Search

X-ray Talbot and Talbot–Lau interferometers consisting of transmission gratings are widely used for X-ray phase imaging, which depicts soft materials. This study exploits the use of a pair of concave and convex parabolic gratings instead of a conventional rectangular phase grating to enhance the phase signal optically. To gain insight into the optimal design, signal enhancement is evaluated by directly measuring the self-image formed downstream of the pair. An increase in the differential phase signals is demonstrated as a function of the distance between the pair, and prospects for deploying this concept into a practical phase imaging technique are discussed. [ABSTRACT FROM AUTHOR]

Optics has advanced through centuries of research into the fundamental properties of light and its interactions with matter. Within this rich history, one optical component stands out: the diffraction grating. Liquid crystals (LCs) have emerged as promising candidates in diffraction gratings. LCs are versatile and adaptable materials influenced by various external factors. Diffractive LC grating devices can be produced through methods such as photo alignment, using polymer walls, or employing patterned electrodes. However, photo alignment poses challenges in terms of manufacturing complexity, and using polymer walls is associated with some drawbacks, such as high driving voltage and slower response times, which must be considered in their application. Currently, research efforts are predominantly focused on manufacturing techniques involving patterned electrodes. In this review, we comprehensively explored the theoretical foundations underpinning diffraction gratings. Additionally, we summarized research on diffractive gratings based on LC using patterned electrodes and conducted a comparative analysis of the characteristics of each device. [ABSTRACT FROM AUTHOR]

We have conducted a computational study on a multi-layered grating structure composed of MXene-Si-Metal for visible and infrared frequencies. The suggested framework is examined across the wavelength range of 0.2–2.5 µm. We have analysed absorption and reflectance values for the various layers of the MXene and Si gratings (5, 10, and 15). This multilayered grating structure is numerically investigated using Finite element methods. The effect of the different metal resonators (Au and Ag) was also reported to identify the impact of metals on the resonating band. The multiple grating layers and resonator can allow tuning the effective resonance peak over this broad wavelength spectrum for various photonics applications—analysed absorption and reflectance values of several metal resonators to locate resonating peaks throughout a wide wavelength band. The proposed structure provides consistent absorption values for high incidence angles ranging from 0° to 80°. A multi-layered structure of MXene and silicon can create an infrared sensor, an ideal absorber, and optical communication applications. [ABSTRACT FROM AUTHOR]

Optics has advanced through centuries of research into the fundamental properties of light and its interactions with matter. Within this rich history, one optical component stands out: the diffraction grating. Liquid crystals (LCs) have emerged as promising candidates in diffraction gratings. LCs are versatile and adaptable materials influenced by various external factors. Diffractive LC grating devices can be produced through methods such as photo alignment, using polymer walls, or employing patterned electrodes. However, photo alignment poses challenges in terms of manufacturing complexity, and using polymer walls is associated with some drawbacks, such as high driving voltage and slower response times, which must be considered in their application. Currently, research efforts are predominantly focused on manufacturing techniques involving patterned electrodes. In this review, we comprehensively explored the theoretical foundations underpinning diffraction gratings. Additionally, we summarized research on diffractive gratings based on LC using patterned electrodes and conducted a comparative analysis of the characteristics of each device.

Diffraction gratings have always been used to effectively couple optical radiation within integrated waveguides. This is also valid for plasmonic structures that support Surface Plasmon Polariton (SPP) waves. Traditional gratings usually excite SPP waves at the interface where they are located or, for thin metal nanostrips, at both interfaces. But reducing the thickness of the metal layer in the presence of a grating has the handicap of increasing the tunnelling of light towards the substrate, which means higher losses and reduced coupling efficiency. In this paper, we design and optimize novel gratings buried within the metallic thin films for selective coupling of SPP waves onto individual interfaces. Compared with traditional superficial gratings, the novel buried ones demonstrate higher efficiency and much lower residual tunnelling of light through the coupling structures. [ABSTRACT FROM AUTHOR]

Recently, multiscale cavity arrays have drawn significant attention due to their excellent optical capturing capability. Here, we successfully constructed a grating microcavity with a nanowire structure that the nanoscale copper oxide nanowires (CuO NWs) with silver nanoparticles (Ag NPs) introduced into the micrometer grating structure, which can provide a large surface area and high-density "hot spots", with the ability to couple with incident light to excite multiscale cavity modes. We demonstrated that the poly-(dimethylsiloxane) (PDMS)/grating/CuO NWs/Ag NPs can serve as highly sensitive, homogeneous, and stable surface-enhanced Raman spectroscopy (SERS) substrates with a minimum detection of 1 × 10–11 M (rhodamine 6G, i.e., R6G) and 1 × 10–9 M (Sudan I). Furthermore, the remarkable hydrophobic properties (water contact angles: 165°) of the PDMS/grating/CuO NWs/Ag NP substrate allow it to directly detect organic pollutants in oil within a mixture of oil and water. [ABSTRACT FROM AUTHOR]

