Resonant Grating Research Articles

Giant enhancement of harmonic generation in all-dielectric resonant waveguide gratings of quasi-bound states in the continuum.

We report the giant enhanced optical harmonic generation in all-dielectric silicon nitride (SiN) based resonant waveguide gratings (RWGs) of quasi-bound states in the continuum (BICs) of ultra-high Q factor and localized field. The BICs are realized by tuning the excitation of the guided modes modulated by geometry parameters of four-part grating layer. At a feasible structure of quasi-BIC for nanofabrication, the SHG and THG are enhanced by 103 and 106, compared with those from the RWGs of traditional two-part grating layer, respectively, and even up to 108 and 1010 compared with those from the planar SiN film, respectively. The resonance wavelength of quasi-BICs can be effectively tuned by the angle of incidence, while almost not affect the enhancement of SHG and THG response. Our results show that the efficiency harmonic generation from all-nonlinear-dielectric RWGs of quasi-BICs has potential applications for the integrated nonlinear photonic devices.

Double Electromagnetically Induced Transparency and Its Slow Light Application Based On a Guided-Mode Resonance Grating Cascade Structure.

In recent years, the achievement of the electromagnetically induced transparency (EIT) effect based on the guided-mode resonance (GMR) effect has attracted extensive attention. However, few works have achieved a double EIT-like effect using this method. In this paper, we numerically achieve a double EIT-like effect in a GMR system with a three-layer silicon nitride waveguide grating structure (WGS), using the multi-level atomic system model for theoretical explanation. In terms of slow light performance, the corresponding two delay times reach 22.59 ps and 8.43 ps, respectively. We also investigate the influence of wavelength detuning of different GMR modes on the transparent window and slow light performance. Furthermore, a wide-band flat-top transparent window was also achieved by appropriately adjusting the wavelength detuning between GMR modes. These results indicate that the EIT-like effect in the WGS has potential application prospects in low-loss slow optical devices, optical sensing, and optical communications.

Design of optoelectronic oscillator based on multiple-length single mode fiber and chirped fiber Bragg grating

Abstract Wireless communication are becoming as a part of human life. If we want to achieve the efficient and affordable communication in wireless technology in optical domain, stable signal and ultra-low phase noise is required. Optoelectronic oscillator is based on converting continues light energy in stable and low phase noise, high-quality (Q) factor is used in wireless communication. If quality factor is low, then the oscillation dies out rapidly. Delay line is used provided higher-quality factor that is used. There are numerous techniques for the photonic generation of microwave signal with high time-bandwidth product and low phase noise. Optoelectronic oscillator (OEO) based generation techniques have been found one of the most interesting technique since last three decades. This approach provides very high frequency microwave signal with lowest possible phase noise. OEO has been designed with miscellaneous architecture by introducing different optical dispersive components such as optical fiber, chirped fiber Bragg grating, polarization modulator, and ring resonator. In this paper, numerous techniques for the design of OEO are reviewed and well demonstrated. There are interesting configurations with substantial improvement in phase noise and frequency of the microwave signals generated. MATLAB simulation has been used for the verification of result explained in this technique.

Phenomenon of Electromagnetic Field Resonance in Metal and Dielectric Gratings and Its Possible Practical Applications

Calculations of the field distribution in the structure of the dielectric substrate/buffer layer/volume phase grating/analyzed medium were performed. It is shown that in the presence of a buffer layer with a low refractive index in the dielectric waveguide leads to a shift of the maximum field at the waveguide resonance into analyzed medium. As a result, the spectral and angular sensitivity of the corresponding sensor increases. Based on the waveguide equation, analytical expressions are obtained that connect the spectral and angular sensitivity of the sensor to the sensitivity of the propagation constant change due to the refractive index change of the analyzed medium. The conditions for the excitation of the resonance of surface plasmon–polariton waves in the structure with a metal or dielectric grating on a metal substrate are also given. The fields that occur at resonance for silver and gold gratings are calculated.

Imprinted Polymer-Based Guided Mode Resonance Grating Strain Sensors.

Optical sensors based on guided mode resonance (GMR) realized in polymers are promising candidates for sensitive and cost effective strain sensors. The benefit of GMR grating sensors is the non-contact, easy optical read-out with large working distance, avoiding costly alignment and packaging procedures. The GMR gratings with resonance around 850–900 nm are fabricated using electron beam lithography and replicated using a soft stamp based imprinting technique on 175 m-thick foils to make them suitable for optical strain sensing. For the strain measurements, foils are realized with both GMR gratings and waveguides with Bragg gratings. The latter are used as reference sensors and allow extracting the absolute strain sensitivity of the GMR sensor foils. Following this method, it is shown that GMR gratings have an absolute strain sensitivity of 1.02 ± 0.05 at 870 nm.

