Typically, a 360º phase-shift is required to implement diffractive optical elements (DOEs) in modern photonics applications. However, the possibility of showing much larger phase-shifts is a very appealing property which provides additional degrees of freedom to produce multiplexed functions onto DOEs. On the other hand, modern liquid crystal on silicon devices (LCoS) add real-time programmability to the functionality of the DOE displayed, but this has been typically demonstrated by parallel-aligned LCoS (PA-LCoS) devices. We show programmable DOEs produced using vertically-aligned LCoS (VA-LCoS) devices, with a phase-shift range largely exceeding 360º. We show some results dealing with blazed gratings and on the analysis of their higher diffraction orders, validating their use for multiorder diffractive optical elements.
The phase-shift exhibited by liquid crystal on silicon devices (LCoS) depends on the voltage applied and the illumination wavelength. Most of the LCoS used in the labs are digitally addressed using a binary pulse width modulated signal. Usually, these devices are characterized for a very small range of the available binary voltage values and for specific wavelengths. In this work, we consider a commercial parallel-aligned liquid crystal on silicon device (PA-LCoS) in which the binary voltages are accessible through the software of the vendor. We perform a complete averaged Stokes polarimetric characterization of the device where we are able to obtain the absolute unwrapped retardance values for a wide range of voltage parameters and across the visible spectrum. This provides a practical approach to evaluate the whole range of phase modulation possibilities, and to analyze some issues related with the physics of the device.
Parallel-aligned liquid crystal on silicon devices (PA-LCoS) can be found nowadays in most of the advanced areas in optics and photonics. Many works have been dedicated to their characterization for optimum utilization in applications. However, usual techniques are based on diffractive or interferometric measurements. Recently, we proposed the use of Stokes polarimetry for a versatile yet easy to implement characterization. We show that the LCoS can modelled as a nonabsorbent reciprocal device which, combined with time-average Stokes polarimetry, enables to demonstrate robust measurements across the whole applied voltage range for the retardance and its flicker. One of the main novelties is that we also obtain the director orientation, which we show that changes across the voltage range, especially at larger applied voltages. This might affect in very sensitive applications. It might also provide a deeper insight into the internal dynamics in the LC layer.
Phase spatial light modulators and, in particular, parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplays are widely used to display programmable diffractive optical elements (DOEs). These are pixelated elements with inherent different characteristics when compared with DOEs produced with micro-optics fabrication techniques. Specifically, programmable DOEs may be affected by the fill factor, time-flicker, fringing-field and interpixel cross talk effects, and limited and quantized modulation depth of the LCoS device. Among the multilevel DOEs, we focus on the important case of the blazed gratings. We develop the corresponding analytical expressions for the diffracted field where, as novelties of this work, fill factor and flicker are introduced together with phase depth and the number of quantization levels. Different experimental-based normalizations are considered, which may lead to wrong conclusions if the fill factor is not considered in the expressions. We also analyze the differences arising between one- and two-dimensional pixelated devices. When compared with numerical procedures, our approach provides an analytical expression that facilitates the design, prediction, and discussion of experiments. As an application, we prove, for the limiting case of no interpixel cross talk, that multiorder DOEs cannot be more efficient than the equivalent single-order DOE. We also show how the results for DOEs with a unit fill factor can be adapted to DOEs with a fill factor smaller than one with a very efficient procedure.
Holographic gratings stored in low-toxicity photopolymer, Biophotopol, have been analyzed to achieve stable and efficient holograms. A curing process allows the hologram stabilization, but at the same time, it could produce a diffraction efficiency (DE) reduction. Here, a detailed low-cost LED curing protocol is shown to stabilize over time 1205 l/mm transmission holograms, and at the same time, a 33% DE increment (with respect non-curing holograms) have been demonstrated. Finally, to obtain a better understanding of DE change, a theoretical fit of our experimental result, based on Kogelnik’s coupled wave theory was carried out and discussed.
