Showing papers on "Diffraction efficiency published in 2018"
TL;DR: A new pair of materials are introduced—tungsten carbide and silicon carbide—to prepare layered structures with smooth and sharp interfaces and with no material phase transitions that hampered the manufacture of previous lenses.
Abstract: Multilayer Laue lenses are volume diffraction elements for the efficient focusing of X-rays. With a new manufacturing technique that we introduced, it is possible to fabricate lenses of sufficiently high numerical aperture (NA) to achieve focal spot sizes below 10 nm. The alternating layers of the materials that form the lens must span a broad range of thicknesses on the nanometer scale to achieve the necessary range of X-ray deflection angles required to achieve a high NA. This poses a challenge to both the accuracy of the deposition process and the control of the materials properties, which often vary with layer thickness. We introduced a new pair of materials-tungsten carbide and silicon carbide-to prepare layered structures with smooth and sharp interfaces and with no material phase transitions that hampered the manufacture of previous lenses. Using a pair of multilayer Laue lenses (MLLs) fabricated from this system, we achieved a two-dimensional focus of 8.4 × 6.8 nm2 at a photon energy of 16.3 keV with high diffraction efficiency and demonstrated scanning-based imaging of samples with a resolution well below 10 nm. The high NA also allowed projection holographic imaging with strong phase contrast over a large range of magnifications. An error analysis indicates the possibility of achieving 1 nm focusing.
110 citations
TL;DR: In this article, a metasurface composed of a subwavelength metallic slit array embedded in an asymmetric dielectric environment can exhibit either extraordinary optical transmission (EOT) or extraordinary optical diffraction (EOD).
Abstract: We show that a metasurface composed of a subwavelength metallic slit array embedded in an asymmetric dielectric environment can exhibit either extraordinary optical transmission (EOT) or extraordinary optical diffraction (EOD). The cascaded refractive indices of the dielectrics can leverage multiple decaying passages into variant subsections with different diffraction order combinations according to the diffraction order chart in the k-vector space, providing a flexible mean to tailor resonance decaying pathways of the metallic slit cavity mode by changing the wavevector of the incident light. As a result, either the zeroth transmission or −1st reflection efficiencies can be enhanced to near unity by the excitation of the localized slit cavity mode, leading to either EOT or EOD in a single structure, depending on the illumination angle. Based on this appealing feature, a multifunctional metasurface that can switch its functionality between transmission filter, mirror, and off-axis lens is demonstrated. Our findings provide a convenient way to construct multifunctional miniaturized optical components on a single planar device.
63 citations
TL;DR: PVG-based couplers for a double-layer waveguide display to realize a full-color near-eye display and presents a unique highly efficient single-order Bragg diffraction with polarized selectivity.
Abstract: In this Letter, we demonstrate polarization volume grating (PVG)-based couplers for a double-layer waveguide display to realize a full-color near-eye display. The polarized interference exposure with photo-alignment methods was employed to generate a birefringent spiral configuration with two-dimensional periodicity in a chiral-dopant reactive mesogen material. Such a structure presents a unique highly efficient single-order Bragg diffraction with polarized selectivity. The prepared PVG couplers exhibited over 80% diffraction efficiency with large diffraction angles at spectra of blue (457 nm), green (532 nm), and red (630 nm). The demonstrated waveguide prototype showed a full-color display with a diagonal field of view of around 35°. The overall optical efficiency was measured as high as 118.3 cd/m2 per lumen with a transparency of 72% for ambient light.
61 citations
TL;DR: A generalized Hartmann-Shack array with metalenses is created which measures phase and phase-gradient profiles of optical beams but also measures spatial polarization profiles at the same time.
Abstract: To define and characterize optical systems, obtaining information on the amplitude, phase, and polarization profile of optical beams is of utmost importance. Polarimetry using bulk optics is well established to characterize the polarization state. Recently, metasurfaces and metalenses have successfully been introduced as compact optical components. Here, we take the metasurface concept to the system level by realizing arrays of metalens 2*3 sub-arrays, allowing to determine the polarization profile of an optical beam. We use silicon-based metalenses with a numerical aperture of 0.32 and a mean measured diffraction efficiency in transmission mode of 28% at 1550 nm wavelength. Together with a standard camera recording the array foci, our system is extremely compact and allows for real-time beam diagnostics by inspecting the foci amplitudes. By further analyzing the foci displacements in the spirit of a Hartmann-Shack wavefront sensor, we can simultaneously detect phase-gradient profiles. As application examples, we diagnose the polarization profiles of a radially polarized beam, an azimuthally polarized beam, and of a vortex beam.
