Showing papers on "Diffraction efficiency published in 1996"
TL;DR: In this paper, a new implementation of the coupled-wave method for TM polarization is proposed, which uses a second-order differential operator established by Neviere together with a scattering-matrix approach.
Abstract: A new implementation of the coupled-wave method for TM polarization is proposed. We use a second-order differential operator established by Neviere together with a scattering-matrix approach. Thus we obtain for metallic gratings a convergence rate as quick as that in TE polarization.
365 citations
TL;DR: M/# is introduced as a metric for characterizing holographic memory systems and it is verified experimentally that the diffraction efficiency of multiple holograms follows the prediction of M/# measured from a single hologram.
Abstract: We introduce M/# as a metric for characterizing holographic memory systems. M/# is the constant of proportionality between diffraction efficiency and the number of holograms squared. Although M/# is a function of many variables in a holographic recording system, it can be measured from the recording and erasure of a single hologram. We verify experimentally that the diffraction efficiency of multiple holograms follows the prediction of M/# measured from a single hologram.
322 citations
TL;DR: In this paper, a theoretical investigation of resonant scattering from two-dimensional gratings is presented, which is explained in terms of the coupling between the incident plane wave and guided modes that can be supported by the twodimensional grating waveguide structure.
Abstract: A theoretical investigation of resonant scattering from two-dimensional gratings is presented. Abrupt changes of diffraction efficiency over a small parameter range have been observed by rigorous coupled-wave analysis. The peak reflection or transmission efficiencies can approach unity. This phenomenon is explained in terms of the coupling between the incident plane wave and guided modes that can be supported by the two-dimensional-grating waveguide structure. Because of the double periodicity, the incident field can be coupled into any direction in the grating plane. The guided modes supported by two-dimensional gratings are found by rigorous solution of the homogeneous problem associated with the scattering (inhomogeneous) problem. The complex propagation constants for the guided modes provide estimates of both the resonance angle and width. In addition, to illustrate the implication of the radical change in the phase and amplitude of the propagating waves, we report a study of finite-beam diffraction in the resonant scattering region. Applications for the structures include polarization-independent narrow-band filters and bandwidth-tunable filters. It is shown that, because of the double resonance, the polarization-independent narrow-band filters have a large angular tolerance.
251 citations
TL;DR: The performance specifications of a holographic three-dimensional disk system are experimentally characterized and a surface density of 10 bits/µm(2) is experimentally demonstrated with a 100-µM-thick photopolymer as the recording medium.
Abstract: The performance specifications of a holographic three-dimensional disk system are experimentally characterized. A surface density of 10 bits/μm^2 is experimentally demonstrated with a 100-μm-thick photopolymer as the recording medium.
202 citations
TL;DR: It is shown that polarization holography may be used for real-time simultaneous measurement of photoinduced linear and circular birefringence in thin phase polarization holographic gratings recorded with two waves with orthogonal linear polarizations in materials in which illumination with linearly/ Circularly polarized light gives rise to linear/circular bireFringence.
Abstract: We investigate thin phase polarization holographic gratings recorded with two waves with orthogonal linear polarizations in materials in which illumination with linearly/circularly polarized light gives rise to linear/circular birefringence. The theoretical analysis shows that the presence of circular photoanisotropy changes significantly the diffraction characteristics of the gratings. The intensities of the waves diffracted in the +1 and −1 orders of diffraction and their ratio depend substantially on the reconstructing-wave polarization. Experiments with films of side-chain liquid-crystalline azobenzene polyester that is a photoanisotropic material of the considered type confirm the unusual polarization properties. It is shown that polarization holography may be used for real-time simultaneous measurement of photoinduced linear and circular birefringence.
167 citations
TL;DR: In this paper, a photopolymer-liquid crystal composite material system for writing in a fast single step, high diffraction efficiency volume holograms, capable of switching in applied electric fields of low voltage.
