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We propose a novel approach to realize unidirectional radiation in an asymmetric single resonator without using an external mirror, which is based on mutual coupling between two degenerate resonant modes through the background scattering of the asymmetric resonator.

A waveguide grating on a transparent substrate can serve as an optical notch filter owing to guided-mode resonance. The filtering wavelength is highly sensitive to an incidence angle. Potential of a two-dimensional grating for an application to three-dimensional angle-fluctuation sensing was investigated. Spectral variations due to the angle fluctuations were theoretically discussed and simulated using the rigorous coupled wave analysis. Incidence and azimuth angles (θ, ψ) are measured from resonance wavelengths while a polarization angle φ is detected from a ratio in transmittance at the resonance wavelengths. Sensitivities by a designed example were estimated to be 5 and 10 nm/° and 0.3 dB/° for θ, ψ, and φ, respectively.

Ethylene (C2H4) has many commercial usage and in agriculture it plays a key role in climacteric fruit ripening. This paper reports on a copper complex-coated nanostructures patterned on the cleaved facet of an optical fiber to realize a high-performance ethylene gas sensor. The novelty of this paper lies in fiber-optic based sensitive and selective monitoring of gaseous ethylene with excellent performance. A periodic array of polymer nanoposts are formed at the fiber tip and coated with titanium dioxide to serve as a guided mode resonant (GMR) device. A direct method of selectivity is developed for recognizing ethylene, by applying a copper (I) complex coating atop the GMR fiber-tip. The nanopatterned fiber-tip GMR sensor exhibits resonance sensitivity to variations in refractive index at the surface. For repeated use, a simple and cost-effective controllable heater is also integrated at the fiber tip to achieve a complete desorption of the analyte molecules from the sensor surface. This is a first-of-its-kind heater-integrated fiber optic sensor utilizing guided mode resonance and coated with a copper (I) complex coating, that is demonstrated for tracking the ethylene-promoted ripening and senescence of banana. The proposed sensor provides a maximum sensitivity of 60 pm/ppm to ethylene gas with a limit of detection of ~4.7 ppm. Compared to our earlier non-specific fiber-tip gas sensor, we improved the limit of detection for ethylene by 170-fold and sensitivity by 60-fold.

In this paper, a novel guided-mode resonances (GMRs) based embedded dual-wavelength filter, which had the bilayer gratings located at the two sides of dielectric substrate and arranged at asymmetric position, was investigated and studied theoretically. As compared to symmetric structures that usually provided single wavelength of transmission resonance, as one normal incidence was used for transverse magnetic polarized light, the designed asymmetric structure could generate two remarkable narrow band wavelengths of transmission resonance. The parameters to affect the resonance wavelengths and the transmission resonance Q value (Q = λ/Δλ) of two bands were the distance between the two metallic gratings, the relatively lateral positions of the upper and lower gratings, the number of structure period, the thicknesses of metallic gratings, and the thickness of dielectric film. By optimizing the designed parameters, a GMR device with two resonance wavelengths located at 1239 and 1302 nm showed relative optimal performance because they had high transmission depth (99.9% and 90%) and ultra-narrow transmission bandwidth (2.8 and 1.8 nm) at the two resonance wavelengths. The presented structure can offer a potential route towards dual-band narrow-band filters and refractive index sensors in the near infrared.

This review wants to give an overview of the photonic crystals-based biosensors for cancer biomarkers detection. Indeed, in the last two decades, 1D, 2D, and 3D photonics crystals have seen an extraordinary development in the direction of medical diagnosis, health assessment, and therapy monitoring. Cancer-related biomarkers can span over a wide range of biological elements including circulating tumor DNA, miRNA, proteins, enzyme, metabolites, as well as circulating tumor cells. Therefore, the review is articulated in three sections reporting on the basics of the most common used 1D, 2D, and 3D photonic crystal configurations followed by the more recent biosensing applications in cancer biomarker detection. These devices include 1D truncated multilayers such as distributed Bragg reflectors and layered gratings, 2D ordered waveguiding slabs with particular emphasis on the micro/nano cavities, and 3D direct and inverse opals. Their added value can be resumed in the capability to strongly confine the electromagnetic radiation interacting more efficiently with the biological sample thus improving the limit of detection. In conclusions, photonic crystal-based biosensors hold great potential in the detection of cancer biomarkers thanks to their ultimate performances guarantying, in the near future, a versatile sensing tool to clinical personnel and physicians.