Plaids consist of two orthogonally oriented gratings. However, their structure may be perceived as a checkerboard with an oblique orientation or as two overlaid gratings. We used a visual search paradigm to investigate how plaids with different perceived structures influence search efficiency for determining whether a preattentive plaid-specific or grating-specific mechanism is involved in representing the plaid. Participants searched for a grating among plaids (Experiment 1) or a plaid among gratings (Experiment 2). Contrast (low vs. high), composed spatial frequency (SF) of the plaid (coherent vs. mixed), and target--distractor orientation relationship (component orientation-- aligned vs. structure orientation--aligned) were manipulated to vary the perceived structure of the plaid. Parallel search was observed when the target was a coherent checkerboard plaid, and orientation manipulation did not influence search efficiency. However, search performance was less efficient when the target plaid was perceived as overlaid gratings. When searching for a grating among plaids, low-SF gratings were located more quickly than high-SF gratings, regardless of the plaid distractor type. The results provide evidence for the existence of a preattentive plaid-specific mechanism that is distinct from the grating-sensitive mechanism. [ABSTRACT FROM AUTHOR]

In the present study, we propose a high sensitive refractive index (RI) liquid biosensor. The arrayed arrangement of gold spherical nanoparticles (NP) laid on a grating surface made of silicon nitride (Si3N4) is implemented. The organization of NP arrays stimulate wave coupling to manage new operation in optical range. Designing the device can be followed through monitoring subtle changes in the refraction indices (RI) of the operating surfaces. The performance of the device is numerically investigated in near-infrared region, yielding a sensitivity value of as large as 470.3 nm/RIU (refractive index unit). It shows a figure of merit more than 59 RIU−1 within the operating wavelength of 900 nm. These results emphasize the role of plasmonic occurrence in the optimizing of NP pattern for biosensor dominance over nonoptic counterparts. The variations of optical response based on changing the geometry of gold nanoparticles (Au NPs) and grating configuration create a significant capability in sensing the RI of various bio analyte materials. Analyses of the results successfully show optimum performance of the proposed biochemical sensing ability for common biosensing applications. First, the present study would lead to the development of a new type of plasmonic device capable of detecting single bacterium and effective in determining the concentration level of bacterial spectrum in drinking water. Afterwards, we proceed with a cleverly designed RI biosensor optimized for waterborne infection due to Escherichia coli (E. coli), Serratia marcescens (S. marcescens), and Mierococcus lysodeikticus (M. lysodeikticus) pathogen. These bacterial pathogens at varied concentrations would be detectable by the proposed biosensor. [ABSTRACT FROM AUTHOR]

Coarse wavelength division multiplexing (CWDM) technology has been widely used in short-reach optical communication systems. By using the same technology in a solid-state photonics-based Lidar, one can achieve significant cost reduction. Beam steering is realized through diffraction of light wave upon grating couplers. However, current design has a small viewing angle and a low angular resolution. We propose a configuration based on Silicon-on-Insulator (SOI) waveguide grating coupler. The viewing angle is increased by 2.5 times with light signals propagating bidirectionally. The angular resolution is doubled through interleaving beams with trans-electrical (TE) polarization and beams with trans-magnetic (TM) polarization. By optimizing the design of a single grating coupler, the output beams are evenly distributed and the transmittance is improved. With 4 CWDM lasers being the source, a 34° beam angle of view and an angular resolution of 1.9° are demonstrated.

In the X-ray single-grating imaging system, the acquisition of frequency information is the key step of phase-contrast and scattering information recovery. In the process of information extraction, it is easy to lead to the degradation of imaging quality due to the Moire Artifact, thus limiting the development and application of X-ray single-grating imaging system. In order to address the above problems, in this article, based on the theoretical analysis of the generation principle of Moire Artifact in imaging system, the advantages and disadvantages of grating rotation method are analyzed, and a method of suppressing Moire artifacts by adjusting grating projection frequency is proposed. The experimental results show that the method proposed here can suppress the Moire noise in the background noise, resulting in a reduction of more than 50% in the standard deviation of the background noise. High quality phase-contrast and scattering images are obtained experimentally, which is of great value to the development of X-ray single-grating imaging technology. [ABSTRACT FROM AUTHOR]

