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The increasing demand for extracting comprehensive information from light through multispectral and polarization imaging has driven the development of advanced photodetection technologies. In response, a polarization‐sensitive narrowband InGaAs photodetector (PD) operating in the short‐wave infrared (SWIR) range is proposed, capable of capturing wavelength, intensity, and polarization data concurrently without additional optical components. The device is formed by integrating an InGaAs PD onto a silicon grating, utilizing the guided‐mode resonance (GMR) effect to amplify absorption at specific target wavelengths. The intrinsic polarization dependence of the 1D GMR structure allows for distinct absorption peaks for TE and TM polarized light. The detection performance of the device, including spectral rejection ratios greater than 30, peak responsivities of 0.46 A W−1, and polarization extinction ratios of up to 41.3 is demonstrated. Precise design of the period and arrangement of the grating enables fabrication of pixel arrays with diverse detection wavelengths and polarization directions, in a single process eliminating the process complexity. This is the only capability of this study among previously reported devices. [ABSTRACT FROM AUTHOR]

Miniaturized spectrometers have significantly advanced real-time analytical capabilities in fields such as environmental monitoring, healthcare diagnostics, and industrial quality control by enabling precise on-site spectral analysis. However, achieving high sensitivity and spectral resolution within compact devices remains a significant challenge, particularly when detecting low-concentration analytes or subtle spectral variations critical for chemical and molecular analysis. This study introduces an innovative approach employing guided-mode resonance filters (GMRFs) to address these limitations. Functioning similarly to notch filters, GMRFs selectively block specific spectral bands while allowing others to pass, maximizing energy extraction from incident light and enhancing spectral encoding. Our design incorporates narrow band-stop filters, which are essential for accurate spectrum reconstruction, resulting in improved resolution and sensitivity. Our spectrometer delivers a spectral resolution of 0.8 nm over a range of 370–810 nm. It achieves sensitivity values that are more than ten times greater than those of conventional grating spectrometers during fluorescence spectroscopy of mouse jejunum. This enhanced sensitivity and resolution are particularly beneficial for chemical and biological applications, facilitating the detection of trace analytes in complex matrices. Furthermore, the spectrometer's compatibility with complementary metal oxide semiconductor (CMOS) technology enables scalable and cost-effective production, fostering broader adoption in chemical analysis, materials science, and biomedical research. This study underscores the transformative potential of the GMRF-based spectrometer as an innovative tool for advancing chemical and interdisciplinary analytical applications. [ABSTRACT FROM AUTHOR]

In this study, terahertz time‐domain spectroscopy (THz‐TDS) is employed for the first time to explore the characteristics of mono‐, bi‐, and tri‐layer graphene coated on guided‐mode resonance filters (GMRFs). Owing to high quality‐factor (Q‐factor) resonances of GMRF, the proposed method significantly enhances the resonance depth variation by up to 9.3, 5.1, and 4.2 times at 0.58 THz in TE mode for mono‐, bi‐, and tri‐layer graphene, respectively, in contrast to conventional THz‐TDS methods relying on amplitude variation at 0.50 THz in TE mode. Excellent agreement is observed between experimental results and theoretical simulations using the Kubo formula and Drude model, even accounting for variations in sidelobes at an incident angle of 0.6 degrees. Through meticulous fitting process between measurements and simulations for the resonances formed by the GMRF and graphene, the study accurately determines the electrical and optical properties of mono‐, bi‐, and tri‐layer graphene, including frequency‐dependent sheet conductivity (σs(ω)), mobility (μ), carrier density (N), and Fermi velocity (vF). Furthermore, in the THz high‐frequency region, the observation reveals that as the number of graphene layers increases, the decrease in σs(ω) occurs more rapidly than in single‐layer graphene, attributed to the screening effect arising from electronic interactions between each graphene layer. [ABSTRACT FROM AUTHOR]

In this study, we developed an optofluidic chip consisting of a guided-mode resonance (GMR) sensor incorporated into a microfluidic chip to achieve simultaneous blood plasma separation and label-free albumin detection. A sedimentation chamber is integrated into the microfluidic chip to achieve plasma separation through differences in density. After a blood sample is loaded into the optofluidic chip in two stages with controlled flow rates, the blood cells are kept in the sedimentation chamber, enabling only the plasma to reach the GMR sensor for albumin detection. This GMR sensor, fabricated using plastic replica molding, achieved a bulk sensitivity of 175.66 nm/RIU. With surface-bound antibodies, the GMR sensor exhibited a limit of detection of 0.16 μg/mL for recombinant albumin in buffer solution. Overall, our findings demonstrate the potential of our integrated chip for use in clinical samples for biomarker detection in point-of-care applications. [ABSTRACT FROM AUTHOR]

Localization of light spots in a given image is a common task in digital processing but is challenging in analog. Herein, a periodic nonlocal metasurface that has an optical transfer function defined in reciprocal space is proposed to resolve this issue. Assuming an ideal optical transfer function that encodes that of a local lens, the selective spot size reduction of incident Gaussian beams and sharpening of a patterned incidence with a Gaussian line shape are demonstrated. A realistic nonlocal metasurface comprising a trilayer structure with air grating on top that operates as a 2D analog light localizer under unpolarized incidence is presented. Nonlocal metasurfaces, combined with conventional optics, are expected to improve the resolution by sharpening the spatial features and find applications in diverse scientific fields such as medical, materials, and life science. [ABSTRACT FROM AUTHOR]

Guided-mode resonance (GMR) is a compelling scheme for optical sensing of various physical quantities, which holds great promise in non-invasive detection of chemical and biological species. Current GMR sensors are mostly based on detection of environmental refractive index change, which presents a challenge for obtaining sensing selectivity as required in practical applications. In this work, we report on a prototype demonstration of using GMR for detecting molecular fingerprint absorption. In a waveguide grating made of a ZnSe layer sandwiched between a Cu film and an Au grating, a mid-infrared GMR is excited and tuned over a wide frequency range of 617.4 cm−1. Coupling of the GMR with a polydimethylsiloxane (PDMS) analyte film reveals the signature absorptions of CH2 group, whose vibrational signal is enhanced by a factor of 2.37 at a frequency detuning of 30 cm−1 between the GMR and the molecular vibration. Our theoretical analysis reveals that both near-field enhancement of GMR and its coupling strength with molecules are responsible for the molecular detection performance. These results suggest that angle-tuned GMR presents an alternative design paradigm for surface-enhanced infrared absorption spectroscopy (SEIRAS). [ABSTRACT FROM AUTHOR]