We incorporate the prediction of flicker to a semiphysical and analytical model describing the angular and wavelength dependencies of retardance in parallel aligned liquid crystal (PA-LC) devices. This makes the model unique due to the wide range of calculation it offers while keeping its simplicity. Prediction of the modulation of retardance and its associated flicker relies on the fitting of the equivalent tilt angle of the molecules as a function of applied voltage. Specific results are given for liquid crystal on silicon (PA-LCoS) microdisplays, central to many spatial light modulation applications such as the generation of structured polarized beams. Experimental characterization results at arbitrary angles and wavelengths prove the predictive capability of the model. To highlight the richness of situations with PA-LCoS devices, we provide results for two different digital addressing sequences producing different levels of flicker. We focus on the application of the PA-LCoS as a polarization state generator (PSG) and we emphasize the ability of our approach to evaluate the performance across the visible spectrum and for a wide range of incidence angles. Our approach offers novel capabilities in the generation of arbitrary states of polarization, both fully and partially polarized.
Parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplays are widely used in spatial light modulation applications, especially in those requiring phase-only modulation. One such application area is programmable diffractive optics which plays a very important role in modern optical imaging systems or in optical interconnections for optical telecommunications. Among the multilevel diffractive optical elements (DOEs) we focus on the important case of the blazed gratings. We develop the corresponding analytical expressions for the diffracted field where, as one of the novelties in the work, an analytical expression including the fill factor and the flicker is obtained. This enables to have a model against to compare the experimental results in a number of situations where fill factor, flicker, period, and number of quantization levels are the variables. This also enables to design appropriate compensation techniques to enhance the performance of the blazed gratings.
In recent years, the development of low-toxicity photopolymers for holographic recording in reflection mode has reached great importance. One of the main advantages of reflection holograms is that they can be reconstructed using white light, which has enabled that many researches have focused on the development of sensors for different types of analytes. Optical data storage and three-dimensional multiplexing of reflection holograms to improve the data storage density have also been investigated through reflection holograms. However, the photopolymers used in these researches have certain undesirable features such as the toxicity of some of their components and non-environmentally compatibility. The common used hydrophilic photopolymers content poly(vinyl alcohol) (PVA) or gelatine binder and monomers related to acrylamide. This compound has a high potential to cause cancer. For this reason, we developed a photopolymer called “Biophotopol” as a recording holographic material for optical applications. “Biophotopol” have a low toxicity, good recycling properties and is environmental-friendly. The basic formulation of “Biophotopol” includes an initiator system which is a free radical generator composed by triethanolamine as co-initiator and plasticizer and sodium salt 5’- 72 riboflavin monophosphate as sensitizer dye, sodium acrylate as polymerizable monomer and PVA as inert binder polymer. Additionally, a cross-linking agent, as N,N’-(1,2-dihydroxyethylene)bisacrylamide (DHEBA) , can also be added. Volume transmission gratins and holographic lens have been fabricated in this photopolymer but not researches have been done to store reflection gratins. Is know that for higher spatial frequencies, the diffraction efficiency decreases considerably as the spatial frequency increases. In this sense, the general aim of this work has been fabricated reflection gratings in the symmetrical experimental setup in “Biophotopol” and to study the dependence of diffraction efficiency on physical thickness, recording intensity and exposure energy. First, films physical thickness was investigated. The maximum diffraction efficiency was obtained for thicknesses around 145 µm. The photopolymer layers uniformity was highly sensitive to drying and environmental conditions during the exposure stage. Therefore, both conditions were investigated and very controlled. An increase in diffraction efficiency was observed when the photopolymer films were cured with a LED lamp to improve the stability of the reflection holograms. The residual dye is eliminated during this process. The maximums diffraction efficiencies around 30 % were obtained for reflection gratings with a spatial frequency of 4738 lines/mm. The index modulation and optical thickness were obtained by fitting procedure through coupled wave theory. Experimental and theoretical results have been interpreted to modify the photopolymer formulation and exposure conditions in order to increase the diffraction efficiencies.
