Characterization of twisted liquid crystal spatial light modulators

ABSTRACT A spatial light modulator (SLM) is a very useful optical tool due its versatility to be manipulated dynamically. We propose a characterization method for reflective SLMs in quasi-normal configuration. This device can work as either amplitude-mostly or phase-mostly modulator. To achieve the modulation, the SLM can be accompanied by two polarizes, or additionally using a quarter-wave plate retarder. By simulating the behaviour of the optical setup for this device; we establish an experimental Jones matrix that repres ent the modulator. In this work we present a more realistic modulator characterization, only assuming that the modulator Jones matrix should be unitary (the modulator do not absorb light). We report this model for ch aracterization of the Holoeye LCR2500 SLM. Keywords: Spatial light modulators, plate retarder, light modulation. 1. INTRODUCTION The use of liquid crystal (LC) SLMs in several areas of optical processing has been highly increased during the last decade. For the appropriate app lication of a LC SLM it is convenient to es tablish an accurate model for the transmittance of the LC cells. The modulation area on these optoelectronic devices is formed by a liquid crystal layer whose molecules change its orientation in presence of an ex ternal electric field, which is induced by means of electrodes that form part of the device. Here we report a novel method to characterize a reflective SLM Holoeye LCR2500, whose structure is formed by an array of 768 u 1024 pixels, and present a pixel pitch of 19 microns. To characterize the SLM modulation it is enough to illuminate the device by a linearly polarized monochromatic beam, which is usually provided by a linear polarizer at the input of the SLM. In addition, a second linear polarizer is employed to analyze the beam transmitted by the SLM cells. The purpose is to establish the parameters of an appropriate Jones matrix to represent the SLM transmittance. Specifically it is convenient to determine the amplitude and phase for each one of the four matrix components M