Topological nature in different areas of physics and electronics has often been characterized and controlled through topological invariants depending on the global properties of the material. The validity of bulk–edge correspondence and symmetry-related topological invariants has been extended to non-Hermitian systems. Correspondingly, the value of geometric phases, such as the Pancharatnam–Berry or Zak phases, under the adiabatic quantum deformation process in the presence of non-Hermitian conditions, are now of significant interest. Here, we explicitly calculate the Zak phases of one-dimensional topological nanobeams that sustain guided-mode resonances, which lead to energy leakage to a continuum state. The retrieved Zak phases show as zero for trivial and as π for nontrivial photonic crystals, respectively, which ensures bulk–edge correspondence is still valid for certain non-Hermitian conditions. [ABSTRACT FROM AUTHOR]

In this study, the off‐axis excited guided‐mode resonance (GMR) hybridization is experimentally investigated in one dimensional (1D) partially etched amorphous silicon (a‐Si) subwavelength grating structures operating in the mid‐infrared wavelength range. The 1D dielectric photonic lattice is a promising platform for studying resonance hybridization effects owing to its simple working principle and ease of electromagnetic design, fabrication, and experimental characterization. It is observed that with increasing duty‐cycle of the gratings, the avoided crossing between the coupled GMR branches underwent band‐closure and subsequent band‐flip, resulting in the Friedrich–Wintgen type bound‐states‐in‐the‐continuum (FW‐BICs) transitioning from the upper to the lower GMR branch. On either side of the band closure, the transmission spectra show an interesting electromagnetically induced transparency (EIT)‐like resonance, which manifests as a transmission peak within a broad transmission dip with increased electric field concentration near the peak. As a conceptual application of coupled GMRs, differential enhancement of infrared absorption from a polymethyl methacrylate (PMMA) layer coated on the grating structure with one of the optical resonances aligned to the absorption feature and the other acting as a built‐in reference is demonstrated. The differential transmission contrast is enhanced by more than two orders of magnitude when compared to that of the native PMMA layer. [ABSTRACT FROM AUTHOR]

Subwavelength resonant lattices offer a wide range of fascinating spectral phenomena under broadside illumination. The resonance mechanism relies on the generation of lateral Bloch modes that are phase matched to evanescent diffraction orders. The spectral properties and the total number of resonance states are governed by the structure of leaky modes and the mode count. This study investigates the effect of interface modifications on the band dynamics and bound-state transitions in guided-mode resonant lattices. We provide photonic lattices comprising rectangular Si3N4 rods with a liquid film with an adjustable boundary. The band structures and band flips are examined through numerical simulations using the rigorous coupled-wave analysis (RCWA) method and analyzing the zero-order spectral reflectance as a function of the incident angle. The band structures and band flips are examined through numerical simulations, and the influences of the refractive index and the thickness of the oil layer on the band dynamics are investigated. The results reveal distinct resonance linewidths corresponding to different refractive indices of the oil layer. Furthermore, the effect of the oil thickness on the band dynamics is explored, demonstrating precise control over the number of propagating modes within the lattice structure. Theoretical simulations and experimental results are presented for a subwavelength silicon-nitride lattice combined with a liquid film featuring an adjustable boundary. The presence of a relatively thick liquid waveguiding region enables the emergence of additional modes, including the first four transverse-electric (TE) leaky modes, which produce observable resonance signatures. Through experimental manipulation of the basic lattice's duty cycle, the four bands undergo quantifiable band transitions and closures. The experimental results obtained within the 1400–1600 nm spectral range exhibit reasonable agreement with the numerical analysis. These findings underscore the significant role played by the interface in shaping the band dynamics of the lattice structure, providing valuable insights into the design and optimization of photonic lattices with adjustable interfaces. [ABSTRACT FROM AUTHOR]

The discovered light modulation capabilities of diatom silicious valves make them an excellent toolkit for photonic devices and applications. In this work, a reproducible surface-enhanced Raman scattering (SERS) enhancement was achieved with hybrid substrates employing diatom silica valves coated with an ultrathin uniform gold film. Three structurally different hybrid substrates, based on the valves of three dissimilar diatom species, have been compared to elucidate the structural contribution to SERS enhancement. The comparative analysis of obtained results showed that substrates containing cylindrical Aulacoseira sp. valves achieved the highest enhancement, up to 14-fold. Numerical analysis based on the frequency domain finite element method was carried out to supplement the experimental results. Our results demonstrate that diatom valves of different shapes can enhance the SERS signal, offering a toolbox for SERS-based sensors, where the magnitude of the enhancement depends on valve geometry and ultrastructure. [ABSTRACT FROM AUTHOR]

A nanograting microring resonator is proposed for achieving concentric mode field profiles as the effect of guided-mode resonance. Based on a numerical simulation of the 2D finite-difference time-domain method, we clarified that the microring resonator with a combination of nanograting microring and sidewall blocks could generate two operating modes. The first is the optical whispering gallery mode, by which the light was in resonance inside the microring by total internal reflection and traveled in a circle around the microring. The second mode is guided-mode resonance, by which the light scattering from the grating structures is in resonance to create concentric magnetic-field distributions. The characteristics of resonance modes of the mode numbers, mode distribution, and Q factors are analyzed at the changes of the microring radius and the nanograting structures. A design of a nanograting bus waveguide with the same grating period as the nanograting microring is verified to achieve a high efficiency of the coupling ratio. [ABSTRACT FROM AUTHOR]

2D resonant gratings enable dual angular tunability by controlling the plane of incidence (POI) under linear polarization. If the POI is set to be perpendicular to the electric field vector (s‐polarization or transverse electric (TE) polarization), an excited TE mode provides spectral tuning. The orthogonally propagating transverse magnetic (TM) mode is robust in angle. Conversely, if the POI is set for p‐polarization, an excited TM mode provides the tuning. Detailed explanations of the underlying physical processes are set forth by decomposing the 2D lattice into equivalent 1D gratings using second‐order effective‐medium theory. This is shown to work extremely well even for a strongly modulated lattice with refractive‐index contrast of 3. With proper design and corresponding experiments, a widely tunable notch filter covering long‐wave infrared bands is demonstrated. Experimentally varying the incidence angle up to 16° under p‐polarization, a notch channel in TM mode tunes across a band exceeding 0.5 µm with the TE channel remaining at a constant wavelength. The interesting appearance of a resonance channel originating in diagonally propagating leaky modes is briefly examined. The analysis and experiments presented can be useful for realizing diverse 2D tunable filters while furnishing methodology for detailed understanding of the attendant near fields and mode structure. [ABSTRACT FROM AUTHOR]

