Showing papers on "Diffraction grating published in 2022"

Replicating the Cynandra opis Butterfly's Structural Color for Bioinspired Bigrating Color Filters

Abstract: Multilayer grating structures, such as those found on the wings of the butterfly Cynandra opis, are able to interact with light to generate structural coloration. When illuminated and viewed at defined angles, such structural color is characterized by exceptional purity and brightness. To provide further insight into the mechanism of structural coloration, two‐photon laser lithography is used to fabricate bioinspired bigrating nanostructures, whose optical properties may be controlled by variation of the height and period of the grating features. Through the use of both spectral measurements and finite‐element method simulations, herein specific feature dimensions are identified that due to the combined effects of multilayer interference and diffraction generate excellent spectral characteristics and high color purity over the entire visible range. Additionally, it is demonstrated that variation of feature period and/or height plays a central role in controlling both hue and purity. Importantly, such tuneable bigrating structures are of significant utility in color filtering applications.

Imaging polarimetry through metasurface polarization gratings.

Abstract: Metasurfaces-subwavelength arrays of phase-shifting elements-present new possibilities for polarization optics and polarimetry. In particular, a periodic, polarization-sensitive metasurface diffraction grating can enable full-Stokes imaging polarimetry with a single polarization-sensitive component. In this work, we show that a suitably-designed metasurface grating can serve as a polarimetric "attachment" to an existing intensity-only imaging system, converting it into one capable of full-Stokes imaging polarimetry. Design rules and tradeoffs governing this adaptation are described and demonstrated using a machine vision imaging system as an example.

High efficiency transmission grating for the ESO CUBES UV spectrograph

Abstract: CUBES is the Cassegrain U-Band Efficient Spectrograph, a high-efficiency instrument operating in the UV spectral range between 300nm and 400nm with a resolution not less than 20000. CUBES is to be installed at a Cassegrain focus of the Very Large Telescope of the European Southern Observatory. The paper briefly reviews various types of devices used as dispersing elements in astronomical spectrographs to achieve high resolution, before identifying binary transmission gratings produced by microlithography as the best candidate technology for the CUBES instrument. We describe the lithographic fabrication technology in general, two different design considerations to achieve the required high-resolution transmission grating, its prototyping by a direct-write lithographic fabrication technology, and the characterization of the achieved optical performance. An outlook to the realization of the grating for the final instrument, taking the most recent developments of lithographic writing capabilities into consideration is given.

Diffraction properties of lights with transverse orbital angular momentum

Abstract: Spatiotemporal optical vortex (STOV) is a unique optical vortex with phase singularity in the space-time domain and the photons in a STOV can carry transverse orbital angular momentum (OAM). The STOV shows many fantastic properties which are worth exploring. Here, we theoretically and experimentally study the diffraction property of STOV, which is a fundamental wave phenomenon. The diffraction behaviors of STOVs are obviously affected by the transverse OAM. The diffraction patterns of STOV pulses diffracted by a grating show multi-lobe structure with each gap corresponding to 1 topological charge. The diffraction properties of lights with transverse OAM are demonstrated clearly and help us understanding the physical properties of STOV, which will be of special applications, such as the realization of fast detection of STOVs with different topological charges, which may pay the way for STOV based optical communication. Photons carrying orbital angular momentum (OAM) is an intrinsic property of optical vortex beams. The orientations of the OAM can be parallel or orthogonal to the propagation direction of the light beam, which are classified as longitudinal and transverse OAM, respectively. Conventional spatial optical vortex beam with phase singularity in the spatial plane possesses longitudinal OAM had been demonstrated [1]. Optical vortex beams have wide applications, such as optical tweezer and microparticle manipulation[2, 3], stimulated emission depletion (STED) microscopy[4], optical communication [5]. Spatiotemporal optical vortex (STOV) is a novel optical vortex with phase singularity in the space-time domain and the photons in a STOV can own transverse orbital angular momentum (OAM) [6-8]. Recently, STOVs were observed in experiments [9] and can be generated by using 4 f pulse shaper system [10, 11]. Furthermore, significant properties of STOV are analyzed, such as the conservation of transverse OAM in nonlinear optical process, second harmonic generation [12, 13], the propagation and generation properties of STOV [10, 14, 15], angular momenta and spin-orbit interaction of STOV [16] and transverse shifts and time delays occurred when STOV reflected and refracted at a planar interface [17]. Moreover, technologies for the measurement of STOV have also been presented, such as transient-grating single-shot supercontinuum spectral interferometry (TG-SSSI) [18] and interference methods [11]. The STOV beam opens a new area of vortex beam and may has special applications. Understanding the physical properties of STOV is not only important in theoretical areas, but also meaningful for the practical application of STOV. Diffraction is a fundamental phenomenon of light wave, which is well known for a conventional polychrome light beam. However, the diffraction property of STOV light has not been reported, to our knowledge. As it is well known that, for a conventional light beam without spatiotemporal coupling, the spectra are diffracted into one continuous line. However, for a STOV light beam with phase singularity in the space-time domain, energy is coupled between

