nonlocal metasurfaces that combine collective momentum-dependent responses with ultrafast electrical modulation, enabling frequency-momentum conversion, adaptive wave-based signal processing, and nonreciprocal optical functionalities. Together, these developments point toward a new generation of reconfigurable, ultrathin photonic systems that compress complex optical operations into a single electrically programmable interface.

Fabrication of cross-scaled ultrasensitive surface-enhanced Raman scattering (SERS) substrates ranging from nanogaps for efficient localized surface plasmon resonances (LSPRs) to mm2-size for easy operation is challenging. Here, we propose femtosecond-laser-induced periodic phase-transition (fs-LIPPT) of 1T'-MoTe2 nanograting template, inducing Au nanostructures for frequency-shift digital-SERS immunoassay. The interference between the incident transverse electric wave and propagation wave in the 2H-MoTe2/SiO2-interlayer waveguide triggers the highly homogeneous periodic 1T' phase-transition pattern. The Au nanoparticles (AuNPs) are subsequently reduced at the 1T' regions in chloroauric acid solution, forming a subwavelength AuNPs@1T'-MoTe2 nanograting with 295.0 ± 8.1nm in period. The Fano resonances by coupling the narrow-band guided-mode resonances supported in the 1T'-MoTe2/SiO2-interlayer nanograting with the broadband LSPRs in AuNPs promote optical localization, achieving the superior performance with a limit of detection in 10-14m and a SERS performance factor of 7.5 × 106 for rhodamine 6G (R6G). A paradigm of frequency-shift digital-SERS immunoassay for serological diagnosis is established using the R6G-labeled AuNPs@1T'-MoTe2 nanograting conjugated with immunoglobulin G of rheumatoid arthritis, by which the discrimination accuracy is unexpectedly close to unity. The present work provides a novel protocol for SERS serum immunoassay, opening opportunities for early diagnosis and accurate prognosis of autoimmune diseases by blood test in the future.

Abstract Liquid biopsy has stimulated strong interest in label-free photonic biosensors capable of detecting low-abundance biomarkers with high stability and reproducibility. Among emerging approaches, topological photonics offers intrinsic robustness against fabrication disorder and environmental perturbations. In this paper, we present a proof-of-concept near-infrared biosensing platform based on a Jackiw–Rebbi (JR) interface state supported by a guided-mode resonance (GMR) metasurface. The proposed structure demonstrates the existence of a topologically induced resonant mode exhibiting a high-quality factor and a clear refractometric response under transverse-magnetic excitation. Numerical simulations confirm a measurable bulk and surface sensitivity in a biofunctionalized configuration targeting IgG proteins. While the analysis is intentionally limited to a single polarization and operating condition, the results validate the feasibility of JR-based metasurfaces as a promising foundation for robust photonic biosensing platforms.

Photonic quasi-bound states in the continuum (quasi-BICs) offer a promising route to achieving high-quality (Q) factors, yet their performance is often critically sensitive to structural variations, making them vulnerable to fabrication imperfections and limiting their practical applications. Here, we address this issue by proposing a strategy based on doping additional cylindrical dielectric couplers into metasurface. By strategically repositioning two of the smaller couplers while keeping the larger ones fixed, we create a perturbation that excites a guided-mode resonance with an exceptionally high Q-factor. Consequently, the achieved Q-factor is three orders of magnitude higher than that obtained through conventional symmetry-perturbation methods. Our design provides an effective solution to the severe performance degradation caused by fabrication defects in traditional symmetry-breaking metasurfaces, establishing a new pathway toward practically reliable high-Q resonances that are resilient to manufacturing tolerances in both classical and quantum photonic platforms.

