Showing papers on "Diffraction efficiency published in 2013"
TL;DR: Improvements of the approach for applications such as holographic image projection, beam steering and switching, and real-time control loops are experimentally demonstrated.
Abstract: Nematic liquid crystal spatial light modulators (SLMs) with fast switching times and high diffraction efficiency are important to various applications ranging from optical beam steering and adaptive optics to optical tweezers. Here we demonstrate the great benefits that can be derived in terms of speed enhancement without loss of diffraction efficiency from two mutually compatible approaches. The first technique involves the idea of overdrive, that is the calculation of intermediate patterns to speed up the transition to the target phase pattern. The second concerns optimization of the target pattern to reduce the required phase change applied to each pixel, which in addition leads to a substantial reduction of variations in the intensity of the diffracted light during the transition. When these methods are applied together, we observe transition times for the diffracted light fields of about 1 ms, which represents up to a tenfold improvement over current approaches. We experimentally demonstrate the improvements of the approach for applications such as holographic image projection, beam steering and switching, and real-time control loops.
109 citations
TL;DR: In this structure, owing to Fano interference, the diffraction intensity of the grating, especially the first-order diffraction, can be significantly enhanced and this investigation may be used to develop novel photonic devices in semiconductor QW systems.
Abstract: We propose a scheme for obtaining an electromagnetically induced grating in an asymmetric semiconductor quantum well (QW) structure via Fano interference. In our structure, owing to Fano interference, the diffraction intensity of the grating, especially the first-order diffraction, can be significantly enhanced. The diffraction efficiency of the grating can be controlled efficiently by tuning the control field intensity, the interaction length, the coupling strength of tunneling, etc. This investigation may be used to develop novel photonic devices in semiconductor QW systems.
102 citations
TL;DR: Experimental evidence of unidirectional transmission of terahertz waves through a pair of metallic gratings with different periods is reported, and it is confirmed that the structure can be used successfully as an asymmetric filter.
Abstract: We report on experimental evidence of unidirectional transmission of terahertz waves through a pair of metallic gratings with different periods. The gratings are optimized for a broadband transmission in one direction, accompanied with a high extinction rate in the opposite direction. In contrast to previous studies, we show that the zero-order nonreciprocity cannot be achieved. Nonetheless, we confirm that the structure can be used successfully as an asymmetric filter.
93 citations
TL;DR: In this paper, a volume Bragg gratings with diffraction efficiency (absolute) ∼90% was demonstrated using Gauss-Bessel laser beams in fused silica glass.
Abstract: Direct laser write of volume Bragg gratings with diffraction efficiency (absolute) ∼90% is demonstrated using Gauss-Bessel laser beams in fused silica glass. Axial multiplexing of ∼ 90 μm long segments of modified optical material was demonstrated and thick Bragg gratings of aspect ratio depth/period ≈234 were achieved with period d = 1.5 μm. Typical fabrication scanning speeds were up to 50 mm/s for gratings with cross sections up to five millimeters made within 1 h time. Potential applications of high efficiency Bragg gratings in a low nonlinearity medium such as silica are discussed.
78 citations
TL;DR: The experimental investigation shows that the Moiré-lenses have a broad adjustable refractive power range with a high efficiency, which allows one to use them for flexible beam steering and for imaging applications.
Abstract: In an earlier publication [Appl. Opt. 47, 3722 (2008)] we suggested an adaptive optical lens, which consists of two cascaded diffractive optical elements (DOEs). Due to the Moire-effect the combined optical element acts as a Fresnel zone lens with a refractive power that can be continuously adjusted by a mutual rotation of the two stacked DOEs. Here we present an experimental realization of this concept. Four designs of these Moire-DOEs (MDOEs) were fabricated in thin (0.7 mm) glass slides by lithography and subsequent etching. Each element was realized as a 16 phase level DOE designed for 633 nm illumination. Our experimental investigation shows that the Moire-lenses have a broad adjustable refractive power range with a high efficiency, which allows one to use them for flexible beam steering and for imaging applications.
66 citations
TL;DR: In this article, a novel grating fabrication method that utilizes common lithographic and microfabrication techniques to produce the high fidelity groove profile necessary to achieve high resolving power grating spectrometers is presented.
