Showing papers on "Diffraction efficiency published in 2000"
TL;DR: In this article, the concept of polarization freedom is employed to design diffraction gratings that are capable of transforming an electromagnetic plane wave into two or three diffraction orders with an arbitrary efficiency distribution among them, such that the combined efficiency of the signal orders is always equal to 100%.
Abstract: The concept of polarization freedom is employed to design diffraction gratings that are capable of transforming an electromagnetic plane wave into two or three diffraction orders with an arbitrary efficiency distribution among them, such that the combined efficiency of the signal orders is always equal to 100%. As a special case we consider paraxial-domain duplicators and triplicators with 100% efficiency, which is not possible for illumination by scalar waves: Diffractive elements that are capable of performing the required wave transformation must modulate the state of polarization of the incident field.
159 citations
TL;DR: In this article, the underlying physical phenomena behind the increased reflection/diffraction efficiency of holographically formed polymer-dispersed liquid crystal gratings formed from blended oligomers are investigated.
Abstract: The underlying physical phenomena behind the increased reflection/diffraction efficiency of holographically formed polymer-dispersed liquid crystal gratings formed from blended oligomers are investigated. Using parameters determined by in situ diffraction measurements during grating formation, a phenomenological diffusion model shows that a composition modulation in the polymer network results in blended oligomer systems. Scanning electron microscope studies reveal polymer morphologies consistent with this hypothesis.
151 citations
Patent•
28 Dec 2000
TL;DR: In this article, volume holographic elements were made from Bragg diffractive gratings in photo-thermo-refractive (PTR) glass with absolute diffraction efficiency ranging from greater than approximately 50% up to greater than 93% and total losses below 5%.
Abstract: Novel volume holographic elements were made from Bragg diffractive gratings in photo-thermo-refractive (PTR) glass with absolute diffraction efficiency ranging from greater than approximately 50% up to greater than approximately 93% and total losses below 5%. Both transmitting and reflecting volume diffractive elements were done from PTR glasses because of high spatial resolution enabling recording spatial frequencies up to 10000 mm−1. The use of such diffractive elements as angular selector, spatial filter, attenuator, switcher, modulator, beam splitter, beam sampler, beam deflectors controlled by positioning of grating matrix, by a small-angle master deflector or by spectral scanning, selector of particular wavelengths (notch filter, add/drop element, spectral shape former (gain equalizer), spectral sensor (wavelength meter/wavelocker), angular sensor (pointing locker), Bragg spectrometer (spectral analyzer), transversal and longitudinal mode selector in laser resonator were described. Combinations of those elements in the same volume are available too.
121 citations
TL;DR: A simple analytical model based on the attenuation properties of the waveguide and a fixed length of the grating aperture is developed, which is in good agreement with experimental filters formed with subwavelength period photoresist gratings and solgel waveguides.
Abstract: We evaluate the effect of finite aperture gratings on the spectral and efficiency characteristics of guided-mode resonance filters. A simple analytical model based on the attenuation properties of the waveguide and a fixed length of the grating aperture is developed. The results from this model are in good agreement with experimental filters formed with subwavelength period photoresist gratings and solgel waveguides.
107 citations
TL;DR: Photorefractive diffraction gratings were studied in cells of homeotropically aligned pentyl-cyanobiphenyl liquid crystal and induced by the simultaneous and nonsimultaneous application of dc and coherent optical electric fields, consistent with a predominantly surface-mediated photorefraction effect.
Abstract: Photorefractive diffraction gratings were studied in cells of homeotropically aligned pentyl-cyanobiphenyl liquid crystal. These holographic gratings were induced by the simultaneous and nonsimultaneous application of dc and coherent optical electric fields. The observed behavior was consistent with a predominantly surface-mediated photorefractive effect. Beam coupling was observed in all cases and led to a model involving screened and unscreened interfacial trapped charges driving a modulation of the easy axis. Holographic gratings could be switched on and off by the application of a small voltage.
