Search Results (444)

This work is devoted to the study of the effect of the oscillating Poiseuille flow on the diffraction of light passing through a nematic layer bounded by a submicron relief at one of the inner surfaces of the plane capillary. In experimental nematic liquid crystal (NLC) cells with a hybrid planar–homeotropic orientation, a photo-profiled PAZO polymer layer with a sinusoidal relief with a depth of 180 and 360 nm and a period of 2 μm was used as a diffraction grating. The experimentally obtained dependencies of the flow-induced changes in the intensity of polarized light at the main and the first diffraction maxima on the amplitude of the low-frequency oscillating pressure gradient applied to the NLC layer are presented. Processing of the obtained results indicates the possibility of modulating the intensity of diffracted polarized light transmitted through the NLC layer by up to 10% when applying an oscillating pressure difference of up to 700 Pa to the layer of corresponding experimental cells in the absence of an analyzer in the optical scheme. Possible mechanisms responsible for the modulation of optical radiation in the main and first diffraction maxima are discussed. The discussed principles of controlling diffracted electromagnetic radiation can be used to create optofluidic modulators operating in both the visible and THz ranges. Full article

This work investigates the performance of a polyvinyl alcohol/acrylamide-based photopolymer (PVA/AA) under pulsed and continuous-wave (CW) laser exposure for holographic recording. Using a versatile setup that allows direct comparison between both regimes, diffraction efficiency (DE), angular responses, and material parameters were analyzed. Comparable maximum DE was achieved with both CW and pulsed laser exposure; however, the pulsed regime produces stronger attenuation along the grating depth, which emphasizes the need to lower the dye concentration. Furthermore, the temporal evolution of DE reveals a smaller influence of oxygen inhibition under CW exposure. Finally, second-order angular reconstructions confirm that pulsed gratings exhibit a better sinusoidal modulation, especially at low frequency rates. These results enhance the understanding of how pulsed exposure affects holographic recording and open pathways for optimizing photopolymer systems in advanced technologies. Full article

Three-dimensional holographic imaging technology is increasingly applied in biomedical detection, materials science, and industrial non-destructive testing. Achieving high-resolution, large-field-of-view, and high-speed three-dimensional imaging has become a significant challenge. This paper proposes and implements a three-dimensional holographic imaging method based on trillion-frame-frequency all-optical multiplexing. This approach combines spatial and temporal multiplexing to achieve multi-channel partitioned acquisition of the light field via a two-dimensional diffraction grating, significantly enhancing the system’s imaging efficiency and dynamic range. The paper systematically derives the theoretical foundation of holographic imaging, establishes a numerical reconstruction model based on angular spectrum propagation, and introduces iterative phase recovery and image post-processing strategies to optimize reproduction quality. Experiments using standard resolution plates and static particle fields validate the proposed method’s imaging performance under static conditions. Results demonstrate high-fidelity reconstruction approaching diffraction limits, with post-processing further enhancing image sharpness and signal-to-noise ratio. This research establishes theoretical and experimental foundations for subsequent dynamic holographic imaging and observation of large-scale complex targets. Full article

Optical transmission gratings with quasi-sinusoidal surface-relief profiles were inscribed in IOG and Pyrex glasses and in Bi₁₂GeO₂₀, Er: LiNbO_3, and Er: Fe: LiNbO₃ crystals by microbeams of carbon, nitrogen, and oxygen ions at ion energies of 5, 6, and 10.5 MeV. Grating constants were 4, 8, and 16 μm. Amplitudes of the surface-relief gratings were in the 10–2000 nm range. The diffraction efficiency of the gratings was measured at a wavelength of 640 nm. Maximum diffraction efficiencies were close to the theoretical maximum of 33% for thin gratings. Grating profiles were measured by optical microscopic profilometry. Measurement of the diffraction efficiencies at higher orders and Fourier analysis of the grating profiles revealed the dependence of the residual nonlinearity of the grating profiles on the implanted ion fluence. The ion microbeam-written gratings can be used as light coupling elements in integrated optics for sensors and telecommunication. Full article

Diffractive sail components may be used in part or whole for in-space propulsion and attitude control. A sun-facing hybrid diffractive solar sail having reflective front facets and transmissive side facets is described. This hybrid design seeks to minimize the undesirable scattering from side facets. Predictions of radiation pressure are compared for analytical geometrical optics and numerical finite difference time domain approaches. Our calculations across a spectral irradiance band from 0.5 to 3 μm suggest the transverse force in a sun facing configuration reaches 48% when the refractive index of the sail material is 1.5. Diffraction measurements at a representative optical wavelength of 633 nm support our predictions. Full article