We are reporting the design procedure for a narrow-band ultra-low-power reflective optical modulator that operates at the critical coupling of an appropriately designed two-dimensional grating with the center frequency of a quarter wavelength distributed Bragg reflector (DBR). By sandwiching a three-layer stack of gated ITO/HfO2/ITO between the DBR and the grating, we can make the optical modulator operational, taking advantage of the tunable property of the ultrathin layer at the ITO/HfO2 interface accumulated by electrons under an ultra-low applied voltage (−0.1 V). The corresponding energy consumption is ∼5.5 fJ/bit. Moreover, our simulations show that the capacitance limited modulation speed is more than 80 Mbps. Our numerical results also predict the influence of possible fabrication errors on the guided-mode resonance wavelength. This investigation shows that a ±3 nm deviation in the grating pitch affects the modulator performance profoundly. Furthermore, the numerical results demonstrate the modulation depth of ∼24 dB is achievable for an appropriately designed modulator with an acceptable insertion loss of ∼0.05 dB. This paper paves the way for developing next-generation optical modulators with high modulation depth, low insertion loss, and ultra-low energy consumption.

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.

In this study, a novel gradient grating period guided-mode resonance (GGP-GMR) biosensor is proposed, and albumin was successfully detected as a test model. The GGP-GMR sensor exhibits a gradient resonant wavelength along the device. At a fixed incident wavelength, light resonates at a specific period such that the light is reflected at this period (or resonant period) and transmitted to other periods. Thus, for a charge-coupled device under the GGP-GMR sensor, a dip-like intensity distribution was measured with a specific pixel of minimum intensity corresponding to the resonant period. The variation in sample concentrations caused changes in the refractive index (RI) on the sensor surface, which induced a shift in the resonant period and in the pixel corresponding to the minimum intensity. A GGP-GMR sensor can achieve a limit of detection of $8.58\times 10^{{-4}}$ RIU within a detection range of sucrose solutions of 0%–60% concentrations that corresponds to the RI from 1.333 to 1.442. In a buffer solution, albumin was successfully detected to measure the clinically relevant concentration. The simple design and easy fabrication of the GGP-GMR sensor combined with its simple readout and optical path design facilitates system miniaturization for handheld devices and its integration with smartphones, which could be beneficial for future point-of-care applications.

In this study, we demonstrated a hydrogen (H2) sensor based on a guided-mode resonance (GMR) filter coated with a layer of palladium (Pd). The sensor consists of three key layers, namely the substrate (replicated grating structure on an optical adhesive), waveguiding layer of TiO2, and active-sensing layer of Pd. The sensor functions as an optical resonator. On absorption of H2, the change of the refractive index in Pd changes the optical response of the sensor. To monitor the output optical response, a transmission setup was used, and two detection modalities—the change in transmission efficiency at a specific wavelength and the shift in the resonant wavelength—were demonstrated. Upon injection of a mixture of 4% H2 and 96% argon, the resonant wavelength shifted 6.38 nm, and transmission efficiency increased by 45% in 24 s.

We present a method to enhance the sensing properties of a 3D metamaterial sensor. The concept is based on the combination of magnetic plasmon (MP) resonance in 3D metamaterials and a dielectric waveguide, in which a narrow-band hybrid MP resonance can be formed by the strong coupling of the MP resonance in the vertical split ring resonators (VSRRs) with a propagating optical waveguide mode in the dielectric waveguide. Because the hybrid MP resonance of the VSRRs are extremely sensitive to the changes in the refractive index of the material surrounding the VSRRs, the designed 3D metamaterial sensor has very high sensitivity (S = 300 nm/RIU, S* = 16/RIU) and figure of merit (FOM = 30, FOM* = 390), which could find potential applications in label-free biosensing.

An ultra-broadband perfect absorber has a wide range of applications which include solar energy harvesting, imaging, photodetection etc. In this regard, InAs nanowire (NW) based structure is investigated in this work for achieving an ultra broadband perfect absorber. Finite difference time domain (FDTD) based numerical analysis has been performed to optimize the InAs nanowire based structure to obtain an efficient light absorber by varying different dimensional parameters. Mie theory and guided mode resonance based theoretical analysis is developed to validate the results and to get an insight into the tunability of the nanowire based structure. Moreover, the theoretical analysis elucidates the underlying physics of light absorption in nanowires. To achieve ultra broadband absorption, multi radii InAs nanowire based arrays are investigated and it is found that they exhibit superior performance compared to single radius NW based structures. The computed light absorption efficiency (LAE) and short circuit current density values are enhanced to 97% and 40.15 mA cm−2 at 10° angle of incidence for the optimized quad radii NW array within the wavelength range of 300 nm to 1000 nm and 300 nm to 1200 nm, respectively. Moreover, the absorption spectra for these structures are polarization independent and exhibit robust performance for varying angle of incidence. In addition, arrangement of the NW array (hexagonal or square) has negligible effect on the absorption spectra. Such ultra-broadband absorption capability of the proposed structure compared to existing works suggests that the InAs nanowire based structure is very promising as light absorber with prospects in the fields of photo detection, solar power generation, perfect cloaking, photochemistry and other thin film photonic devices.