Abstract: Future NASA X-ray spectroscopy missions will require high throughput, high resolving power grating spectrometers Off-plane reflection gratings are capa- ble of meeting the performance requirements needed to realize the scientific goals of these missions We have identified a novel grating fabrication method that utilizes common lithographic and microfabrication techniques to produce the high fidelity groove profile necessary to achieve this performance Application of this process has produced an initial pre-master that exhibits a radial (variable line spacing along the groove dimension), high density (>6000 grooves/mm), laminar profile This pre- master has been tested for diffraction efficiency at the BESSY II synchrotron light facility and diffracts up to 55 % of incident light into usable spectral orders Fur- thermore, tests of spectral resolving power show that these gratings are capable of obtaining resolving powers well above 1300 (λ/�λ ) with limitations due to the test apparatus, not the gratings Obtaining these results has provided confidence that this
66 citations
TL;DR: Large-scale gratings with conformal coating have been installed successfully in the 500 TW Scarlet laser system and it was confirmed by electromagnetic field modeling using the finite element method, which showed that non-conformal coating morphology gives rise to significant local field enhancement near groove edges, lowering the diffraction efficiency and increasing Joule heating.
Abstract: Laser-induced femtosecond damage thresholds of Au and Ag coated pulse compression gratings were measured using 800 nm laser pulses ranging in duration from 30 to 200 fs. These gratings differ from conventional metal-on-photoresist pulse compression gratings in that the gratings patterns are generated by etching the fused silica substrate directly. After etching, the metal overcoating was optimized based on diffraction efficiency and damage threshold considerations. The experiment on these gratings was performed under vacuum for single-shot damage. Single-shot damage threshold, where there is a 0% probability of damage, was determined to be within a 400–800 mJ/cm2 range. The damage threshold exhibited no clear dependence on pulse width, but showed clear dependence on gold overcoat surface morphology. This was confirmed by electromagnetic field modeling using the finite element method, which showed that non-conformal coating morphology gives rise to significant local field enhancement near groove edges, lowering the diffraction efficiency and increasing Joule heating. Large-scale gratings with conformal coating have been installed successfully in the 500 TW Scarlet laser system.
66 citations
01 Jan 2013
TL;DR: In this article, the main equations of diffraction theory are discussed, including diffractive optical transformations, and calculations of diffractive elements (DOE) in the geometrical optics approximation.
Abstract: Main equations of diffraction theory Diffractive optical transformations Calculation of diffractive optical elements (DOE) in the geometrical optics approximation Calculation of DOE in the scalar approximation of diffraction theory Multi-order DOE Calculations of diffraction gratings in electromagnetic theory Electromagnetic calculations of micro-optics elements Analysis of transverse laser radiation modes Formation of self-reproducing multi-mode laser beams Optical handling of micro-objects using DOE Synthesis of DOE on diamond polycrystalline films. Appendix: Nanophotonics and diffractive computer optics.
56 citations
TL;DR: In this paper, the inherent constraints of the spatial light modulator are taken into consideration for achieving improved intensity uniformity and enhanced diffraction efficiency. And the parallel fabrication of aspheric microlens arrays (AMLAs) by taking advantage of holographic femtosecond laser direct-writing is reported.
Abstract: Manufacture of aspheric microlens has always been technically challenging for conventional approaches due to their complex curved profile and tiny sizes. Two-photon polymerization is capable of producing arbitrary shape with high spatial resolution, apart from the disadvantage of ultra-low rate of yield resulting from point-by-point writing strategy. Here, we report parallel fabrication of aspheric microlens arrays (AMLAs) by taking advantage of holographic femtosecond laser direct-writing. The inherent constraints of the spatial light modulator are taken into consideration for achieving improved intensity uniformity and enhanced diffraction efficiency. Closely-packed AMLAs with designable optical parameters are readily fabricated with excellent optical performance.
54 citations
TL;DR: Two different simulation models for the spatial light modulator (SLM) are shown, one based on the measured subpixel Jones matrices of the SLM and the other based on a direction-dependent convolution model, which optimize different blazed gratings written in the SLm according to their diffraction efficiency.
