Using the Liquid Crystal Spatial Light Modulators for Control of Coherence and Polarization of Optical Beams

Abstract

Beginning from the mid-1980’s the liquid crystal (LC) spatial light modulators (SLMs) have been used in many optical applications, such as optical data processing, beam shaping, optical communication, adaptive optics, real-time holography, etc. In these applications LC-SLMs are used for both amplitude and phase modulation of optical field. The modulation characteristics of LCSLMs have been widely studied and reported (Lu & Saleh, 1990). A special attention has been given to the optimization of LC-SLM parameters in order to provide the amplitude-only and phase-only modes of modulation (Yamauchi & Eiju, 1995). Recently, in connection with the heightened interest in the vector coherence theory of electromagnetic fields (Ostrovsky et al, 2009a), a new possible application of LC-SLMs has been found. It has been shown (Shirai & Wolf, 2004) that LC-SLM of certain configuration can realize the controlled changes of statistical properties of an electromagnetic beam, namely the degree of coherence and the degree of polarization. This fact can be successfully used for generating a secondary partially coherent and partially polarized optical source with the desired characteristics. Somewhat later the technique proposed by Sahirai and Wolf has been improved using the systems of two LC-SLMs coupled in series (Ostrovsky et al., 2009b) or in parallel (Shirai et al., 2005). Unfortunately, the mentioned techniques have not been yet realized in practice because of the lack of commercial LC-SLMs with proper characteristics. Here we propose an alternative technique that uses widely available commercial LC-SLMs and, hence, can be easily realized in practice. In this chapter, we present a comparative analysis of the techniques for controlling coherence and polarization by LC SLMs. When doing this we consider both the known, properly referenced, techniques and the original ones proposed by the authors. We illustrate the efficiency of the proposed technique with the results of numerical simulation and physical experiments. To facilitate the perception of material, we anticipate the main matter by the backgrounds concerning the fundamentals of vector coherence theory and the elements of theory and design of LC-SLMs. We hope that this chapter will help the specialists and postgraduate students in optics and optoelectronics to be well guided in the subject dispersed in numerous publications.