All-dielectric nanostructures have attracted attention for highly efficient light manipulation. Higher Q-factor Fano resonance can be excited due to the rich phenomenology of optical modes supported by high-index dielectric materials with low intrinsic material loss, including both electric and magnetic multipolar Mie resonances. So far, there have been few studies done on the sensing with Fano-resonant all-dielectric resonator nanostructures. Here, an all-dielectric self-referenced optical sensor is numerically demonstrated based on Si quadrumers and mirror-symmetric 1-D photonic crystals (1DPCs) hybridstructure, operating at the infrared wavelength range with higher sensing performance and much more stable reference signal. Magnetic Fano resonance and Fabry-Perot resonance were combined into such a hybridstructure for the first time. The influences of the gap distance, including Δx and Δy , on the coupling effects between the Si nanodimers along the polarization direction and the 1DPCs are systematically discussed. The sensing performance has been numerically investigated in different analytes with the sensitivity and figure of merit (FOM) of 760 nm/RIU and 1515 RIU−1 respectively, which paves the way to be a much more sensitive detection of small refractive index changes in an unstable environment and suggests potential applications in biological and chemical sensing.

The structural arrangement of fibrous tissue is linked to the onset and progression of Alzheimer’s disease, heart disease, fibrosis, and cancer, yet its visualization remains challenging with conve...

With few-layer black phosphorus (BP)-based one-dimensional photonic crystal (1DPC), a novel optical biosensor based on the guided-mode resonance (GMR) is proposed for enhancing the sensitivity. Due to the strong coupling of the GMR with itself, the resonance dip of GMR signal will split into more resonance dips with the addition of basic constituent unit. The resonance dips are found to be deeper and deeper to enhance the resonance with the addition of period of 1DPC. Of particular interest is that the enhanced GMR signal can produce a contribution to improve the sensitivity of the biosensor. Therefore, the ultrasensitive GMR biosensor with few-layer BP-based 1DPC is designed to get a high sensitivity (Smax = 20683 RIU−1). For a comparison to the conventional surface plasmon resonance (SPR) sensor (Smax = 59 RIU−1), the sensitivity of the proposed GMR sensor has been enhanced 350 times. The BP-based 1DPC configuration, which could be developed as a promising replacement of metallic thin film, has enriched the application of GMR phenomenon in the biosensing technologies.

This work presents the design, fabrication, and characterization of a novel two-dimensional (2D) all-optical and polarization-independent tunable guided-mode resonance filter. This filter is composed of a 2D sub-wavelength photonic crystal nanostructure with a dye-doped liquid crystal layer in a doped-nanoparticle-induced homeotropic alignment. Experimental results show that the resonant wavelength of the filer can be all-optically and polarization-independently tuned for red- and blue-shifting if the cell is illuminated successively by UV and green beams. The all-optical and polarization-independent tunability of the filter is attributed to the phase transition between homeotropic ( H ) and isotropic ( I ) state, resulting in variations in the LC refractive index between the ordinary index ( n o) and refractive index in I state ( n i) via either UV-beam-induced trans-cis or green-beam-induced cis-trans back isomerization. In addition, the optically tunable cycle of the filter is repeatable for many times without significant decay or damage. This filter has potential applications, such as optical filters in signal processing, optical switches in communications technology, and optical sensors.

In this paper, the intensity distributions of the magnetic field in the proposed sandwich grating were studied. The results indicated that there were two apparent enhanced transmission peaks. The magnetic intensity distributions of these two peaks manifest that the narrow higher transmission enhancement peak was caused by guided mode resonance and the other wide low one was formed by surface plasmon resonance. The resonant wavelength was estimated by the momentum matching conditions of resonance.