Augmented reality (AR) displays are pivotal for delivering immersive experiences in the metaverse, thus driving significant research interest. Current AR systems, predominantly relying on diffraction principles, often suffer from low efficiency and face challenges in realizing monolithic full-color operation. Herein, we propose an AR system that integrates a broadband and highly efficient meta-grating in-coupler and an elliptical meta-grating out-coupler onto a single thin glass substrate. The meta-gratings, with unique nanostructures, enable coupling efficiency exceeding 60% for red (R), green (G), and blue (B) wavelengths across the entire field of view (FOV). Image-bearing light is first coupled into a single-layer optical waveguide via the meta-grating, then undergoes two-dimensional expansion through the elliptical meta-grating, and is ultimately coupled into the human eye to form a large AR FOV. Experimentally, we fabricated an optical waveguide prototype and validated the system’s high efficiency and color-enhanced imaging capabilities. This work advances the development of monolithic, trichromatic, highly efficient, and large FOV AR displays based on meta-grating technology. Full article

Augmented reality (AR) technology blends digital content with the real world to create immersive experiences. Diffractive waveguides, a key AR component, are popular because they balance weight, size, image quality, and ease of production. However, traditional glass-based waveguides have drawbacks like narrow viewing angles, blurry images, and rainbow-like distortions. To solve these issues, we developed ultra-thin, lightweight AR glasses using silicon carbide (SiC) and a new design method called the Period-Limited theory (PL theory). Our simulations show that the system works efficiently across red, green, and blue colors, removing rainbow distortions while keeping images clear and vibrant. Tests confirm that the design eliminates rainbow effects, provides a wide 55° field of view (FOV), and keeps each lens extremely light (just 2.12 g). This work offers a practical way to make compact, high-performance AR glasses with excellent display quality. Full article

Nanostructures with the two-dimensional (2D) periodicity are attracting increasing attention due to their promising applications in planar optical devices and their potential for scalable industrial production. While Rigorous Coupled-Wave Analysis (RCWA) has proven to be an efficient electromagnetic solver for simulating the diffraction of large-scale periodic nanostructures, it has been largely applied in nanostructures with one-dimensional (1D) periodicity and suffers from potentially low computational stability. In this study, we present a step-by-step formulation of the RCWA algorithm for 2D stratified grating structures. Through dimensionality reduction, we show that the boundary conditions in 2D gratings can be transformed into forms analogous to those of 1D gratings. Additionally, we implement a hybrid matrix algorithm to enhance the computational stability of the RCWA. The stability and accuracy of the hybrid matrix-enhanced RCWA algorithm are compared with other recursive methods. An exemplary application in metalens demonstrates the effectiveness of our algorithms. Full article

Micro- and nanopatterning is crucial for advanced photonic, electronic, and sensing devices. Yet achieving large-area periodic nanostructures with a 75 nm half-pitch on low-cost laboratory systems remains difficult, because conventional near-ultraviolet laser interference lithography (LIL) suffers from Gaussian-beam non-uniformity and a narrow exposure latitude. Here, we report a cost-effective deep-ultraviolet (DUV) dual-beam LIL system based on a 266 nm laser and diffractive flat-top beam shaping, enabling large-area patterning of periodical nanostructures. At this wavelength, a moderate half-angle can be chosen to preserve a large beam-overlap region while still delivering 150 nm period (75 nm half-pitch) structures. By independently tuning the incident angle and beam uniformity, we pattern one-dimensional (1D) gratings and two-dimensional (2D) arrays over a Ø 1.0 cm field with critical-dimension variation < 5 nm (1σ), smooth edges, and near-vertical sidewalls. As a proof of concept, we transfer a 2D pattern into Si to create non-metal-coated nanodot arrays that serve as surface-enhanced Raman spectroscopy (SERS) substrates. The arrays deliver an average enhancement factor of ~1.12 × 10⁴ with 11% intensity relative standard deviation (RSD) over 65 sampling points, a performance near the upper limit of all-dielectric SERS substrates. The proposed method overcomes the uneven hotspot distribution and complex fabrication procedures in conventional SERS substrates, enabling reliable and large-area chemical sensing. Compared to electron-beam lithography, the flat-top DUV-LIL approach offers orders-of-magnitude higher throughput at a fraction of the cost, while its centimeter-scale uniformity can be scaled to full wafers with larger beam-shaping optics. These attributes position the method as a versatile and economical route to large-area photonic metasurfaces and sensing devices. Full article

In recent years, with the continuous advancement of technology and the expansion of application scenarios, AR has become a highly regarded field. However, AR still faces several challenges in practical usage. Notable shortcomings include inadequate image uniformity, low diffraction efficiency. Among these, the insufficient image uniformity stands out as a significant issue directly affecting user experience. The analysis of uniformity improvement in this study is limited to the simulated scenario of monochromatic blue light (LED light source), aiming to optimize the insufficient uniformity of the image output of the diffractive optical waveguide-based AR technology scheme. We improve the details of the input grating in the waveguide, such as the morphological characteristics of the grating, the detail parameter, etc. In addition, we propose to incorporate a photonic crystal film in the waveguide as an innovative study and find that the incorporation of the photonic crystal thin film significantly improves the uniformity of the output image in the diffractive optical waveguide scheme. In order to further verify the effect of the photonic crystal film on the uniformity of its image output, we also compare different types of coupled gratings and find that they all have a positive effect. Thus, the photonic crystal film demonstrated effective control over the diffraction optical waveguide scheme. This research offers new insights and design approaches for enhancing the output image uniformity based on diffraction optical waveguide technology, providing a new path for improving image uniformity in AR displays. Full article

