Abstract:This paper describes the fundamentals of phase-only liquid crystal on silicon (LCOS) technology, which have not been previously discussed in detail. This technology is widely utilized in high efficiency applications for real-time holography and diffractive optics. The paper begins with a brief introduction on the developmental trajectory of phase-only LCOS technology, followed by the correct selection of liquid crystal (LC) materials and corresponding electro-optic effects in such devices. Attention is focused… Show more
“…Parallel-aligned liquid crystal on silicon microdisplays (PA-LCoS) [1] [2] are widely used as SLMs in a wide range of applications [3] [4] . They enable phase-only modulation of light wavefronts without coupled amplitude modulation, and with millions of addressable pixels.…”
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.
“…Parallel-aligned liquid crystal on silicon microdisplays (PA-LCoS) [1] [2] are widely used as SLMs in a wide range of applications [3] [4] . They enable phase-only modulation of light wavefronts without coupled amplitude modulation, and with millions of addressable pixels.…”
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.
“…Among them, parallel-aligned LCoS (PA-LCoS) are especially interesting since they enable phase-only operation without coupled amplitude modulation [2][3] [4] , what is interesting for a wide range of optics and photonics applications, such as in diffractive optics [5] , optical storage [6] [7] , optical metrology [8] , reconfigurable interconnects [9] [10] , wavefront sensing of structured light beams [11] , holographic optical traps [12] , or quantum optical computing [13] . In particular LCoS microdisplays are one of the competing technologies to implement reconfigurable optical interconnects and more specifically wavelength selective switches (WSS) for optical telecommunications [14][15] [16] [17] .…”
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.
“…La primera consiste en un sistema micro-mecánico de micro-espejos movibles [7] y la segunda es usando un material electro-óptico como los cristales líquidos sobre silicio LCoS (del inglés LiquidCrystalonSilicon).Los SLM -LCoS funcionan como un retardador de la fase de la luz, ya que las moléculas alargadas del cristal líquidotienen una anisotropía óptica, lo que hace que sean birrefringentes,es decir,tienen 2 índices de refracción (ordinario y extraordinario), de modo que se produce un retardo entre las componentes de la luz [8].…”
Cómo citar este trabajo How to cite this paperA. Cofré Hernríqez, "Desarrollo de un sistema basado en un LCOS-SLM para la generación de espectros sintonizables" Revista Doctorado UMH, vol. 2, no 2, p.2, 2016. [Online].Desarrollo de un sistema basado en un LCOS-SLM para la generación de espectros sintonizablesDevelopment based on a LCoS-SLM for generatingtunable spectra system
RESUMENEmpleando un modulador espacial de luz de cristal líquido sobre silicio (LCoS-SLM) como un retardador pixelado programable, se ha logrado desarrollar un sistema óptico que permite controlar el espectro de una fuente de luz láser de supercontínuo. El haz polarizado pasa por una red de difracción que descompone sus componentes espectrales, que se proyectansobre el LCoS-SLM, al cual aplicamos desde un ordenador diferentes máscaras de nivel de gris, logrando modificar la fase de cada longitud de onda. Al recombinarse el haz completo y atravesar por un analizador permite el paso de la intensidad de la luz de cada longitud de onda de acuerdo a la nueva fase que ésta adquirió en el modulador. Para la creación de las máscaras se analizaron tres métodos, el primero basado en un ajuste de Cauchy, el segundo en una interpolación de los valores obtenidos por un muestreo rápido y la última propuesta en la creación de una tabla con todos los valores.Finalmente presentamos los diferentes resultados que se obtuvieron como la elección de ciertas longitudes de onda y la creación de un filtro paso banda variable.Palabras clave: Dispositivo cristal líquido, modulador, espectro, polarización.
ABSTRACTWe used a liquid crystal on silicon spatial light modulator (LCoS-SLM) as a programmable pixelated retarder. We have developed an optical system that allows to control the spectrum of a supercontinuum laser light source. The polarized beam passes through a diffraction grating which splits the spectral components. Then is projected onto the LCoS-SLM where we apply from a computer different masks gray level, in order to modify the phase of each wavelength.After recombination and passage through an analyzer,the different wavelengths pass or not according to the new phase acquired in the modulator. Three methods were analyzed for creating masks, the first based on aCauchy relation fit, the second in an interpolation of the values obtained by rapid sampling and the latest proposal on creating a table with all values. Finally, we present the different results obtained as the choice of certain wavelengths and creating a variable pass band filter.
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