57 citations
TL;DR: In this article, a quantum optical model involving a plasmonic nanostructure (PN) was proposed for controlling the diffraction efficiency of an electromagnetically induced grating in a four-level quantum system.
Abstract: A quantum optical model involving a plasmonic nanostructure (PN) is proposed for controlling the diffraction efficiency of an electromagnetically induced grating in a four-level quantum system. By tuning the distance between the PN and the four-level quantum system, diffraction efficiency can be adjusted and energy can be transferred from zero order to higher orders. Moreover, due to the presence of the PN, the medium becomes phase-dependent and therefore, phase control of grating can be possible by changing the relative phase of the applied fields.
49 citations
TL;DR: In this paper, a new optical approach for highly efficient, compact, and fiber compatible laser beam steering using an in-fiber diffraction grating is proposed and experimentally demonstrated for the first time to the best knowledge.
Abstract: Diffraction gratings have been widely used in wavelength-controlled nonmechanical laser beam steering for high data-rate indoor optical wireless communications. Existing free-space diffraction gratings suffer from inherent difficulties of limited diffraction efficiency, bulky configuration, high cost, and significant coupling loss with optical fiber links. In this paper, a new optical approach for highly efficient, compact, and fiber compatible laser beam steering using an in-fiber diffraction grating is proposed and experimentally demonstrated for the first time to our best knowledge. In-fiber diffraction is made possible based on a 45° tilted fiber grating (TFG), where wavelength-dependent lateral scattering is obtained due to the strongly tilted grating structure. Improved diffraction efficiency of 93.5% has been achieved. In addition, the 45° TFG works perfectly for both light emission and reception, enabling full-duplex optical wireless transmission. Utility of the 45° TFG in all-fiber laser beam steering for multiuser full duplex optical wireless communications has been verified in experiments. About 1.4 m free-space full-duplex wireless transmission has been demonstrated with data rate up to 12 Gb/s per beam using 2.4 GHz bandwidth OFDM signals.
49 citations
TL;DR: This research created a ray-trace model of the optical system to optimize the component parameters and implemented the solution in a prototype that demonstrates the merit of the approach.
Abstract: The field of view of traditional heads-up display systems is limited by the size of the projection optics. Our research is focused on overcoming this limitation by coupling image-bearing light into a waveguide using holographic elements, propagating the light through that waveguide, and extracting the light several times with additional holographic optical elements. With this configuration, we demonstrated both longitudinal magnification and pupil expansion of the heads-up display. We created a ray-trace model of the optical system to optimize the component parameters and implemented the solution in a prototype that demonstrates the merit of our approach. Longitudinal magnification is achieved by encoding optical power into the hologram injecting the light into the waveguide, while pupil expansion is obtained by expanding the size of the hologram extracting the light from the waveguide element. To ensure uniform intensity of the image, the diffraction efficiency of the extracting hologram is modulated according to the position. Our design has a 12°×8° field of view at a viewing distance of 10 in. (250 mm), with infinite longitudinal magnification and a 1.7× lateral pupil expansion.
48 citations
TL;DR: In this article, a replicated X-ray reflection grating in an extreme off-plane geometry is presented, which demonstrates a total diffraction efficiency of ~60% from 0.34 to 1.2 keV at a grazing angle of 15, with single-order efficiency ranging from 35% to 65% for energies within the blaze envelope.
Abstract: We present the methodology used to fabricate an X-ray reflection grating and describe a technique for grating replication. Further, we present the experimental procedure and results of a study to measure the diffraction efficiency of a replicated X-ray reflection grating in an extreme off-plane geometry. The blazed grating demonstrates a total diffraction efficiency of ~60% from 0.34 to 1.2 keV at a grazing angle of ~15, with single-order efficiency ranging from ~35% to 65% for energies within the blaze envelope. The diffraction efficiency of the grating measured relative to the reflectivity of the metal coating averages ~90% above 0.34 keV. Data collected as a function of beam position on the grating indicate a relative variation in total efficiency of <1% rms across the grating surface.