In this work, the results of modelling the diffraction of a plane wave by the structures of type dielectric grating/dielectric layer/metal substrate are presented. The strongest field enhancement is achieved for TE polarization under of waveguide mode resonance. In addition, the reflection coefficient is zero under such resonance conditions. Waveguide mode resonance can be realized in a wide range of wavelengths by changing the grating parameters. The spectral characteristics of three types of periodic structures were modelled. The first and second structures contain a dielectric layer, while the third one does not. The waveguide mode resonance and, accordingly, zero reflection coefficient can be obtained with carefully selected structure parameters. Resonant values of the grating thicknesses and periods were determined. Numerical modelling was done with Rigorous Coupled Wavelength Analysis. The thicknesses different from the resonant ones significantly affect the reflection coefficient from the periodic structure, as was established. Absolute permissible deviation values of the thicknesses of the gratings and dielectric layers from the calculated resonance values were estimated. The waveguide mode resonance is sensitive to the incident wavelength on the periodic structure. The reflection coefficient and the field distribution along the grating period were calculated. Studied structures can be effectively used as substrates for SERS-type devices due to field enhancement and zero reflection coefficient under waveguide resonance. The strongest field on the grating surface is observed for the structure without a dielectric layer, namely, dielectric grating deposited on the metal substrate. In addition, the benefits of such periodic structures include lower manufacturing costs. [ABSTRACT FROM AUTHOR]

This paper introduces an ultra-broadband perfect absorber. The absorber comprises just two layers. By introducing sub-grating structures in the groove of the rectangle grating, a broadband absorber is realized. The proposed structure operates in the wavelength range of 420nm-1543 nm, exhibiting an absorptivity greater than 90%. To enhance our comprehension of the physical mechanism behind broadband absorption, we analyze the distributions of current density, electric field, and magnetic field within the structure. The ultra-broadband absorption is achieved through multiple resonances of the structure. Additionally, the absorber demonstrates good absorption performance at large incident angles. By modifying the proposed structure to possess centrosymmetry, the absorber becomes impervious to incident waves with varying polarization angles. Owing to the simple structure, the absorber may have a wider range of applications, including photovoltaic devices and light-emitting devices. [ABSTRACT FROM AUTHOR]

Both the colourful cholesteric liquid crystal polymer network (CLCN) patterns and the gratings have attracted much attention for their applications as optical materials. Herein, the photochromic cholesteric liquid crystal (CLC) mixtures were prepared using a photoisomerizable chiral dopant. The structural colour of the CLC mixtures was tunable by changing the chiral dopant concentration and the intensity of the 365-nm irradiation light. The CLCN gratings with a structural colour were prepared using the UV nanoimprinting lithography method. The structural colours of the CLCN gratings originate from both the cholesteric and the grating structures. Moreover, a patterned CLCN grating was prepared using a photochromic CLC mixture, which could be applied for decoration and anti-counterfeiting. [ABSTRACT FROM AUTHOR]

This work proposes a quick measurement of the refractive index of dielectric nanofilm via a fabricated topological grating that comprises indium tin oxide (ITO) strips and nanowalls with an extremely high aspect ratio of 25. As the topological grating is capped with a dielectric nanofilm, the parabolic fields of the nanowalls destructively interfere with those of the ITO strips. This destructive interference weakens the photonic jets of the topological grating, decreasing its diffraction efficiency. The decrease in the diffraction efficiency determines the refractive index of the nanofilm without measuring its thickness in advance because the efficiency decrease is independent of the thickness. In other words, the photonic jets of the topological grating are manipulated by the refractive index of the nanofilm. The experimental results verify that refractive indices of titanium‐dioxide, silicon‐dioxide, and bovine‐serum‐albumin nanofilms with a thickness much smaller than the visible wavelengths can be measured by using the proposed topological grating. Therefore, topological gratings have great potential to develop advanced materials, fascinating devices, and innovative instruments. [ABSTRACT FROM AUTHOR]

In the focus of the presented work is the analysis of a rear side reflection grating in context of a perovskite/silicon tandem solar cell. The typical configuration of a perovskite/Si tandem device requires a hole transport layer at the rear side of the silicon solar cell (p-i-n bottom cell structure). As such a poly-Si passivating contact like TOPCon is an attractive candidate. Until now, research faces the challenge to deposit p-TOPCon layers with good surface passivation properties on textured surfaces. A planar surface would avoid this issue and due to its smaller surface area intrinsically allowing for a better passivation. The optical disadvantage of the planar rear side can be eliminated by an appropriate optical grating at the rear side which enables ideal light trapping. In this work a new approach is developed to describe the optical properties of a diffraction grating as structured rear side reflector in a silicon bottom cell. The light distribution and the parasitic absorption per grating interaction are fitted to reflectance and absorptance measurements of a III-V on silicon triple-junction device with a rear grating structure. Compared to previous models, this new approach makes it possible to reliably quantify the different loss mechanisms in the spectral region above 1000 nm. An application of the simulation model to a perovskite/silicon tandem device shows the potential of the system with rear side grating. In addition, an integration of a TOPCon tunnel junction is evaluated and a process chain for the integration of a structured rear side reflector into the tandem system is discussed.