Full Geometric Control of Hidden Color Information in Diffraction Gratings under Angled White Light Illumination.

Abstract: Under white light illumination, gratings produce an angular distribution of wavelengths dependent on the diffraction order and geometric parameters. However, previous studies of gratings are limited to at least one geometric parameter (height, periodicity, orientation, angle of incidence) kept constant. Here, we vary all geometric parameters in the gratings using a versatile nanofabrication technique, two-photon polymerization lithography, to encode hidden color information through two design approaches. The first approach hides color information by decoupling the effects of grating height and periodicity under normal and oblique incidence. The second approach hides multiple sets of color information by arranging gratings in sectors around semicircular pixels. Different images are revealed with negligible crosstalk under oblique incidence and varying sample rotation angles. Our analysis shows that an angular separation of ≥10° between adjacent sectors is required to suppress crosstalk. This work has potential applications in information storage and security watermarks.

High-efficiency nine-port beam splitting output enabled by a dielectric lamellar sandwiched fused-silica grating

Abstract: High-efficiency multi-beams output from diffraction optical element (DOE) with equal energy in parallel is of intense interest because high-performance multiple output beams can improve transmission rate of some key optical signals. Herein, we design a novel sandwiched fused-silica diffraction grating, which can operate at the high-efficiency nine-port beam splitting output with good uniformity. By performing rigorous coupled-wave analysis (RCWA) method, grating parameters and fabrication errors are optimized and discussed for TE and TM-polarized modes. A theoretical simplified modal method (SMM) can insight into an explicit light-matter coupling mechanism in grating area. In addition, for better evaluating real performances of the grating, incident spectral bandwidth of the grating can be fully investigated based on RCWA approach and finite-element method (FEM). Thus, this work can open up a possible way for optimizing more high-performance polarization-independent or polarization-dependent higher-order-port diffraction gratings.

High-efficiency nine-port beam splitting output enabled by a dielectric lamellar sandwiched fused-silica grating

Abstract: High-efficiency multi-beams output from diffraction optical element (DOE) with equal energy in parallel is of intense interest because high-performance multiple output beams can improve transmission rate of some key optical signals. Herein, we design a novel sandwiched fused-silica diffraction grating, which can operate at the high-efficiency nine-port beam splitting output with good uniformity. By performing rigorous coupled-wave analysis (RCWA) method, grating parameters and fabrication errors are optimized and discussed for TE and TM-polarized modes. A theoretical simplified modal method (SMM) can insight into an explicit light-matter coupling mechanism in grating area. In addition, for better evaluating real performances of the grating, incident spectral bandwidth of the grating can be fully investigated based on RCWA approach and finite-element method (FEM). Thus, this work can open up a possible way for optimizing more high-performance polarization-independent or polarization-dependent higher-order-port diffraction gratings.