Abstract: Electrically switchable volume holograms lead to the possiblity of real-time electro-optical control of diffractive optic components. We report here on the development of a novel photopolymer-liquid crystal composite material system for writing in a fast single step, high diffraction efficiency volume holograms, capable of switching in applied electric fields of low voltage. Switching of a first-order Bragg diffracted beam into the zero-order with an applied field of ~10 V/µm was observed. With the addition of a surfactant to our pre-polymer syrup, we observed lowering of the switching fields to ~5 V/µm. We report response times for switching and relaxation in the order of microseconds. Low voltage, high resolution scanning electron microscopy studies show that the Bragg gratings formed consist of periodic polymer dispersed liquid crystal planes. The addition of surfactant leads to formation of very uniform small (20–40 nm) nematic droplets. A simple model based on the shape of the liquid crystal droplets...
153 citations
TL;DR: In this paper, a poly(4-nitrophenyl)-3-[N-[2-(methacryloyloxy)ethyl]carbazolyl]]diazene was prepared and its photoinduced birefringence, diffraction grating, and photorefractive asymmetric two-beam gain coupling were studied.
Abstract: Poly{(4-nitrophenyl)-3-[N-[2-(methacryloyloxy)ethyl]carbazolyl]]diazene} was prepared and its photoinduced birefringence, diffraction grating, and photorefractive asymmetric two-beam gain coupling were studied. The monomer was obtained by performing azo coupling in a two-phase water−dichloromethane system in the presence of a phase transfer catalyst. Photoinduced birefringence of up to 0.09 was observed and diffraction efficiencies of up to 25% were obtained, with atomic force microscopy studies revealing that the grating profile exhibited a sinusoidal shape. Asymmetric two-beam coupling is observed, indicating photorefractive properties, but the energy transfer phenomena are more complex, involving also diffraction by the photoinduced gratings. The combination of these three optical propertiesphotoinduced birefringence, surface gratings, and two-beam couplingis believed to be unique and may eventually produce an all-optical device built of a single polymer film.
134 citations
TL;DR: In this article, an asymptotic expansion of a multiple integral for knife-edge diffraction is derived, which expresses the field in terms of single edge diffraction, and a similar expansion for higher order UTD diffracted fields is proposed by means of a set of transition functions.
Abstract: An asymptotic expansion of a multiple integral for knife-edge diffraction is derived. The expansion expresses the field in terms of single-edge diffraction. By considering this expression, a similar expansion for higher order UTD diffracted fields is proposed. By means of a set of transition functions, the result removes some of the shortcomings of the original set out of the UTD when the incident field is not a ray-optical field.
96 citations
TL;DR: In this paper, a two-region formulation of the rigorous electromagnetic boundary element method (BEM) is developed and applied to practical diffractive cylindrical lenses of continuous profile and with discrete levels (32, 8, and 2).
Abstract: A novel two-region formulation of the rigorous electromagnetic boundary element method (BEM) is developed and applied to practical diffractive cylindrical lenses of continuous profile and with discrete levels (32, 8, and 2). The performance of these diffractive lenses is presented for incident waves of TE and TM polarization, for a range of beam profiles, and for normal and nonnormal incidence. An optimum width of the Gaussian beam is determined. The BEM is shown to be accurate and versatile, providing the numerical and graphical results that are needed for analysis and design of diffractive elements.
92 citations
TL;DR: In this paper, the authors report on a high optical quality, long-life guest-host photorefractive polymer composite which exhibits a 60% device steadystate diffraction efficiency and 120 cm−1 two-beam coupling gain, well in excess of its absorption of 3.5 cm− 1, at a wavelength of 676 nm.
Abstract: We report on a high optical quality, long‐life guest‐host photorefractive polymer composite which exhibits a 60% device steady‐state diffraction efficiency and 120 cm−1 two‐beam coupling gain, well in excess of its absorption of 3.5 cm−1, at a wavelength of 676 nm. In contrast to alternative composite materials of comparable high dye content, this performance has been achieved without unacceptably compromising device lifetime or ease of fabrication and storage. This is an efficient, easily prepared and comparatively stable polymer composite with device lifetimes under storage conditions already exceeding eight months and no indication of sample degradation with repeated holographic read–write cycles.
88 citations
Patent•
15 May 1996TL;DR: In this article, an illumination system for use in photolithography having an array optical element near the formation of a desired illumination field is described. But there is no condenser following the array or diffractive optical element.