We have included a Parallel Aligned Liquid Crystal on Silicon (PA-LCoS) microdisplay in a Holographic Data Storage System (HDSS). This novel display, widely accepted as Spatial Light Modulator (SLM), presents some advantages and disadvantages. One of these disadvantages is the anamorphic and frequency dependent effect. In this work we want to test this effect and see its effects in the complete optical process involved in the HDSS. We will use stripe-based patterns with different orientation (vertical and horizontal). To check the limits, we will increase the data density by decreasing the minimum stripe width. For evaluating the degradation suffered by the data page, we use the Bit Error Rate (BER) as figure of merit. We make a BER calculation from the statistical analysis of the histogram. In addition to the anamorphic effects we evaluate the degradation effects introduced by the non-uniformity in the illumination. To this goal we divide the image in several regions that are processed in the same way that the entire image. The error analysis of the entire optical system is useful for its calibration and fine adjustment. Once we have characterized the experimental setup we introduce the holographic material. Thus, by making the same analysis, we can evaluate the errors introduced by the material. As holographic material we use Polyvinyl Alcohol Acrylamide (PVA/AA), that has been characterized and developed in previous works by our group.
Liquid crystal on silicon (LCoS) displays have become the most attractive microdisplays for all sort of spatial light modulation applications. Among the different LCoS technologies, parallel aligned LCoS (PA-LCoS) are especially interesting. They offer unique capabilities as spatial light modulators (SLM), since they enable phase-only modulation without coupled amplitude modulation, and with millions of addressable pixels. In this work we evaluate and demonstrate the various capabilities offered by a novel and simplified physical model for parallel aligned liquid crystal devices (PA-LC), thus also applicable to PA-LCoS microdisplays. The model provides the voltage dependent retardance values, necessary for spatial light modulation applications, for a very wide range of incidence angles and any wavelength in the visible. First, it needs to be calibrated through a reverse-engineering approach. In this calibration, the values obtained for two of the three parameters provide the correct values for important internal properties of these devices related with the birefringence, cell gap and director profile. Therefore, the proposed model can be used as a means to inspect internal physical properties of the cell. Last but not least the model is useful to simulate the retardance for novel PA-LC devices as a function of the LC compound and cell gap. Therefore, it is not only a reverse-engineering model but it also constitutes an analytical alternative to the usual numerical approaches for PA-LC devices design and construction.
Simplified analytical models with predictive capability enable simpler and faster optimization of the performance in applications of complex photonic devices. We recently demonstrated the most simplified analytical model still showing predictive capability for parallel-aligned liquid crystal on silicon (PA-LCoS) devices, which provides the voltage-dependent retardance for a very wide range of incidence angles and any wavelength in the visible. We further show that the proposed model is not only phenomenological but also physically meaningful, since two of its parameters provide the correct values for important internal properties of these devices related to the birefringence, cell gap, and director profile. Therefore, the proposed model can be used as a means to inspect internal physical properties of the cell. As an innovation, we also show the applicability of the split-field finite-difference time-domain (SF-FDTD) technique for phase-shift and retardance evaluation of PA-LCoS devices under oblique incidence. As a simplified model for PA-LCoS devices, we also consider the exact description of homogeneous birefringent slabs. However, we show that, despite its higher degree of simplification, the proposed model is more robust, providing unambiguous and physically meaningful solutions when fitting its parameters.
Recently we demonstrated a novel and simplified model enabling to calculate the voltage dependent retardance provided
by parallel aligned liquid crystal devices (PA-LCoS) for a very wide range of incidence angles and any wavelength in the
visible. To our knowledge it represents the most simplified approach still showing predictive capability. Deeper insight
into the physics behind the simplified model is necessary to understand if the parameters in the model are physically
meaningful. Since the PA-LCoS is a black-box where we do not have information about the physical parameters of the
device, we cannot perform this kind of analysis using the experimental retardance measurements. In this work we
develop realistic simulations for the non-linear tilt of the liquid crystal director across the thickness of the liquid crystal
layer in the PA devices. We consider these profiles to have a sine-like shape, which is a good approximation for typical
ranges of applied voltage in commercial PA-LCoS microdisplays. For these simulations we develop a rigorous method
based on the split-field finite difference time domain (SF-FDTD) technique which provides realistic retardance values.