103 citations
TL;DR: In this article, a model with which to describe and predict the formation of gratings during exposure in holographic photopolymers is presented, which combines the action of photopolymerization and of free-monomer diffusion during holographic exposures.
Abstract: We present a model with which to describe and predict the formation of gratings during exposure in holographic photopolymers. This model combines the action of photopolymerization and of free-monomer diffusion during holographic exposures. We consider the free-monomer density to be spatially varying, during exposure, with a single first-harmonic term out of phase with respect to the intensity interference pattern. Examples of behavior predicted by the model include the variation of the saturation diffraction efficiency with recording exposure intensity and with beam intensity modulation, as well as the variation of recorded grating modulation during dark diffusion transient. The model is supported by experiments carried out by exposure of DuPont HRF-150-38 holographic photopolymers.
93 citations
Patent•
24 Aug 2000TL;DR: In this paper, a volume diffractive element (Bragg grating) fabrication in photosensitive silicate glasses doped with silver, cerium, fluorine, and bromine was proposed.
Abstract: A novel process is proposed for the volume diffractive element (Bragg grating) fabrication in photosensitive silicate glasses doped with silver, cerium, fluorine, and bromine. The process employs a photo-thermo-refractive (PTR) glass of high purity exposed to ultraviolet (UV) radiation of a He—Cd laser at 325 nm followed by thermal development at temperatures from 480° C. to 580° C., preferably at 520° C., from several minutes to several hours. Absolute diffraction efficiency up to 95% was observed for 1 mm thick gratings. Maximum spatial frequency recorded in PTR glass was about of 10,000 mm −1 . No decreasing of diffraction efficiency were detected at low spatial frequencies. Original glasses were transparent (absorption coefficient less than 1 cm −1 ) from 350 to 4100 nm. Induced losses in exposed and developed glass decreased from 0.3 to 0.03 cm −1 between 400 and 700 nm, respectively, and did not exceed 0.01-0.02 cm −1 in the infrared (IR) region from 700 to 2500 nm.
88 citations
TL;DR: Holographic UV mirrors were recorded in a volume of photothermorefractive glass doped with silver, cerium, and fluorine, and did not deteriorate under the long-time effects of optical irradiation and heating up 400 degrees C.
Abstract: Holographic UV mirrors were recorded in a volume of photothermorefractive glass. This photosensitive silicate glass doped with silver, cerium, and fluorine is transparent in the near-UV, visible, and near-IR spectral regions, and its induced refractive-index change reaches 10(-3). UV radiation of a He-Cd laser at 325 nm was used for Bragg grating recording with a spatial frequency of approximately 9200 mm(-1). The absolute diffraction efficiency of the recorded mirror reached 12.6% at 325 nm and did not deteriorate under the long-time effects of optical irradiation and heating up 400 degrees C.
83 citations
TL;DR: In this article, phase-type gratings formed by photochemical phase transitions of a polymer azobenzene liquid crystal have been characterized and the sensitivity of the material was improved by a factor of 23 in the liquid-crystalline phase owing to effective induction of the photochemical phases in the bright fringes of the interference pattern.
Abstract: Phase-type gratings formed by photochemical phase transitions of a polymer azobenzene liquid crystal have been characterized. The sensitivity of the material was improved by a factor of 23 in the liquid-crystalline phase owing to effective induction of the photochemical phase transition in the bright fringes of the interference pattern. A mechanism for grating formation in films based on dynamics both in grating formation and for the photochemical phase transition has been proposed. Observation of the grating structure with a polarizing optical microscope confirmed that the isotropic phase induced photochemically was arranged at well defined separations. The polymer azobenzene liquid crystal showed a storage capability of >100 Mbits cm−2 which corresponds to a resolution of 1000 lines mm−1. We also attempted holographic image storage using a photomask as an object.
83 citations
Patent•
18 Dec 2000
TL;DR: In this article, an optical apparatus is disclosed for processing light that based on a pair of diffraction gratings operating in tandem, with one of the gratings being a fixed diffraction grating and with the other grating being electrically programmable.