45 citations
21 May 2018
TL;DR: DigiLens waveguide gratings are printed into a proprietary polymer and liquid crystal mixture that can provide any required combination of diffraction efficiency and angular bandwidth in a thin waveguide with high transparency and very low haze as discussed by the authors.
Abstract: DigiLens’s Switchable Bragg Grating (SBG) waveguides enable switchable, tunable and digitally reconfigurable color waveguide displays with a field of view, brightness and form factor surpassing those of competing technologies. DigiLens waveguides can be laminated to integrate multiple optical functions into a thin transparent device. DigiLens waveguide gratings are printed into a proprietary polymer and liquid crystal mixture that can provide any required combination of diffraction efficiency and angular bandwidth in a thin waveguide with high transparency and very low haze. The waveguide combines two key components: an image generation module, essentially a pico projector, and a holographic waveguide for propagating and expanding the image vertically and horizontally. Color is provided by a stack of monochrome waveguides each capable of addressing the entire field of view, incorporating an input rolled K-vector grating, a fold grating, and an output grating. Rolling the K-vectors expands the effective angular bandwidth of the waveguide. Fold gratings enable two-dimensional beam expansion in a single waveguide layer, which translates into lower manufacturing cost, reduced haze, and improved image brightness. The design of these complex SBGs is complicated by their birefringent properties, taking the design of DigiLens waveguides well beyond the frontiers of established ray-tracing codes. Our paper summarizes the key features of DigiLens waveguide technology and discusses our optical design methodology, with examples from DigiLens’s current waveguide HUD products.
31 citations
TL;DR: For the high-accuracy reconstruction of the wavefront (amplitude and phase) transmitted by the fabricated gratings, this work used a computational technique based on the sparse modeling of phase and amplitude.
Abstract: Surface relief gratings and refractive index gratings are formed by direct holographic recording in amorphous chalcogenide nanomultilayer structures As2S3−Se and thin films As2S3. The evolution of the grating parameters, such as the modulation of refractive index and relief depth in dependence of the holographic exposure, is investigated. Off-axis digital holographic microscopy is applied for the measurement of the photoinduced phase gratings. For the high-accuracy reconstruction of the wavefront (amplitude and phase) transmitted by the fabricated gratings, we used a computational technique based on the sparse modeling of phase and amplitude. Both topography and refractive index maps of recorded gratings are revealed. Their separated contribution in diffraction efficiency is estimated.
30 citations
TL;DR: In this article, the optical phase and temperature response of a liquid cooled SLM exposed to picosecond laser powers up to 2π radians with average power up to 130 W was investigated.
Abstract: Spatial light modulators (SLMs) addressed with computer generated holograms (CGHs) can create structured light fields on demand when an incident laser beam is diffracted by a phase CGH. The power handling limitations of these devices based on a liquid crystal layer has always been of some concern. With careful engineering of chip thermal management, we report the detailed optical phase and temperature response of a liquid cooled SLM exposed to picosecond laser powers up to 〈P〉 = 220 W at 1064 nm. This information is critical for determining device performance at high laser powers. SLM chip temperature rose linearly with incident laser exposure, increasing by only 5 °C at 〈P〉 = 220 W incident power, measured with a thermal imaging camera. Thermal response time with continuous exposure was 1–2 s. The optical phase response with incident power approaches 2π radians with average power up to 〈P〉 = 130 W, hence the operational limit, while above this power, liquid crystal thickness variations limit phase response to just over $\pi $ radians. Modelling of the thermal and phase response with exposure is also presented, supporting experimental observations well. These remarkable performance characteristics show that liquid crystal based SLM technology is highly robust when efficiently cooled. High speed, multi-beam plasmonic surface micro-structuring at a rate R = 8 cm2 s−1 is achieved on polished metal surfaces at 〈P〉 = 25 W exposure while diffractive, multi-beam surface ablation with average power 〈P〉 =100 W on stainless steel is demonstrated with ablation rate of ~4 mm3 min−1. However, above 130 W, first order diffraction efficiency drops significantly in accord with the observed operational limit. Continuous exposure for a period of 45 min at a laser power of 〈P〉 = 160 W did not result in any detectable drop in diffraction efficiency, confirmed afterwards by the efficient parallel beam processing at 〈P〉 = 100 W. Hence, no permanent changes in SLM phase response characteristics have been detected. This research work will help to accelerate the use of liquid crystal spatial light modulators for both scientific and ultra high throughput laser-materials micro-structuring applications.