Leaky modes in tilted fiber Bragg grating (TFBG) present attractive properties but it has been generally underestimated and ignored. Herein, we systematically investigate the enhancement mechanism and the sensing performance of the enhanced leaky mode resonance (eLMR) combs in ‘dielectric graphene’ integrated TFBG in theory. The investigation is conducted using the Fresnel reflection theory and the effective refractive index method. The graphene induces a highly polarization-dependent influence on the internal reflection and mode coupling of the TFBG, resulting in the s-polarized cladding guided mode being highly lossy and the leaky modes becoming guided. This is verified by the propagation length and extinction ratio. The p-/s-polarized coupling coefficient $ \kappa$ with the core guided mode presents a sudden large increase at the position where the mode transition occurs from the cladding guided modes to the leaky modes in both bare and coated TFBG. But the s-polarized $ \kappa$ is further increased by the graphene. Therefore, the mode coupling associated with the s-polarized guided leaky modes is greatly enhanced whereas it is efficiently suppressed for the lossy cladding guided modes, leading to the eLMR combs in the TFBG. It is found that the sensing performance of the eLMR combs appears a quasi-periodic property, evidenced by two groups of amplitude evolution with the surrounding refractive index (SRI). By choosing the optimal eLMR combs, a quasi-continuous SRI sensing is realized. The results demonstrate that the eLMR combs present highly sensitive performance with the average sensitivity up to 5180.4 dB/RIU and 12227.8 dB/RIU for these two groups respectively. Moreover, the eLMR combs present several advantages including insensitive wavelength shift, high figure of merit and wide application fields. This research extends our knowledge and will serve as a base for future studies on the leaky mode resonance.

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.

Optical sensors are extensively used in different fields of engineering. Multilayer thin film manufactured utilizing the Layer-by-Layer self-assembly method has obtained many applications such as mass sensors, smoke sensors, ammonia gas sensors, membranes. At the time of synthesis, in-situ monitoring of film growth, as well as precise control of film thickness, are of excellent significance for various applications. The deposition rate and film density are two of the various parameters that determine the nature of the accumulated film. On-line monitoring of thin-film thickness has been enhanced as an inherent part for thin-film formation with wanted features. This works aims to develop a convenient simulation method to determine the thickness of the film based upon optical signal processing using FPGA and Verilog HDL.

We have developed large-scale one-dimensional photonic crystals from standard recordable Blu-ray disks, tailored to sense unlabeled biorecognition events on their surface. These materials rely on coating, with layers of 80 nm of titanium oxide, nanogrooved polycarbonate plates obtained from regular disks. As a result, they present guided-mode resonances that we have demonstrated that can be exploited to quantify biorecognition events by means of the bandgap positions in the transmission spectra. These photonic crystals have displayed well-correlated dose-response curves in immunoassays to quantify IgGs, C-reactive protein, and lactate dehydrogenase. The detection limit reached is 16 ng/mL, 2μg/mL, and 18 ng/mL, respectively. Herein we describe the experimental procedures and methods to fabricate and functionalize these photonic crystals, perform immunoassays on them, set up an optical system to measure their response, and process the resulting data to perform bioanalytical determinations in label-free format.

All-dielectric binary gratings, with and without slab waveguides, are designed to generate polarization-independent guided-mode resonance filters (GMRFs) operating in the THz frequency region using the rigorous coupled-wave analysis (RCWA) method. The filling factor and thickness of the grating were adjusted to have equal resonance frequencies of transverse electric (TE)- and transverse magnetic (TM)-polarized THz beams. The single polarization-independent resonance for a binary grating without a slab waveguide was obtained at 0.459 THz with full width at half maximum (FWHM) values of 8.3 and 8.5 GHz for the TE and TM modes, respectively. Moreover, double-layered polarization-independent resonances for binary gratings with slab waveguides were obtained at 0.369 and 0.442 THz with very high Q-factors of up to 284. This is the first study to propose a polarization-independent GMRF with two resonant frequencies.

Metalens is a planar optical component that uses nanostructures with a thickness on the order of the wavelength to manipulate the wavefront of the incident light. A key problem, especially in color imaging and display applications, is the correction of chromatic aberration, which is an inherent effect caused by the dispersion of periodic lattices and resonance modes. However, the current achromatic metalenses either use the PB phase method that is only valid for circularly polarized light or nanostructures with complex cross sections that are difficult to manufacture. Here, we designed a broadband achromatic metalens for linearly polarized light from 450 to 800 nm. Rectangular titanium dioxide nanofins of various lengths and widths were applied to modulate the phase and dispersion of the incident light. The metalens can fulfill three target phases simultaneously by using an optimization method. The designed metalens has a stable focus from 450 to 800 nm with an average focusing efficiency of 64%. It can be potentially applied in microscopes, lithography machines, sensors, and displays.