Abstract: An illumination system for use in photolithography having an array optical element near the formation of a desired illumination field. Light or electromagnetic radiation from an illumination source is expanded and received by a multi-image optical element forming a plurality of secondary illumination sources in a plane. A condenser receives the light from the plurality of illumination sources. A array or diffractive optical element is placed on or near the focal point of the condenser. The illumination plane formed at the focal point of the condenser is within the near field diffraction pattern of the array or diffractive optical element. There is no condenser following the array or diffractive optical element. The use of the array or diffractive optical element permits the use of a condenser between the multi-image optical element and the array or diffractive optical element having a smaller numerical aperture than the emergent numerical aperture of the diffractive optical element, and generates a desired angular distribution with little dependance on the illumination source profile.
TL;DR: Polarization-selective computer-generated holograms made with form-birefringent nanostructures were designed, fabricated, and evaluated experimentally at 1.5 microm in good agreement with the design and modeling predictions.
Abstract: Polarization-selective computer-generated holograms made with form-birefringent nanostructures were designed, fabricated, and evaluated experimentally at 1.5 µm. The fabricated element showed a large polarization contrast ratio (>250:1) and a high diffraction efficiency (>40% for a binary phase level element). The experimental evaluation was in good agreement with the design and modeling predictions.
TL;DR: In this paper, third-order, one-dimensional, semiconductor-air gratings have been designed, fabricated, and evaluated by optical waveguide transmission measurements, showing a clear band edge around 840-850 nm.
Abstract: Third‐order, one‐dimensional, semiconductor‐air gratings have been designed, fabricated, and evaluated by optical waveguide transmission measurements. Gratings with as little as six unit cells show a clear band edge around 840–850 nm. Owing to our approach of semiconductor‐rich lattices with small airgaps, the diffractive spreading loss is sufficiently small (∼50% in the passband) for meaningful results to be extracted. The measurements indicate that the optical waveguide approach is a good starting point for the study of photonic microstructures and that practical device concepts can be implemented.
07 May 1996
TL;DR: In this article, fine-grained polymer dispersed liquid crystals have been used for switchable focus diffractive lenses, and it appears possible to shift optical power between widely separated focal points with a modulation ratio 100:1 on a 10 - 50 microsecond(s) time scale.
Abstract: Fine-grained polymer dispersed liquid crystals have recently become available for electrically switchable holographic elements. We explore applications of this novel material to switchable focus diffractive lenses. Several fabrication approaches, holographic and non-holographic, are demonstrated and compared with respect to design flexibility, diffraction efficiency, switching dynamic range, and optical quality. It appears possible to shift optical power between widely separated focal points with a modulation ratio 100:1 on a 10 - 50 microsecond(s) time scale.
TL;DR: A spherical diffractive lens fabricated in fused quartz for use at the 632.8-nm wavelength is demonstrated, constructed by use of a modulated two-dimensional binary grating with a high transmitted zerothorder efficiency.
Abstract: We demonstrate a spherical diffractive lens fabricated in fused quartz for use at the 632.8-nm wavelength. The lens is constructed by use of a modulated two-dimensional binary grating with a high transmitted zeroth-order efficiency. Rigorous eigenmode analysis is used to correlate the desired phase modulation with the fill factor. Fabrication requires only one lithography step. Using the lens, we were able to image a focal spot with a diffraction-limited spot size (FWHM).
TL;DR: In this article, the authors reported the results of dynamic phase grating formation in an anthraquinone derivative dichroic dye-doped nematic liquid crystal in which an external DC electric field was used to change the planar alignment of liquid crystal molecules into a near homeotropic one.
Abstract: In this paper we report the results of dynamic phase grating formation in an anthraquinone derivative dichroic dye-doped nematic liquid crystal in which an external DC electric field was used to change the planar alignment of liquid crystal molecules into a near homeotropic one. This field was also needed to produce an efficient grating via photoconductivity-induced molecular reorientation in a degenerate two-wave mixing experiment with He - Ne (632.8 nm) laser light serving as a low power excitation source. The characteristic of the measured effect shows that the mechanism of grating formation is evidently a non-photorefractive one. A diffraction efficiency of up to 20% has been measured in the system. Fast hologram recording and erasing times (1 ms) make this system attractive for image processing applications.