11 Mar 2018
TL;DR: With a limited number of built-in power monitors to detect the optimum operating points of all switch units, a 32 × 32 MZI-based silicon electro-optical switch operating with nanosecond speeds is demonstrated.
Abstract: With a limited number of built-in power monitors to detect the optimum operating points of all switch units, we demonstrated a 32 × 32 MZI-based silicon electro-optical switch operating with nanosecond speeds.
TL;DR: A set of diffractive optical elements for multiple-stripe structured illumination was designed, fabricated and characterized that has the potential for reducing complexity, number of optical components, power consumption and costs of structured light projectors in mobile and stationary 3D sensors.
Abstract: A set of diffractive optical elements for multiple-stripe structured illumination was designed, fabricated and characterized. Each of these elements with a single layer of binary surface relief combines functions of a diffractive lens, Gaussian-to-tophat beam shaper, and Dammann beam splitter. The optical investigations of laser light patterns at 20° fanout angle reveal up to 88% diffraction efficiency, high contrast, and nearly diffraction limited resolution. The developed technology has the potential for reducing complexity, number of optical components, power consumption and costs of structured light projectors in mobile and stationary 3D sensors.
20 Oct 2018
TL;DR: Numerical and experimental results show the implementation of volumetric diffractive optics equivalent functionality via cascaded planar elements through two-layer continuous phase-only design on a single SLM with a folded setup improves system performance such as diffraction efficiency, spatial/spectral selectivity, and number of multiplexing functions relative to 2D devices.
Abstract: Volumetric computer-generated diffractive optics offer advantages over planar 2D implementations, including the generation of space-variant functions and the multiplexing of information in space or frequency domains. Unfortunately, despite remarkable progress, fabrication of high volumetric space-bandwidth micro- and nano-structures is still in its infancy. Furthermore, existing 3D diffractive optics implementations are static while programmable volumetric spatial light modulators (SLMs) are still years or decades away. In order to address these shortcomings, we propose the implementation of volumetric diffractive optics equivalent functionality via cascaded planar elements. To illustrate the principle, we design 3D diffractive optics and implement a two-layer continuous phase-only design on a single SLM with a folded setup. The system provides dynamic and efficient multiplexing capability. Numerical and experimental results show this approach improves system performance such as diffraction efficiency, spatial/spectral selectivity, and number of multiplexing functions relative to 2D devices while providing dynamic large space-bandwidth relative to current static volume diffractive optics. The limitations and capabilities of dynamic 3D diffractive optics are discussed.
TL;DR: An optimization method based on the differential evolution algorithm is proposed for in-coupling grating design to improve coupling efficiency and compensate for natural vignetting in large-field-of-view waveguide displays.
Abstract: Illuminance nonuniformity caused by natural vignetting can seriously affect the display quality of large-field-of-view (FOV) waveguide displays. In this paper, an optimization method based on the differential evolution algorithm is proposed for in-coupling grating design to improve coupling efficiency and compensate for natural vignetting. The in-coupling grating parameters are optimized to achieve efficiency distributions in which efficiency increases continuously with incidence angle, realizing uniform illuminance over a large FOV of 45°. The angular uniformity reaches 0.89. Additionally, average diffraction efficiency reaches 89.13% for transverse-electric polarization at 532 nm and 76% in the wavelength region between 450 and 700 nm.
TL;DR: A conceptually new in-fiber diffraction design opens the way towards cost-effective, compact and high-resolution OTSI systems for image-based high-throughput detection and measurement.
Abstract: Most overlooked challenges in ultrafast optical time stretch imaging (OTSI) are sacrificed spatial resolution and higher optical loss. These challenges are originated from optical diffraction devices used in OTSI, which encode image into spectra of ultrashort optical pulses. Conventional free-space diffraction gratings, as widely used in existing OTSI systems, suffer from several inherent drawbacks: limited diffraction efficiency in a non-Littrow configuration due to inherent zeroth-order reflection, high coupling loss between free-space gratings and optical fibers, bulky footprint, and more importantly, sacrificed imaging resolution due to non-full-aperture illumination for individual wavelengths. Here we report resolution-improved and diffraction-efficient OTSI using in-fiber diffraction for the first time to our knowledge. The key to overcome the existing challenges is a 45° tilted fiber grating (TFG), which serves as a compact in-fiber diffraction device offering improved diffraction efficiency (up to 97%), inherent compatibility with optical fibers, and improved imaging resolution owning to almost full-aperture illumination for all illumination wavelengths. 50 million frames per second imaging of fast moving object at 46 m/s with improved imaging resolution has been demonstrated. This conceptually new in-fiber diffraction design opens the way towards cost-effective, compact and high-resolution OTSI systems for image-based high-throughput detection and measurement.