Light trapping structures are necessary for optimal light absorption in thin-film solar cells for improving its efficiency. Absorption in thin-film solar cells can be improved by revising the geometry of solar cell structure. The diffraction phenomenon is at the heart of spectral research of light. In this article, absorption enhancement in silicon thin-film absorber layer is investigated via optical grating structure. Fabrication of an effective light-trapping through engineering metallic grating structures realized to enlarge the optical path length of light within the absorber layer. Grating fabrication technology was employed by using a laser beam to write patterns on bare metallic chromium films. Circular patterns were written using polar coordinate laser writer. These particular efforts showed increased absorption of light in the ultraviolet (UV) and near infrared (NIR) part of the solar spectrum and that is effective in achieving performance close to 98% absorption at shorter wavelengths, i.e., from 400 to 500 nm with a 2-μm grating period. Thus, these fabricated grating structures can be used as efficient backside reflector in thin-film solar cells. [ABSTRACT FROM AUTHOR]

In the present study, five nano logical gates have been designed by means of eight rectangular Kerr nonlinear resonators in a unique plasmonic structure. All the logical gates were simulated with a single nano plasmonic composition, capitalizing on the two-dimensional Finite-Difference-Time-Domain method. The results showed that, on average, the transmission differences for the AND, NOR, OR, NAND, and XOR gates were 98%, 99%, 200%, 94%, and 96%, respectively, with a time response of 50 femtoseconds for all gates. In addition, it was found that the calculation of manufacturing tolerance can be considered as a practical method to consider the production error of logic gates. In the end, this paper provides positive outcomes for the future of computational integrated circuits in photonics. [ABSTRACT FROM AUTHOR]

In this paper, a new structure of SiGe thin film solar cell using a carbon nanotubes (CNT) grating layer is proposed. CNT grating layer is used which reduces the reflection loss from the surface and maximizing optical absorption in the active layer of the cell. In order to reduce the carrier recombination in the back contact, a GaAs back-surface field (BSF) layer was used. The simulation results show that the efficiency of the proposed structure is 29.32%. Furthermore, we were able to increase the efficiency to 31.3% by optimizing the structural parameters including the depth and number of grating periods. [ABSTRACT FROM AUTHOR]

This article introduces a double-sided vibrating MOEMS gyroscope which uses a readout circuit with a novel technique based on an asymmetric Au grating. The proposed asymmetric grating has an innovative structure, as well as the hybrid surface plasmon polariton (SPP) mechanism is suggested for the first time in this device. Modeling and simulations are performed using numerical studies aimed at achieving low dimensions, high sensitivity, and broad measurement range. The provided gyroscope has a measurement range of ± 11460 °/s, a mechanical sensitivity of 0.2671 nm/°/s , an optical sensitivity of 1.9066 μW/°/s, a total sensitivity of 0.7626 μA/°/s, and a resolution of 52.449 μ°/s. Moreover, the characteristics of a proof mass of 0.2543 μg, an operational wavelength of λ = 630 nm , a bandwidth of 1.496 kHz , and a measurement time of 1 ms are obtained. [ABSTRACT FROM AUTHOR]

Metamaterial-based quarter-wave plates (QWPs) have emerged as promising candidates for advanced polarization control in a variety of optical applications, owing to their unique properties, such as ultra-thin profiles and tailored spectral responses. We design an ultra-thin, high-efficiency, and broadband QWP in transmission mode based on a TiO 2 /Au grating structure. We show that multiple reflections and the near-field effects associated with the integration of these devices pose challenges that must be considered when combining multiple metamaterials. We present insights that facilitate improved design methodology and the optimization of integrated metamaterial QWPs and other metadevices. Our results contribute to the development of miniaturized and high-density advanced lightwave and polarization control devices in optical systems. [ABSTRACT FROM AUTHOR]

Most existing multi-channel spectrometers are constructed by physically stacking single-channel spectrometers, resulting in their large size, high weight, and limited number of channels. Therefore, their miniaturization is urgently needed. In this paper, a microlens array grating is designed for miniature multi-channel spectrometers. A transmissive element integrating microlens arrays and gratings, the MLAG, enables simultaneous focusing and dispersion. Using soft lithography, the MLAG was fabricated with a deviation of less than 2.2%. The dimensions are 10 mm × 10 mm × 4 mm with over 2000 available units. The MLAG spectrometer operates in the 400–700 nm wavelength range with a resolution of 6 nm. Additionally, the designed MLAG multi-channel spectrometer is experimentally verified to have independently valid cells that can be used in multichannel spectrometers. The wavelength position repeatability deviation of each cell is about 0.5 nm, and the repeatability of displacement measurements by the chromatic confocal sensor with the designed MLAG multi-channel spectrometer is less than 0.5 μm. [ABSTRACT FROM AUTHOR]

We propose a coupled-mode theory for resonant diffraction gratings with a varying period. We consider diffractive structures, in which the reciprocal lattice vector, a quantity inversely proportional to the period, varies linearly in the direction of periodicity. It is shown that optical properties of such a structure essentially depend on the period change rate. On the basis of a comparison with the results of rigorous numerical simulations using the rigorous coupled-wave analysis, high accuracy of the proposed theoretical model is demonstrated. In particular, the developed coupled-mode theory describes the broadening of the resonant peak and the appearance of secondary maxima caused by a non-zero period change rate. The obtained results can be used for the development of linear variable filters based on resonant diffraction gratings with varying parameters.

