Improved maximum uniformity and capacity of multiple holograms recorded in absorbent photopolymers

Sergi Gallego,Augusto Beléndez,Elena Fernández,Manuel F Ortuño,Cristian Neipp,Inmaculada Pascual

doi:10.1364/oe.15.009308

Abstract

In order to use photopolymers in the recording of holographic memories, high physical thickness is required. This generates many problems associated with the attenuation of light in the recording due to Beer's law. One of the more significant disadvantages is the fact that there are differences between the physical thickness of the material and the optical thickness of the holograms recorded. The optical thickness characterizes the angular selectivity of the holograms and determines the separation between two consecutive holograms in angular peristrophic multiplexing. In this work we propose a new method to record many holograms multiplexed with similar diffraction efficiency values taking into account the different effective optical thickness of each hologram.

Highlights

Great advances have been made in the use of photopolymers as data storage media [1,2,3]
In the first approximation of the problem of multiplexing many holograms in the same volume of light absorbent material, it is easy to understand that the effective optical thickness of the holograms will be greater initially and the limit of the effective optical thickness is the physical thickness of the layer
We present the analysis of some materials where the effective optical thickness never achieves values close to the physical thickness of the layer

Summary

Introduction

Great advances have been made in the use of photopolymers as data storage media [1,2,3]. Sheridan and co-workers proposed an interesting schedule based on a two dimensional non-local diffusion model to obtain holograms with the same diffraction efficiency using these materials [3] In these studies the authors assume that the diffraction efficiency only depends on the refractive index modulation of the grating because the thickness of the gratings is considered constant; in other words the physical and effective optical thickness have the same value. In our recent experimental studies [9] we observed some problems when multiplexing many holograms using iterative algorithms [10] These problems are due to the variation in the effective optical thickness of the gratings recorded during the multiplexing process. We studied the differences between the effective optical thicknesses of each grating and the influence of different parameters on the optimal times to obtain gratings with the same diffraction efficiencies

Theoretical model

Results and discussions

High velocities of the bleaching process

High velocities of grating formation

Conclusion