Twisted Nematic Liquid Crystal Spatial Light Modulator Research Articles

Combined Jones–Stokes Polarimetry and Its Decomposition into Associated Anisotropic Characteristics of Spatial Light Modulator

Jones–Stokes polarimetry is a robust in vitro polarimetric technique that can be used to investigate the anisotropic properties of a birefringent medium. The study of spatially resolved Jones matrix components of an object is a heuristic approach to extract its phase and polarization information. However, direct interpretation of Jones matrix elements and their decomposition into associated anisotropic properties of a sample is still a challenging research problem that needs to be investigated. In this paper, we experimentally demonstrate combined Jones–Stokes polarimetry to investigate the amplitude, phase, and polarization modulation characteristics of a twisted nematic liquid crystal spatial light modulator (TNLC-SLM). The anisotropic response of the SLM is calibrated for its entire grayscale range. We determine the inevitable anisotropic properties viz., diattenuation, retardance, isotropic absorption, birefringence, and dichroism, which are retrieved from the measured Jones matrices of the SLM using Jones polar decomposition and a novel algebraic approach for Jones matrix decomposition. The results of this study provide a complete polarimetric calibration of the SLM within the framework of its anisotropic characteristics.

Characterization of a spatial light modulator using polarization-sensitive digital holography.

We show a digital holographic approach for polarimetric characterization of a twisted nematic liquid crystal spatial light modulator (TNLC-SLM). An experimental scheme is designed to perform polarization analysis of the SLM with gray levels. This is realized by simultaneous detection of the polarization states of the light from the SLM for a given gray level with the help of a specially designed spatial-frequency multiplex polarization interferometer. This provides amplitude and phase characteristics of the SLM in a single shot. In order to characterize the SLM, we perform Jones matrix imaging at its various gray values (driving voltages), and corresponding results are presented. These results are expected to be useful in designing and developing various SLM-based experiments in the scalar and vectorial domain.

Investigation of the optical properties of the liquid crystal-based devices via Mueller matrix formalism

A model approach for the Mueller matrix (MM) of the twisted nematic liquid crystal spatial light modulator (TNLC-SLM) was proposed. In the first part of the study, the MM of the TNLC cell in the absence of applied voltage was investigated both theoretically and experimentally. In the second part, the model approach was improved by considering the reorientation of both tilt and azimuth angles of the liquid crystal (LC) molecules in the presence of applied voltage. Comparison of the theoretical MM elements with the experimental ones from the literature showed that, instead of decaying exponentially, the azimuth angle rotates with respect to the cell walls in a critical voltage range before the molecules are completely untwisted. It also pointed out that the effect of the tilt and the azimuth angles of the molecules on the optical properties of the light travelling in the LC cell could change depending on the polarization state of the input light and the voltage applied to the cell.

Spatial Light Interference Microscopy (SLIM) using twisted-nematic liquid-crystal modulation

We report the use of a twisted nematic liquid-crystal spatial light modulator (TNLC-SLM) for quantitative phase imaging. The experimental setup is a new implementation of the SLIM principle, which is a phase shifting, white light method for quantitative phase imaging. The approach is based on switching between the phase and amplitude modulation modes of the SLM. Our system is able to deliver a 0.99 nm spatial and 1.33 nm temporal pathlength sensitivity while retaining the optical transverse resolution. The system is implemented as an additional module mounted to a conventional microscope, which makes the system very easy to deploy and integrate with other imaging modalities.

Full-field phase modulation characterization of liquid-crystal spatial light modulator using digital holography

A direct quantitative phase measurement method to characterize intrinsic phase modulation from an entire active area of transmissive twisted-nematic liquid-crystal spatial light modulator (TN-LCSLM) is presented using digital holography (DH). The change in birefringence of liquid crystal material with respect to addressed gray scale produces phase modulation of wavefront transmitted through TN-LCSLM. Existing methods for phase modulation characterization of LCSLM mainly provides point measurement on its total active region. In this paper, the DH method is evolved to extract quantitative phase information of an entire active area from a single digital hologram formed using the complex wavefront transmitted through TN-LCSLM.

All optical phase-only filtering correlation with binarized inputs by a ferroelectric liquid-crystal spatial light modulator

All optical phase-only filtering correlator is constructed with an optically addressed ferroelectric liquid-crystal spatial light modulator (FSLM) for a binarized input object and a twisted-nematic liquid-crystal spatial-light modulator for a computer-generated phase-only filter. In order to improve the discrimination capability of a phase-only filtering correlator, a binarized amplitude with maximum contrast in a FSLM is used for an object input. The contrast of binarized intensities can be maximized by adjusting the rotation angles of a FSLM and polarizers. The threshold level of binarized input objects can be controlled by changing the power of a laser incident on a FLSM. Experimental results with a high discrimination capability are presented to support the numerical correlation performance.

Phase shifting digital holography implemented with a twisted-nematic liquid-crystal display

We describe and experimentally demonstrate a phase shifting method based on the lateral displacement of a grating implemented with a twisted-nematic liquid-crystal spatial light modulator. This method allows an accurate implementation of the phase shift without requiring moving parts. The technique is implemented in a Mach-Zehnder digital holography setup in which the field transmitted by the sample object freely propagates to the hologram plane.

Improvement of the complex modulated characteristic of cascaded liquid crystal spatial light modulators by using a novel amplitude compensated technique

To achieve the full complex modulated range of the cascaded twisted nematic liquid crystal spatial light modulator (TNLC-SLM), we propose and demonstrate a novel amplitude compensated technique. Optical reconstructions of complex digital holograms with higher image quality are discussed in both analytical and experimental results.

Complex modulation with a twisted-nematic liquid-crystal spatial light modulator: double-pixel approach.

I modify the double-phase holographic code to implement complex modulation with a transmission twisted-nematic liquid-crystal display. This device is employed in the mostly phase configuration, for which the phase modulation is coupled with a nonconstant amplitude modulation. The modified double-phase code implements arbitrary complex modulation employing the constrained complex modulation of the display.

Transmission variations in liquid crystal spatial light modulators caused by interference and diffraction effects

We report on the characteristics of a newly developed high- resolution (6403480 pixels) parallel-aligned liquid crystal spatial light modulator (LCSLM) as a function of wavelength. Phase-only operation over a range of 2p rad is easily achieved by operating at shorter wave- lengths. We also measure an unexpected effect—the transmitted light intensity changes with applied voltage. Our experiments show that thin- film interference and pixel diffraction effects are responsible for this ob- served behavior. The diffraction effect is caused by a nonuniform electric field across each pixel. This nonuniform electric field introduces a blazing effect that changes the intensity distribution in the various diffracted or- ders as a function of applied voltage. These same kinds of effects have been observed with several other twisted-nematic LCSLMs. Because of the complicated polarization effects caused by these twisted-nematic liq- uid crystal devices, however, the diffraction and interference effects are more easily studied using the parallel-aligned LCSLM. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)01006-5)