A low-refractive-index grating layer with symmetrical triangular/trapezoidal grooves covered with a high-refractive-index Si layer is used to design a broadband guided-mode resonant reflector. Software Rsoft is used to simulate the reflection and transmission spectra as well as the internal electric field distribution at the resonant wavelength. It is discovered that the interaction between resonant modes promotes the formation of a wideband spectrum. The reflector has been proven to provide wideband (Δλ > 450 nm) and high reflectivity (R > 98.4%) spectra over a wide range of base angles from 44° to 72°, and the maximum high reflectivity (R > 99%) spectral range in transverse electric polarization is 458 nm, spanning 1422 to 1880nm. The results not only demonstrate excellent tolerance to the base angle and grating depth but also provide more possibilities for the design of broadband reflectors.

Resonant periodic nanostructures provide perfect reflection across small or large spectral bandwidths depending on the choice of materials and design parameters. This effect has been known for decades, observed theoretically and experimentally via one-dimensional and two-dimensional structures commonly known as resonant gratings, metamaterials, and metasurfaces. The physical cause of this extraordinary phenomenon is guided-mode resonance mediated by lateral Bloch modes excited by evanescent diffraction orders in the subwavelength regime. In recent years, hundreds of papers have declared Fabry-Perot or Mie resonance to be basis of the perfect reflection possessed by periodic metasurfaces. Treating a simple one-dimensional cylindrical-rod lattice, here we show clearly and unambiguously that Mie resonance does not cause perfect reflection. In fact, the spectral placement of the Bloch-mode-mediated zero-order reflectance is primarily controlled by the lattice period by way of its direct effect on the homogenized effective-medium refractive index of the lattice. In general, perfect reflection appears away from Mie resonance. However, when the lateral leaky-mode field profiles approach the isolated-particle Mie field profiles, the resonance locus tends towards the Mie resonance wavelength. The fact that the lattice fields remember the isolated particle fields is referred here as Mie modal memory. On erasure of the Mie memory by an index-matched sublayer, we show that perfect reflection survives with the resonance locus approaching the homogenized effective-medium waveguide locus. The results presented here will aid in clarifying the physical basis of general resonant photonic lattices., Comment: 9 pages, 5 figures

The electric dipole (ED) and magnetic dipole (MD) resonances in a slab of dielectric nanostructures induced by oblique light incidence were analyzed in terms of guided-mode wave theory for transverse electric (TE) and transverse magnetic (TM) polarization. Owing to the symmetry breaking in TE and TM polarizations at oblique incidences of light, the resonance modes produced different features, which were analyzed with comprehensive studies of energy fluxes associated with the resonance modes. The MD resonances are excited by the guided-mode wave with an energy flux in the opposite direction in the incident plane for TM polarization and excited by two guided-mode waves with energy fluxes orthogonal to the incident plane for TE polarized light. Meanwhile, the ED resonances are excited by the guided-mode waves with energy fluxes in both directions, incident plane, and out of the incident plane for both TE and TM polarizations. The proposed analyses provide clear explanations of the stability or vanishing of resonance modes, with variations in the inter-distance between nanostructures near the Rayleigh anomaly condition, which were verified by the experimental measurements performed with 2D arrays of Si nanostructures for various incident angles with TE and TM polarizations.

It is difficult for single-layer metal metasurfaces to excite in-plane component of magnetic dipole moment, so achieving giant intrinsic optical chirality remains challenging. Fortunately, displacement current in dielectric metasurfaces can form the in-plane magnetic moment which is not orthogonal to the electric dipole moment and forms intrinsic chirality. Here, we show a lossless all-silicon metasurface which achieves giant intrinsic chirality in terahertz band. The leaky waveguide mode in the chiral silicon pillars simultaneously excite the in-plane electric and magnetic dipole moments, which triggers the spin-selected backward electromagnetic radiation, and then realizes the chiral response. The theoretical value of circular dichroism in the transmission spectrum reaches 69.4%, and the measured one is 43%. Based on the photoconductivity effect of the silicon metasurface, we demonstrate optical modulation of the intrinsic chirality using near-infrared continuous wave. In addition, by arranging the two kinds of meta-atoms which are enantiomers, we show the spin-dependent and tunable near-field image display. This simple-prepared all-silicon metasurface provides a new idea for the design of terahertz chiral meta-devices, and it is expected to be applied in the fields of terahertz polarization imaging or spectral detection.