TL;DR: The fabricated MLA behaves excellent optical focusing and imaging performance, which could be used to sense the change of the liquid refractive index (RI) and acquire high sensitivity and broad dynamic measurement range, respectively.
Abstract: In this study, a high-efficiency single-pulsed femtosecond laser assisted with chemical wet etching method has been proposed to obtain large-area concave microlens array (MLA). The quasi-periodic MLA consisting of about two million microlenses with tunable diameter and sag height by adjusting laser scanning speed and etching time is uniformly manufactured on fused silica and sapphire within 30 minutes. Moreover, the fabricated MLA behaves excellent optical focusing and imaging performance, which could be used to sense the change of the liquid refractive index (RI). In addition, it is demonstrated that small period and high RI of MLA could acquire high sensitivity and broad dynamic measurement range, respectively. Furthermore, the theoretical diffraction efficiency is calculated by the finite domain time difference (FDTD) method, which is in good agreement with the experimental results.
TL;DR: The spatial differentiation resulting from coupling and interference of spatial modes is shown and the theoretical condition for spatial differentiation based on spatial coupled-mode theory is derived.
Abstract: We propose a grating-based spatial differentiator to process a synthetic three-dimensional optical field, where several conventional two-dimensional optical images are stacked at multiple wavelengths. The device simultaneously enables both spatial differentiation and demultiplexing during light diffraction. We show the spatial differentiation resulting from coupling and interference of spatial modes and derive the theoretical condition for spatial differentiation based on spatial coupled-mode theory. We numerically investigate field transformation during diffraction and demonstrate spatial differentiation with image processing of edge detection for a synthetic three-dimensional optical field, where four images are stored at different wavelengths.
TL;DR: It is demonstrated that a square array of eight 120 fs pulsed beams from eight fiber outputs is coherently combined into one beam using the diffractive combiner, the first two-dimensional diffractive beam combination for ultrashort pulses.
Abstract: We demonstrate, to the best of our knowledge, the first two-dimensional diffractive beam combination for ultrashort pulses—a highly scalable technique capable of using a diffractive optic pair to combine large arrays of ultrashort pulsed beams. A square array of eight 120 fs pulsed beams from eight fiber outputs is coherently combined into one beam using the diffractive combiner. The experimental results show that the combined pulse preserves the input pulse width and shape, and the combining efficiency is measured to be close to the limit of the manufactured diffractive optic. An analysis shows that the combining loss due to uncompensated temporal and spatial dispersions is negligible.
TL;DR: A high-efficiency polarization-independent wideband multilayer dielectric reflective bullet-alike cross-section (combination of trapezoidal-rectangular grating profile) fused-silica beam combining grating (BCG) used in the -1st order for spectral beam combining (SBC) is designed and fabricated.
Abstract: A high-efficiency polarization-independent wideband multilayer dielectric reflective bullet-alike cross-section (combination of trapezoidal-rectangular grating profile) fused-silica beam combining grating (BCG) used in the -1st order for spectral beam combining (SBC) is designed and fabricated. Exact grating profile parameters are optimized by using the rigorous coupled-wave analysis and simulated annealing algorithm. As a comparison, traditional pure trapezoidal and pure rectangular gratings are also designed. Numerical results show that such a bullet-alike cross-section BCG exhibits wide bandwidth with the lowest maximum electric field enhancement in the grating material, which is greatly beneficial for the promotion of the power scaling level of the grating-based SBC system. A two-step dry-etching procedure is developed to fabricate such a grating. The averaged diffraction efficiency of greater than 91% was experimentally demonstrated.
TL;DR: Nanoscale material analyses of the modifications composing the gratings show that they rely on laser-induced stress associated with a positive refractive index change as confirmed with phase-shift interferometry, and it is shown that the grating diffraction efficiency depends strongly on the laser writing speed.