Siliceous diatom frustules present a huge variety of shapes and nanometric pore patterns. A better understanding of the light modulation by these frustules is required to determine whether or not they might have photobiological roles besides their possible utilization as building blocks in photonic applications. In this study, we propose a novel approach for analyzing the near-field light modulation by small pennate diatom frustules, utilizing the frustule of Gomphonema parvulum as a model. Numerical analysis was carried out for the wave propagation across selected 2D cross-sections in a statistically representative 3D model for the valve based on the finite element frequency domain method. The influences of light wavelength (vacuum wavelengths from 300 to 800 nm) and refractive index changes, as well as structural parameters, on the light modulation were investigated and compared to theoretical predictions when possible. The results showed complex interference patterns resulting from the overlay of different optical phenomena, which can be explained by the presence of a few integrated optical components in the valve. Moreover, studies on the complete frustule in an aqueous medium allow the discussion of its possible photobiological relevance. Furthermore, our results may enable the simple screening of unstudied pennate frustules for photonic applications. [ABSTRACT FROM AUTHOR]

The properties of topological edge states of resonant photonic lattices are reported. The canonical 1D lattice embodies all chief qualities necessary for a complete comprehension of the variety of fundamental physical processes at play. Radiating topological edge states are understood in terms of leaky‐mode resonance stimulated by counter‐propagating Bloch modes. As a free‐space electromagnetic wave illuminates the junction between band‐flipped photonic lattices, quasi‐leaky resonant light is localized at the interface, which embodies the characteristics of the closed‐band state of the composite lattice. Rigorous numerical examples with Ge/ZnSe‐based lattices with a finite number of periods and having homogeneous sublayers illustrate the resonance properties of the constituent lattices, the band‐closed lattice, and the composite lattice hosting the radiant edge state. The topological interface is seen to radiate effectively near the wavelength where the band closes. With the insight gained from the 1D analysis, a representative 2D lattice is similarly treated. As orthogonal leaky modes are supported by 2D lattices, the interface‐bound energy flow picture is more intriguing. Thus, lateral TE and TM modes can be excited to run along the topological interface or normal to it. Versatile power flow, energy density, and radiation characteristics are then available at the 2D topological interface. [ABSTRACT FROM AUTHOR]

We present wideband guided-mode resonant (GMR) gratings made of Si on a SiO 2 substrate. Based on the base angle of the grating as the crystal orientation angle (54.74°) of Si, the design process of reflectors suitable for TM-polarized waves is demonstrated in the near-infrared (NIR) and mid-infrared (MIR) wavelengths. Benefiting from the mutual attraction and interaction of the two GMR modes, the bandwidth of reflectivity above 99% for the reflector under the NIR and MIR bands reaches 297 nm (from 1416 nm to 1713 nm) and 657 nm (from 3154 nm to 3811 nm), respectively. In addition, the effects of the incident light source state and the structural parameters on the performance of the reflector are analyzed in detail. The results show that the reflector will maintain good tolerance and stability during fabrication and use. This work will be compatible with the wet etching process in the microelectromechanical system, and the results can be extended to the design of broadband GMR reflectors in other wavelength bands. • This is the first demonstration of the design process for a broadband reflector for TM-polarized waves, using the crystal orientation angle of silicon (54.74°) as the base angle of the grating. • The reflector's bandwidth of reflectivity above 99% under the near- and mid-infrared bands reaches 291 nm (from 1415 nm to 1706 nm) and 642 nm (from 3158 nm to 3800 nm), respectively, due to the mutual attraction and interaction of the two guided-mode resonance (GMR) modes. • It is found that GMR reflectors in both bands have large tolerances for polarization angle and geometrical parameters of the structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Both analytically and numerically evaluated the resonant conditions in a guided-mode resonant structure. • Explored and investigated all-in-one transmission setup for different possible (classical and conical) excitation configurations. • Proposed tunable single-wavelength based sensing, eliminating the need for costly spectrometers. • Achieved sensitivity of ∼ 166 mW/RIU with He-Ne laser at resonant wavelength of 632.8 nm. We explore guided-mode resonant (GMR) structures in an unconventional way for low-cost yet effective bio-sensing applications. In contrast to regular broadband source-based wavelength interrogation techniques, single wavelength-based measurements can successfully eliminate the requirement of a costly spectrometer for rapid label-free detection and analysis. We have fabricated a silicon–nitride grating-waveguide structure and investigated it theoretically as well as experimentally under normal, angular, and conical incidences following an all-in-one transmission geometry. Such studies avoid unnecessary fabrication of multiple chips and promote a wide operational range of the GMR sensor. To validate the proposed cost-effective intensity-based sensing, we have analyzed our fabricated single GMR chip under different combinations of two-axis rotation to confirm its suitability under commonly available laser sources. Finally, using a He-Ne laser, a sensitivity of ∼ 166 mW/RIU is recorded experimentally on an average for the fabricated GMR device, operating at the resonant wavelength of 632.8 nm. The current study provides an in-depth investigation to promote possibilities for utilizing GMR structures in an inexpensive intensity-based bio-detection scheme through the demonstrated proof-of-concept. [ABSTRACT FROM AUTHOR]

Electro-tunable metamaterials opened new doors to realize spatial light modulation at nanoscale by engineering meta-atoms at sub-wavelength scale. In this study, we propose a novel design of polarization-insensitive spatial light modulator that can operate in both transmission and reflection modes. We leverage GMR (guided-mode resonance)-effect of grating waveguide and ENZ (epsilon-near-zero) phenomenon of ITO (indium-tin-oxide) to realize an efficient electro-optic modulation. The proposed design consists of a two-dimensional array of silicon-nitride nanograting on top of ITO-integrated silicon-on-insulator platform. Effective medium theory combined with temporal coupled-mode analysis is used to examine the excitation of waveguide mode via coupling of spatial light. Upon applying external bias-voltage when ITO exhibits ENZ-effect by accumulating free-carriers at ITO–Al2O3 interface, the resonance feature disappears due to large modal loss. A modulation depth of ~0.96 (~0.85) in reflection (transmission)-mode is achieved for normally incident plane wave with random polarization angle at $1.55 ~\mu \text{m}$ wavelength. In addition, the operating wavelength can be shifted by utilizing frequency-scaling property of the proposed design. With ~774 Mbps modulation speed, the proposed scalable design paves the way toward the realization of tunable flat-optical components for integrated nanophotonic systems. [ABSTRACT FROM AUTHOR]