These values are used as the experimental measurements to which the simplified model is fitted. From this analysis we
learn that the simplified model is very robust, providing unambiguous solutions when fitting its parameters. We also
learn that two of the parameters in the model are physically meaningful, proving a useful reverse-engineering approach,
with predictive capability, to probe into internal characteristics of the PA-LCoS device.
Liquid-crystal on Silicon (LCoS) microdisplays are one of the competing technologies to implement wavelength selective switches (WSS) for optical telecommunications. Last generation LCoS, with more than 4 megapixels, have decreased pixel size to values smaller than 4 microns, what increases interpixel cross-talk effects such as fringing-field. We proceed with an experimental evaluation of a 3.74 micron pixel size parallel-aligned LCoS (PA-LCoS) device. At 1550 nm, for the first time we use time-average Stokes polarimetry to measure the retardance and its flicker magnitude as a function of voltage. We also verify the effect of the antireflection coating when we try to characterize the PA-LCoS out of the designed interval for the AR coating. Some preliminary results for the performance for binary gratings are also given, where the decrease of modulation range with the increase in spatial frequency is shown, together with some residual polarization effects.
Multiplexed diffraction gratings were recorded in 300 μm thick layers of Biophotopol photopolymer by using peristrophic multiplexing schema. Thirteen sinusoidal phase gratings were stored in a low toxicity recording medium. The diffraction efficiency conservation of the multiplexed diffraction efficiency obtained was studied along the time.
We introduce a polyvinil alcohol/acrylamide (PVA/AA) photopolymer compound in a holographic memory testing
platform to provide experimental results for storage and retrieval of information. We also investigate different
codification schemes for the data pages addressed onto the parallel-addressed liquid crystal on silicon (PA-LCoS) device,
used as the data pager, such as binary intensity modulation (BIM), and hybrid-ternary modulation (HTM), and we will
see that an actual approximation for HTM can be obtained with a PA-LCoS device. We will also evaluate the effect of
the time fluctuations in the PA-LCoS microdisplays onto the BIM and HTM regimes. Good results in terms of signal-tonoise
ratio and bit-error ratio are provided with the experimental system and using the PVA/AA photopolymer produced
in our lab, thus showing its potential and interest for future research focused on this material with highly tunable
properties.
Holographic data storage systems (HDSS) have been a promising and very appealing technology since the first laser developments in the sixties. Impact of ongoing advances in the various components needs to be explored in its specific application to HDSS. In this sense, continuous progress is being produced in spatial light modulator (SLM) technology where parallel-addressed liquid crystal on silicon (PA-LCoS) microdisplays have replaced previous liquid-crystal displays (LCD) in most of optics and photonics applications. PA-LCoS microdisplays are well adapted to display phaseonly elements without coupled amplitude. In this paper, we analyse how PA-LCoS devices can also be used to display the widely applied binary intensity modulated (BIM) data pages. We also investigate hybrid-ternary modulated (HTM) data pages, which are very much demanding on the phase and amplitude modulation properties of an SLM. HTM data pages combine the ease of detection of BIM data pages, together with a large reduction of the DC term of the Fourier Transform of the data page. This reduction is necessary to avoid saturation of the recording material dynamic range. Simulated results show the magnitude of the expected DC term in the Fourier plane. We have verified the good performance of PA-LCoS to display BIM data pages. We have also obtained that pure HTM data pages cannot be produced with PA-LCoS devices, however, a rather close performance is obtained when implementing the pseudo-HTM data pages. In this work a more complete study of pseudo-HTM modulation is offered.