TL;DR: In this paper, a photorefractive polymer system based on a substituted polysiloxane backbone is described, which exhibits high holographic diffraction efficiency and reasonable writing speed, in addition to high optical clarity and low optical scattering characteristics.
Abstract: A photorefractive polymer system based on a substituted polysiloxane backbone is described. In addition to high holographic diffraction efficiency and reasonable writing speed, the material reported exhibits excellent optical clarity and low optical scattering characteristics. These latter optical properties are necessary in high density holographic digital data storage applications. The utility of the polysiloxane based photorefractive polymers for storage applications is demonstrated by recording digital data at a density of 0.52 Mbit/cm2 and reading it back without error.
TL;DR: The study of bacteriorhodopsin films finds that the hydrated BR films exhibit significantly higher refractive-index modulation than do dry films, and the film holographic properties were found to be relatively insensitive to the grating frequency and thegrating-tilt angle.
Abstract: Several different bacteriorhodopsin (BR) films are characterized with respect to general holographic properties. Experimental measurements include diffraction efficiency and sensitivity as functions of the writing intensity and grating frequency, hologram thermal-decay behavior, diffraction efficiency as a function of the grating tilt within the film and the modulation depth, and estimates of the refractive-index change from the diffraction-efficiency data. The films studied include those made from wildtype BR and the genetic variants D96N and D96N/T46V. The film holographic properties were found to be relatively insensitive to the grating frequency and the grating-tilt angle. The diffraction efficiency dropped off more sharply as a function of the modulation depth than did a purely linear medium, and only the hydrated wildtype film exhibited significant behavior variation with different writing intensities because of its short M-state lifetime. The maximum diffraction efficiency measured was approximately 7.5% for a hydrated D96N BR film. We also find that the hydrated BR films exhibit significantly higher refractive-index modulation than do dry films.
Patent•
27 Jun 1996
TL;DR: In this paper, a three-beam generating diffraction grating, a transmission type holographic optical element and a condenser lens are disposed in the light path in which the laser lights from the semiconductor lasers propagate toward the recording surface of an information recording medium.
Abstract: An optical pickup apparatus includes a semiconductor laser generating a light having a short wavelength for reproduction of a high-density information recording medium and a semiconductor laser outputting a light for reproduction of an information recording medium with low recording density. A three-beam generating diffraction grating, a transmission type holographic optical element and a condenser lens are disposed in the light path in which the laser lights from the semiconductor lasers propagate toward the recording surface of an information recording medium. The laser light emitted from each semiconductor laser is transmitted through the three-beam generating diffraction grating and divided into three beams and then transmitted through the transmission type holographic optical element and passed through the condenser lens to reach the recording surface of the information recording medium. The transmission type holographic optical element is formed so that the product of the diffraction efficiency of the laser light in the forward optical path and the separated diffraction efficiency of the returned light increases as the wavelength of the laser light decreases. The three-beam generating diffraction grating has grooves with such depth that the diffraction efficiency of the main beam in the three-divided beams is smaller and the diffraction efficiency of the sub-beams is larger as the wavelength of the laser light is shorter.
Patent•
25 Jan 1996TL;DR: In this paper, the authors proposed a dynamic multiple-wavelength filter which selects at least one wavelength from a beam of radiation incident on a Stratified volume Holographic Optical Element (SVHOE) in accordance with the Bragg condition.
Abstract: A dynamic multiple-wavelength filter which selects at least one wavelength from a beam of radiation incident on a Stratified volume Holographic Optical Element (SVHOE) in accordance with the Bragg condition. The SVHOE has a number n of grating layers i and a hologram of a grating vector Ki is recorded in each grating layer i. A number n-1 of buffer layers are interposed between grating layers i such that the layers SVHOE presents an alternating structure of grating and buffer layers. The filter has a diffraction efficiency control, preferably based on the ECD effect, for selectively varying the diffraction efficiency η in at least one grating layer i to select from the beam of radiation a narrow bandwidth centered about Bragg wavelength λB i of grating layer i.