In this work, fabrication of a dielectric photonic crystal device and numerical study of its spectral characteristics as a refractive index sensor are presented for near infrared range. The proposed nanosensor device is composed of low-cost dielectric materials, i.e., silicon dioxide and niobium pentoxide, and is fabricated using focused ion-beam milling lithography. In the first part, the fabrication process of the device is discussed, along with the process parameters and their effects on the structural properties of the resulting photonic crystal elements. In the second part, the device is numerically tested as a sensor for the biological refractive index range of 1.33 to 1.4. The performance considerations of the biosensor device are studied for 12 different structural profiles based on the fabrication results. It is shown that the angular-wall-profile of the fabricated structures downgrades the performance of the sensor, and the optimum value of hole depth should be in the range of 930–1500 nm to get the best performance. A sensitivity of 185.117 nm/RIU and a figure of merit of 9.7 were recorded for the optimum design of the device; however, a maximum sensitivity of 296.183 nm/RIU and a figure-of-merit of 13.184 RIU−1 were achieved. The device is recommended for a variety of biosensing applications due to its inert material properties, stable design and easy integration with fiber-optic setups. [ABSTRACT FROM AUTHOR]

Pyroelectric detectors are often broadband and require external filters for wavelength‐specific applications. This paper reports a tunable, narrowband, and lightweight pyroelectric infrared detector built upon a flexible membrane of As2S3−Ag−P(VDF‐TrFE) with subwavelength grating, which is capable of both on‐chip filtering and photopyroelectric energy conversion. The top surface of this hybrid membrane is a corrugated As2S3−Ag film contributing to narrowband light absorption in the near‐infrared (NIR) regime, and the bottom part is a polyvinylidene fluoride‐trifluoroethylene (PVDF‐TrFE) membrane for the conversion of the absorbed light to an electrical signal. Uniquely, applying a bias voltage to the PVDF‐TrFE membrane enables the tuning of the device's absorption and pyroelectric characteristics owing to the piezoelectrically induced mechanical bending. The resonator exhibited a resonant absorption coefficient of 80% and a full‐width‐half‐maximum of 15 nm within the NIR, a responsivity of 1.4 mV mW−1, and an equivalent noise power of 13 µW Hz−1/2 at 1560 nm. By applying a 15‐V bias to the PVDF‐TrFE membrane, the absorption coefficient decreased to 18% due to the change in the grating period and incident angle. The narrowband and tunable features of the As2S3−Ag−P(VDF‐TrFE) pyroelectric detector will benefit a variety of potential applications in sensors, optical spectroscopy, and imaging. [ABSTRACT FROM AUTHOR]

We present a nanoscale laser based on an asymmetric guided-mode resonance (AGMR) structure. The AGMR creates hybrid resonant modes, which consist of the newly generated quasi-bound states in the continuum (quasi-BICs) and the intrinsic GMR mode. By modifying the structural parameters, the GMR and quasi-BICs modes can be matched with the pump and emission wavelengths of the gain medium, respectively. Therefore, high-intensity near fields of the GMR as the resonant optical pumping mode and high quality (Q) factor of the quasi-BICs as the resonant-emitting mode jointly contribute to the low-threshold lasing behavior. The finite-difference time-domain method is used to analyze the lasing characteristics, and a threshold of 14.2 μJ/cm2 is obtained, which is approximately ten times lower than that of a single-coupled mode laser. By adjusting the asymmetry parameters and fill factor of the grating, the threshold can be further reduced to 8.9 μJ/cm2. Additionally, we have also studied the feasibility of the AGMR structure by adjusting the simulation boundary conditions from periodic to perfectly matched layer to simulate a finite-sized structure. The findings provide a new way to excite hybrid modes, opening up possibilities for applications that demand highly confined fields and high Q-factors. • A quasi-BIC nanoscale laser based on guided-mode resonance structure is proposed. • Asymmetric and composite grating is introduced to excite the quasi-BICs resonance. • The lasing threshold is reduced by double matching of the GMR and quasi-BICs mode. • Lasing performance can be optimized by adjusting the structural parameters. • The effect of the number of grating periods on the lasing threshold is discussed. [ABSTRACT FROM AUTHOR]

A polarization‐independent refractive index (RI) sensor with a sensitivity of 50 nm/RIU is demonstrated. The proposed RI sensor simply consists of a liquid crystal (LC) polymeric polarization grating film and one glass substrate. The wavelength shift over the RI of the surrounding medium is investigated through anisotropic rigorous coupled‐wave analysis. Such an LC‐based polarization‐independent RI sensor not only enables the usage of an unpolarized light source but also manifests a high sensitivity, offering great potential for the integration with display systems. [ABSTRACT FROM AUTHOR]

The bound state in the continuum (BIC) explores the extraordinary optical properties of a system possessing wave characteristics that gained recent importance for practical applications, including lasing, sensing, optical tweezing, nonlinear interactions, and many more. Unlike a pure optical or plasmonic system, a hybrid architecture with coupled photonic–plasmonic characteristics can offer the intermittent resonant modes for suitable applications. Therefore, BIC modes are investigated here in such a photonic–plasmonic hybrid structure made up of a dielectric sinusoidal grating deposited on a flat metal layer via low‐cost fabrication methods. Such a design has not been subjected to the investigation of BIC formation so far. The structure‐supported resonant modes are numerically studied by analyzing the reflection characteristics in the parametric space. The Friedrich–Wintgen bound state (FW‐BIC) is produced by the interference of distinct resonance channels, further resulting in a quasi‐BIC hybrid mode revealed in the parametric sweep. An additional angular scan demonstrates the intrinsic symmetry‐protected BIC (SP‐BIC), and its hybridization with a plasmonic mode results in a distinct FW‐BIC mode and a quasi‐BIC hybrid mode. The experimentally obtained spectral characteristics in the angular resolved scan between 5 to 20 degrees verify the quasi‐BIC hybrid modes with good quality factors and enhanced field confinement. [ABSTRACT FROM AUTHOR]