Abstract: The fringing field effect of liquid-crystal displays causes a crosstalk between neighboring pixels, so that a desired sharp phase edge gets blurred. This blurring effect influences the diffraction efficiency of holograms, which are displayed on the spatial light modulator (SLM). In this paper, we show two different simulation models for the SLM, one based on the measured subpixel Jones matrices of the SLM and the other based on a direction-dependent convolution model. Using these models we optimize different blazed gratings written in the SLM according to their diffraction efficiency followed by an experimental verification.
53 citations
Patent•
08 Oct 2013
TL;DR: In this article, a method for fabricating high quality diffractive waveplates and their arrays that exhibit high diffraction efficiency over large area, the method being capable of inexpensive large volume production.
Abstract: The objective of the present invention is providing a method for fabricating high quality diffractive waveplates and their arrays that exhibit high diffraction efficiency over large area, the method being capable of inexpensive large volume production. The method uses a polarization converter for converting the polarization of generally non-monochromatic and partially coherent input light beam into a pattern of periodic spatial modulation at the output of said polarization converter. A substrate carrying a photoalignment layer is exposed to said polarization modulation pattern and is coated subsequently with a liquid crystalline material. The high quality diffractive waveplates of the present invention are obtained when the exposure time of said photoalignment layer exceeds by generally an order of magnitude the time period that would be sufficient for producing homogeneous orientation of liquid crystalline materials brought in contact with said photoalignment layer. Compared to holographic techniques, the method is robust with respect to mechanical noises, ambient conditions, and allows inexpensive production via printing while also allowing to double the spatial frequency of optical axis modulation of diffractive waveplates.
TL;DR: The proposed grating is optically tunable for diffractive and nondiffractive states with a small response time that depends on the exposure energy and LC parameters and can be erased and rewritten for different diffraction characteristics.
Abstract: An optically tunable and rewritable liquid crystal (LC) diffraction grating cell has been revealed that consists of an optically active and an optically passive alignment layer. The grating profile is created by confining the LC director distribution in alternate planar and twisted alignment domains by means of photoalignment of the LCs. The proposed grating is optically tunable for diffractive and nondiffractive states with a small response time that depends on the exposure energy and LC parameters. In addition, the grating can be erased and rewritten for different diffracting characteristics. These optically tunable diffractive elements could find application in various photonic devices.
TL;DR: In this article, the authors proposed high efficiency 1D silicon-silicon carbide (Si-SiC) and Si-SiO grating structures which can be used as optical interconnects in optical communication system.
TL;DR: This work presents the fabrication of such submicrometer scale structures by three dimensional laser two-photon photolithography, results of their optical properties measurements and compare the latter with numerical simulations.
Abstract: Simple diffraction structures having the form of a regular grid of pillars can generate a significant range of hues in white light transmission due to color-dependent diffraction into higher orders. We present the fabrication of such submicrometer scale structures by three dimensional laser two-photon photolithography, results of their optical properties measurements and compare the latter with numerical simulations.
TL;DR: In this article, a fabrication technique and results of studies of silicon binary diffractive optical elements (DOEs): a diffractive lens and a 1 : 2 diffractive beam splitter with an aperture diameter of 30 mm for the terahertz spectral range.
Abstract: This paper presents a fabrication technique and results of studies of silicon binary diffractive optical elements (DOEs): a diffractive lens and a 1 : 2 diffractive beam splitter with an aperture diameter of 30 mm for the terahertz spectral range. The elements were fabricated in two versions: with and without an antireflection coating of parylene C. The DOE characteristics were investigated in the beam of the Novosibirsk free electron laser at a wavelength of 141 μm. The results are given of a study of the radiation resistance of the coating, which remained intact upon exposure to an average radiation power density of 4 kW/cm2; the peak power in a 100 ps pulse was almost 8 MW/cm2. Experimental estimates of the diffraction efficiency of the elements coated with the antireflection coating are in good agreement with theoretical estimates.