We proposed a high-performance integrated optical sensor based on a stacked resonant compound grating (SRCG). The transmission spectrum of a SRCG is investigated by the theoretical model that combines the coupled mode theory with the eigenmode information of the grating structures. It is found that the spectral width of the SRCG is controlled by changing its structural parameters such as the strip depth, the period of the grating, and cavity length. The simulation results, which are verified by finite element method (FEM), show that the sensitivity of the sensor is 401.8 nm/RIU with its figure of merit (FOM) as high as 57404. The presented sensor is a promising application for high-performance biosensing.

Herein, a tunable thermal-optical ultra-narrowband grating absorber is realized. Four ultra-sharp absorption peaks in the infrared region are achieved with the absorption efficiency of 19.89%, 98.41%, 99.14%, and 99.99% at 1144.34 nm, 1190.92 nm, 1268.58 nm, and 1358.70 nm, respectively. Benefiting from an extremely narrow bandwidth (0.27 nm), a maximum Q-factor over 4400 is obtained for the absorber. Moreover, the spectral response can be artificially tuned by controlling the temperature via the strong thermo-optic effect of silicon resonator. The high absorption contrast ratio of 23 dB is demonstrated by only increasing the temperature by 10 °C, showing an order of magnitude better than that of the previously demonstrated performance in the infrared image contrast manipulation. Also, the absorption intensity can be precisely regulated via tuning the polarization state of incident light. Strong tunability extending to temperature and polarization states makes this metasurface promising for applications in a high-performance switch, notch filter, modulator, etc.

We report an all-dielectric optical amplitude modulator based on guided-mode resonance. This design consists of a silicon nitride nanograting placed on indium-tin-oxide (ITO) integrated silicon-on-insulator platform. By leveraging the electro-tunable epsilon-near-zero effect of ITO, we achieve ~ 15 dB modulation depth at 1550 nm wavelength.

A broadband reflector with a reflectance up to 97.8% over a 144 nm spectral range from 1476 to 1620 nm is proposed by comprising double-layer subwavelength gratings with one grating layer embedded in SiO2 layer. An analysis of the resonance leaky modes with overlapping gratings shows the physical mechanism of the wide broad high-reflectivity band. The tolerance of structural parameter is analyzed and the variation of bandwidth is explained by combining the behaviors of the two guided mode resonances. The guided mode resonance and high refractive index contrast properties lead to a good angular tolerance that exhibited an angular insensitivity (~ 11°) at 1550 nm. Overall, the broadband reflector may benefit the monolithic integration of optoelectronic devices.

This Conference Presentation, “Angle-dependent resonance modes in terahertz photonic crystals and metasurfaces,” was recorded at SPIE Optics + Photonics 2021 held in San Diego, California, United States.

Thermal radiation is nominally broadband, incoherent, and isotropic, so controlling the spectral, temporal, and directional characteristics of thermal emission is an important frontier in imaging and chemical fingerprinting. The use of thermal metasurfaces, whose emission properties can be finely tailored, has recently become of great interest. Here we theoretically demonstrate the thermal emission of a metasurface arising from the coupled emission from a plasmonic mode in graphene nanoribbons and the guided mode resonance of a 1D photonic crystal. We also discuss the utility of a computationally cheap approach based on coupled-mode theory to model the device scattering characteristics.

We demonstrate efficient and compact electro-optic free-space modulators that employ hybrid high-Q Mie resonators embedded in low-loss, high-performance electro- optic molecules to achieve full amplitude modulation of a telecom carrier. By minimizing losses and maximizing the overlap between all interacting fields, we shift the resonance by 11 nm.

We propose an approach to realize a multi-band on-chip photonic spin Hall effect and selective excitation of whispering gallery modes (WGMs) by integrating metasurfaces with microcavities. Free-space circularly polarized light with opposite spin angular momentum can effectively excite WGMs with opposite propagation directions at fixed wavelengths. Moreover, the different WGMs with different propagation directions and polarizations can be selectively excited by manipulating the number of antennas. We demonstrate that the optical properties (i.e., coupling efficiency, peak positions, and peak widths) of the proposed metasurface-integrated microcavities can be easily tailored by adjusting different geometric parameters. This study enables the realization of chiral microcavities with exciting novel functionalities, which may provide a further step in the development of photonic integrated circuits, optical sensing, and chiral optics.