New, high-coherent-flux X-ray beamlines at synchrotron and free-electron laser light sources rely on wavefront sensors to achieve and maintain optimal alignment under dynamic operating conditions. This includes feedback to adaptive X-ray optics. We describe the design and modeling of a new class of binary-amplitude reflective gratings for shearing interferometry and Hartmann wavefront sensing. Compact arrays of deeply etched gratings illuminated at glancing incidence can withstand higher power densities than transmission membranes and can be designed to operate across a broad range of photon energies with a fixed grating-to-detector distance. Coherent wave-propagation is used to study the energy bandwidth of individual elements in an array and to set the design parameters. We observe that shearing operates well over a ±10% bandwidth, while Hartmann can be extended to ±30% or more, in our configuration. We apply this methodology to the design of a wavefront sensor for a soft X-ray beamline operating from 230 eV to 1400 eV and model shearing and Hartmann tests in the presence of varying wavefront aberration types and magnitudes.

Diffraction gratings have always been used to effectively couple optical radiation within integrated waveguides. This is also valid for plasmonic structures that support Surface Plasmon Polariton (SPP) waves. Traditional gratings usually excite SPP waves at the interface where they are located or, for thin metal nanostrips, at both interfaces. But reducing the thickness of the metal layer in the presence of a grating has the handicap of increasing the tunnelling of light towards the substrate, which means higher losses and reduced coupling efficiency. In this paper, we design and optimize novel gratings buried within the metallic thin films for selective coupling of SPP waves onto individual interfaces. Compared with traditional superficial gratings, the novel buried ones demonstrate higher efficiency and much lower residual tunnelling of light through the coupling structures.

The present work examines the absorption enhancement of Transparent Conducting Oxides (e.g., Aluminum doped Zinc Oxide (AZO), Gallium doped Zinc Oxide (GZO), and Indium doped Tin Oxide (ITO) for widely used telecom spectral window around λ = 1550 nm. This is by virtue of the fact that the silica-based optical fiber exhibits minimum loss in this window. It is well established that one-dimensional metallic lamellar grating can significantly enhance light absorption through diffraction and excitation of surface plasmon polaritons (SPPs) at the metal-dielectric interface. This results in subwavelength confinement and hence, enhanced optical absorption in the absorbing layer near the grating. The absorption enhancement can be tuned in different spectral regions by controlling grating parameters, such as grating period, grating height, and grating aspect ratio. The present work focused on establishing Transparent Conducting Oxides (TCOs) as effective plasmonic materials for metallic grating to optimize optical absorption in the near-infrared (NIR) spectral region. The role of TCOs and the grating parameters in fine-tuning the optical absorption enhancement is investigated. Moreover, TCO grating-based designs optimized for absorption enhancement in and around the telecommunication wavelength are proposed.

The results of studies of ring quantum-cascade lasers with surface emission due to a second-order grating formed in the top cladding layers are presented. Surface emission near 7.85 μm with a low threshold current density (3.8 kA/cm2), in comparison with ridge quantum-cascade lasers of the same cavity length is demonstrated. The results of measurements of the intensity distribution of the near and far fields at different pumping levels are presented. The estimated value of the angle of beam extraction relative to the surface normal is in the range 5.7°–6.7°. [ABSTRACT FROM AUTHOR]

Fast and accurate determination of ethanol concentration is important in alcohol industries for testing the purity and quality of their products. Here, we demonstrate a quick, robust, and accurate technique to estimate the concentration of ethanol in aqueous solutions. Our method utilizes the principle of diffraction of light in the presence of high frequency ultrasound waves that create diffraction grating in solution. A monochromatic light interacts with this acoustic grating and produces an intensity distribution pattern, which was used to determine the ethanol concentration. We measured ethanol concentrations in various alcoholic solutions and beverages at room temperature with very high accuracy down to 2 % over a concentration range of 30–100 %. The experimental results have been supported with analytical calculations and simulations. We believe that our method will benefit alcohol production industries and lead to the development of portable, inexpensive, and reliable ethanol concentration measurement devices. [ABSTRACT FROM AUTHOR]