Accurate Morphology-Related Diffraction Behavior of Light-Induced Surface Relief Gratings on Azopolymers

Abstract: Holographic relief gratings can be fabricated directly on the surface of azobenzene-containing materials (or simply azomaterials) without additional development steps. Despite often being described to have ideal sinusoidal profiles, the developing surface morphology in large amplitude gratings can affect the light distribution of the writing interferogram, causing profile deformations and deviations in the expected diffraction behavior. In this work, we characterize the temporal evolution of the surface relief grating (SRG) morphology fabricated by means of interference lithography on azopolymer films, quantitatively relating the results of a Fourier analysis of their surface profiles to the accurate measurement of efficiencies in the transmitted diffraction orders. A reliable surface structuration dynamics is empirically extracted from the analysis and used to formulate a simple but detailed diffraction model that, within the scalar diffraction theory, exhaustively describes the diffraction behavior of real SRGs without the need of complex rigorous electromagnetic theories. Our results add a deeper insight in the quantitative description of the morphology and the diffraction behavior of SRGs, which can contribute to their adoption for operating high-performance, reconfigurable, compact, and lightweight diffractive optical devices.

Study of a liquid crystal impregnated diffraction grating for active waveguide addressing

Abstract: Liquid Crystals are birefringent materials, which address many applications such as visualization with Liquid Crystal Display (LCD) or beam shaping with Liquid Crystal on Silicon devices (LCoS). Recently, several research teams proposed using liquid crystals in photonics devices applied to new kinds of projection displays. Augmented Reality (AR) is one of the domains, which could benefit from these developments, thanks to the necessity to create active and transparent optical function. In this contribution, we present recent works at CEA Leti to develop a switchable photonic extraction grating adapted to a specific near-eye device. Two different technics are detailed and studied with FDTD simulations. We also show first experimental characterization of an impregnated diffraction grating used in a free space optical set-up

High-Uniformity Submicron Gratings with Tunable Periods Fabricated through Femtosecond Laser-Assisted Molding Technology for Deformation Detection.

Abstract: As one of the important diffractive optical elements, the submicron gratings on flexible substrates can actively and precisely control the dispersion and steering characteristics of beams and have been widely applied in deformation detection technologies. Herein, we propose a spatially modulated femtosecond laser-assisted molding technology for efficiently fabricating high-uniformity large-area submicron gratings with tunable periods on flexible substrates. The technology first uses a cylindrically focused femtosecond laser-assisted chemical etching method to form a regular submicron grating on silicon; subsequently, the structure is cast with polydimethylsiloxane, a useful flexible substrate with a small Young's modulus, and cured to obtain a high-uniformity large-area submicron grating with a tunable period. The grating exhibits high mechanical stability and sensitivity and favorable optical properties. In the present study, as the deformation of the grating increased from 0 to 10%, the diffraction angle changed by 6.5°. Under illumination by a broad-band white-light source, distinguishable multicolor diffraction patterns were clearly observed. Drawing on this characteristic, we fabricated a deformation sensor. The grating fabricated by using the proposed technology also has potential applications in optical sensors and soft robots.

Effect of nonuniform pit structure on self-imaging of periodical gratings.

Abstract: Self-imaging possibilities for periodical gratings that have nonuniform pit structure are theoretically investigated. The diffraction of periodic arrays in the deep Fresnel region is analyzed according to the scalar diffraction theory. The expressions of the diffraction intensities of three different gratings that have binary square, binary circle, and Gaussian pit structure are considered. Talbot images of gratings with nonuniform pit structure are predicted to appear at multiple certain distances. The present paper shows that even a structure in short-range disorder may take on the self-imaging effect in a Fresnel field.