Guided-mode resonance (GMR) displays a wide range of optical properties that could prove useful for many applications in photonics. We report the enhancement of laser emission from the GMR sparse grating-based dye laser. The enhancement is due to an introduction of the low-refractive-index (low-n) separation layer, which causes a strong interaction between the local electric field and dye molecules. Finite-difference time-domain method is used to study how the structure’s geometry, including the thickness of the separation layer and the fill factor of the grating, affects the electric field and laser intensity. The results show that the emission can be enhanced by a factor of up to 8 compared with high-refractive-index SU-8 as the separation layer. The laser intensity reaches to the maximum value when the fill factor of the grating is 0.2, i.e., the sparse grating is used. The threshold of the low-n GMR dye laser is also examined. This design can effectively improve the performance of pumped photonic band-edge lasers.

We proposed a doped silicon microhole arrays metasurface absorber that works in the long-wave infrared region. The absorbance of the absorber is significantly increased, we found the real part of the doped silicon refractive index decreases, which leads to the decrease of the equivalent refractive index of the structure. Guided mode resonance exists in the structure, which forms Fano resonance after interaction with external radiation. Fano resonance can limit the electromagnetic field in the structure, improve the interaction between light and doped silicon, and realize the purpose of absorption enhancement.Simulated results verify that the absorbance of the absorber with the optimized structure above 37.7% at 9.67 μm.

Periodic guided-mode resonance structures which provide perfect reflection across sizeable spectral bandwidths have been known for decades and are now often referred to as metasurfaces and metamaterials. Although the underlying physics for these devices is explained by evanescent-wave excitation of leaky Bloch modes, a growing body of literature contends that local particle resonance is causative in perfect reflection. Here, we address differentiation of Mie resonance and guided-mode resonance in mediating resonant reflection by periodic particle assemblies. We treat a classic 2D periodic array consisting of silicon spheres. To disable Mie resonance, we apply an optimal antireflection (AR) coating to the spheres. Reflectance maps for coated and uncoated spheres demonstrate that perfect reflection persists in both cases. It is shown that the Mie scattering efficiency of an AR-coated sphere is greatly diminished. The reflectance properties of AR-coated spherical arrays have not appeared in the literature previously. From this viewpoint, these results illustrate high-efficiency resonance reflection in Mie-resonance-quenched particle arrays and may help dispel misconceptions of the basic operational physics.

Guided mode resonance filter (GMRF) has recently attracted much attention due to its simple structure and high spectral filtering capability [1] . GMRF design relies on a subwavelength grating placed over a high index optical guided medium, where the spectral filtering occurs due to interference between the diffracted light and leaky waveguide modes at resonance condition [1] . The resonance can be tuned by altering the geometrical and material parameters, for instance, grating period, filling factor, duty cycle, waveguide thickness and refractive index [1] . However, there is a challenge to dynamically control the GMRF spectral response by active tuning of the resonance wavelength. In this study we present a new design of CMOS compatible, polarization-insensitive graphene/Si tunable guided-mode resonance filter with a high extinction ratio, where the resonance is tuned by modulation of graphene doping. Graphene is a 2D semimetal with appealing electrical, mechanical and optical properties, and it provides an active tuning of optical loss and effective refractive index by capacitive effect using electrostatic doping [2] . Our designs show a polarization-insensitive operation of electrically controlled reflection, high extinction ratio (ER) (>11 dB) and high (> 12dB) spectral tunability, which is important for applications such as wavelength division multiplexing, laser devices, add/drop filters and more [3] , [4] .

Non-linear optics in resonant metasurfaces opens a new paradigm for realizing active photonic functionalities using surface relief structures. One such compelling photonics functionality is the use of silicon or germanium sub-wavelength grating structures as frequency up-conversion surfaces in front of conventional visible/ near-IR detectors to detect longer wavelengths in the infrared range (> 2 μm). Third harmonic generation (THG) can be utilized for the up-conversion of photons to the visible/ near-IR wavelength range. Furthermore, THG on resonant metasurfaces can aid in achieving multi-fold enhancement in the nonlinear wavelength conversion process due to resonant field enhancement in these structures. The resonant field enhancement mechanism can be broadly classified as guided mode resonances (GMR) in periodic gratings [1] and Mie resonances in isolated structures [2] . Enhanced THG from single Germanium nanodisk has been reported for 1.65 μm by exciting anapolar mode [3] . In the present work, zero contrast gratings (ZCGs) [4] , consisting of partially etched GMR structures are utilized to achieve resonances in the 2.4-2.5 μm wavelength range. The resonant enhancement of THG up-conversion to the near-IR wavelength range at ~800 nm is experimentally demonstrated.