The load-carrying belt of conveyor machines for clods of iron ore concentrate operates in a complex, aggressive dust and gas environment and cyclic "heating-cooling" modes. At the same time, the constituent elements of the load-bearing fabric - gratings also work under the influence of shock and abrasive loads, which leads to their intensive wear, as well as an increase in the regulated working gaps between adjacent gratings, and, therefore, to their premature replacement. In order to predict the degree of wear of the working surfaces of parts (grills), numerical models have been developed at the micro, macro, and meso levels. These models work in various combinations, but in the given conditions of operation of burning machines, due to the specifics of their work, meso- and micromodels rarely appear. The results of the analysis of the defects of the grates, which have failed, indicate the manifestation of macro-models, the schematization of which takes place mainly in the form of an erosive wear model. On the basis of macro models, Bitter's dependences were modified to calculate the degree of erosive wear of grates, and it was also established that to significantly reduce the degree of wear of pallets, it is recommended to use drum-type loading devices that ensure unloading of material with an angle of attack α=35÷45°. At the same time, the best recommended material for grates is steel 30Х14Г8Ю2Л. [ABSTRACT FROM AUTHOR]

An efficient light management technique is proposed and investigated by developing a TCAD model for microcrystalline silicon based thin film solar cell. The model includes physical insight related to some optical phenomenon like scattering and diffusive reflection of light as well as some electrical phenomena like carrier transport at the heterointerfaces. Two different structures, which comprises of sawtooth and grating-type back nanotextured in combination with random front nano-textured absorber layers are considered in this work. It has been observed that sawtooth or grating type back nano-textured absorber layer results in enhanced absorption of incident photons as compared to the planar back absorber layer. Also, the grating type back-textured absorber provides better performance compared to its sawtooth counterparts. Finally, the depth and period of grating are optimized in order to maximize the power conversion efficiency of grating-back-textured with random-front-textured absorber. The optimized structure results in an efficiency of 12.325% which corresponds to an improvement of 3.975% compared to the random front and back nano-textured thin film solar cell. [ABSTRACT FROM AUTHOR]

In this research, we present numerical simulations of the electromagnetic properties of a Ge/SiO2 grating structure with a distributed Bragg reflector at the bottom for efficient infrared absorption. We developed a single-period model to simulate an infinite periodic structure and used a Flouquet boundary condition to ensure periodic continuity. We verified the model's accuracy by testing different mesh densities and comparing the results to theoretical calculations based on Fresnel equations. We found that using 13 meshes per wavelength resulted in an error of less than 1%. Our simulations showed that the structure has a wide incident angle range of 100 degrees at a wavelength of 1550 nm. The absorbance spectrum of the design exhibits broadband properties, covering the primary wavelengths used in optical communications. The absorbance peaks reached 85.95% and 77.08% at 1340 and 1545 nm, respectively, with a minimum absorbance of 40% around 1400 nm. [ABSTRACT FROM AUTHOR]

Vertical-cavity surface-emitting lasers (VCSELs) have been widely used in consumer electronics, light detection and ranging, optical interconnects, atomic sensors, and so on. In this paper, a VCSEL with the surface metastructure like one-dimensional high-contrast grating (HCG), based on the HCG-DBR vertical cavity, was first designed and fabricated. The polarization characteristic of the HCG-VCSEL were experimentally studied. The p-doped top 4-pair DBR for the current spreading and the direction shift between the HCG and the elliptical oxide aperture may result in a low orthogonal polarization suppression ratio in the HCG-VCSEL. Then, the Bloch surface wave surface-emitting laser (BSW-SEL), based on the HCG-DBR metastructure, is proposed for single-mode, high-efficiency, and high-power output with a low divergence angle. The mode field and the far field profile of the BSW-SEL are calculated for verification. The surface-emitting lasers with surface metastructures are useful for the sensing applications and optical interconnects. [ABSTRACT FROM AUTHOR]

In this study, a dual−core D-shaped photonic crystal fiber (PCF) surface plasmon resonance sensor coated with gold grating is designed and analyzed using the finite-element method (FEM). The surface plasmon resonance (SPR) effect between the fiber core modes and surface plasmon polariton (Spp) modes is used to measure the analyte refractive index. The effects of the PCF structure parameters (polishing depths, large holes, and small holes) and grating parameters (grating heights, grating periods, and grating duty) are discussed, and a two-feature interrogation method that combines wavelength and intensity interrogations is introduced to enhance the resolution. The results show that the grating and dual-core play important roles in enhancing the sensor properties. The proposed sensor achieves an average wavelength sensitivity of 994.5 nm/RIU when the analyte refractive index increases from 1.33 to 1.37. Furthermore, a maximum amplitude sensitivity of 181.049 RIU−1 is obtained. The two-feature interrogation is determined to have a resolution of 2.03 × 10−6 RIU, which is better than the wavelength and amplitude interrogations. The proposed sensor has a good sensing performance and is highly suitable for practical applications. [ABSTRACT FROM AUTHOR]