Abstract: Diffraction gratings are transversally inscribed in the bulk of monolithic crystalline silicon with infrared nanosecond laser pulses. Nanoscale material analyses of the modifications composing the gratings show that they rely on laser-induced stress associated with a positive refractive index change as confirmed with phase-shift interferometry. Characterizations of the optical properties of the gratings, including the diffraction angles and the efficiency of the different orders, are carried out. The refractive index change obtained from these measurements is in good agreement with the phase-shift measurements. Finally, we show that the grating diffraction efficiency depends strongly on the laser writing speed.
TL;DR: With the example of an alpha-iodic acid crystal, it is shown that in this case a peculiar character of optical anisotropy originates unique variants of acousto-optic interaction that are fundamentally impossible in uniaxial crystals.
Abstract: With the example of an alpha-iodic acid crystal, we demonstrate the unusual peculiarities of acousto-optic interaction in gyrotropic biaxial crystals. Basic attention is given to the most interesting cases of anisotropic diffraction in geometry, when the wave vector of ultrasound is directed almost orthogonally to one of the optical axes, and the directions of incident and diffracted light beams are close to the optical axis. It is shown that in this case a peculiar character of optical anisotropy originates unique variants of acousto-optic interaction that are fundamentally impossible in uniaxial crystals. A wide variety of frequency dependences of the Bragg angles allows choosing optimal configurations of crystal cuts for each specific acousto-optic device. The influence of the effect of optical activity on diffraction characteristics is examined as well.
TL;DR: In the proposed system, spatial frequency filtering by the liquid lens and image shape distortion seriously affected the hologram image, however, the feasibility of the proposed switchable holographic optical element using a liquid lens was verified.
Abstract: We report a switchable holographic optical element based on a liquid lens for a see-through display For the switchable holographic optical element, we recorded two optical components in the holographic film in two steps A numerical simulation was also done to define the recording and reconstruction conditions After the recording process, the entire system was changed from 4f optics to Maxwellian optics by changing wavefront of the reference wave using a liquid lens The diffraction efficiency was 046 for a single element recording and around 014 for a double element recording The holographic display and the Maxwellian display were successfully switched without any crosstalk The field of view and eye box of the holographic display were 1° and 436 mm, respectively, and the field of view and the eye box of the Maxwellian display were 38° and 232 um, respectively In the proposed system, spatial frequency filtering by the liquid lens and image shape distortion seriously affected the hologram image However, we successfully verified the feasibility of our proposed switchable holographic optical element using a liquid lens
TL;DR: A head-mounted display (HMD) system based on a wedge-shaped holographic waveguide that can present holographic virtual images with tunable distance is achieved and the virtual image can be obtained without aberration with experimental verification.
Abstract: In this study, a head-mounted display (HMD) system based on a wedge-shaped holographic waveguide that can present holographic virtual images with tunable distance is achieved. The compact computer-generated-hologram system using a spatial light modulator was employed to offer the dynamic image, where the probe beam for the hologram reconstruction is a convergent wave, and the DC term of the diffraction wave can be blocked by a barrier. The wedge-shaped holographic waveguide element was used as the combiner of the HMD system to generate a compact structure. A wedge with a polished surface was designed for in-coupling the image into the waveguide, and a reflection-type holographic optical element (HOE) was used for out-coupling the image from the waveguide. The astigmatism aberration and deformation of the diffraction images at various distances are analyzed and then are compensated. Finally, the virtual image can be obtained without aberration with experimental verification.
TL;DR: This paper presents a practical support for PQ/PMMA photopolymers in applications of transient information holographic storage by experimentally examined under nanosecond pulsed exposure and investigates the dark enhancement effect and real-time diffraction grating strength.
Abstract: Ultrafast holographic recording in bulk phenanthrenequinone dispersed poly (methyl methacrylate) photopolymers is experimentally examined under nanosecond pulsed exposure. A modified interference optical system is set to investigate the dark enhancement effect and real-time diffraction grating strength. Single transmission diffraction grating is recorded in a 6 nanosecond pulse exposure. Grating enhancement formation with different pulse quantity, repetition rate and spatial frequency are also measured. Diffraction efficiency is enhanced by increasing the pulse number as well as the single-pulse energy. The grating strength of 0.58 within 1.8 μs cumulative exposure time is obtained. Moreover, holographic reciprocity failure occurring in the ultrafast holographic storage is analyzed. This paper presents a practical support for PQ/PMMA photopolymers in applications of transient information holographic storage.
