Effective angular and wavelength modeling of parallel aligned liquid crystal devices

Parallel aligned liquid crystal (PA-LC) devices are widely used in many optics and photonics applications to control the amplitude, phase and/or state of polarization (SOP) of light beams. Simplified models yet with a good predictive capability are extremely useful in the optimal application of these devices. In this paper we propose and demonstrate the validity of a novel model enabling to calculate the voltage dependent retardance provided by parallel-aligned liquid crystal (PA-LC) devices for a very wide range of incidence angles and any wavelength in the visible. We derive the theoretical expressions, and both experimental and theoretical retardance results are obtained showing a very good agreement. The proposed model is robust and well adapted to a reverse-engineering approach for the calibration of its parameters, whose values are obtained without ambiguities. The model is based on only three physically related magnitudes: two off-state parameters per wavelength and one global voltage dependent parameter, the tilt angle of the LC molecules. To our knowledge it represents the most simplified model available for PA-LC devices yet showing predictive capability. Not only eases the design of experiments dealing with unconventional polarization states or complex amplitude modulation, but it also serves to analyze the physics and dynamics of PA-LC cells since we have estimation for their voltage dependent tilt angle within the device.Work supported by Ministerio de Trabajo y Competitividad of Spain (projects FIS2011-29803-C02-01 and FIS2011-29803-C02- 02), by Generalitat Valenciana of Spain (projects PROMETEOII/ 2015/015, ISIC/2012/013 and GV/2014/076), and by Universidad de Alicante (project GRE12-14)

Influence of index matching on AA/PVA photopolymers for low spatial frequency recording

Photopolymers present appealing optical properties for holographic and diffractive applications. They enable modulation of the electrical permittivity and thickness and are self-processing, and layers with a wide range of thicknesses and properties can be fabricated on demand. In order to obtain a complete characterization of the material, low spatial frequency analysis has become a fundamental tool because the motion of the components inside of the material can be measured. We propose to use an index matching component to carry out a complete characterization and to differentiate the “apparent” and the real monomer diffusion. We also have quantified the minimum thickness to obtain the phase modulation of 2 required for the fabrication of many diffractive elements such as lenses, axicons, or blazed gratings. Finally, we have studied the influence of the thermal effects in the thickness variations.The work was supported by the “Ministerio de Economía y Competitividad” of Spain under projects FIS2011-29803-C02-01 and FIS2011-29803-C02-02 and by the “Generalitat Valenciana” of Spain under projects PROMETEO/2011/021 and ISIC/2012/013

Electrical dependencies of optical modulation capabilities in digitally addressed parallel aligned liquid crystal on silicon devices

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.This work was supported by the Ministerio de Trabajo y Competitividad of Spain (projects FIS2011-29803-C02-01 and FIS2011-29803-C02-02), by the Generalitat Valenciana of Spain (projects PROMETEO/2011/021 and ISIC/2012/013), and by the Universidad de Alicante (project GRE12-14)

Robustness of average Stokes polarimetry characterization of digitally addressed parallel-aligned LCoS displays

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. Recently we proposed a novel polarimetric method, based on Stokes polarimetry, enabling the characterization of their linear retardance and the magnitude of their associated phase fluctuations, if existent, as it happens in most of digital backplane PA-LCoS devices. In this work we describe the characterization technique together with its predictive capability, and we show some experimental analysis we have performed to delimitate its robustness dealing with the repeatibility and reproducibility of the technique. The calibrated retardance and phase fluctuation values can then be used to estimate the performance of the PA-LCoS device in applications, such as in diffractive optics.Work supported by Min. de Trabajo y Competitividad of Spain (projects FIS2011-29803-C02-01 and FIS2011-29803-C02-02), by Gen. Valenciana of Spain (projects PROMETEO/2011/021 and ISIC/2012/013), and by Universidad de Alicante (project GRE12-14)

Averaged Stokes polarimetry applied to evaluate retardance and flicker in PA-LCoS devices

Recently we proposed a novel polarimetric method, based on Stokes polarimetry, enabling the characterization of the linear retardance and its flicker amplitude in electro-optic devices behaving as variable linear retarders. In this work we apply extensively the technique to parallel-aligned liquid crystal on silicon devices (PA-LCoS) under the most typical working conditions. As a previous step we provide some experimental analysis to delimitate the robustness of the technique dealing with its repeatability and its reproducibility. Then we analyze the dependencies of retardance and flicker for different digital sequence formats and for a wide variety of working geometries.Work supported by Ministerio de Trabajo y Competitividad of Spain (projects FIS2011- 29803-C02-01 and FIS2011-29803-C02-02), by Generalitat Valenciana of Spain (projects PROMETEO/2011/021 and ISIC/2012/013), and by Univ. de Alicante (project GRE12-14)

Predictive capability of average Stokes polarimetry for simulation of phase multilevel elements onto LCoS devices