Метод розрахунку основних характеристик хвилевідно-щілинної антени

In most works devoted to the design of a waveguide slot antenna, is not considered their use for use in everyday life. Therefore, the aim of this article is the study and calculation of the main parameters of slotted waveguide antennas and statistical characteristics of antenna radiation, which could result not only in aviation but also the use life of the common man, for example, in systems of direct satellite television channels. Single slit emitter has a weak directivity property. Therefore, practical use of multi-element slotted antennas, directional properties which significantly depend on the number of cracks, their relative position on the walls of the waveguide and mode of operation of the transmission line. Accordingly, distinguish between resonant and not resonant antennas. Each of these classes, it is possible to build the so-called agreed cracks. The drawback of slot antennas is their narrow scope. Multi-element slot antennas are also used in cases when you need to create a fan chart orientation.The article presents the formulas and calculated the main characteristics of the antenna, namely the calculation of resonant gratings, made using the energy method. This method has quite high accuracy in the calculation of the exactly resonant waveguide-slot antenna arrays or lattices of the traveling wave with the configured slots. The disadvantage of the energy method is that it doesn't go far enough to consider the impact of design features of such antennas: the thickness of the wall of the waveguide, presence of sealants and protective coatings, non-ideal conductivity of the metal, the difference of the shape of the cracks from the square. For these reasons, it is reasonable accurate electrodynamic simulation of slotted waveguide arrays of different types, with the aim of using it to refine the results of engineering calculations, which is the purpose of further research of the authors.

Low-power all-optical tunable sharp trapped-mode resonances in asymmetrical planar WS2 exciton-polariton gratings

Exciton polaritons, quasiparticles that strongly integrate transition metal dichalcogenides with large exciton binding energies and optical fields, exhibit unique properties due to their strong excitonic nonlinearity. However, intrinsic absorption losses pose a fundamental obstacle to all-optical tunability in exciton-polaritons due to the relatively broad resonance spectra. Therefore, it is necessary to determine structural configurations based on transition metal dichalcogenides to enhance the field distribution. Herein, the experimental details of a narrow trapped-mode based on asymmetric WS2 localized exciton-polaritons dual gratings are presented. The transmission value at the trapped mode wavelength can be tuned from 0.844 to 0.53 for an excitation power of 14.93 MWcm−2 with a pump wavelength of 366 nm. This is attributed to the narrow trapped-mode resonance and strong field enhancement in the asymmetric gratings. A relaxation time of approximately 35 ps is obtained, which is determined by the exciton lifetime of the WS2 flake. This work provides a foundation for the application of exciton-polaritons in all-optical devices.

Simultaneous Temperature and Strain Sensing With Hybrid Resonator of Fiber Bragg Grating and Whispering Gallery Resonator

This study proposes a hybrid resonance structure of fiber Bragg grating (FBG) and whispering gallery resonator (WGR) in a single optical fiber to simultaneously measure temperature and strain. Bragg grating written in the fiber itself provides the first sensing signal in conjunction with the second signal produced by a whispering gallery mode (WGM) propagating along the circumferential cross-section of the FBG. Under changes in temperature and strain, variation in the refractive index or diameter (or length) of the fiber occurs, which also shifts the resonance frequency of each structure. Taking advantage of the difference in thermo- and strain-optic coefficients of FBG and WGR, such an integration of two different sensing techniques at an identical spot thus provides a $2\,\,{\times }\,\,2$ matrix to the characteristic equation of temperature–strain sensing that realizes a cross-sensitivity-free sensing with high accuracy. An uncertainty of ±1.91 °C and $\pm 36.2~{\mu \varepsilon }$ was achieved in the experimental verification.

Detection of Small‐Molecule Aggregation with High‐Throughput Microplate Biophysical Methods

Small-molecule drug discovery can be hindered by the formation of aggregates that act as non-selective inhibitors of drug targets. Such aggregates appear as false positives in high-throughput screening campaigns and can bedevil structure-activity relationships during compound optimization. Protocols are described for resonant waveguide grating (RWG) and dynamic light scattering (DLS) as microplate-based high-throughput approaches to identify compound aggregation. Resonant waveguide grating and dynamic light scattering give equivalent results for the compound test set, as assessed with Bland-Altman analysis. © 2019 The Authors. Basic Protocol 1: Resonant waveguide grating (RWG) in 384-well or 1536-well plate format to detect compound aggregation Basic Protocol 2: Dynamic light scattering (DLS) in 384-well plate format to detect compound aggregation.

Broadly tunable laser based on novel metallic resonant leaky-mode diffraction grating

We present a fibre laser broadly tunable in a wavelength range from 1058 nm to 1640 nm based on a new type of metallic resonant leaky-mode diffraction grating and three fibre-pigtailed semiconductor optical amplifiers. For TM polarization in Littrow configuration, the grating has experimentally measured diffraction efficiency into the -1st reflected order of more than 90 % over a spectral range of 1417 nm to 1700 nm. The laser covered a spectral range of 331 nm within a tuning band of 558 nm without any adjustment of optics and its tuning range was limited by amplification bands of available semiconductor optical amplifiers.