A tunable narrowband metamaterial perfect absorber (NMPA) with single absorption peak at both normal incidence and oblique incidence is proposed. The spectral responses of the designed NMPA are calculated using finite-difference time-domain (FDTD) method. By using an Ag guided-mode resonance grating layer with great fill factor, the designed NMPA exhibits single resonance peak, which is converted to heat due to the strong surface plasmon resonance around the Ag grating and the Ag substrate. An NMPA sample is fabricated and the spectral responses are measured to verify the theoretical results. The experimental results are consistent with the theoretical ones. [ABSTRACT FROM AUTHOR]

We propose a two-dimensional grating waveguide structure based on guided-mode resonance (GMR) to greatly enhance the Goos-Hänchen (GH) shift due to the asymmetric Fano peak. In addition, the enhancement of the GH shift is located at the peak of the reflectivity, which enables a more accessible measurement compared to the conventional GH shift enhancement based on Brewster angle or transmission-type resonance. In particular, such structure supports four channels for the GH shift enhancements, with a maximum value of 4.8 × 10 4 λ 0 for the positive one and -6000 λ 0 for the negative one. Our results benefit the potential applications for optical sensors, optical filters, optical absorbers and surface plasmon resonators, etc. • We propose a structure supports four channels for enhancements of the Goos-Hänchen (GH) shift based on Guided-mode resonance. • The peak of the GH shift is located at the peak of the reflectivity. • The maximum positive GH shift reaches 48000 λ 0 and the maximum negative GH shift reaches − 6000 λ 0. [ABSTRACT FROM AUTHOR]

A single-layer guided-mode resonance (SGMR) structure as a refractive index sensor is proposed and experimentally demonstrated with enhanced sensing ability. The sensitivity enhancement is discussed based on the distribution of electric fields. It is found that the electric field distribution is concentrated in grating groove at TE polarization resonance, which significantly increases the strength of evanescent waves in analyte region. In the experiment, the bulk sensitivity with TE polarization is 229.43 nm/RIU, and 125.89 nm/RIU in TM polarization. In addition, based on the SGMR structure, the measured figure of merit (FOM) under TE polarization increased by about 351% compared with that under TM polarization. The results show that deep modulation within the SGMR structure leads to higher bulk sensitivity and increased FOM, which is desirable in sensors. The proposed SGMR has a simpler structure, it provides another method for optimizing GMR sensor and facilitates their practical application. [ABSTRACT FROM AUTHOR]

A cavity-resonator-integrated guided-mode resonance mirror (CRIGM) consists of a grating coupler integrated in a waveguide cavity formed by a pair of distributed Bragg reflectors (DBRs) on a high-reflectance substrate. It is theoretically predicted that a CRIGM can give interesting characteristics of not only a narrow band-stop reflection spectrum but also flat high reflectance with steep reflection-phase spectrum according to its structure, whereas only a CRIGM with a band-stop reflection spectrum has been confirmed experimentally so far. This time, the cause of undesirable reflectance drop in a CRIGM for flat high reflectance spectrum is investigated theoretically and experimentally. It is theoretically shown that the CRIGM reflectance at the resonance wavelength is affected considerably by a slight reduction of the DBR reflectance. A CRIGM with a rib-structured channel for high lateral confinement is designed and fabricated to keep the DBR reflectance high by suppressing a propagation loss of a guided wave. The improvement of the CRIGM reflection spectrum is confirmed experimentally by measurement of the reflection spectra of the fabricated devices. [ABSTRACT FROM AUTHOR]

In this paper, a route to ultra-broadband absorption is suggested and demonstrated by a feasible design. The high absorption regime (absorption above 90%) for the suggested structure ranges from visible to mid-infrared (MIR), i.e., for the wavelength varying from 478 to 3278 nm that yields an ultra-wide band with the width of 2800 nm. The structure consists of a top-layer-patterned metal-insulator-metal (MIM) configuration, into the insulator layer of which, an ultra-thin 5 nm layer of manganese (Mn) is embedded. The MIM configuration represents a Ti-Al2O3-Ti tri-layer. It is shown that, without the ultra-thin layer of Mn, the absorption bandwidth is reduced to 274 nm. Therefore, adding only a 5 nm layer of Mn leads to a more than tenfold increase in the width of the absorption band. It is explained in detail that the physical mechanism yielding this ultra-broadband result is a combination of plasmonic and non-plasmonic resonance modes, along with the appropriate optical properties of Mn. This structure has the relative bandwidth (RBW) of 149%, while only one step of lithography is required for its fabrication, so it is relatively simple. This makes it rather promising for practical applications. [ABSTRACT FROM AUTHOR]

A dielectric guided-mode resonance (GMR) notch filter with multiple channels was designed to operate in the mid-wave infrared (MWIR, 3 ∼ 4 μ m). The transmission characteristics of filters were analyzed using a finite difference time domain (FDTD) method. In the structure of notch filter, two different periodic (p 1 = 1. 6 μ m and p 2 = 2. 0 μ m) silicon (Si) grating waveguide layers (GWLs) are constructed on the CaF 2 substrate. Si waveguide layer thickness and CaF 2 cladding layer thickness were designed based on optical interference principle to give maximum transmission across the MWIR. The transmission spectrum presents two narrow band located at 3. 410 μ m and 3. 833 μ m with not only a high bandstop coefficient (>99%), but also a broadband high transmission (>90%) off-resonance. The resonant wavelengths can be flexible modulated in wide range by changing grating periods or filling factors, and it is proved that filter is stable and useful in actual atmospheric conditions. Because of the good performance in the bandstop features, the multiband GMR notch filter designed in this method may have a potential for a variety of imaging or detection applications. [ABSTRACT FROM AUTHOR]

The tunable narrow band perfect metamaterial absorber (PMA) based on guided-mode resonance (GMR) for the visible spectral region is proposed. The PMA is composed of a one-dimensional grating layer, two waveguide layers and an Ag substrate. Tunable narrow band PMAs are designed using rigorous coupled-wave analysis by comparing the GMR effects for the filters and absorbers. Afterwards, two tunable PMA samples are fabricated through thin-film deposition and ultraviolet lithographic patterning. Finally, the reflection spectra of the fabricated PMA samples are measured. The absorption spectra obtained by subtracting the measured reflection spectra from 1 are consistent with the theory. [ABSTRACT FROM AUTHOR]

