Grating Layer Research Articles

Design and performance study of narrowband polarized colloidal quantum dots photodetector

Abstract Colloidal quantum dot-based (CQD) photodetectors have shown exceptional potential for low-cost, room-temperature broadband imaging. However, the isotropic optical properties of the CQD absorber hinder the capability for multi-dimensional photodetection, such as polarization. Here, we design and theoretically study a CQD photodetector with an encapsulation layer and metal grating layer, which can achieve narrowband polarization sensitivity with a full width at half maximum (FWHM) of 230 nm at a wavelength of 2 μm. We first investigate the effect of the geometric parameters of the architecture. Moreover, we examine the broadband polarized optical properties and analyze the corresponding mechanisms. A large linear polarization ratio of 66 is obtained at an illuminated light wavelength of 2 μm. These results contribute to offering a promising design for constructing narrowband polarized CQD photodetectors, particularly for quantum information processing in the realms of quantum communication and quantum cryptography.

Optimization of the inverted "T"-shaped double-layer subwavelength grating design integrated on an InSb detector

Polarization detectors have significant applications in fields such as target background contrast enhancement and free-space optical communication. While the technology for polarization detection using polarizers and waveplates added to detector lenses is well-established, there is still limited research on on-chip integrated polarization detection based on hypersurface technology. In this paper, we present a novel inverted "T"-shaped double-layer subwavelength grating structure, integrated into an InSb detector for polarization detection in the mid-infrared wavelength region (3–5 μm). This structure primarily consists of a high refractive index dielectric layer and a subwavelength grating layer, which together improve the grating's transmittance and extinction ratio. Using the finite-difference time-domain (FDTD) method, we simulate and optimize the effects of various grating parameters on polarization performance. The results show that the optimized grating achieves a TM wave transmittance of nearly 80% within the 3–5 μm wavelength range, with an extinction ratio exceeding 45 dB, and is suitable for a wide range of incidence angles from 0° to 70°.

Scattering singularities in Fano-resonant multilayer grating structure with phase-change materials

In non-Hermitian systems, the singularities refer to poles or zeros of the scattering and transfer matrices. Here, we investigate the kinds of singularities in a non-parity-time-symmetric multilayer structure which mainly consists of double layers of silver grating and one layer of phase-change material Ge2Sb2Te5 (GST). When the GST is in its crystalline phase, a unidirectional zero-reflection singularity, i.e., exceptional point (EP) is achieved with the aid of Fano resonance. Interestingly, a coherent perfect absorber (CPA)-laser singularity adjacent to the EP is observed in the Fano peak. Meanwhile, a few CPA singularities exist at other wavelengths. By switching the GST from its crystalline to amorphous phase, the CPA-laser singularity will be absent, and the CPA singularity can be switched to a laser singularity. The scattering spectra near the singularities are sensitive to a tiny perturbation of the gain material and the environmental refractive index. The study is beneficial for making switchable active optical implementations.

Stacked subwavelength grating with high transmission

We propose a stacked subwavelength grating scheme generated multi-mode coupling that is continuously tunable in the visible range with high transmittance. This scheme uses BK7 glass as the substrate, onto which a layer of polydimethylsiloxane (PDMS) thin film is added. Each layer of the stacked grating is composed of different materials, from top to bottom are Ag-MgF2-BK7-Ag. By coupling different propagation modes generated by different grating layers, various transmission spectra throughout the entire visible range can be achieved. This scheme can not only allow the tuning range of the resonant peak cover the entire visible, but also bring extremely high transmittance, accompanied by sidebands below 10%, and the maximum peak transmittance can exceed 98%. Based on the mode matching method, this article has analyzed the magnetic field distribution in the entire structure space and the diffraction efficiency of all levels of diffraction waves. Our findings have potential applications in multispectral image sensors.

Highly Accurate Pneumatically Tunable Optofluidic Distributed Feedback Dye Lasers.