Abstract: An optical apparatus is disclosed for processing light that based on a pair of diffraction gratings operating in tandem, with one of the gratings being a fixed diffraction grating and with the other grating being electrically programmable. The combination of the fixed and electrically-programmable diffraction gratings provides a spectral resolution and dispersion higher than that of either diffraction grating when used alone. These two diffraction gratings can be formed on different substrates, or alternately be combined to form a composite diffraction grating. The electrically-programmable diffraction grating can be operated in either a singly-periodic mode or a multi-periodic mode to select particular wavelengths of the incident light for analysis and detection, or for transferring between optical fibers (e.g. wavelength division multiplexing or demultiplexing). In some cases, a prism can be substituted for the fixed diffraction grating or used in addition to the fixed grating. The optical apparatus has applications for use in remote spectral analysis, spectrometry, and optical fiber communications.
78 citations
TL;DR: A diffractive Alvarez lens is demonstrated that consists of two separate phase plates, each having complementary 16-level surface-relief profiles that contain cubic phase delays that produce a variable astigmatic focus.
Abstract: A diffractive Alvarez lens is demonstrated that consists of two separate phase plates, each having complementary 16-level surface-relief profiles that contain cubic phase delays. Translation of these two components in the plane of the phase plates is shown to produce a variable astigmatic focus. Both spherical and cylindrical phase profiles are demonstrated with good accuracy, and the discrete surface-relief features are shown to cause less than λ/10 wave-front aberration in the transmitted wave front over a 40 mm×80 mm region.
TL;DR: An analytical proof is given to show that the observed identity is merely a manifestation of the electromagnetic reciprocity theorem for the 0th-order diffraction of symmetrical gratings.
Abstract: In a recent paper [J. Opt. Soc. Am. A16, 1108 (1999)] Logofǎtu et al. demonstrated by experimental and numerical evidence that the 0th-order cross-polarization (s to p and p to s) reflection coefficients of isotropic, symmetrical, surface-relief gratings in conical mount are identical. Here an analytical proof is given to show that the observed identity is merely a manifestation of the electromagnetic reciprocity theorem for the 0th-order diffraction of symmetrical gratings. The above result is further generalized to bianisotropic gratings, to the 0th-order cross-polarization transmission coefficients, and to the mth-order reflection and transmission coefficients when the wave vector of the incident plane wave and the negative of the wave vector of the mth reflected order are symmetrical with respect to the plane perpendicular to the grating grooves.
Patent•
19 May 2000
TL;DR: In this paper, a light panel that includes a light source and a panel element operatively connected to the light source is considered, and a diffractive outcoupling system is arranged on the panel element over a light surface of the panel elements and is operative to outcouple the light beams from inside the panel.
Abstract: A light panel that includes a light source and a panel element operatively connected to the light source. The panel element includes a substantially transparent light transmitting material and is operative as a waveguide panel inside which light beams received from the light source propagate with total reflection. A diffractive outcoupling system is arranged on the panel element over a light surface of the panel element and is operative to outcouple the light beams from inside the panel element. The diffractive outcoupling system includes a plurality of local grating elements. The local grating elements have a plurality configurations and are optimized such that a diffraction efficiency is a function of location.
TL;DR: In this article, a multilevel surface-relief-type diffractive optical elements are designed which are capable of generating a large number of Gauss-Laguerre modes with arbitrary mode indices in different diffraction orders of the element.
TL;DR: In this article, the authors measured the diffraction efficiency and analyzed the gratings characteristics for various writing beams polarizations in three polymers containing the same azo-dye, and revealed that the molecular mechanisms of holographic recording in the studied compounds are different.
TL;DR: This work provides further insight into the behavior of blazed-binary gratings and shows that they operate efficiently under symmetrical mounting and over a wide field-angle interval.