TL;DR: A spatial-light-modulator-based method that allows for highly uniform, close to Gaussian spots with diffraction limited resolution using a wavelength of 780 nm and the lateral and axial resolution limits of spots generated by the new algorithm are found to be close to the diffraction limit.
Abstract: The generation of multi foci is an established method for high-speed parallel direct laser writing, scanning microscopy and for optical tweezer arrays. However, the quality of multi foci reduces with increasing resolution due to interference effects. Here, we report on a spatial-light-modulator-based method that allows for highly uniform, close to Gaussian spots with diffraction limited resolution using a wavelength of 780 nm. We introduce modifications of a standard algorithm that calculates a field distribution on the entrance pupil of a high numerical aperture objective splitting the focal volume into a multitude of spots. Our modified algorithm compares favourably to a commonly used algorithm in full vectorial calculations as well as in point-spread-function measurements. The lateral and axial resolution limits of spots generated by the new algorithm are found to be close to the diffraction limit.
TL;DR: In this article, the diffraction efficiency of a phase-only spatial light modulator with a large dynamic phase range was studied. But the authors used a phase only device that reached 4 π phase modulation depth for the wavelength of 454 nm.
TL;DR: In this article, the effect of laser pulse energy and grating thickness on the dispersive properties of the volume phase gratings is investigated, with the aim of improving the performance of the gratings in the mid-infrared.
Abstract: We report on the ultrafast laser inscription (ULI) of volume phase gratings inside gallium lanthanum sulphide (GLS) chalcogenide glass substrates. The effect of laser pulse energy and grating thickness on the dispersive properties of the gratings is investigated, with the aim of improving the performance of the gratings in the mid-infrared. The grating with the optimum performance in the mid-infrared exhibited a 1st order absolute diffraction efficiency of 61% at 1300 nm and 24% at 2640 nm. Based on the work reported here, we conclude that ULI is promising for the fabrication of mid-infrared volume phase gratings, with potential applications including astronomical instrumentation and remote sensing.
TL;DR: In this paper, the authors demonstrate that broadband blazing over almost one octave can be achieved by combining advanced optical design strategies and artificial dielectric materials that offer dispersion chromatism much stronger than those of conventional bulk materials.
Abstract: Surface topography dictates the deterministic functionality of diffraction by a surface. In order to maximize the efficiency with which a diffractive optical component, such as a grating or a diffractive lens, directs light into a chosen order of diffraction, it is necessary that it be "blazed". The efficiency of most diffractive optical components reported so far varies with the wavelength, and blazing is achieved only at a specific nominal energy, the blaze wavelength. The existence of spurious light in undesirable orders represents a severe limitation that prevents using diffractive components in broadband systems. Here we experimentally demonstrate that broadband blazing over almost one octave can be achieved by combining advanced optical design strategies and artificial dielectric materials that offer dispersion chromatism much stronger than those of conventional bulk materials. The possibility of maintaining an efficient funneling of the energy into a specific order over a broad spectral range may empower advanced research to achieve greater control over the propagation of light, leading to more compact, efficient and versatile optical components.
TL;DR: A phase lookup table is determined that can be used for any situation where a first-order (blazed) diffractive element is modified to produce higher orders with desired intensity and/or phase relation.
Abstract: We report a method to generate phase-only diffractive beam splitters allowing asymmetry of the target diffracted orders, as well as providing a tailored phase difference between the diffracted orders. We apply a well-established design method that requires the determination of a set of numerical parameters, and avoids the use of image iterative algorithms. As a result, a phase lookup table is determined that can be used for any situation where a first-order (blazed) diffractive element is modified to produce higher orders with desired intensity and/or phase relation. As examples, we demonstrate the phase difference control on triplicators, as well as on other generalized diffractive elements like bifocal Fresnel lenses and phase masks for the generation of vortex beams. Results are experimentally demonstrated by encoding the calculated phase pattern onto parallel-aligned liquid crystal spatial light modulators.
TL;DR: The disappearance of laser-conditioning effects for the highest-damage-threshold samples suggests a transition from a contamination-driven laser-damage mechanism to defect-driven damage for well-cleaned components.