Abstract We propose a high-quality refractive index sensing by utilizing the characteristic guided-mode resonance (GMR) excited in a simple one-dimensional all-dielectric nano-slit array. We demonstrate a figure of merit up to 12000, which is higher than that achieved in most plasmonic refractive index sensors. We show that high-quality sensing performance can be sustained over a broadband range in near infrared region with relatively large variations in both grating depth and angle of incidence. Such a GMR-based all-dielectric sensing device with the ease of fabrication is expected to hold great promise for realizing broadband refractive index sensors with high performance and compactness. Highlights • High-quality refractive index sensing utilizing the guided-mode resonance (GMR) excited in a one-dimensional all-dielectric nano-slit array. • A figure of merit up to 12000 is obtained, higher than that achieved in most plasmonic refractive index sensors. • High-quality sensing performance can be sustained over a broadband range in near infrared spectral region. • Ease of fabrication, broadband refractive index sensors with high performance and compactness. [ABSTRACT FROM AUTHOR]

We introduce an approach for creating optical filters with narrow bandwidth and high transmittance within the visible light spectrum. By combining the interferometric properties of the film system and the diffraction properties of the sub-wavelength grating, we have designed a bandpass filter based with a two-dimensional subwavelength metal grating structure and an Al2O3-air bilayer coating. The Al2O3-air bilayer coating not only suppresses random scattering leakage in the short-wavelength range but also maintains the relative stability of the central wavelength position, which lead to reduced sidebands and increased transmittance of resonance peaks. Moreover, to reduce electromagnetic energy loss in the waveguide layer, we optimized the thickness of the buffer layer and introduced a bottom Al2O3 layer, enabling the filter to achieve a low full width at half-magnitude. By adjusting the grating period, the filter achieves narrow bandwidth and high transmittance resonant peaks across the entire visible spectrum. The proposed approach presents a metal grating-based guided-mode resonance transmissive filter, exhibiting a low sideband of 23%, high transmittance of 85%, a narrow bandwidth of less than 5 nm, and tunability across the entire visible light spectrum. The proposed design is experimentally validated and the results demonstrate that this method is effective in achieving excellent filtering performance in the visible spectrum. [ABSTRACT FROM AUTHOR]

We proposed a multi-band graphene absorber composed of a resonant compound grating (RCG), monolayer graphene, a thin silver layer, and a distributed Bragg reflector (DBR). A multi-band near-perfect absorption spectrum can be determined by three different physical mechanisms, including guided mode resonance (GMR), quasi-bound states in the continuum (quasi-BIC), and Tamm plasmon polaritons states (TPPs). Interestingly, the quasi-BIC mode can be achieved by changing grating layer spacing. In addition, the BIC mode can also be realized by varying grating periods. The variation of the absorption peak can be observed by changing the spacing layer thickness of the DBR structure, and the waveguide layer and grating layer thickness of the compound grating. Simulation results show that the absorption peaks of the three modes excited by our proposed absorbers are high as 80% at an incident light angle of 25°. • A multi-band absorption spectrum can be determined by three physical mechanisms, including GMR, quasi-BIC, and TPPs. • Parameters enable independent tuning of peak wavelength and intensity, with absorption rates reaching up to 99.8%. • Each spectrum has a high absorption peak in a wide range of incidence angles and can maintain three narrow-band spectra. [ABSTRACT FROM AUTHOR]

Abstract One-dimensional photonic crystal slabs are periodic optical nanostructures that produce guided-mode resonance. They couple part of the incident light into the waveguide generating bandgaps in the transmittance spectrum, whose position is sensitive to refractive index variations on their surface. In this study, we present one-dimensional photonic crystal slab biosensors based on the internal nanogrooved structure of Blu-ray disks for label-free immunosensing. We demonstrated that this polycarbonate structure coated with a critical thickness of TiO 2 generates guided-mode resonance. Its optical behavior was established comparing it with other compact disk structures. The results were theoretically calculated and experimentally demonstrated, all them being in agreement. The bioanalytical performance of these photonic crystals was experimentally demonstrated in a model assay to quantify IgGs as well as in two immunoassays to determine the biomarkers C-reactive protein and lactate dehydrogenase (detection limits of 0.1, 87, and 13 nM, respectively). The results are promising towards the development of new low-cost, portable, and label-free optical biosensors that join these photonic crystals with dedicated bioanalytical scanners based on compact disk drives. Highlights • One-dimension photonic crystal slabs based on Blu-ray disks coated with a thin layer of TiO 2. • Guided-mode resonance behavior simulated and experimentally characterized. • An experimental sensitivity of 28 nm RIU−1 in bulk. • Sensitive and selective quantification of IgG, CRP, and LDH in label-free conditions. [ABSTRACT FROM AUTHOR]

Highlights • A nonpolarizing GMRF with different grating periods along the x and y axes was designed for oblique incidence. • A tunable nonpolarizing GMRF incorporating an electrically driving liquid crystal cell was fabricated. • Nonpolarizing resonance spectra tuned by electrically driving the refractive index of liquid crystal cell were measured. Abstract A tunable nonpolarizing guided-mode resonance filter (GMRF) incorporating an electrically driving polymer-dispersed liquid crystal (PDLC) cell is designed, fabricated and demonstrated. By studying the dependence of the resonance wavelength on the grating period, the two-dimensional (2D) nonpolarizing GMRF is designed using different grating periods along the x and y axes at oblique incidence. The 2D electrically driving GMRF sample is fabricated through thin-film deposition, electron beam lithography and PDLC injection. Moreover, the resonance spectra of the fabricated sample are measured by a spectrometer and the measured results are consistent with the theory. Thus the nonpolarizing resonance spectra can be tuned by electrically driving the refractive index of PDLC cell in real time. [ABSTRACT FROM AUTHOR]