Abstract: Blazed-binary gratings for which a blazed effect with binary etches is achieved under normal incidence offer first-order diffraction efficiencies larger than those of blazed-echelette gratings in the resonance domain [Opt. Lett.23, 1081 (1998)]. We provide further insight into the behavior of blazed-binary gratings and show that they operate efficiently under symmetrical mounting and over a wide field-angle interval. These properties are illustrated with theoretical and experimental results obtained for an ≈1000-line/mm grating at 633 nm.
TL;DR: Diffractive optics are applied to six-wave mixing processes to provide a single optic approach to attaining the required, relatively complex, phase-matching geometry to discriminate against lower-order nonlinear responses.
Abstract: Diffractive optics are applied to six-wave mixing processes to provide a single optic approach to attaining the required, relatively complex, phase-matching geometry to discriminate against lower-order nonlinear responses. The diffractive optics were designed specifically for broad-bandwidth operation and passive phase locking of the appropriate pulse pairs for use in femtosecond two-dimensional Raman studies of the dynamic structure of liquids. The fifth-order signal was studied in liquid CS2; two different colors were used for the excitation and the probe to reduce background scatter, as were two different phase-matching geometries with different degrees of suppression of cascaded third-order processes.
27 Nov 2000
TL;DR: In this article, the authors fabricated and experimentally studied diffractive optical elements intended to focus near IR light into a ring and a twin-spot Fabrication technology and the performances of the fabricated optical elements are discussed.
Abstract: We fabricated and experimentally studied diffractive optical elements intended to focus near IR light into a ring and a twin-spot Fabrication technology and the performances of the fabricated optical elements are discussed
TL;DR: In this paper, a coupled-wave theory that includes the effects of the birefringence of the liquid crystal must be used to explain the diffraction properties of these anisotropic volume gratings.
Abstract: We have fabricated electrically switchable holographic gratings, using Polaroid Corporation’s DMP-128 photopolymer filled with the nematic liquid crystal E7. It is shown that a coupled-wave theory that includes the effects of the birefringence of the liquid crystal must be used to explain the diffraction properties of these anisotropic volume gratings. Furthermore, a detailed comparison of theory and experiment provides information about the alignment of the liquid crystal within the polymer host.
TL;DR: An overview of work directed toward the creation of arbitrary micron-scale patterns of electroactive polymer films by the application of photolithography can be found in this paper, where the spatially-patterned films are characterized by using optical and scanning electron microscopy.
Abstract: This manuscript presents an overview of work directed toward the creation of arbitrary micron-scale patterns of electroactive polymer films by the application of photolithography. A brief overview of work by other groups in the field is followed by a detailed description of work from our own labs which resulted in the development of methods to pattern a variety of different electroactive materials, including Ru− and Os−polypyridine complexes, viologen-based polymers, and a low-potential polythiophene. The discussion provides detail on the photolithographic methodology. In addition, the spatially-patterned films are characterized by using optical and scanning electron microscopy. The voltammetric and spectroelectrochemical properties of several of the lithographically-patterned films are also presented. Finally, photolithography is applied to fabricate electrochromic optical diffraction gratings. The diffraction efficiency of these electroactive gratings can be modulated by an electrochemical stimulus. The...
TL;DR: In this paper, the authors reported on the direct fabrication of refractive index gratings by irreversible photoinduced bleaching (photobleaching) into azo-dye-containing polymer films with a large second-order optical nonlinearity.
Abstract: We report on the direct fabrication of refractive index gratings by irreversible photoinduced bleaching (photobleaching) into azo-dye-containing polymer films with a large second-order optical nonlinearity. Gratings were formed into azo-dye-doped or attached polymer films upon exposure to an interference pattern of two laser beams from second harmonic light at 532 nm of a mode-locked Nd: yttrium–aluminum–garnet laser. To investigate whether the refractive index grating is formed into the azo-dye-containing polymer films by the two-beam interference exposure, IR spectroscopy was examined. Absorption strength from an azo bond in the exposed polymer film reduced selectively as compared with that of unexposed film. Although surface relief structure with a few nanometers depth on the polymer film was observed by using atomic force microscopy, the modulation depth of the grating was very small. So, we considered that the effect of the relief structure to diffraction efficiency obtained here is negligible. Furth...