Cross-stacking of guided-mode resonance gratings for polarization-independent flat-top filtering

A guided-mode resonance filter (GMRF) consists of a subwavelength grating on a thin-film waveguide and can provide narrowband filtering with fewer layers in contrast to a multilayer dielectric mirror. A GMRF normally shows a peaky reflection spectrum and polarization dependency. In this Letter, two GMRFs are orthogonally stacked to give polarization-independent narrowband flat-top filtering. The GMRFs are designed by numerical methods and then fabricated and stacked. Each GMRF is formed by corrugation of a T i O 2 grating layer on a SiN guiding core layer on a S i O 2 substrate. A narrowband flat-top filter is demonstrated with a 7 nm full-width at half-maximum.

Ultra-Narrow Spectral Response of a Hybrid Plasmonic-Grating Sensor

We configure and analyze a nanostructured device that hybridizes grating modes and surface plasmon resonances. The model uses an effective index of refraction that considers the volume fraction of the involved materials, and the propagation depth of the plasmon through the structure. Our geometry is an extruded low-order diffraction grating made of dielectric nano-triangles. Surface plasmon resonances are excited at a metal/dielectric interface, which is separated from the analyte by a high-index dielectric layer. The optical performance of the refractometric sensor is highly competitive in sensitivity and figure of merit (FOM) because of the the ultra-narrow spectral response (below 0.1 nm). Moreover, it is operative within a wide range of the index of refraction (from 1.3 till 1.56), and also works under normal incidence conditions.

Resonant diffraction gratings with polarization-dependent efficiencies

Subwavelength-structures with different fill factors in the lateral dimensions result in unique phase shifts for the different polarization states of transmitted light. By using this additional degree of freedom for diffractive optical elements, we yield additional functionalities for compact optical systems with DOEs. As a fully operable example we present a binary subwavelength-grating which acts as a polarizing beamsplitter for TE- and TM-polarization over a wide range of incidence angles. We show our design approach, the manufacturing process with Soft-UV-Nanoimprint-Technology, as well as experimental results. We will also lay out possibilities for the design and application of multilevel polarization-functionalized gratings.

Reconfigurable all-dielectric Fano metasurfaces for strong full-space intensity modulation of visible light.

Dynamically reconfigurable nanoscale tuning of visible light properties is one of the ultimate goals both in the academic field of nanophotonics and the optics industry demanding compact and high-resolution display devices. Among various efforts incorporating actively reconfigurable optical materials into metamaterial structures, phase-change materials have been in the spotlight owing to their optical tunability in wide spectral regions including the visible spectrum. However, reconfigurable modulation of visible light intensity has been limited with small modulation depth, reflective schemes, and a lack of profound theoretical background for universal design rules. Here, all-dielectric phase-change Fano metasurface gratings are demonstrated for strong dynamic full-space (reflection and transmission) modulation of visible intensities based on Fano resonances. By judicious periodic couplings between densely arranged meta-atoms containing VO2, phase-change induced thermo-optic modulation of full-space intensities is highly enhanced in the visible spectrum. By providing intuitive design rules, we envision that the proposed study would contribute to nanophotonics-enabled optoelectronics technologies for imaging and sensing.

Temporal coherence and polarization modulation of pulse trains by resonance gratings.

We analyze the effects of subwavelength-period resonance gratings on temporally partially coherent optical plane-wave pulse trains. The interaction of the grating with pulses is simulated with the Fourier modal method and finite-difference time-domain method whose performances are compared. Both TE and TM linearly polarized Gaussian Schell-model pulse trains are examined, and partial temporal coherence is modeled with the identical elementary-pulse method. The polarization-dependent response of the grating is seen to lead to significant variations in the average intensity, polarization properties, and degree of temporal coherence of the reflected (and transmitted) pulse trains when the coherence time and polarization state of the incident field are altered. As an important example, we demonstrate that a fully polarized incident pulse train can become partially polarized in grating reflection. The results find use in tailoring of random electromagnetic pulse trains.

Compact Inner-Wall Grating Slot Microring Resonator for Label-Free Sensing.