TL;DR: In this paper, the effect of substrate material selection for multilayer diffractive optical elements (MLDOEs) on polychromatic integral diffraction efficiency (PIDE) was studied in the oblique incident situation.
TL;DR: The first hologram in transmission mode based on a c-Si metasurface in the visible range shows high fidelity and high efficiency, with measured transmission and diffraction efficiencies of ~65% and ~40%, respectively.
Abstract: This paper reports on the first hologram in transmission mode based on a c-Si metasurface in the visible range. The hologram shows high fidelity and high efficiency, with measured transmission and diffraction efficiencies of ~65% and ~40%, respectively. Although originally designed to achieve full phase control in the range [0-2π] at 532 nm, these holograms have also performed well at 444.9 nm and 635 nm. The high tolerance to both fabrication and wavelength variations demonstrate that holograms based on c-Si metasurfaces are quite attractive for diffractive optics applications, and particularly for full-color holograms.
TL;DR: In this article, a physical model is built to study the DE distribution of out-coupling grating with consideration of the whole field of view, which is more consistent with the actual situations to realize a uniform imaging output for a waveguide-based near-eye display system.
Abstract: Planar waveguide structure has benefits to expand the exit pupil of the near-eye display. To achieve a uniform output luminance within the expanded exit pupil, a specific distribution of diffractive efficiency (DE) should be set for the out-coupling grating. In this paper, a physical model is built to study the DE distribution of out-coupling grating with consideration of the whole field of view. Compared to the previous works, which only considered the central view angle, this model is more consistent with the actual situations to realize a uniform imaging output for a waveguide-based near-eye display system. Also, a planar waveguide with two holographic volume gratings as the in- and out-coupling gratings is fabricated to verify the proposed DE distribution. In experiments, a spatial light modulator is applied as the spatial luminance modulator, and the coupling grating with the proposed DE distribution is fabricated by the holographic interference exposure setup. The results show a high consistency between the simulation and the experiment.
TL;DR: In this paper, the authors studied the dependence of the diffraction efficiency on the recording angle and thickness of a series of azopolymer layers, and the results indicated that the highest diffraction efficiencies were obtained for the sample with thickness 2400nm and for recording angle 10°.
Abstract: Azopolymers are one of the most efficient materials able to record the polarization state of light. They have numerous applications, such as data storage and diffractive optical elements with unique polarization properties. An essential parameter for each diffractive element is its diffraction efficiency η. In order to optimize the recording conditions and obtain high-efficient polarization holographic gratings, in the present work we study the dependence of the diffraction efficiency on the recording angle and thickness of a series of azopolymer layers. Three recording angles are used − 10°, 20° and 30° and three series of thin films with thicknesses 470, 850 and 2400 nm from the water-soluble azopolymer PAZO. The gratings are inscribed by two plain waves with left and right circular polarization from a He-Cd gas laser (442 nm). The diffraction efficiency of the gratings is probed with a right hand circularly polarized beam from a probe laser with wavelength 635 nm. The kinetics of diffraction efficiency η(t) in the + 1 diffraction order are presented and compared. Our experimental results indicate that highest diffraction efficiency (more than 40%) is obtained for the sample with thickness 2400 nm and for recording angle 10°. As the holographic recording in azopolymers is usually accompanied by formation of surface relief gratings, the surface topography of the recorded samples is also investigated by atomic force microscopy.
TL;DR: In this article, a single-groove grating for five-port TE-polarization beam splitting under normal incidence at the wavelength of 1550 nm is presented, and the transmitted diffraction efficiency of the gratings is over 94.5% with uniformity better than 2%.
Abstract: A single-groove grating for five-port TE-polarization beam splitting under normal incidence at the wavelength of 1550 nm is presented. The transmitted diffraction efficiency of the gratings is over 94.5% with uniformity better than 2%. A physical view of diffraction inside the grating is presented by the simplified modal method (SMM). Initial parameters of the grating profiles are obtained by use of SMM and then optimized by employing rigorous coupled-wave analysis and the simulated annealing algorithm.