Because the ohmic loss of metal materials affects the transmission efficiency of metasurface, we design a transmission-type all-dielectric coded metasurface element structure based on the principle of Pancharatnam-Berry geometric phase. We digitally encode these cell structures to construct a coded metasurface. In order to flexibly regulate the transmission angle of vortex beam encoded metassurface, we introduce the Fourier convolution principle in digital signal processing to perform the Fourier convolution addition operation for two different coding sequences. A new coding sequence is constructed by Fourier convolution operation of digital coding unit. Through this operation, the number of elements on the coded metasurface is constant, and the scattering angle of the vortex beam is flexibly controlled. In order to realize the multifunctional integration of phase vortex beams, we introduce the principle of digital coding addition in the complex domain to add two digitally coded metasurface sequences with different functions to realize the multifunctional superposition.

X-ray Talbot and Talbot–Lau interferometers consisting of transmission gratings are widely used for X-ray phase imaging, which depicts soft materials. This study exploits the use of a pair of concave and convex parabolic gratings instead of a conventional rectangular phase grating to enhance the phase signal optically. To gain insight into the optimal design, signal enhancement is evaluated by directly measuring the self-image formed downstream of the pair. An increase in the differential phase signals is demonstrated as a function of the distance between the pair, and prospects for deploying this concept into a practical phase imaging technique are discussed.

A conical-diffraction-based cross-dispersed spatial heterodyne spectrometer (CDCDSHS) is presented. Conical diffraction is introduced, and one grating in the SHS is rolled around the central normal of its surface to expand the spectral range. The two-dimensional fringes are generated by the longitudinal-dispersion grating and the lateral-dispersion gratings through conical diffraction. Mathematical expressions are given for the parameter of an interferogram with varying spectral features and for the intensity distribution. Two examples are numerically simulated to demonstrate the performance of the spectrometer. The simulations show that the designed spectrometer can limit the interferogram of each spectral feature to be recorded by certain given rows of pixels on the charge-coupled device to avoid multiplexing disadvantages, and it can obtain clear features in each detailed spectrum with a higher signal-to-noise ratio than the conventional SHS while eliminating the need for filters or moving parts. Replacing the lateral-dispersion grating in the designed spectrometer with a mosaic grating can increase the spectral resolution and broaden the detectable spectral range. The designed spectrometer is also compact, very stable, and high-throughput. All mentioned advantages make the CDCDSHS a good prospect in broadband, high-resolution, high-sensitivity spectral measurement.

Organic photomechanical crystals transform molecular‐scale photoisomerization events into largescale crystal shape changes. The results in this paper demonstrate that this photomechanical motion can be harnessed to reconfigure reflective elements on the crystal surface to actively control light propagation. This is accomplished by using a single organic photomechanical crystal composed of 1,2‐bis(2,4‐dimethyl‐5‐phenyl‐3‐thienyl)‐3,3,4,4,5,5‐hexafluoro‐1‐cyclopentene, which undergoes a reversible ring‐open to ring‐closed photoisomerization. Electron beam lithography patterning followed by a sublimation development step leaves periodically positioned, 120 nm deep grooves that are coated with gold metal to form a reflective grating on the crystal surface. Under UV irradiation, expansion of the bulk crystal increases the grating period by ≈5% and changes the diffraction angle of a 633 nm probe laser beam by 0.7° (first order) and 1.3° (second order). The grating period change can be reversed by visible light exposure and repeated for multiple cycles. The crystal expansion and thus the diffraction angle can also be continuously tuned by controlling the duration of light exposure. Anisotropic crystal expansion and contraction due to molecular photoisomerization enables low‐power light sources to steer light beams continuously over a range of diffraction angles. [ABSTRACT FROM AUTHOR]

In this work, a method using transmission interferometry is proposed to detect micro defects (streaks, inclusions, air bubbles, grooves, cracks, etc.) present in transparent materials surface. This technique is non-destructive and non-contact for the analysis of transparent and optical components whose surfaces vary from a few mm2 to larger sizes. The purpose of this method is to provide a means as simple as possible and to identify defects with low contrast, and in particular barely visible defects, and to differentiate between the defects. The transmission system generates interference fringes by the superposition of two microscopic periodic structures. According to the principle of the method, the image of the periodic microscopic structure, transmitted by the laser beam, traverses the sample. It then superposed on the reference microscopic structure; to generate the interference fringes, which materialize the presence of defects in the material. Changes in the shape of interference fringes inform the presence and dimensions of defects. This technique makes it possible to clearly identify microscopic and submicroscopic defects, thanks to the high resolution of the system. The optical device used allows high defect magnification of up to 1000 times. This control and measurement method allows for real-time inspection. It provides high detection resolution, allowing better observation of defects, which facilitates the automation of measurements and controls. Therefore, the proposed method can be suitable for the detection of surface defects in transparent optical objects such as optical films, lenses, and prisms. [ABSTRACT FROM AUTHOR]