In this paper, we present and analyze a compact inner-wall grating slot microring resonator (IG-SMRR) with the footprint of less than 13 μm × 13 μm on the silicon-on-insulator (SOI) platform for label-free sensing, which comprises a slot microring resonator (SMRR) and inner-wall grating (IG). Its detection range is significantly enhanced without the limitation of the free spectral region (FSR) owing to the combination of SMRR and IG. The IG-SMRR has an ultra-large quasi-FSR of 84.5 nm as the detection range, and enlarged factor is up to over 3 compared with the conventional SMRR. The concentration sensitivities of sodium chloride solutions and D-glucose solutions are 996.91 pm/% and 968.05 pm/%, respectively, and the corresponding refractive index (RI) sensitivities are 559.5 nm/RIU (refractive index unit) and 558.3 nm/RIU, respectively. The investigation on the combination of SMRR and IG is a valuable exploration of label-free sensing application for ultra-large detection range and ultra-high sensitivity in future.

Analytical design of flat-top transmission filters composed of several resonant structures.

Resonant properties of composite structures consisting of several identical resonant structures (e.g. multilayer thin-film structures or guided-mode resonance gratings) separated by phase-shift layers are investigated theoretically. Using the scattering matrix formalism, we analytically demonstrate that, at properly chosen thicknesses of the phase-shift layers, the composite structures comprising two or four resonant diffractive structures with a Lorentzian transmittance profile optically implement the Butterworth filters of the order two or three, respectively, and enable achieving flat-top transmission spectra with steep slopes and low sidebands. In addition, we show that the composite structures consisting of three or four second-order Butterworth filters can accurately approximate the fourth- or fifth-order Butterworth filters, respectively. The presented theoretical results are confirmed by rigorous numerical simulations of composite structures consisting of the so-called W-structures (simple three-layer resonant structures comprising a high-index core layer and two low-index cladding layers in a high-index dielectric environment). The simulation results confirm the formation of flat-top transmittance peaks, the shape of which fully agrees with the derived theoretical description. Moreover, we demonstrate an exceptionally simple mechanism of controlling the transmittance peak width, which consists in changing the thicknesses of the cladding layers of the initial W-structure and enables generating flat-top transmission peaks with a significantly subnanometer width.

Resonant properties of composite structures consisting of several resonant diffraction gratings.

We theoretically and numerically investigate resonant optical properties of composite structures consisting of several subwavelength resonant diffraction gratings separated by homogeneous layers. Using the scattering matrix formalism, we demonstrate that the composite structure comprising N gratings has a multiple transmittance zero of the order N. We show that at the distance between the gratings satisfying the Fabry-Pérot resonance condition, an (N - 1)-degenerate bound state in the continuum (BIC) is formed. The results of rigorous numerical simulations fully confirm the theoretically predicted formation of multiple zeros and BICs in the composite structures. Near the BICs, an effect very similar to the electromagnetically induced transparency is observed. We show that by making the proper choice of the thicknesses of the layers separating the gratings, nearly rectangular reflectance or transmittance peaks with steep slopes and virtually no sidelobes can be obtained. In particular, one of the presented examples demonstrates the possibility of obtaining an approximately rectangular transmittance peak with a significantly subnanometer width. The presented results may find application in the design of optical filters, sensors and devices for optical differentiation and transformation of optical signals.

Near-complete violation of Kirchhoff's law of thermal radiation with a 0.3 T magnetic field.

The capability to overcome Kirchhoff's law of thermal radiation provides new opportunities in energy harvesting and thermal radiation control. Previously, design towards demonstrating such capability requires a magnetic field of 3T, which is difficult to achieve in practice. In this work, we propose a nanophotonic design that can achieve such capability with a far more modest magnetic field of 0.3 Tesla, a level that can be achieved with permanent magnets. Our design uses guided resonance in low-loss dielectric gratings sitting on a magneto-optical material, which provides significant enhancement on the sensitivity to the external magnetic field.

Lightweight Torque Sensor Based on a Gradient Grating Period Guided-Mode Resonance Filter

This paper describes the design, fabrication, and testing of a lightweight and compact torque sensor system based on a gradient grating period guided-mode resonance (GGP-GMR) filter and a flexure–elastic-force-sensing element. The GMR filter exhibits a characteristic resonant reflection, when illuminated with a broadband light source at normal incidence. Instead of a fixed grating period, the GGP-GMR filter consists of grating periods varying from 250 to 550 nm with an increment of 2 nm. Given the flexibility of the plastic-based GGP-GMR filter, it can be bent conform to the cylindrical surface of the flexure. The applied torque induced deformation of the flexure and angular displacement of the attached GGP-GMR. For a stationary light source, the angular displacement of the GGP-GMR filter results in illumination at different locations (grating periods), leading to a shift of the resonant reflection wavelength. The magnitude of shift in the reflection wavelength can be correlated to the magnitude of deformation and the applied torque. In addition, commercial software based on the finite element method was used to simulate the proposed design, which indicates that the flexure made of medium-carbon steel can withstand the torque of 35 Nm without yielding. Furthermore, the simulation results (torque-induced deformation) were consistent with those obtained using the proposed torque sensor system. Torque measurements from 0 to 25 Nm showed good linearity. The limit of detection achieved was 0.77 Nm.