Optofluidic dye lasers integrated into microfluidic chips are promising miniature coherent light sources for biosensing. However, achieving the accurate and efficient tuning of lasers remains challenging. This study introduces a novel pneumatically tunable optofluidic distributed feedback (DFB) dye laser in a multilayer microfluidic chip. The dye laser device integrates microfluidic channels, grating structures, and vacuum chambers. A second-order DFB grating configuration is utilized to ensure single-mode lasing. The application of vacuum pressure to the chambers stretches the soft grating layer, enabling the sensitive tuning of the lasing wavelength at a high resolution of 0.25 nm within a 7.84 nm range. The precise control of pressure and laser tuning is achieved through an electronic regulator. Additionally, the integrated microfluidic channels and optimized waveguide structure facilitate efficient dye excitation, resulting in a low pump threshold of 164 nJ/pulse. This pneumatically tunable optofluidic DFB laser, with its high-resolution wavelength tuning range, offers new possibilities for the development of integrated portable devices for biosensing and spectroscopy.

Tailoring full-Stokes thermal emission from twisted-gratings structures

Abstract Polarized thermal emission finds extensive applications in remote sensing, landmine detection, and target detection. In applications such as ellipsometry and biomedical analysis, the generation of emission with controllable polarization is preferred. It is desired to manipulate the polarization state over the full Stokes parameters. While numerous studies have demonstrated either linear or circular polarization control using metamaterials, full-Stokes thermal emission has not been explored. Here, a microstructure based on two layers of silicon carbide gratings is proposed to tailor the polarization state of thermal emission, covering the full-Stokes parameter range. The bilayer twisted-gratings structure breaks mirror symmetry. Wave interference at the interfaces and diffraction by the gratings enhance the emission dichroism, resulting in almost completely polarized emission. By adjusting the twist angle between the gratings, the polarization state can be continuously tuned from linear to circular, nearly covering the entire surface of Poincaré sphere. This study provides a design for tailoring full-Stokes emission with notable advantages over other plasmonic metasurfaces.

Characterization of a High-performance PCF-SPR Sensor for Biomedical Applications

Background: Surface plasmon resonance (SPR) based fibre optic sensors are becoming increasingly popular in biomedical applications. However, the sensor performance is degraded because of low sensitivity with inadequate detection accuracy and figure of merit. Objectives: The first objective of this study is to design a D-shaped photonic crystal fibre (PCF) using COMSOL multiphysics. The second objective is to enhance the performance of the designed sensor in terms of sensitivity and detection accuracy using single and dual metal layer structures. In addition, the performance of the proposed sensor is compared with the existing one. Methods: In this study, the performance of the PCF-SPR sensor is improved using a D-shaped photonic crystal fibre (PCF) and two metals as grating layers. The work in this paper is divided into two parts. In the first part, the gold metal layer with optimized thickness is used to achieve good sensitivity. In the second part, the combination of gold and silver dual metal layers with optimized thickness is used to achieve good detection accuracy. Moreover, the performance of the proposed sensor is compared to other published D-shaped PCF sensors. Results: The proposed D-shaped PCF-SPR sensor is designed and simulated using COMSOL multiphysics. The results in terms of sensitivity (S) and detection accuracy (DA) are obtained using a single metal layer and dual metal layers with optimum thickness. Moreover, the transmission coefficient and loss curve have been calculated using different refractive indices of the material. In addition, the simulation results are validated for cancer detection using the proposed sensor. Conclusion: An improvement of the D-shaped PCF sensor for cancer detection is presented in terms of S and DA using single or dual metal layer structures and COMSOL multiphysics. In a single metal layer structure, only gold is used as a grating layer, and the thickness of the grating layer is optimized for achieving high sensitivity. Similarly, a combination of gold and silver is used as the grating layer in the dual metal layer structure for achieving a high DA. Moreover, the obtained results of the proposed PCFSPR sensor are compared with the published results and found that the proposed sensor can be used with a high degree of S and DA for biomedical applications and also can be used in the bio-sensing field.

Near-perfect multi-band graphene absorber with a compound grating-based resonant structure

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°.