TL;DR: The silica gel-methyl methacrylate organically modified ceramic is proposed for recording of volume holograms and Virtually no changes in diffraction efficiency were observed after thermal-heating, light-curing, and long-term-aging experiments.
Abstract: The silica gel–methyl methacrylate organically modified ceramic is proposed for recording of volume holograms. Both low-spatial-frequency (54 line pairs/mm−1) and high-spatial-frequency (1400 line pairs/mm−1) holographic gratings were successfully recorded in the medium by interference of two coherent beams of 351.1-nm wavelength. High diffraction efficiencies (93%) and extremely low absorption and scattering coefficients were measured during the holographic reconstruction by a 632.8-nm He–Ne beam. The optimum UV recording exposure was ~3 J cm−2. A grating refractive-index modulation amplitude of 1.1 × 10−4 was achieved. Virtually no changes in diffraction efficiency were observed after thermal-heating, light-curing, and long-term-aging experiments.
Patent•
07 Nov 1996
TL;DR: In this article, a color filter has a hologram device for spectrally diffracting an incident light into plural light beams of different wavelength regions and selectively converging the plural light beam on respective plural picture element electrodes corresponding to the different wavelengths.
Abstract: An improved color filter and a color image display apparatus employs the filter, the color filter has a hologram device for spectrally diffracting an incident light into plural light beams of different wavelength regions and selectively converging the plural light beams on respective plural picture element electrodes corresponding to the different wavelength regions. The hologram device has such characteristics that S-polarized components of the incident light are diffracted at a maximum diffraction efficiency at a predetermined incident angle of the incident light, and P-polarized components of the incident light are diffracted as such that a difference between the maximum diffraction efficiency of the S-polarized components and the diffraction efficiency of the P-polarized components is not less than 30%, and the diffracted S-polarized components are formed as the plural light beams to be converged on the plural picture element electrodes corresponding to the different wavelength regions.
TL;DR: Nearly index-matched optical elements are described that have application to aspherical, diffractive, and hybrid refractive -diffractive elements that results in an achromatic phase, thereby allowing for diffractive elements with high efficiency over broad spectral bands.
Abstract: Nearly index-matched optical elements are described that have application to aspherical, diffractive, and hybrid refractive–diffractive elements. Owing to the small difference in index, tolerances on the interfacial surface profile are much looser than for conventional aspherical and diffractive elements. A condition on both the index and the dispersion is described that results in an achromatic phase, thereby allowing for diffractive elements with high efficiency over broad spectral bands. Properties of the elements are described and compared with those of conventional diffractive elements. Analytical results and experimental measurements with an inexpensive element with 40 waves of asphericity are presented.
TL;DR: Coupled-wave analysis indicates that very high diffraction efficiencies are theoretically feasible for this class of device, even when the devices employ rectangular grating profiles, implying simplified fabrication techniques for experimentally achieving high efficiencies by use of deep-etch submicrometer fabrication techniques.
Abstract: To date, optical diffraction gratings filled with liquid crystals have not produced high (>50%) diffraction efficiencies in nonzero diffractive orders. Rigorous coupled-wave analysis indicates, however, that very high diffraction efficiencies (99% in single-wavelength polarized illumination) are theoretically feasible for this class of device, even when the devices employ rectangular grating profiles. These theoretical predictions with rectangular rather than blazed profiles imply simplified fabrication techniques for experimentally achieving high efficiencies by use of deep-etch submicrometer fabrication techniques.
TL;DR: A theoretical model is developed that predicts achievable diffraction efficiency as a function of oxidation state, doping level, photovoltaic field, crystal length, and region of beam overlap and is compared with experimental results for achievablediffraction efficiency and erasure-time constant.
Abstract: We show that the oxidation state of Fe in LiNbO3 has two competing effects on the diffraction efficiency of multiple holograms in 90 degree-geometry holographic storage. For crystals with moderate absorption, the saturation space-charge field is larger after high-temperature reduction treatment. However, reduction also increases absorption, which reduces the overall diffraction efficiency. We develop a theoretical model that predicts achievable diffraction efficiency as a function of oxidation state, doping level, photovoltaic field, crystal length, and region of beam overlap. We compare this model with experimental results for achievable diffraction efficiency and erasure-time constant.