Monolithic dual-wedge prism-based spectroscopic single-molecule localization microscopy

Abstract: Abstract By manipulating the spectral dispersion of detected photons, spectroscopic single-molecule localization microscopy (sSMLM) permits concurrent high-throughput single-molecular spectroscopic analysis and imaging. Despite its promising potential, using discrete optical components and managing the delicate balance between spectral dispersion and spatial localization compromise its performance, including nonuniform spectral dispersion, high transmission loss of grating, high optical alignment demands, and reduced precision. We designed a dual-wedge prism (DWP)-based monolithic imaging spectrometer to overcome these challenges. We optimized the DWP for spectrally dispersing focused beam without deviation and with minimal wavefront error. We integrated all components into a compact assembly, minimizing total transmission loss and significantly reducing optical alignment requirements. We show the feasibility of DWP using ray-tracing and numerical simulations. We validated our numerical simulations by experimentally imaging individual nanospheres and confirmed that DWP-sSMLM achieved much improved spatial and spectral precisions of grating-based sSMLM. We also demonstrated DWP-sSMLM in 3D multi-color imaging of cells.

Direct single-pass writing of two-phase binary diffraction gratings in a Ge2Sb2Te5 thin film by femtosecond laser pulses

Abstract: • Femtosecond illumination produces non-ablative LIPSS on the surface of GST225 film. • High-quality elongated structures are recorded by a single scan of the laser beam. • The recorded two-phase structure is a reflective diffraction grating. The formation of alternating amorphous-crystalline structures on the surface of Ge 2 Sb 2 Te 5 thin film upon the single-pass direct writing by a femtosecond laser beam was demonstrated. We obtained high quality periodic surface structures in non-ablative mode and determined the optimal laser fluence, pulse number and scanning speed for their scaling. The produced structures were stripes up to 1-mm long and consisted of up to 50 parallel amorphous-crystalline lines oriented perpendicular to the light polarization. These two-phase binary stripes had a period equal to the recording beam wavelength and exhibited diffraction grating behavior due to remarkable optical contrast. Diffraction spectra were investigated experimentally and also simulated using scalar and vector theory of diffraction.

Light-Induced Dynamic Holography

Abstract: Holographic photomobile polymers (H-PMP) are a novel class of photomobile materials in which holograms can be optically recorded. They can be used in a large variety of applications, including optical switches and color selectors. In this work, we show one of the most important properties of the photomobile film, which is the photophobicity of the unpolymerized parts of the photomobile mixture. In order to investigate this property, we recorded a transmission phase grating on an H-PMP film, and used a different experimental technique to measure the diffraction efficiency, surface tension, and mixture properties. The results allowed for a better understanding of the mechanism of the light-controlled bending observed in these compounds.

Visible light waveband Dammann grating based on all-dielectric metasurface.

Abstract: Dammann gratings (DGs) can generate a spot array in a particular arrangement. In recent years, DGs have been used in many fields such as laser beam splitting and optical coupling. Nanograting encoding technology can achieve a high signal-to-noise ratio and high-efficiency diffraction distribution; it also provides new design ideas for realizing the miniaturization and deviceization of DGs. In this work, we have comprehensively studied the DG based on an all-dielectric metasurface, which can produce a 5×5 diffraction spot array with a diffraction angle of 20∘×20∘. In an operation waveband from 650 to 690 nm, the DG has superior performance with high efficiency ≥60%; meanwhile, it achieves a relative low contrast ratio ≤0.33. Owing to high efficiency, wide waveband performance, and polarization insensitive property, the all-dielectric metasurface DG can provide possibilities for various application, including laser technology and optical information processing.

Optical Fiber Diffraction Gratings

Abstract: Optical fiber diffraction gratings with periodic structure across the fiber section and fabricated by femtosecond laser are proposed and demonstrated. The diffraction patterns can be clearly observed and greatly enhanced by adopting multiple layer gratings. An optical fiber in-line Mach-Zehnder interferometer can be constructed by use of multiple layer diffraction grating pairs. The fiber diffraction gratings represent a new type of optical fiber device featured with high robustness, good operation stability and great potential for many photonics applications.