Abstract: A low-temperature chemical cleaning approach has been developed to improve the performance of multilayer dielectric pulse-compressor gratings for use in the OMEGA EP laser system. X-ray photoelectron spectroscopy results guided the selection of targeted cleaning steps to strip specific families of manufacturing residues without damaging the grating's fragile 3D profile. Grating coupons that were cleaned using the optimized method consistently met OMEGA EP requirements on diffraction efficiency and 1054 nm laser-damage resistance at 10 ps. The disappearance of laser-conditioning effects for the highest-damage-threshold samples suggests a transition from a contamination-driven laser-damage mechanism to defect-driven damage for well-cleaned components.
TL;DR: In this paper, the fabrication procedure and optical characterization of ferroelectric liquid-crystal (FLC) gratings based on photo-alignment is described, which can be operated with high frequency of around 2 kHz at the electric field of 6.67 V/μm.
Abstract: This paper describes the fabrication procedure and optical characterization of ferroelectric liquid-crystal (FLC) gratings based on photo-alignment. The fabrication procedure includes only one side photo-alignment substrate, while the other substrate does not have any alignment layer. Both 1D and 2D gratings have been fabricated. The proposed diffraction element shows high diffraction efficiency ~ 65% and fast response time of 50 μs, which is much faster than the existing technologies. Such gratings can be operated with high frequency of around 2 kHz at the electric field of 6.67 V/μm. Moreover, the proposed grating can be erased and rewritten optically for different grating vector in simple steps. Therefore, with these advance features, such gratings have high potential to be applied in verity of devices and for the improvement of some important existing devices.
TL;DR: In this article, the authors extended the simulation method for the writing mechanism for the Bayfol® HX photopolymer film, which is a new class of recording materials for volume holography and is commercialized in 2010 and is offering the advantages for full-color recording and moisture resistance without any chemical or thermal processing.
Abstract: Bayfol® HX film is a new class of recording materials for volume holography. It was commercialized in 2010 and is offering the advantages for full-color recording and moisture resistance without any chemical or thermal processing, combined with low shrinkage and detuning. These photopolymers are based on the two-chemistry concept in which the writing chemistry is dissolved in a preformed polymeric network. This network provides the necessary mechanical stability to the material prior to recording. In addition to the well-known security and imaging applications, Bayfol® HX film also offers a new opportunity for the manufacturing of volume Holographic Optical Elements (vHOEs) in new optical and optoelectronic applications. For the implementation of holographic recording layouts and associated exposure schedules for these HOEs detailed understanding of the photopolymer material properties and the knowledge how to achieve the optical requirements of dedicated holographic applications are necessary. In this paper we extend the application of our simulation method for the writing mechanism for the Bayfol® HX photopolymer film. Different photopolymer product variations, including development of photopolymer grades with improved bleaching properties and increased dynamical range, which enable simultaneous multi-color recording, while maintaining a high diffraction efficiency of the recorded holograms are covered. The model is investigated experimentally by recording and evaluation of specifically designed directional diffuser vHOEs as they would be used e.g. for light shaping or light management purposes. One important observation is the capability of Bayfol® HX film type photopolymers to form highly efficient diffraction gratings even at very high intensity ratios of the reference beam versus the object beam.
TL;DR: In this article, a three-dimensional, polarization-sensitive optical model combining ray tracing and rigorous coupled-wave analysis was introduced to investigate silicon solar cells with pyramidal front-side texturing and back-side gratings.
Abstract: Back-side diffractive gratings enhance a solar cell's efficiency by trapping light inside the cell and increasing the probability of absorption. We introduce a three-dimensional, polarization-sensitive optical model combining ray tracing and rigorous coupled-wave analysis to investigate silicon solar cells with pyramidal front-side texturing and back-side gratings. Parameter optimization is performed to increase the short-circuit current density for a linear binary grating with grating period p and height h. For the investigated 180-µm-thick pyramidally textured silicon solar cells, the simulation yields a maximum enhancement of the short-circuit current density by ΔJSC = 1.79 mA/cm2 corresponding to an absolute efficiency increase of Δη = 0.90%. Furthermore, we report on fabrication and reflectance measurements of solar cells with gratings and key challenges in achieving efficiency gains using back-side diffractive gratings. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this article, a binary phase diffractive optical element that generates a set of optical vortices in a single laser beam with given weights to transmit information was developed, where the weight distribution in the form of the superposition is a code of the information and the phase element was calculated considering with the tradeoff between energy efficiency, accuracy of information transmitted and compliance technology to the manufacture of diffractive elements.