Dual-band independently tunable graphene absorber based on guided-mode resonance gratings

Fluorescence enhancement lies at the heart of many optical biosensing and diagnostic technologies, yet most photonic approaches still rely on intrinsically bright emitters or fabrication-intensive nanoresonators. Here, we introduce an unconventional strategy that turns a nominally "weak" photonic mode into a powerful resource. Through simple, frugal interface engineering, we show that leaky guided-mode resonances (GMRs), often regarded as optical loss channels, can be harnessed to amplify the excitation of two orthogonally polarized bound states in the continuum (BICs) within a one-dimensional photonic crystal. This synergistic interaction enables deterministic control of quantum dot (QD) photoluminescence, yielding wavelength-specific emission enhancement up to 691× for semiconductor QDs and 206× for biomass-derived carbon QDs, while achieving degrees of polarization up to 96% and angular divergences as small as 1.3°. Angle-resolved spectroscopy and back-focal-plane imaging, corroborated by time-resolved fluorescence decay analysis, reveal the mechanistic interplay between GMR-assisted excitation and BIC-mediated radiative extraction. By reimagining leaky modes as excitation amplifiers rather than parasitic losses, this work establishes a physically transparent, sustainable, and scalable route to polarization-encoded on-chip light sources and fluorescence-based diagnostic technologies.

Spectrally engineered multifrequency nanolasers are highlydesirablefor on-chip photonics, multiplexed biosensing, and display technologies,yet achieving them within a compact platform remains challenging.Here, we demonstrate multimode lasing from symmetry-broken TiO2 metasurfaces integrated with an SU8 slab waveguide containingrhodamine 6G. By coengineering guided-mode resonances, surface latticeresonances near Rayleigh anomalies, and quasi-bound states in thecontinuum, we realize complementary high-Q feedback pathways thatoverlap with the gain spectrum. The lasing emission direction is tailoredthrough outcoupling via second-order Bragg diffraction and Rayleighanomaly conditions, supporting both normal and oblique emission. Experimentsreveal discrete lasing outputs across ≈100 nm bandwidth (548–648nm), spanning the full rhodamine 6G emission band, with thresholdsas low as ∼7 nJ (35.7 μJ/cm2) and up to fourconcurrent lasing peaks from a single device. These results establisha metasurface-dye platform for multifrequency and angle-selectivelasing, opening new opportunities for compact, multifunctional nanophotonicsources.

Miniaturizing optical spectrometers is constrained by the trade-off between spectral resolution and optical path length. We present an ultra-compact architecture leveraging angular dispersion of guided-mode resonances (GMR) for spectral encoding. Exploiting phase-matching at oblique incidence yields deterministic mapping, where incidence angle linearly tunes resonant wavelength. Our symmetric multi-layer architecture, a low-index metasurface-grating sandwiched between high-index guiding layers, achieves high-Q resonances (Q>103). Tailored for 550-1700 nm, we theoretically demonstrate 23.1 nm/° sensitivity with 0.75 nm resolution (≈12 cm-1), enabling Raman fingerprinting of bacterial isolates with strain-level differentiation. This compact (≈1 nm) solid-state solution advances consumer-grade chemical sensing, lab-on-chip diagnostics, and smartphone spectroscopy.

Brillouin zone folding (BZF) has emerged as an effective mechanism to achieve guided-mode resonances (GMRs) with high quality (Q) factors in momentum space, offering a feasible approach for wide-angle nonlinear conversions. Nevertheless, exploring high-efficiency nonlinear effects driven by multiple pump beams across a wide angular range remains challenging. In this work, we theoretically demonstrate double ultrahigh Q GMRs via BZF in an all-dielectric metasurface and achieve high-efficiency degenerate four-wave mixing (dFWM) and third-harmonic generation (THG) across a wide angular range. The theoretical nonlinear conversion efficiencies for both THG and dFWM remain nearly constant with the incident angle changing from 0° to 10°. Moreover, the BZF-based dual GMRs system also exhibits wide-angle high-efficiency dFWM under different perturbations. This work proposes a strategy for developing high-performance wide-angle nonlinear on-chip photonic devices and offers a practical pathway for the integration and advancement of nonlinear optical components in real-world applications.