Optical properties of periodically and aperiodically nanostructured p-n junctions

Recently, semiconductor nanograting layers have been introduced and their optical properties have been studied. Spectroscopic ellipsometry has shown that nanograting significantly modifies the dielectric function of c-Si layers. Photoluminescence spectroscopy reveals the emergence of an emission band with a remarkable peak structure. It has been observed that nanograting also alters the electronic and magnetic properties. In this study, we investigate the quantum efficiency and spectral response of Si p-n junctions fabricated using subwavelength grating layers and aperiodically nanostructured layers. Our findings indicate that the quantum efficiency and spectral response are enhanced in the case of nanograting p-n junctions compared to plain reference junctions. Aperiodically nanostructured junctions exhibit similar results to nanograting junctions. However, aperiodic nanostructuring is a more straightforward fabrication method and, consequently, more appealing for the solar cell industry.

High responsivity photodetectors based on graphene/WSe2 heterostructure by photogating effect

Graphene, with its zero-bandgap electronic structure, is a highly promising ultra-broadband light absorbing material. However, the performance of graphene-based photodetectors is limited by weak absorption efficiency and rapid recombination of photoexcited carriers, leading to poor photodetection performance. Here, inspired by the photogating effect, we demonstrated a highly sensitive photodetector based on graphene/WSe2 vertical heterostructure where the WSe2 layer acts as both the light absorption layer and the localized grating layer. The graphene conductive channel is induced to produce more carriers by capacitive coupling. Due to the strong light absorption and high external quantum efficiency of multilayer WSe2, as well as the high carrier mobility of graphene, a high photocurrent is generated in the vertical heterostructure. As a result, the photodetector exhibits ultra-high responsivity of 3.85 × 104 A/W and external quantum efficiency of 1.3 × 107%. This finding demonstrates that photogating structures can effectively enhance the sensitivity of graphene-based photodetectors and may have great potential applications in future optoelectronic devices.

Structuring light beams via nonlinear diffraction in 3D nonlinear photonic crystal

We show that nonlinear diffraction in nonlinear photonic crystal offers a convenient way to generate structured light at new frequencies. To this end we fabricate a 3D nonlinear photonic crystal containing two layers of fork-shaped ferroelectric domain gratings. Illumination of the structure by a fundamental Gaussian beam leads to the generation of two co-propagating second harmonic vortices with opposite topological charges, whose subsequent interference forms Hermite–Gaussian (HG) beams in far field.

An axisymmetric metal and metal-oxide grating-structured self-reference fiber optic SPR sensor

An optical-fiber-based surface plasmon resonance (SPR) sensing probe consisting of axisymmetrical grating is proposed and studied theoretically for the detection of the refractive index (RI). The sensing probe is formed by depositing a plasmonic metal layer on a bare core of optical fiber, followed by an axisymmetric grating layer and an analyte. The grating consists of metal and metal oxide in an alternate manner. The proposed structure of a single channel provides two resonance modes in the transmission SPR spectra. It is found that the mode present at the lower wavelength remains fixed, and the mode present at the higher wavelength is varied when the RI of the analyte is varied, so that the previous one works as a reference mode while the latter one works as a sensing mode. These properties provide the self-referencing capability of the proposed RI sensor in ambient conditions. We have calculated the sensitivity, detection accuracy (DA) and signal to width ratio (SWR) using the SPR spectra of various probes of different combinations of plasmonic metal and metal-oxide gratings to enhance the study. The best performing probe is found to be Ag/Cu-ITO. This optimum probe attained a maximum SWR of 42, sensitivity of 5400 nm RIU−1 and DA of 0.08 nm−1 with the self-referencing capability. The optimum probe also works well for a dispersive analyte within the spectral range. The use of metal oxide provides better adsorption of the analyte as well as high sensitivity. The cumulative properties of self-referencing and the metal oxide of the designed probe make it accurate and useful for the detection of biological elements in the ambient atmosphere.