Optical diffraction simulation of a digital micromirror device

Abstract: We present a 3D electromagnetic simulation of a digital micromirror device (DMD) from 0.4 µm to 5 µm, which accurately models DMD reflectance and contrast ratio, including the effects of diffraction. A DMD is a spatial light modulator with a wide range of applications, including projection displays, 3D printing, and imaging spectroscopy. The physical structure of the DMD induces strong wavelength-dependent diffraction effects that impact the stray light, optical throughput, and pupil illumination distribution of a system. To quantify this, we perform a 3-dimensional electromagnetic finite-difference time-domain simulation, illuminating the DMD with a focused, incoherent beam, explicitly calculating the near-field electric fields, and calculating the far-field distribution of light. The far-field data determines diffraction efficiency and the distribution of light across the pupil. With these models, we are able to study the DMD’s optical efficiency in three key regimes: the specular regime, where the DMD behaves like a segmented mirror with a diffractive component (λ < 1 µm); the diffraction-dominated regime, which is also described by analytic diffraction grating theory (3 µm < λ < 5 µm); and, uniquely, the transition region, where the specular reflection and diffraction contributions are comparable (1 µm < λ < 3 µm). Our results inform system performance parameters, provide optical design constraints, and create a framework of use cases for DMDs.

Smartphone-Based Refractive Index Optosensing Platform Using a DVD Grating

Abstract: A low-cost, smartphone-based optical diffraction grating refractometer is demonstrated. Its principle of operation is based on the dependence of the diffraction efficiency of a DVD grating on the surrounding refractive index. The studied configuration uses the built-in LED flashlight and camera of a smartphone as a light source and a detector, respectively, to image the DVD grating diffraction pattern. No additional optical accessories, such as lenses, fibers, filters, or pinholes, are employed. The refractive index sensor exhibits a linear response in the refractive index range of 1.333–1.358 RIU (refractive index unit), with a sensitivity of 32.4 RIU−1 and a resolution of 2 × 10−3 RIU at the refractive index of water. This performance makes the proposed scheme suitable for affinity-based biosensing and a promising optosensing refractometric platform for point-of-need applications.

Smartphone-Based Refractive Index Optosensing Platform Using a DVD Grating

Abstract: A low-cost, smartphone-based optical diffraction grating refractometer is demonstrated. Its principle of operation is based on the dependence of the diffraction efficiency of a DVD grating on the surrounding refractive index. The studied configuration uses the built-in LED flashlight and camera of a smartphone as a light source and a detector, respectively, to image the DVD grating diffraction pattern. No additional optical accessories, such as lenses, fibers, filters, or pinholes, are employed. The refractive index sensor exhibits a linear response in the refractive index range of 1.333-1.358 RIU (refractive index unit), with a sensitivity of 32.4 RIU-1 and a resolution of 2 × 10-3 RIU at the refractive index of water. This performance makes the proposed scheme suitable for affinity-based biosensing and a promising optosensing refractometric platform for point-of-need applications.

Enhanced diffraction efficiency with angular selectivity by inserting an optical interlayer into a diffractive waveguide for augmented reality displays.

Abstract: The overall efficiency and image uniformity are important criteria for augmented reality display. The conventional in-coupling grating design intending to improve only the first-order diffraction efficiency without considering the multiple interactions with diffracted light in the waveguide is insufficient. In this work, the back-coupling loss (BCL) on the in-coupling surface relief grating, and the power of light arriving at the out-coupling grating over that of incident light (denoted as optical efficiency in waveguide, OEW) are introduced for the design of in-coupling grating. A simple and effective method to increase diffraction efficiency with unique angular selectivity is demonstrated by inserting an interlayer between the waveguide and grating. The optimized average OEW and its uniformity under a field of view of 40° are increased from 8.02% and 24.83% to 8.34% and 35.02% by introducing a region-selective MgF2 interlayer.