In this work the split-field finite-difference time-domain method (SF-FDTD) has been extended for the analysis of two-dimensionally periodic structures with third-order nonlinear media. The accuracy of the method is verified by comparisons with the nonlinear Fourier Modal Method (FMM). Once the formalism has been validated, examples of one- and two-dimensional nonlinear gratings are analysed. Regarding the 2D case, the shifting in resonant waveguides is corroborated. Here, not only the scalar Kerr effect is considered, the tensorial nature of the third-order nonlinear susceptibility is also included. The consideration of nonlinear materials in this kind of devices permits to design tunable devices such as variable band filters. However, the third-order nonlinear susceptibility is usually small and high intensities are needed in order to trigger the nonlinear effect. Here, a one-dimensional CBG is analysed in both linear and nonlinear regime and the shifting of the resonance peaks in both TE and TM are achieved numerically. The application of a numerical method based on the finite- difference time-domain method permits to analyse this issue from the time domain, thus bistability curves are also computed by means of the numerical method. These curves show how the nonlinear effect modifies the properties of the structure as a function of variable input pump field. When taking the nonlinear behaviour into account, the estimation of the electric field components becomes more challenging. In this paper, we present a set of acceleration strategies based on parallel software and hardware solutions.
Phase-only modulation is necessary in a great number of modern spatial light modulation applications, and the spatial light modulator (SLM) technology of choice is usually the parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplay. Various degradation effects have been analyzed in the literature which may be introduced by SLMs and whose quantitative knowledge enables to select the best working conditions and/or to design specific compensation strategies to diminish negative effects. In this paper we concentrate on the phase flicker typically produced by PA-LCoS devices. The availability of a recent polarimetric-based method, the average Stokes polarimetric technique, to measure the linear retardance and its flicker amplitude eases the capability to simulate the performance of spatially varying phase multilevel elements typically addressed onto PA-LCoS devices. A representative element is the blazed grating. Recently we demonstrated the capability of the calibration provided by the average Stokes polarimetric technique to predict the performance of blazed gratings, both their average diffraction efficiency, static analysis, and its associated time fluctuation, dynamic analysis. In the present work we take advantage of the demonstrated predictive capability of our approach to analyse to find the wide range of applicability of PA-LCoS devices in applications in spite of flicker.
A wide range of chemical compositions are possible to design photopolymers. These materials are also appealing for diffractive and holographic applications due to their capability to modulate the refractive index and/or the thickness when illuminated. Some of the most interesting applications for photopolymers are the optical data storage, security systems, surface relief photo-embossing, diffractive and refractive optical elements, holographic elements, solar concentrators, optical detectors and hybrid optoelectronic 3-D circuitry. Looking for an optimized chemical composition for each application many different photopolymers compositions may be needed enabling a variety of materials properties: materials with low or high rates of monomer diffusion, low or high values of shrinkage, long or short length of polymer chains and low or high light absorption. In parallel many models are presented in order to predict the photopolymers recording and the post exposure evolution. In this work we use one of these experimentally checked models to study the influence of the material characteristics in the final diffractive optical element recorded in the material. We study the changes in the surface relief and in the refractive index in order to understand the importance of each material property in the final diffractive optical element recorded.
Parallel-aligned liquid crystal on silicon (PA-LCoS) displays have become the most attractive spatial light modulator device for a wide range of applications, due to their superior resolution and light efficiency, added to their phase-only capability. Proper characterization of their linear retardance and phase flicker instabilities is a must to obtain an enhanced application of PA-LCoS. We present a novel polarimetric method, based on Stokes polarimetry, we have recently proposed for the measurement of the linear retardance in the presence of phase fluctuations. This can be applied to electrooptic devices behaving as variable linear retarders, and specifically to PA-LCoS. The method is based on an extended Mueller matrix model for the linear retarder containing the time-averaged effects of the instabilities. We show experimental results which validate the predictive capability of the method. The calibrated retardance and phase fluctuation values can then be used to estimate the performance of the PA-LCoS device in spatial light modulation applications. Some results will be given.