A new type of high-sensitive transmission gas sensor based on the coupled gratings (CGs) and the corresponding Fabry-Pérot-like (FP-like) model for evaluating the resonance peaks are presented. The estimated locations of the FP-like resonance obtained by this theoretical model are well agreed with those of the exact results. It is shown that a narrow FP-like channel with high transmissivity occurs in the opaque background of the CGs, and its location is shifted linearly with the variation of the refractive index (RI) of the gaseous analyte. The transmission peak of the sideband can be selected as a reference, and it remains nearly fixed as the RI of the analyte is varied. Good sensing properties of the CGs sensor can be maintained, regardless of whether the two grating membranes are laterally aligned or not. The sensitivity of the CGs sensor is immune to the variation of the RI of the substrate. By selecting the higher order FP-like mode (m = 4), sensitivity as high as 748 nm/RIU with the figure of merit of 374 can be achieved. [ABSTRACT FROM AUTHOR]

We present the design and realization of a graphene-based absorber with nearly 60% absorption efficiency using the encapsulated cascaded gratings (ECGs). The absorption locations can be estimated by using the dispersion relation of the ECGs, and it is confirmed that the absorption of the graphene-based ECGs is resulted from the excitation of the guided mode resonance (GMR). The absorption location is almost immune to the variation of the thickness of the top grating, and the absorption location is red-shifted with the increase of the fill factor. The shift of the absorption peak can be adjusted to the design value by tuning the incident angle as the grating period is altered. Multiple absorption bands can be achieved by increasing the thickness of the bottom grating. The absorption properties can be tailored based on the dispersion diagram of the ECGs structure. [ABSTRACT FROM AUTHOR]

Modal analysis on resonant excitation of two-dimensional (2-D) waveguide grating filters (WGFs) is proposed. It is shown that the 2-D WGFs can support the excitation of a resonant pair, and the locations of the resonant pair arising from the TE and TM guided-mode resonances (GMRs) can be estimated accurately based on the modal analysis. Multichannel filtering using the resonant pair is investigated, and the antireflection (AR) design of the 2-D WGFs is also studied. It is shown that the reflection sideband can be reduced by placing an AR layer on the bottom of the homogeneous layer, and the well-shaped reflection spectrum with near-zero sideband reflection can be achieved by using the double-faced AR design. By merely increasing the thickness of the homogeneous layer with other parameters maintained, the spectrally dense comb-like filters with good unpolarized filtering features can be achieved. The proposed modal analysis can be extended to study the resonant excitation of 2-D periodic nanoarrays with diverse surface profiles. [ABSTRACT FROM AUTHOR]

We treat fundamental resonance effects in hybridized metal-dielectric elements that may find applications in absorption, sensing, and displays. The hybrid structures support guided-mode resonance (GMR) and surface plasmon resonance (SPR) operating independently or in unison. Numerical simulations of periodic resonant films coated in gold that effectively combine principles of both resonance effects show viability of absorbers with equalized spectra and hybrid waveguides. The experimentally measured spectra show qualitative agreement with theoretical models. We introduce a hybrid GMR/SPR refractive-index sensor consisting of a thin aluminum film integrated with a subwavelength silicon-dioxide grating. The sensor operates between the Rayleigh wavelengths of the cover and the substrate. A GMR is excited by TE-polarized light and is subsequently attenuated by the Rayleigh anomaly as the cover index increases. In transverse-magnetic-polarized light, it operates as a Rayleigh sensor with sharp spectral features that would be easily monitored with a spectrum analyzer. As a final device example, we present simulation results pertaining to a one-dimensional color filter utilizing SPR, GMR, and the Rayleigh anomaly and convert it into a polarization insensitive two-dimensional device. With dual periods along orthogonal directions, two resonant peaks are induced within the visible spectrum for unpolarized input light rendering a colormixing effect. The output color of the dual pixel is tunable with the input polarization state. [ABSTRACT FROM AUTHOR]

In order to achieve the enhancement and manipulation of light absorption in graphene monolayer within the visible (Vis) and near infrared (NIR) regions, a design of absorber inspired by contact coupled gratings with an absentee layer is demonstrated. It is proved that the absorptance of monolayer graphene can be greatly enhanced to near unity through rigorous coupled-wave analysis (RCWA) numerical calculation. The thickness of grating and homogeneous absentee layers can significantly change the linewidth and resonant mode position in absorption spectrum. Furthermore, the lateral shift of the contact coupled gratings changes the magnetic field distributions in the grating cavity and the surface-confined mode at the cover/grating interface, thus facilitating the dynamic control of the spectral bandwidth of the graphene absorber. The proposed devices could be efficiently exploited as tunable and selective absorbers, allowing to realize other two-dimensional (2D) materials-based selective photo-detectors. [ABSTRACT FROM AUTHOR]

We propose a tunable single-/dual-band of graphene absorber with a resonant asymmetric grating based on lithium niobate on insulator (LNOI). The single-/dual-band of the absorber can be dynamically switched by changing the incident angle, and the increase of the spacing between the two peaks reduces the crosstalk in adjacent channels as the incident angle increase. Meanwhile, the resonant wavelength is adjusted by applying a voltage to lithium niobate (LN), changing the refractive of LN. The wavelength shifts caused by a slight change in incident angle can be regulated back through the electro-optical effect of LN. Furthermore, the effects of the structural parameters and the incident angle on the bandwidth are investigated by the finite element method (FEM). This structure has promising applications in optical filters, sensors, thermal emitters, and spatial optical measurements. • A dynamically tunable single-/dual-band of the graphene absorber is achieved by a resonant asymmetric grating based on LNOI. • The graphene-LN absorber realize the wavelength-tunability with low voltage and simultaneously achieve tunable single-/dual-band. • One perfect absorption peak can be split into two independent peaks as the angle changes. [ABSTRACT FROM AUTHOR]

Seawater salinity is a critical physical parameter in oceanography, affecting ocean circulation, marine ecosystems, and climate. However, current salinity measurement methods have limitations in terms of efficiency, convenience, and integration. Therefore, the development of advanced salinity measurement technology is crucial for ocean exploration and research. In this study, we designed a high-sensitivity ocean refractive index sensor using the guided-mode resonance, which exhibits superior performance in terms of transmission efficiency (approximately 1), full width at half maximum (0.210 nm), and figure of merit (5675.924). Furthermore, we obtained a set of optimized parameters by conducting a systematic study on the relationship between different structural parameters and resonance wavelength, which significantly improves the performance. Additionally, the variation trend of resonance wavelength with the change of refractive index in seawater was studied, which demonstrates that our optimized scheme achieves highly sensitive seawater salinity measurement with good process tolerance, polarization insensitivity, and a wide wavelength working interval. This high-sensitivity ocean refractive index sensor has great potential for a wide range of applications in future ocean exploration studies, such as ocean environment monitoring, marine ecology management, and oceanographic research. • Refractive index sensing in a simple 2D grating structure. • FOM can be flexibly controlled by geometric parameters and incidence angle. • The object under test with a small refractive index difference can also be detected. [ABSTRACT FROM AUTHOR]