TL;DR: In this article, an economic liquid crystal-polymer dispersion material that can be used for storing optical holographic images was developed, and the authors demonstrate the use of thin samples of this material for such an application.
Abstract: We have developed an economic liquid crystal-polymer dispersion material that can be used for storing optical holographic images. In this paper, we demonstrate the use of thin samples of this material for such an application. The obtained results show that the written gratings-holograms are permanent, but are electrically switchable. Furthermore, the diffraction efficiency is high and does not change significantly after many tests over a period of months. Thus, we believe this material is promising for practical uses.
TL;DR: In this paper, the origin of the domain contrast is explained in terms of the unit cell symmetry and a new coupled-mode view of the dynamical theory of x-ray diffraction.
Abstract: Antiparallel ferroelectric (180-deg) domains have been observed by high-resolution x-ray diffraction imaging in barium titanate and strontium barium niobate. This technique permits the imaging of domains in thick (1-mm) samples with high spatial resolution (1 µm). These domains are visible in both Laue and Bragg geometry but only in those diffraction images for which the diffraction vector has some component along the [001] axis (optical axis). The origin of the domain contrast is explained in terms of the unit cell symmetry and a new coupled-mode view of the dynamical theory of x-ray diffraction. This model also permits determination of domain location relative to the sample surfaces through the analysis of the domain fringe contrast.
TL;DR: The BPM is quantitatively compared with the rigorous coupled-wave analysis for the cases of single and multiplexed gratings and is shown that the BPM, even in its most rudimentary form, is a powerful and accurate calculational method that is especially suited for analyzing the many multiplexing grating diffraction problem.
Abstract: Multiplexed holographic structures have been suggested to provide large capacity and parallel access as three-dimensional storage media. One of the most widely used techniques in the literature for analyzing such structures has been the coupled-wave analysis and its variations. Another approach that is becoming increasingly popular because of the ease with which it can be implemented is the beam propagation method (BPM). The BPM is quantitatively compared with the rigorous coupled-wave analysis for the cases of single and multiplexed gratings. Normal and off-normal incidence as well as TE and TM polarizations are considered for single (slanted and unslanted) and multiplexed gratings. It is shown that the BPM, even in its most rudimentary form, is a powerful and accurate calculational method that is especially suited for analyzing the many multiplexed grating diffraction problem.
TL;DR: In this article, a theoretical model that incorporates intensity saturation for describing holographic diffraction in dynamic photoanisotropic organic materials is presented, and numerical simulations of diffraction versus intensity and polarization are compared with the experimental results.
Abstract: The photoisomerization of a highly anisotropic dye molecule depends not only on the intensity but also on the polarization state of the acting light with respect to the molecular axis. Polarization-dependent isomerization of uniformly oriented distributions of anisotropic dye molecules produces an orientational distribution of photoexcited states. Saturation occurs when all the molecules aligned in a particular orientation are isomerized so further photoexcitation cannot occur. This anisotropic saturation occurs first in the direction aligned with the incident polarization. We investigate this anisotropic saturation behavior and present a theoretical model that incorporates intensity saturation for describing holographic diffraction in dynamic photoanisotropic organic materials. Numerical simulations of diffraction versus intensity and polarization are provided and compared with the experimental results.
TL;DR: In this paper, the diffraction of a plane wave by a grating of finite conductivity is considered, assuming that the incident wave vector is not orthogonal to the grooves.
Abstract: Starting from the Maxwell equations, we solve the problem of the diffraction of a plane wave by a grating of finite conductivity, assuming that the incident wave vector is not orthogonal to the grooves. We make use of the method of fictitious sources, and the diffraction problem is thus reduced to two canonical problems: (1) the computation of the electromagnetic field radiated in free space by known sources and (2) the least-squares problem. The algorithm that we propose was implemented on an IBM 530 computer, and some numerical results are given by way of illustration.