Parallel aligned liquid crystal on silicon (PA-LCoS) displays have found wide acceptance in applications requiring phase-only modulation. Among LCoS devices, and PA-LCoS as a specific case, digital addressing has become a very common technology. In principle, modern digital technology provides some benefits with respect to analog addressing such as reduced interpixel cross-talk, lower power consumption and supply voltage, gray level scale repeatability, high programmability, and noise robustness. However, there are also some degradating issues, such as flicker, which may be enhanced. We analyze the characteristics of the digital pulse width modulated voltage signals in relation to their effect on the optical modulation capabilities of LCoS displays. We apply calibration techniques developed in our laboratory, basically the classical linear polarimeter extended to take into account the existence of flicker. Various digital sequence formats are discussed, focusing the analysis on the variations in the magnitude of the applied voltages across the LC layer. From this analysis, we obtain how to amplify the retardance dynamic range and how to enhance linearity in the device without enhancing flicker and without diminishing the number of available quantization levels. Electrical configurations intended for phase-only and intensity modulation regimes, useful in diffractive optics, are given.
We focus on the evaluation of the applicability of the classical and well-established linear polarimeter to the measurement of linear retardance in the presence of phase flicker. This analysis shows that there are large errors in the results provided by the linear polarimeter when measuring the linear retardance of a device. These errors depend on the specific retardance value under measurement. We show that there are some points where this limitation can be used to measure the fluctuation amplitude consistently. An elegant method is further proposed, enabling the measurement of the average retardance value, thus extending the applicability of the classical linear polarimeter. Experimental characterization results are provided for various electrical sequences addressed onto a parallel aligned liquid crystal on silicon (LCoS) display. Good agreement is obtained with experiment, thus validating the linear polarimeter methodology proposed. Furthermore, results are provided for the LCoS in two reflection geometries, perpendicular incidence with and without nonpolarizing beam splitter, demonstrating robustness of the method. As a result, the evaluation of both phase modulation range and flicker magnitude for any electrical sequence addressed can be easily obtained, which is very important for optimal use of LCoS displays in applications.
Among the existent technologies of spatial light modulator devices, parallel aligned liquid crystal on silicon displays
(PA-LCoS) have found wide acceptance. They are especially interesting since they provide phase-only modulation with
no coupling of amplitude modulation. Optimal use of these devices requires proper calibration of their modulation
capabilities in order to minimize some degradation effects found in the literature, such as flicker or anamorphic and
frequency dependent modulation. In this work we apply calibration techniques developed in our lab, basically the
classical linear polarimeter adapted to be able to take into account the existence of flicker. This method enables to obtain
both the average retardance and a good estimation of the magnitude of the phase fluctuation when flicker is present.
Various addressing formats are discussed and variations in the magnitude of the applied voltages are considered in order
to amplify the retardance dynamic range and to enhance linearity in the device. Finally, two electrical configurations
intended for phase-only and amplitude-mostly modulation regimes, useful e.g. in diffractive optics, are given.
Recently the possibility to record phase diffractive optical elements (DOEs) onto photopolymers has been explored. Two
of their properties when they are illuminated are useful to this goal: the relief surface changes and the refractive index
modifications. The recording intensity distribution with a sinusoidal profile is the easiest profile to record in a
holographic recording material, i.e. it can be obtained by the simple interference of two plane wave beams or
alternatively using a spatial light modulator. This second method is more flexible and opens the possibility to record a
wide range of diffractive elements such as binary, blazed gratings, diffractive lenses, etc. Sharp profiles may as well be
recorded. In general they present a clear smoothing of the edges due to various reasons: the cut-off frequency (a low pass
filtering) of the optical system, quality of the spatial light modulation, inhibition period, finite size of polymer chains,
monomer diffusion, and non-linearities in the recording process. In this work we have analyzed the importance of some
of these aspects of the photopolymer and the experimental set-up in order to record high quality DOEs. The
photopolymer analyzed is based on polyvinylalcohol/acrylamide. To achieve this goal we have used a diffusion model to
simulate the DOE’s recording with different recording intensities distributions.