Single-order diffraction gratings with quasi-random structures are effective optical elements in suppressing harmonics contamination. However, background intensity fluctuations introduced by quasi-random structures may affect the measurement of the spectra and the fluctuations lack quantitative description. A unified theoretical method is provided to describe quasi-random diffraction structures with arbitrary distribution functions and an arbitrary number of microstructures. The effect of the number of microstructures and distribution functions on the level of background fluctuations is evaluated. This work provides important guidance for the design and optimization of single-order diffraction gratings, which are attractive for spectral analysis and monochromator applications in synchrotron beam lines. [ABSTRACT FROM AUTHOR]

[Display omitted] Optical encryption, exploiting degrees of freedom of light as parameters to encode and decode information, plays an indispensable role in our daily life. Responsive structural color materials can give real-time visible feedback to external stimuli and provide ideal candidates for optical encryption. However, the development of existing responsive structural color materials is hindered by poor repeatability and long feedback time. Meanwhile, there are only few strategies to exploit structural colors in multichannel information encryption. Herein, bioinspired by the structural color variation due to a change in angle arising from the movement of animal's scales or feathers, we developed a general multichannel information encryption strategy using a two-dimensional deformable kirigami arranging orientations of the grating arrays by design. The kirigami grating sheet shows rapid, repeatable, and programmable color change. This strategy utilizes the topological space deformation to guide the change of optical property, which suggests new possibilities for spatial and spectral encryption as well as mechano-sensing and camouflage. [ABSTRACT FROM AUTHOR]

This paper focuses on creating one-dimensional diffractive grooved structures of antigen proteins on glass substrates for the label-free detection of antibodies to dairy allergens. In particular, the fabrication of protein structures is carried out by combining microcontact printing with physisorption, imines coupling, and thiol-ene click chemistry. The work first sets up these patterning methods and discusses and compares the main aspects involved in them (structure, biolayer thickness, functionality, stability). Homogeneous periodic submicron structures of proteins are created and characterized by diffractive measurements, AFM, FESEM, and fluorescence scanning. Then, this patterning method is applied to proteins involved in cow milk allergy, and the resulting structures are implemented as optical transducers to sense specific immunoglobulins G. In particular, gratings of bovine serum albumin, casein, and β-lactoglobulin are created and assessed, reaching limits of detection in the range of 30–45 ng·mL−1 of unlabeled antibodies by diffractive biosensing. [ABSTRACT FROM AUTHOR]

In this paper, an accurate and efficient method for the analysis of coupled perfectly conducting annular rings is presented. The problem is first formulated as a couple of Integral Equation (IEs) in the Vector Hankel Transform (VHT) domain, considered as unknowns in the cylindrical harmonics of the unknown surface current density. As a second step, Galerkin's method is applied with suitable expansion functions. The selected functions have two main properties: they reconstruct the expected physical behavior of the nth cylindrical harmonic at the edges of the annular rings, and their VHT transform is analytical and can be expressed in closed-form. Consequently, the method is effective and the problem is regularized, as testified by the truncation error. Comparisons with the commercial software CST Microwave Studio have been carried out and are presented to validate the method. [ABSTRACT FROM AUTHOR]

Metamaterial-based quarter-wave plates (QWPs) have emerged as promising candidates for advanced polarization control in a variety of optical applications, owing to their unique properties, such as ultra-thin profiles and tailored spectral responses. We design an ultra-thin, high-efficiency, and broadband QWP in transmission mode based on a TiO2/Au grating structure. We show that multiple reflections and the near-field effects associated with the integration of these devices pose challenges that must be considered when combining multiple metamaterials. We present insights that facilitate improved design methodology and the optimization of integrated metamaterial QWPs and other metadevices. Our results contribute to the development of miniaturized and high-density advanced lightwave and polarization control devices in optical systems.

Most existing multi-channel spectrometers are constructed by physically stacking single-channel spectrometers, resulting in their large size, high weight, and limited number of channels. Therefore, their miniaturization is urgently needed. In this paper, a microlens array grating is designed for miniature multi-channel spectrometers. A transmissive element integrating microlens arrays and gratings, the MLAG, enables simultaneous focusing and dispersion. Using soft lithography, the MLAG was fabricated with a deviation of less than 2.2%. The dimensions are 10 mm × 10 mm × 4 mm with over 2000 available units. The MLAG spectrometer operates in the 400–700 nm wavelength range with a resolution of 6 nm. Additionally, the designed MLAG multi-channel spectrometer is experimentally verified to have independently valid cells that can be used in multichannel spectrometers. The wavelength position repeatability deviation of each cell is about 0.5 nm, and the repeatability of displacement measurements by the chromatic confocal sensor with the designed MLAG multi-channel spectrometer is less than 0.5 μm.