Patent•
21 Dec 2000
TL;DR: In this article, a diffraction grating that achieves high diffraction efficiency at all polarizations for optical signals at telecommunications wavelengths is provided, which has a substrate and a plurality of reflective faces oriented at respective blaze angles θb spaced along the substrate surface.
Abstract: A diffraction grating that achieves high diffraction efficiency at all polarizations for optical signals at telecommunications wavelengths is provided. The diffraction grating has a substrate and a plurality of reflective faces oriented at respective blaze angles θb spaced along the substrate surface, with the blaze angles substantially differ from the Littrow condition. Each reflective surface is supported by a support wall connected substantially with the substrate surface.
TL;DR: The observation of optical vortices in a laser beam propagating through the stripe pattern of a cholesteric liquid crystal, which shows up as spots of zero light intensity in the diffraction maxima.
Abstract: We report the observation of optical vortices in a laser beam propagating through the stripe pattern of a cholesteric liquid crystal. The liquid crystal is confined in a cell with homogeneous boundary conditions and forms a diffraction phase grating. Optical vortices are produced by edge dislocations of the cholesteric grating. The vortices show up as spots of zero light intensity in the diffraction maxima. There is one spot in each +1 and -1 diffraction maximum and two spots in diffraction maxima +2 and -2.
TL;DR: The gratings produced by the method are of sufficient quality for use in high-resolution spectrographs in the visible and near IR (lambda approximately = 500-5000 nm) and are measured to have peak diffraction efficiencies at lambda = 632.8 nm.
Abstract: We have fabricated large, coarsely ruled, echelle patterns on silicon wafers by using photolithography and chemical-etching techniques. The grating patterns consist of 142-µm-wide, V-shaped grooves with an opening angle of 70.6°, blazed at 54.7°. We present a detailed description of our grating-fabrication techniques and the results of extensive testing. We have measured peak diffraction efficiencies of 70% at λ = 632.8 nm and conclude that the gratings produced by our method are of sufficient quality for use in high-resolution spectrographs in the visible and near IR (λ ≃ 500–5000 nm).
TL;DR: A one-step method, which is based on the effective medium theory, for the fabrication of a multilevel phase CGH, showed that the reconstructed wave field is in good agreement with that simulated by a computer, indicating the effectiveness of the proposed method.
Abstract: A conventional method to synthesize diffractive optical elements and computer-generated holograms (CGH’s) with high diffraction efficiency relies on an increase of phase levels. To fabricate such a device, one should perform electron-beam (e-beam) lithography with multiple-dose exposures or multiple-step photolithography. Here we describe a one-step method, which is based on the effective medium theory, for the fabrication of a multilevel phase CGH. The phase modulations required in cells of a CGH are constructed by means of dividing these cells into fine (subwavelength) structures. The surface features of these fine structures control their corresponding indices, and their values can be calculated according to the effective medium theory. By proper selection of the fine structures, based on the requirements of the phase modulation of the cells, a CGH with multilevel phases is synthesized when a binary structure is relieved on the dielectric material. Then the CGH can be fabricated by direct e-beam lithography or one-step photolithography through an amplitude mask followed by an ion-etching treatment. The experimental results showed that the reconstructed wave field is in good agreement with that simulated by a computer, indicating the effectiveness of the proposed method.
TL;DR: Photosensitive ZrO(2) gel films were patterned with a two-beam interference method by use of a 325-nm-wavelength He-Cd laser for the first time to the authors' knowledge to achieve maximum diffraction efficiency.