The implementation of split-field finite difference time domain (SF-FDTD) applied to light-wave propagation through periodic media with arbitrary anisotropy method in graphics processing units (GPUs) is described. The SF-FDTD technique and the periodic boundary condition allow the consideration of a single period of the structure reducing the simulation grid. Nevertheless, the analysis of the anisotropic media implies considering all the electromagnetic field components and the use of complex notation. These aspects reduce the computational efficiency of the numerical method compared with the isotropic and nonperiodic implementation. Specifically, the implementation of the SF-FDTD in the Kepler family of GPUs of NVIDIA is presented. An analysis of the performance of this implementation is done, and several applications have been considered in order to estimate the possibilities provided by both the formalism and the implementation into GPU: binary phase gratings and twisted-nematic liquid crystal cells. Regarding the analysis of binary phase gratings, the validity of the scalar diffraction theory is evaluated by the comparison of the diffraction efficiencies predicted by SF-FDTD. The analysis for the second order of diffraction is extended, which is considered as a reference for the transmittance obtained by the SF-FDTD scheme for periodic media.
The implementation of the Split-Field Finite Difference Time-Domain (SP-FDTD) method in Graphics Pro-
cessing Units is described in this work. This formalism is applied to light wave propagation through periodic media with arbitrary anisotropy. The anisotropic media is modeled by means of a permittivity tensor with non-diagonal elements and absorbing boundary conditions are also considered. The split-field technique and the periodic boundary condition allow to consider a single period of the structure reducing the simulation grid. Nevertheless, the analysis of anisotropic media implies considering all the electromagnetic field components and the use of complex notation. These aspects reduce the computational efficiency of the numerical method compared to the isotropic and non-periodic implementation. With the upcoming of the new generation of General-Purpose Computing on Graphics Units many scientific applications have been accelerated and others are being developed into this new parallel digital computing architecture. Specifically, the implementation of the SP-FDTD in the Fermi family of GPUs of NVIDIA is presented. An analysis of the performance of this implementation is done and several applications have been considered in order to estimate the possibilities provided by both the formalism and the implementation into GPU. The formalism has been used for analyzing different structures and phenomena: binary phase gratings and twisted-nematic liquid crystal cells. The numerical predictions obtained by means of the FDTD method here implemented are compared with theoretical curves achieving good results, thus validating the accuracy and the potential of the implementation.
Novel liquid crystal on silicon displays (LCoS) technology has found widespread use in a number of applications dealing
with the spatial modulation of the properties of a light wavefront. Parallel aligned LCoS (PA-LCoS) are especially
interesting since they provide phase-only modulation with no coupling of amplitude modulation. However, typically
LCoS are digitally addressed and this has been proven as a drawback since it causes fluctuations in the phase
modulation. In this work we concentrate on PA-LCoS. We analyse the application of a classical polarimetric method for
retardance measurement, which makes use of only linearly polarized light, typically used in wave plates. We analyse the
effect of phase fluctuations on the measurements and provide a refinement of the method which allows estimating both
the average retardance and the magnitude of the phase fluctuation. We demonstrate both theoretically and experimental
that this extension of a classical method is both simple and very well suited for the measurement of the modulation
properties of novel PA-LCoS.
Typically 4-f systems are considered as the basis for holographic memory setups. However, other geometries, such as the
convergent correlator, may also be considered. This is a setup widely used in optical processing architectures but not so
much explored in holographic data storage systems. It provides some benefits when used in optical processing such as
flexibility in the adjustment between Fourier filter dimensions and the Fourier transform of the scene. It also allows a
wider freedom in the choice of the optical systems (lenses) used in the setup since it is no longer necessary that their
focal lengths match, and the total length of the setup may be shortened. In this paper we make use of Fourier optics
techniques to analyze the validity and possible benefits of this setup in its application to holographic memories. We
consider the recording and the reconstruction steps. Both analytical expressions and simulated results are given.
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