Tunable optical reflectance using a monolithic encapsulated grating in fused silica is presented based on the guided-mode resonance (GMR) effect. The resonance location can be altered by slightly varying the thickness of the top layer. For small thickness of the grating layer, the variation of the grating thickness can be tailored to create variable optical reflectance at the same operating wavelength with the filter linewidth and the reflection sidebands kept almost the same. By proper choosing the grating thickness, the novel dual functional device that combines functions of narrowband filtering and three-port beam splitting in the resonance domain can be obtained using the monolithic encapsulated grating. Multiline reflection filters can be obtained by increasing the thickness of the top layer, and tunable reflectivity for multiple operating wavelengths can be obtained by changing the grating thickness. [ABSTRACT FROM AUTHOR]

Photonic multiline filters exhibiting periodic resonance lines on a dense spectral grid in a broad wavelength range are demonstrated. We design the filters using rigorous numerical methods and then proceed with experimental verification by patterning, etching, and collecting spectral data. We use standard double-side-polished 300-µm-thick silicon wafers for the experiments. On one side of the wafer, we place a shallow grating whereas the other side has a quarter-wave antireflection layer. An example filter with a ~200-nm-deep TiO2 grating on the wafer yields 12 narrow resonance peaks within a 10-nm wavelength range centered at 1550 nm. The spectral width of each filter peak is ~0.1 nm with a free spectral range of ~0.8 nm. Peak efficiency approaches 80% with low sidebands between the resonant filter lines. We discuss briefly design of polarization-independent periodic filters and the concept of Brewster-angle filters. Possible applications include spectral sam. pling and wavelength discretization as used, e.g., in sensing gas species and quantifying toxic gas concentrations. [ABSTRACT FROM AUTHOR]

An electro‐optic filter based on guided‐mode resonance for optical communication has been designed and fabricated. The rigorous coupled‐wave analysis is used to calculate the reflection spectra of the designed filter. The grating structure of the filter is patterned by interference lithography with two ultraviolet laser beams. The polymer‐dispersed liquid crystal is injected into the gap between the glass substrate and the bottom of the grating to fabricate the electro‐optic filter. The measured spectra of the fabricated filter exhibit a 38.7 nm shift of the resonant reflected wavelength by controlling the applied voltage. [ABSTRACT FROM AUTHOR]

We proposed an all-dielectric resonant cavity based on a zero-contrast grating (ZCG), enabling the perfect absorption of monolayer graphene at the wavelength of 1550 nm band. The mechanism of dual-band perfect absorption, which is verified by the coupled-mode theory (CMT), can be attributed to the critical coupling of Fabry–Perot cavity resonance and guided-mode resonance (GMR) in the ZCG-based cavity. The absorption peaks can be tuned by tailoring the structural parameters, such as the thickness of the waveguide layer in the ZCG, and the cavity length. Interestingly, we find that the critical coupling of the system can be robustly controlled by changing the grating thickness and grating period of ZCG. The proposed structure has potential application prospects for high-performance graphene-based optoelectronic devices. • An all-dielectric zero-contrast grating-based resonant cavity can achieve dual-band perfect absorption of monolayer graphene in the near-infrared. • The excitation of the Fabry–Perot cavity resonance and guided-mode resonance is theoretically demonstrated in the absorber. • The critical coupling of the graphene absorber can be robustly controlled by tailoring the structural parameters of zero-contrast grating. [ABSTRACT FROM AUTHOR]

In this paper, an all-dielectric frequency selective surface (ADFSS) was developed using genetic algorithms and fast Fourier transforms (FFTs) to generate random geometries. This device showed a stop-band fractional bandwidth (FBW) of 54% and a field of view of 16°. The optimized FSS was manufactured by three-dimensional (3-D) printing and the frequency response was measured in the laboratory. This device was also tested in the pass band at a high pulsed microwave power of \bf45.26\;\bfMW/\bfm^\bf2 and no damage was observed. This is the first known demonstration of a 3-D printed ADFSS. [ABSTRACT FROM PUBLISHER]

The attribute of bound states in the continuum (BICs) for highly efficient flat-top filter by using a slanted guided-mode resonance (GMR) grating is developed in this work. By introducing a slanted angle θ , the fully symmetric grating is broken to transform the dark BICs into bright quasi-BICs mode. Theoretical analysis based on the finite-different time-domain method is applied to evaluate the filtering performances. It is found that the GMR and quasi-BICs peaks combine at θ = 31. 4 ° , and the flat-top filtering response is realized at the central wavelength of 1550 nm under normal incidence. Moreover, the linewidth-tunable and central wavelength-tunable spectral response can be varied according to the change in the coupling strength of the GMR grating by changing the structural parameters such as period, fill factor and refractive index of the grating. It is the first report of a flat-top filter designed by combining GMR and quasi-BICs. The proposed structure shows promise for application in high-performance optical communication systems. • Quasi-BICs resonance is excited in a slanted GMR grating with single layer. • Flat-top filtering is firstly achieved by combing the GMR and quasi-BICs effect. • Spectral responses could be tuned by changing the structural parameters. • The central wavelength of the working band maintains 100% reflection efficiency. [ABSTRACT FROM AUTHOR]

We fabricate reflection color filters for three primary colors using silicon two-dimensional triangular-lattice subwavelength gratings on the same quartz substrate. The grating periods are 480, 390, and 300 nm for red, green, and blue filters, respectively. All of the color filters have the same thickness of 100 nm, which enables the simple fabrication of a color filter array. Maximum reflectances of 75 and 46% are obtained at wavelengths of 647.1 and 522.1 nm for the red and green filters, respectively. The blue filter has a double-peaked spectrum with a reflectance of 30% at the peak wavelengths of 450.0 and 502.7 nm. By rigorous coupled-wave analysis, the dimensions of each color filter are designed, and the calculated theoretical reflectance is compared with the measured one. [ABSTRACT FROM AUTHOR]