Photopolymer are appealing materials for diffractive elements recording. Two of their properties when they are illuminated are useful for this goal: the relief surface changes and the refractive index modifications. To this goal the linearity in the material response is crucial to design the optimum irradiance for each element. In this paper we measured directly some parameters to know how linear is the material response, in terms of the refractive index modulation versus exposure, then we can predict the refractive index distributions during recording. We have analyzed at different recording intensities the evolution of monomer diffusion during recording for photopolymers based on PVA/Acrylamide. This model has been successfully applied to PVA/Acrylamide photopolymers to predict the transmitted diffracted orders and the agreement with experimental values has been increased. M. Elvin, "A highly elastic and adhesive gelatin tissue sealant for gastrointestinal surgery and colon anastomosis,"

The parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplay has become a widely used device for the photonics community. It is a very versatile tool that can perform several tasks which transforms it into a key element in many different photonics applications. Since our group is interested in holography, in this chapter, we want to use these displays as the data entry point for a holographic data storage system (HDSS). Due to the novelty of this kind of device, we have done an intense work characterizing it. These efforts are reflected in this chapter where the reader will find two different characterization methods that will enable to predict the performance of the device in a specific application. Additionally, we present how a phase-only device can be used as a data pager using different modulation schemes and combined with a photopolymer as the holographic recording material.

We have included a Parallel Aligned Liquid Crystal on Silicon (PA-LCoS) microdisplay in a Holographic Data Storage System (HDSS). This novel display, widely accepted as Spatial Light Modulator (SLM), presents some advantages and disadvantages. One of these disadvantages is the anamorphic and frequency dependent effect. In this work we want to test this effect and see its effects in the complete optical process involved in the HDSS. We will use stripe-based patterns with different orientation (vertical and horizontal). To check the limits, we will increase the data density by decreasing the minimum stripe width. For evaluating the degradation suffered by the data page, we use the Bit Error Rate (BER) as figure of merit. We make a BER calculation from the statistical analysis of the histogram. In addition to the anamorphic effects we evaluate the degradation effects introduced by the non-uniformity in the illumination. To this goal we divide the image in several regions that are processed in the same way that the entire image. The error analysis of the entire optical system is useful for its calibration and fine adjustment. Once we have characterized the experimental setup we introduce the holographic material. Thus, by making the same analysis, we can evaluate the errors introduced by the material. As holographic material we use Polyvinyl Alcohol Acrylamide (PVA/AA), that has been characterized and developed in previous works by our group.

The technologies based on holographic and photonic techniques related to the optical storage and optical processing of information are rapidly evolving. One of the key points of this evolution are the new recording materials able to perform under the most specific situations and applications. In this sense, the importance of the photopolymers is growing spectacularly. This is mainly due to their versatility in terms of composition and design together with other interesting properties such as self-processing capabilities. In this chapter, we introduce the diffractive optical elements (DOE) generation in these materials and some of the most important parameters involved in this process. The deep knowledge of the material is essential to model its behavior during and after the recording process and we present different techniques to characterize the recording materials. We also present a 3D theoretical diffusion model able to reproduce and predict the experimental behavior of the recording process of any kind of DOE onto the photopolymers. The theoretical results will be supported by experimental analysis using a hybrid optical-digital setup, which includes a liquid crystal on silicon display. Besides this analysis, we study a method to improve the conservation and characteristics of these materials, an index-matching system.

The concept of phase, introduced on the study of the Diffractive Optical Elements (DOEs), presents slight understanding difficulties by the students. The phase DOEs are obtained by variations of the thickness or the refractive index of the recording medium, as opposition to the amplitude DOEs, which are obtained by the modulation of the absorption of the recording medium.It is presented some experiences to introduce the phase concept by means of thickness and refractive index variation, using photopolymers as the phase recording media. These experiences consist in a zero-spatial frequency limit analysis based on a reflection and transmission interferometer and the recording of different types of low spatial frequency DOEs, such as sinusoidal gratings or blazed gratings, generated using a Spatial Light modulator (SLM) to modulate the recording beam. With these experiments, it is possible to measure and observe on real time the thickness and refractive index variations of the material and compare the diffraction efficiencies (DEs) of different types of grating.The experiences proposed are suitable for the students of different subjects such as "Optical fundamental for Engineering", basic subject included in the second course for obtaining a Telecommunication Degree, for "Photonics and Optoelectronic devices", mandatory subject taught during the second year of Telecommunication master or the optative subject "Acquisition and Optical Treatment of Images" from the Master in robotics-automatic all taught at the University of Alicante. In all cases, the experiences are not only very useful to introduce the concepts to study, but also are useful also to introduce the students into the work of a research laboratory and some of the equipment and procedures that are used on it.