The effects of grating anatase on the photovoltaic performance of perovskite based solar cells

Stimulated by the extraordinary power conversion efficiency (PCE) of hybrid organic-inorganic perovskites (HOIP) based solar cells (SCs), the derivative studies on inorganic perovskites (IOP) based SCs have been intensely investigated. In order to overcome the disadvantages of CsPbBr3, most prominently the unfavorable larger band gap (2.3eV), a grating layer of mesoporous anatase TiO2(mp-TiO2) has been inserted into the conventional configuration of SCs. The grating layer acts as the electron transfer layer (ETL) and light absorption strengthening layer at the same time. Due to the combined effects, the increased contacting area increased the fill factor (FF) and enhanced light trapping in the grating layer increased the short-current density, the average PCE of IOP based SCs has increased from 5.67% to 7.58%, which is a ca. 34% increase relatively. Furthermore, research on traditional HOIP-based SCs is also conducted. Interestingly, the increasing PCE mechanism is quite different from their inorganic counterparts, which should be attributed to the strain effect of different film structures. Thus, the strain-induced defect charge-state transitions of MAPbI3 by the grating layer increased the open-circuit voltage (Voc); and similarly, the increased contacting area also increased the FF, resulting in a 13% increase for PCE.

Improvement of on-pixel polarizer with 0.35 μm CMOS process for electro-optic imaging systems

In this paper, we propose an improved on-pixel polarizer structure for an image sensor, which was fabricated using the 0.35 μm standard CMOS process with dual metal layers (Metal 1 and Metal 2), i.e. two layers of gratings with metal-wiring layers were stacked. By designing the line/space ratio as 0.7/0.7 μm, the extinction ratio was significantly improved at a wavelength of 780 nm, which was over 1.4 times higher than that of a single-layer grating, and the detection sensitivity of the polarization change was enhanced by more than 1.8 times. We also demonstrated electro-optical imaging at radio frequency using this image sensor.

Fano-Like Resonance of Heat-Reconfigurable Silicon Grating Metasurface Tuned by Laser-Induced Graphene.

We propose a heat-reconfigurable metasurface composed of the silicon-based gold grating. The asymmetric Fano-like line shape is formed due to the mutual coupling of the local surface plasmon (LSP) in the gap between the two layers of Au gratings and the surface propagating plasmon (SPP) on the surface of the Au gratings. Then, we effectively regulate the Fano resonance by applying a bias voltage to laser-induced graphene (LIG), to generate Joule heat, so that the resonant dip of one mode of the Fano resonance can shift up to 28.5 nm. In contrast, the resonant dip of the other mode barely changes. This effectively regulates the coupling between two resonant modes in Fano resonance. Our study presents a simple and efficient method for regulating Fano-like interference in the near-infrared band.

Two-dimensional simple structured ultranarrow-band metamaterial perfect absorber with dielectric nanocylindrical array

A two-dimensional (2D) simple structured ultranarrow-band metamaterial perfect absorber (MPA) with nanocylindrical array is studied both theoretically and experimentally. Using a dielectric 2D cylindrical array as the top grating layer of the MPA, an ultranarrow nonpolarizing absorption peak at normal incidence is obtained. Furthermore, we use the same dielectric material to simplify the topology of the ultranarrow-band MPA, and the number of film layers in the MPA is reduced from 3 to 1. By optimizing its structural parameters and metal substrate, the highest ultranarrow nonpolarizing absorption peak that approaches 1 at normal incidence is obtained. To analyze the absorption physical mechanism, the heat power density distributions of the optimized MPA are simulated to see where the incident light is absorbed. Moreover, numerical simulation results show that the main transverse-electric absorption peak of the optimized MPA is insensitive to the incident angle, and the main transverse magnetic absorption peak is sensitive to the incident angle. Finally, we fabricate an MPA sample with dielectric nanocylindrical array and measure its absorption spectra to make a further comparison. The experimental data are consistent with the theoretical ones. This method might be helpful to reduce the manufacture difficulty and cost of the ultranarrow-band MPAs and also to promote the development of applications of the ultranarrow-band MPAs.