Abstract: The calculation algorithm of binary phase diffractive optical element that generates a set of optical vortices in a single laser beam with given weights to transmit information was developed. The weight distribution in the forming optical vortices superposition is a code of the information. The phase element is calculated considering with the trade-off between energy efficiency, accuracy of information transmitted and compliance technology to the manufacture of diffractive elements.
TL;DR: In this article, a volume holographic absorption grating induced by localized surface plasmon resonance effect in a bulk gold nanoparticles doped photopolymer was used to enhance the holographic performance.
Abstract: We report on the enhanced holographic performance by employing a strong volume holographic absorption grating induced by localized surface plasmon resonance effect in a bulk gold nanoparticles doped photopolymer. The contributions of plasmon-induced volume holographic absorption grating is characterized through the Kogelnik's coupled wave model and demonstrated experimentally by using two-beam interference technology. At the 0.05 vol. % concentration of the gold nanoparticles in the bulk photopolymer, 101.8% increase in the diffraction efficiency and more than four times suppression of the first side lobe in angular selectivity have been achieved.
TL;DR: In this paper, a polarization independent switchable phase grating based on polymer stabilized blue phase liquid crystal is proposed, which achieves high efficiency due to the sharp rectangular phase profile which shows good agreement with the simulation results.
Abstract: A polarization independent switchable phase grating based on polymer stabilized blue phase liquid crystal is proposed. A high efficiency of the phase grating has been achieved because of the sharp rectangular phase profile which shows good agreement with the simulation results. The diffraction efficiency of the 1st order is 38%, the response time is in the submillisecond range, and the phase grating is independent of the polarization of the incident light. The voltage-induced hysteresis characteristics are also investigated.
TL;DR: The chromatic properties of diffraction are exploited by using multicolor LED illumination and the possibilities and limits given by the use of a liquid crystal spatial light modulator to display the diffractive patterns are discussed.
Abstract: We present a method to increase the number of simultaneously imaged focal planes in diffractive multi-plane imaging. We exploit the chromatic properties of diffraction by using multicolor LED illumination and demonstrate time-synchronous imaging of up to 21 focal planes.We discuss the possibilities and limits given by the use of a liquid crystal spatial light modulator to display the diffractive patterns. The method is suitable for wide-field transmission and reflection microscopy.
Patent•
11 Jan 2013TL;DR: An optical imaging system includes a first diffractive optical element that receives a multi-wavelength beam of light and separates the received beam into diffractive orders as discussed by the authors, and an optical lens that focuses each of the multiwavelength beams of the diffractive order to a different location on an image plane at the same time.
Abstract: An optical imaging system includes a first diffractive optical element that receives a multi-wavelength beam of light and separates the received beam of light into diffractive orders. The optical imaging system also includes a second diffractive optical element that includes panels displaced along the second diffractive element in at least one direction, where each panel is positioned to receive and pass the multi-wavelength beam of one of the diffractive orders. A refractive optical element is positioned to receive multi-wavelength beams of the diffractive orders that pass through the second diffractive element, and an optical lens that receives the multi-wavelength beams of the diffractive orders that pass through the refractive element and focuses each of the multi-wavelength beams of the diffractive orders to a different location on an image plane at the same time.
TL;DR: The efficiency of the suggested techniques of the optical layout process are demonstrated by using the example of the design and analysis of a zoom lens intended for use in security cameras for day or night vision.
Abstract: The requirements for selecting the initial scheme for a compact plastic zoom lens are formulated. The main stages of the initial scheme of the transformation, incorporating the diffractive lens and replacement of the lenses’ glasses by optical plastics, are presented. The efficiency of the suggested techniques of the optical layout process are demonstrated by using the example of the design and analysis of a zoom lens intended for use in security cameras for day or night vision.