Abstract: Photosensitive ZrO2 gel films were patterned with a
two-beam interference method by use of a 325-nm-wavelength He–Cd laser
for the first time to our knowledge. The ZrO2 gel films
were prepared from
Zr(O-n-C4H9)4
chemically modified with benzoylacetone. We fabricated uniform
gratings with a 0.5-µm period on Si or SiO2
substrates by etching the gel films in ethyl alcohol after UV
irradiation. A maximum diffraction efficiency of 28% was attained
with the grating fabricated on Si substrate under a Littrow mounting
condition by use of a 633-nm-wavelength He–Ne laser. Blazed
gratings could also be fabricated.
TL;DR: It is found that the present method offers rather good performance for metallic gratings operating in the visible and near-infrared regions of the spectrum, especially for TM polarization.
Abstract: The numerical performance of a finite-difference modal method for the analysis of one-dimensional lamellar gratings in a classical mounting is studied. The method is simple and relies on first-order finite difference in the grating to solve the Maxwell differential equations. The finite-difference scheme incorporates three features that accelerate the convergence performance of the method: (1) The discrete permittivity is interpolated at the lamellar boundaries, (2) mesh points are located on the permittivity discontinuities, and (3) a nonuniform sampling with increased resolution is performed near the discontinuities. Although the performance achieved with the present method remains inferior to that achieved with up-to-date grating theories such as rigorous coupled-wave analysis with adaptive spatial resolution, it is found that the present method offers rather good performance for metallic gratings operating in the visible and near-infrared regions of the spectrum, especially for TM polarization.
Patent•
21 Jul 2000TL;DR: In this article, a collimator is provided to collimate light from a lambertian light source in which light from the fluorescent lamp is reflected towards an exit slit and the light which leaves the slit at 180 degrees and is collimated in one direction to +/−1/2 degree.
Abstract: A collimator is provided to collimate light from a lambertian light source in which light from a fluorescent lamp is reflected towards an exit slit and in which light which leaves the slit at 180 degrees and is collimated in one direction to +/−1/2 degree. The collimator is utilized in one application to maximize the diffraction efficiency of a diffractive color separator microlens array to increase the brightness of a color liquid crystal display and to increase color saturation. In order to provide collimation, the light exiting the exit slit is collimated by parabolic surfaces of an optical waveguide to provide a beam which has a collimation of +/−3 degrees in one direction. This light in one embodiment is spread out by a reflective array and is further collimated by a cylindrical lens array so that it exits a panel with the required +/−1/2 degree collimation.
TL;DR: Three-dimensional analysis of subwavelength diffractive optical elements (DOE's) using the finite-difference time-domain (FDTD) method is presented, and efficient 3D FDTD methods that exploit DOE properties, such as symmetry, are applied.
Abstract: We present a three-dimensional (3D) analysis of subwavelength diffractive optical elements (DOE’s), using the finite-difference time-domain (FDTD) method. To this end we develop and apply efficient 3D FDTD methods that exploit DOE properties, such as symmetry. An axisymmetric method is validated experimentally and is used to validate the more general 3D method. Analyses of subwavelength gratings and lenses, both with and without rotational symmetry, are presented in addition to a 2 × 2 subwavelength focusing array generator.
TL;DR: In this article, the authors proposed an iterative Fourier transform (IFTA) algorithm for beam-shaping diffractive optical elements, which is applicable for any desired intensity distribution with any intensity cross-section of the incident beam.
Abstract: Beam-shaping diffractive optical elements give a desired intensity distribution in the diffraction plane over areas much larger than the diffraction limited spot size. Such elements can be designed using geometrical optics methods or iterative-Fourier-transform algorithms (IFTAs). The usefulness of geometrical optics methods is considerably limited for two reasons: first the number of cases for which a solution exists is small and second the design solution, if it exists, often does not work in practice. Then IFTAs can be used. They are applicable for any desired intensity distribution in the diffraction plane with any intensity cross-section of the incident beam. The IFTA presented in this paper uses a novel set of operations that introduce a minimum disturbance of the fields while still leading to an improved performance. This makes the method robust, insensitive to stagnation and capable of iteratively distributing an increasing portion of the light in the diffraction plane into the desired ar...