Narrow-linewidth broadband tunable external cavity diode lasers (NBTECDLs), with their broadband tuning range, narrow linewidth, high side-mode suppression ratio (SMSR), and high output power, have become important laser sources in many fields such as optical communication, spectral analysis, wavelength division multiplexing systems, coherent detection, and ultra-high-speed optical interconnection. This paper briefly describes the basic theory of NBTECDLs, introduces NBTECDLs with diffraction grating type, fiber Bragg grating (FBG) type, and waveguide type, and conducts an in-depth analysis on the working principles and performance characteristics of NBTECDLs based on different NBTECDL types. Then, it reviews the latest research progress on Littrow-type, Littman-type, FBG-type, and waveguide-type NBTECDLs in detail and compares and summarizes the characteristics of Littrow-type NBTECDLs, Littman-type NBTECDLs, FBG-type NBTECDLs, and waveguide-type NBTECDLs. Finally, it looks at the structural features, key technologies, optical performance, and application fields of the most cutting-edge research in recent years and summarizes the challenges and future development directions of NBTECDLs. Full article

The TECSL has attracted much attention due to its wide tuning range, narrow linewidth, high output power, and excellent SMSR. It holds irreplaceable value in optical communication, spectroscopy analysis, and biomedical applications. The demand for a wide tuning range, high power, narrow linewidth, and a high SMSR has driven the development of high-performance TECSL structures. This paper comprehensively discusses five key TECSL structures: Littrow-type structures, Littman-type structures, filter-type structures, fiber-type structures, and waveguide-type structures, and elaborates on their structures and principles. This paper reviews the research process of different type-structure TECSLs, analyzes the advantages and disadvantages of different external cavity structures, and explores the future development trends of TECSLs. The review shows that the Littrow-type structure TECSL achieved an extremely wide tuning range using diffraction gratings, reaching up to 360 nm. The Littman-type structure TECSL demonstrated excellent spectral purity, achieving an SMSR of 71.03 dB. The filter-type structure TECSL was able to achieve flexible wavelength selection using tunable filters, achieving a linewidth of 570 Hz. The fiber-type structure TECSL has a linewidth of up to 600 Hz. The waveguide-type structure TECSL can achieve a linewidth as low as 0.252 kHz and a tuning range of up to 120.9 nm. Full article

A novel encoding method based on the orbital angular momentum (OAM) mode and radial mode of composite vortex beams is proposed. The superposition of two vortex beams generates 32 different types of composite vortex beams: one of them is a Laguerre–Gaussian (LG) beam with a fixed OAM mode and radial mode, and the other is a LG beam containing four radial modes (p = 0, 1, 2, 3) and eight OAM modes with the same interval (l = ±3, ±5, ±7, ±9). A specially designed composite fork-shaped grating (CFG) is utilized to generate the intensity array pattern, and the received composite vortex beam is diffracted into a Gaussian beam with the relevant coordinates. Based on the coordinates and the number of bright rings in the intensity pattern, the OAM modes and radial modes of the two vortex beams composing the superposition state are determined, and finally the received composite vortex beam is decoded into the initially propagated information sequence. The correctness and effectiveness of the proposed encoding are confirmed through the comparative analysis of the correlation of the optical fields at both the transmitter and receiver in the two scenarios of interval and non-interval encoding. The proposed encoding method can significantly improve the efficiency of information transmission and its resistance to interference, holding great potential for future applications in free-space optical communication. Full article

The precise alignment of individual diffraction grating units within a tiled grating assembly (TGA) is essential for enhancing the quality of optical throughput and overall functional performance of such kinds of optical systems. This study presents a comprehensive simulation analysis of TGAs comprising two and four gratings to assess the sensitivity of optical imaging performance to a range of induced alignment errors. The misalignments are systematically introduced to the grating sections in the tiled grating assemblies, and their effects in far-field imaging are examined and compared. The results highlight the critical role of accurate alignment in maintaining coherent beam combination and optimal system performance. Zemax OpticStudio^®-based simulations offer valuable insights for designing high-performance, large-aperture grating systems and pave the way for future experimental validation and integration. Full article

A spectral filter utilizing dispersive prisms and an optical fiber collimator is presented as an attractive alternative to diffraction grating-based spectral filters. A simplified analytical expression for this prism-based spectral filter is derived. A spectral filter constructed using SF11 flint glass prisms demonstrates Gaussian spectral filter profiles with bandwidths of 8 nm and 4 nm, closely matching with theoretical predictions. Using these filters, we demonstrate two types of mode-locking regimes: a dissipative soliton (DS) pulse and a self-similar (SS) pulse. The dissipative soliton pulses deliver 3.3 nJ with dechirped pulse durations of 206 fs, while the self-similar pulses deliver 2.1 nJ with durations of 120 fs. The results demonstrate that the prism-based filters are well-suited for ultrafast mode-locked fiber lasers. Full article