Dense spectral beam combining of quantum cascade lasers by multiplexing a pair of blazed gratings

Abstract: A method of compressing spectral bandwidth in spectral beam combining (SBC) of quantum cascade lasers (QCLs) by multiplexing a pair of blazed gratings arranged in a V-shaped configuration is proposed. The spectral interval can be compressed by increasing the number of diffractions via the round-trip propagation between gratings. Experimental results show that the SBC spectral interval of three diffractions is narrowed to 1/3 that of a single diffraction. The SBC power can be further improved within a given spectrum range by increasing the number of QCLs, which provides a feasible scheme to scale the SBC power and the brightness of QCLs.

Single-exposure multi-wavelength diffraction imaging with blazed grating

Abstract: Multi-wavelength diffraction imaging is a lensless, high-resolution imaging technology. To avoid multiple exposures and enable high-speed data collection, here an innovative setup for the single-exposure multi-wavelength diffraction imaging based on a blazed grating is proposed. Since the blazed angle varies with the wavelength, the diffraction patterns for the individual wavelengths can be separated from each other and recorded in a single measurement at one time. A method of high-precision position alignment between different wavelength patterns is proposed in our system to achieve good image quality and high resolution. Experiments on a phase-only USAF resolution target and biological samples were carried out to verify the effectiveness of our proposed method. This proposed setup has such advantages as a simpler structure, fast recording, and algorithm robustness.

The Development Progress of Surface Structure Diffraction Gratings: From Manufacturing Technology to Spectroscopic Applications

Abstract: The high-precision diffraction grating is an important chromatic dispersion component that has been widely used in many fields, including laser beam combining, chirped pulse compression, spectroscopy, among others. In this paper, we review the development status of reflection and transmission gratings with high diffraction efficiency and high laser-induced damage thresholds, such as metal-film and multilayer-dielectric-film gratings. Then, we review the basic principles and most recent stages in the development of manufacturing techniques, such as mechanical scribing, holographic exposure, electron-beam lithography, and nanoimprinting.

Enhanced refractometer for aqueous solutions based on perfluorinated polymer optical fibres

Abstract: The use of the new CYTOP (Cyclized Transparent Optical Polymer) fibres for the inscription of optical structures and the detection of different parameters has started to gain importance in the past decade. This work presents the design, simulation and manufacture of a CYTOP-based surrounding refractive index sensor for aqueous solutions, given its high sensitivity in the range 1.315 - 1.333 (at 1550 nm wavelength). The structure is based on a bent and polished fibre (in order to increase its sensitivity), the polished area being the surface on which a diffraction grating is inscribed with a femtosecond laser. The interaction of the field propagated by the fibre with the grating causes diffraction of certain orders towards the outside, depending, among other things, on the refractive index of the fluid. In addition to a maximum sensitivity of -208.8 nm/RIU and a remarkable insensitivity to temperature, it offers a spectral fingerprint of each sensed fluid.

Substrate-wave-induced antireflection in metasurfaces.

Abstract: We address the antireflection (AR) properties of periodic surfaces, or metasurfaces, supporting substrate waves. The work is motivated by recent literature where AR bands formed by substrate-wave propagation are incorrectly attributed to Mie scattering. In contrast, as clearly shown here, substrate-wave generation with corresponding AR signatures is a diffractive effect due to a periodic lattice and is not due to particle scattering as in Mie resonance. Treating both 1D and 2D surfaces, we demonstrate a clear quantitative connection between major AR loci and corresponding total substrate transmittance loci via maps in period versus wavelength. As shown, this holds for fully dispersed, lossy surfaces as well. The results presented here serve to elucidate the physical properties of periodic metasurfaces placed on substrates admitting propagating diffraction orders and may inform the design and implementation of grating-based AR structures.