Parallel-aligned (PA) liquid-crystal on silicon (LCoS) microdisplays are especially appealing in a wide range of spatial light modulation applications since they enable phase-only operation. Recently we proposed a novel polarimetric method, based on Stokes polarimetry, enabling the characterization of their linear retardance and the magnitude of their associated phase fluctuations or flicker, exhibited by many LCoS devices. In this work we apply the calibrated values obtained with this technique to show their capability to predict the performance of spatially varying phase multilevel elements displayed onto the PA–LCoS device. Specifically we address a series of multilevel phase blazed gratings. We analyze both their average diffraction efficiency (“static” analysis) and its associated time fluctuation (“dynamic” analysis). Two different electrical configuration files with different degrees of flicker are applied in order to evaluate the actual influence of flicker on the expected performance of the diffractive optical elements addressed. We obtain a good agreement between simulation and experiment, thus demonstrating the predictive capability of the calibration provided by the average Stokes polarimetric technique. Additionally, it is obtained that for electrical configurations with less than 30° amplitude for the flicker retardance, they may not influence the performance of the blazed gratings. In general, we demonstrate that the influence of flicker greatly diminishes when the number of quantization levels in the optical element increases.This work was supported by the Ministerio de Trabajo y Competitividad of Spain (Projects FIS2011-29803-C02-01 and FIS2011-29803-C02-02), by the Generalitat Valenciana of Spain (Projects PROMETEO/2011/021 and ISIC/2012/013), and by the University de Alicante (Project GRE12-14)

Polarimetric characterization of PA-LCoS displays under different geometries and electrical configurations

Recientemente hemos propuesto un nuevo método de caracterización de pantallas PA-LCoS basado en polarimetría de Stokes. Este método nos permite conocer tanto el retardo medio para cada nivel de gris como la amplitud de la fluctuación para cada nivel. También se estudió la robustez, repetibilidad y reproducibilidad del método. En este trabajo queremos mostrar la elevada capacidad de predicción de este método bajo distintas geometrías de trabajo y bajo diversas configuraciones eléctricas. En definitiva, mostramos como con el método de caracterización utilizado podemos predecir el estado de polarización a la salida del sistema, sin importar que configuración o geometría de trabajo utilicemos, lo cual es de gran importancia de cara al uso de PA-LCoS en aplicaciones ópticas y fotónicas.We have recently proposed a novel polarimetric method, based on Stokes polarimetry for PA-LCoS displays. This method allows us to know the average retardance and the fluctuation amplitude for every gray-level. The robustness, repeatability and reproducibility were studied too. In this work we want to show the high predictive capability of this method, for different working geometries and for different electrical configurations. That is, we demonstrate that, using this method, we can predict the state of polarization reflected by the PA-LCoS whatever the working geometry or the electrical configuration. This will be very useful in optics and photonics applications that use PA-LCoS displays.Este trabajo ha sido realizado gracias al apoyo del Ministerio de Economía y Competitividad bajo los proyectos FIS2011-29803-C02-01 y FIS2011-29803-C02-02, de la Generalitat Valenciana bajo los proyectos PROMETEO/2011/021 e ISIC/2012/013 y de la Universidad de Alicante con el proyecto GRE12-14

Exploring binary and ternary modulations on a PA-LCoS device for holographic data storage in a PVA/AA photopolymer

We focus on the novelty of three elements in holographic data storage systems (HDSS): the data pager, where we introduce a parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplay; the recording material, where we consider the highly versatile PVA/AA photopolymer; and also in the architecture of the object arm, where a convergent correlator system is introduced. We show that PA-LCoS devices cannot implement pure hybrid-ternary modulated (HTM) data pages but a rather close approximation. Validation of the HDSS expressions for the convergent correlator and comparison with the widespread 4-f system is performed. Experimental results with PVA/AA material showing bit-error rates (BER) in the range of 10−3, further show its potential application for HDSS, and also demonstrate the validity of the testing platform and PA-LCoS calibration and optimization.Work supported by Ministerio de Trabajo y Competitividad of Spain (projects FIS2011- 29803-C02-01 and FIS2011-29803-C02-02), by Generalitat Valenciana of Spain (projects PROMETEOII/2015/015 and ISIC/2012/013), and by Univ. de Alicante (project GRE12-14

Extended linear polarimeter to measure retardance and flicker: application to liquid crystal on silicon devices in two working geometries

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.This work was supported by the Ministerio de Trabajo y Competitividad of Spain (projects FIS2011-29803-C02-01 and FIS2011-29803-C02-02), by the Generalitat Valenciana of Spain (projects PROMETEO/2011/021 and ISIC/2012/013), and by Universidad de Alicante (project GRE12-14)

Voltage dependence of retardance, flicker, and director angle orientation in reflective liquid crystal devices by average Stokes polarimetry

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.Ministerio de Ciencia e Innovación, Spain (FIS2017-82919-R (MINECO/AEI/FEDER, UE); PID2019-106601RB-I00); Generalitat Valenciana, Spain (GV/2019/021; CDEIGENT/2018/024); Universidad de Alicante, Spain (UATALENTO18-10)