Tunable Bloch surface wave constructed by two-dimensional lithium niobate grating for biosensor

In this study, a Bloch surface wave (BSW) biosensor coupled with a two-dimensional lithium niobate grating was designed. The influence of the nonlinear characteristics of lithium niobate on the BSW sensor was theoretically investigated, and the tunability of the BSW was studied using the excitation schemes of n e and n o. To confine the energy on the surface of the solution in contact with the sensor, we introduce a distributed Bragg reflector mirror (DBR) consisting of four pairs of 76% and 42% porosity porous silicon films. A layer of lithium niobate grating is deposited on top of DBR to excite Bloch surface waves(BSW) and introduce the concept of azimuth detection in the study of the tunable properties of lithium niobate. Then, the azimuth angle of the resonance peaks excited along the n e and n o directions of lithium niobate varied by approximately 5°.

Multiparametric Guided-Mode Resonance Biosensor Monitoring Bulk and Surface-Film Variations

A guided-mode resonance (GMR) sensor with multiple resonant modes is used to measure the collection of biomolecules on the sensor surface and the index of refraction of the sensor environment (bulk). The number of sensor variables that can be monitored (biolayer index of refraction, biolayer thickness, and bulk, or background, index of refraction) is determined by the number of supported resonant modes that are sensitive to changes in these variable values. The sensor we use has a grating and homogeneous layer, both of which are made of silicon nitride (Si3N4), on a quartz substrate. In this work, we simulate the sensor reflection response as a biolayer grows on the sensor surface at thicknesses from 0 to 20 nm and biolayer indices of refraction from 1.334 to 1.43 RIU; simultaneously, we vary the bulk index of refraction from 1.334 to 1.43 RIU. In the specified span of sensor variable values, the resonance wavelength shifts for 2023 permutations of the biolayer index of refraction, biolayer thickness, and bulk index of refraction are calculated and accurately inverted. Inversion is the process of taking resonant wavelength shifts, for resonant modes of a sensor, as input, and finding a quantitative variation of sensor variables as output. Analysis of the spectral data is performed programmatically with MATLAB. Using experimentally measured resonant wavelength shifts, changes in the values of biolayer index of refraction, biolayer thickness, and bulk index of refraction are determined. In a model experiment, we deposit Concanavalin A (Con A) on our sensor and subsequently deposit yeast, which preferentially bonds to Con A. A unique contribution of our work is that biolayer index and biolayer thickness are simultaneously determined.

A novel method for fabricating guided-mode resonance filters by dip-coating colloidal nanospheres

A guided-mode resonance filter (GMRF) with nanosphere grating layer fabricated by a modified dip-coating method is designed and demonstrated through experiment. The influence of waveguide thickness, radius of nanosphere, incident angle and polarization characteristics on the spectral reflectance are investigated, and optimized structure parameters are obtained. Field distributions of the designed GMRF at resonance and non-resonance wavelength are simulated, and proved that GMR effect will generate when strong coupling occurs between the waveguide layer and the grating layer. In the end, GMRF with 260 nm diameter nanospheres grating layer is experimentally fabricated, neat hexagonal close row structure and a maximum reflectance of 82 % at around 402.3 nm wavelength are obtained.

Quasi-bound state in the continuum supported by a compound grating waveguide structure for high-figure-of-merit refractive-index sensing

Herein, we realize quasi-bound states in the continuum (quasi-BICs) in a compound grating waveguide structure with a complex lattice. The first layer of the structure is a grating layer composed of two dielectric ridges with different heights and the same width, while the second layer of the structure is a dielectric waveguide layer supporting the guided mode. As the height difference in two dielectric ridges changes from a non-zero value to zero, the lattice of the structure turns from a complex lattice with the period Λ to a simple lattice with the half of the previous period Λ′=Λ/2. Therefore, the previous excitable odd-order resonant guided modes cannot be excited and become BICs. Assisted by the ultra-high Q factor of the quasi-BIC, we achieve high-performance refractive-index sensing at near-infrared wavelengths. Under the proper design, the optimum sensitivity and figure of merit (FoM) reach 676.8 nm/RIU and 9543 RIU−1, respectively. Compared with the reported refractive-index sensors based on surface plasmon polaritons, localized surface plasmon resonances, and Bloch surface waves, the optimum sensitivity achieved in this work reaches the same order of magnitude, while the optimum FoM achieved in this work is one or two orders of magnitude higher. Our work reveals that quasi-BICs would become a powerful competitive mechanism to achieve high-performance refractive-index sensing.