Here, electrically tunable amplitude and phase modulators are designed by the hybridization of indium tin oxide (ITO) into a guided-mode resonance mirror (so-called GMRM), which consists of a high-...

We investigated on the interaction between a single guided-mode resonance and Fabry–Perot resonance (FPR) in a high contrast grating (HCG) from a viewpoint of Fano resonance. It has been found that the background reflection due to the FPR in the HCG is useful to implement flat-top broadband reflectors via tailoring the phase polarity of Fano resonance. The novel conceptual approach was elucidated theoretically with the temporal coupled-mode theory (TCMT), which was confirmed by the Si HCG broadband reflector design of 380-nm bandwidth for R > 99.9 from 1400 to 1780 nm (a fractional bandwidth of 24.5%). The TCMT model was in good agreement with the rigorous coupled wave analysis calculation. We believe that our approach provides expanded understanding on Fano resonance in a grating, enabling more intuitive and simpler design of a flat-top broadband reflector with grating structures.

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.

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 CaF2 substrate. Si waveguide layer thickness and CaF2 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.

We present the design, fabrication, and experimental characterization of silicon nitride based medium-index contrast gratings on glass substrate for fluorescence enhancement in the yellow to red spectral range with resonances for both incident excitation and fluorescence emission wavelengths under surface normal incidence. A comparison of the design space to realize resonant field enhancement in high-index contrast silicon and medium-index contrast silicon nitride grating structures is presented. The one-dimensional sub-wavelength grating structures studied here are designed with large duty cycle (similar to 80%) to account for the medium refractive index contrast (Delta n similar to 0.5) between silicon nitride and the glass substrate to ensure that the device operates in the two-mode regime. The resonant enhancement of fluorescence is experimentally verified using rhodamine-B isothiocyanate dye as the fluorophore of interest. A resonant enhancement of 10.8 times is demonstrated in this sample when compared to un-patterned film for transverse electric-transverse magnetic (TE-TM) polarization combination. We have also performed simulation study with plane wave excitation and incoherent dipole array emission to model the resonant excitation and emission processes, respectively. The simulations corroborate well with the best observed experimental results for the doubly resonant fluorescence configuration. Silicon nitride based medium contrast gratings are a promising platform to fabricate scalable structures for resonant enhancement of light-matter interaction with potential applications in high-sensitivity biological fluorescence assays and as a platform for polarization selective interrogation of light emission from nanoscale emitters attached to the grating.

The sensing abilities of a metal-assisted guided mode resonance (MAGMR)-based structure are compared with that of a conventional guided mode resonance (GMR)-type structure operating at the same resonance wavelength. By studying the electric field intensities at resonance, it has been found that the MAGMR sensor offers a superior and more uniform sensitivity over the entire sensor surface as compared to the GMR sensors, where the sensing takes place primarily at the trenches between the grating elements. The MAGMR sensor also shows an asymmetric field profile with 44.96% of the total field extending into the sensing region at resonance in comparison with that value of 25.62% for the GMR sensor. The bulk and surface sensitivity values have also been evaluated for a range of refractive indices and analyte thicknesses, and it has been observed that the MAGMR sensor offers superior sensitivity values over the GMR sensor for all the considered cases. The limit of detection has then been calculated for both the structures, where the MAGMR structure shows a 9-fold improvement in comparison with the GMR structure for an identical readout scheme.

Active waveband selective switches for the telecommunication wavebands are fabricated and demonstrated. This type of active waveband selective switch is composed of a guided-mode resonance filter, a twisted nematic liquid crystal (TN-LC) layer, and a linear polariser. In voltage-off status, a fabricated active waveband selective switch with grating period of 893.86 nm exhibits high resonance peak with wavelength around 1311.2 nm. In voltage-on status, this switch exhibits a high resonance peak with wavelength around 1551.3 nm. The measured reflection peaks of another active waveband selective switch with grating period of 872.84 nm are located at 1309.1 and 1549.4 nm in voltage-on status and voltage-off status, respectively. Thus, light waveband can be tuned between O-band and C-band by electrically driving the TN-LC layer of this type of active waveband selective switch in real time.