3 Dimensional analysis of holographic photopolymers based memories

Abstract

Abstract:One of the most interesting applications of photopolymers is as holographic recording materials for holographic memories. One of the basic requirements for this application is that the recording material thickness must be 500 µm or thicker. In recent years many 2-dimensional models have been proposed for the analysis of photopolymers. Good agreement between theoretical simulations and experimental results has been obtained for layers thinner than 200 µm. The attenuation of the light inside the material by Beer's law results in an attenuation of the index profile inside the material and in some cases the effective optical thickness of the material is lower than the physical thickness. This is an important and fundamental limitation in achieving high capacity holographic memories using photopolymers and cannot be analyzed using 2-D diffusion models. In this paper a model is proposed to describe the behavior of the photopolymers in 3-D. This model is applied to simulate the formation of profiles in depth for different photopolymer viscosities and different intensity attenuations inside the material.

Holographic grating evolution in photopolymer materials

“…Also, the extracted parameter values shown in Table 1. are comparable to those presented in the literature [1][2][3][4][5][6][7][8][9][10][11][12].…”

“…Our specific aim is to increase our understanding of what takes place inside the photopolymer material during exposure, i.e. to explain the effects of the variation of the absorbance of the photosensitive dye with time [3][4][5], and the suppression of monomer radical production due to the presence of inhibitors [5][6][7]. We thus aim to extend the validity of our Non-Local Photopolymerization Driven Diffusion (NPDD) model [8][9][10][11][12], based on a deeper understanding of the photochemical and mass transport effects.…”

3-dimensional analysis of holographic memories based on photopolymers using finite differences method

“…The initial value of α [α (t=0)=α 0 ] can be obtained if the transmittance and the physical thickness of the layer are known. In our material [20] for layers with a physical thickness around 800 µm, the transmittance is around 0.82%; in others words, the values of α 0 for this composition are around 0.006 µm -1 [20]. The absorption of the layer changes as a function of the time it takes for the dye to be consumed.…”

“…The attenuation of light inside the material according to Beer's law results in an attenuation of the index profile inside the material and in some cases the effective optical thickness of the material is lower than the physical thickness [19]. Some approximations have been made in order to understand the profile recorded in thick photopolymers [20]. In this study we use a Finite-Difference method to solve the 3 dimensional local problem.…”

“…The intensity distribution is assumed constant along y, but attenuated in depth along the Z axis. The depth attenuation changes the angular response of the grating stored in the material [21] and determines the optical thickness and ultimate storage capacity of each material composition [19][20]. Assuming Beer's law explains the attenuation of light intensity with depth, the recording intensity can be written as:…”