**1. Introduction**

In this chapter, we present an analysis on the use of modern parallel-aligned liquid crystal on silicon displays (PA-LCoS) in diffractive optics and holographic data storage (HDS). The PA-LCoS acts as a spatial light modulator (SLM) in different roles: as data entry point,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

state of polarization (SOP) converter, phase-only modulator, or amplitude-mostly modulator. All these roles are interesting in many research fields [1–3].

PA-LCoS devices have become widely used in diffractive optics due to its ease of operation and phase-only modulation capabilities, because of its high spatial resolution and high light efficiency [3]. The liquid crystal (LC) technology has achieved a high level of maturity and enables us to have a data entry point in HDS for a high data density recording, and it provides us with the ability to design different modulation schemes.

In order to incorporate this kind of microdisplays into a complete holographic data storage system (HDSS), we have done an intense work to characterize PA-LCoS devices. As a phaseonly device, we need to know the retardance introduced for every gray level. The microdisplay is digitally addressed with a pulsed voltage signal. This fact implies a fluctuation in the phase that will be reflected in the optical response [4–7]. For that reason, for a full characterization, we need to obtain the average retardance and the fluctuation amplitude for every gray level. This enables us to select the best device configuration for our application.

Even though PA-LCoS are widely used by the photonics community, these phase-only devices have not been intensively applied in holographic data storage applications. These devices could be a key element for a phase multilevel data page coding. If the trend is to use this kind of coding scheme, a right characterization and a profound knowledge will be useful.
