<title>Optimization of holograms recorded in DuPont photopolymer</title>

Abstract

Substrate-Mode gratings are used to couple and influence the signals that propagate in planar-integrated optical systems. Volume holograms are especially well suited for this role because they allow the recording of slanted fringe gratings. Photopolymer are among the best candidates for such applications due to easy handling, dry development process, high diffraction efficiency and replication possibilities. In this paper, we investigate the recording dynamics of OmnidexTM photopolymer from DuPont. We use the theoretical diffusion model proposed by Zhao and Mouroulis in order to simulate the recording process. Two different experiments are described that lead to the quantitative determination of kinetic parameters in this material. These values are introduced in the diffusion model and different recording procedures are simulated. The conclusion shows that it could be valuable to let the material in the dark for several minutes before develop it. This investigation should improve the understanding of recording process and consequently it should permit to build more efficient components.

Accurate diffraction efficiency control for multiplexed volume holographic gratings

“…recorded sequentially with non-parallel grating vector orientations. During the first exposure, a 1-D diffusion equation [5], [6] in the following describes the monomer concentration ( ) , where κ is a constant and o I is the average irradiance), and V is the fringe visibility. The initial conditions of equation 2depend on the final conditions of equation 1, and the final monomer concentration after recording can be written in the form of ( )…”

“…Equation (2) is difficult to solve in the case of non-orthogonal multiplexing. Moreover, the diffusion model involves some material parameters [6] that are not available at this stage. Therefore, this model cannot be used directly for diffraction efficiency control, especially in the case of non-orthogonal multiplexing.…”

“…3 shows the normalized diffraction efficiency of the two gratings as a function of second-exposure time. The calculated curves by solving two uncoupled 1-D diffusion equations using the parameters from curve fitting [5], [6] are also shown in Fig. 3 as shown in Fig.…”

“…If two gratings are non-orthogonally multiplexed, the process of the second grating formation is coupled with the change of the first grating during the second exposure. Due to the complexity of solving the diffusion equation and the lack of information about material parameters [6] , this model cannot be used directly for diffraction efficiency control, especially in the case of non-orthogonal multiplexing. Based on the experimental evaluations of the grating formation characteristics in dry photopolymer films, we develop the practical recording schedules for the fabrication of holographic gratings under accurate diffraction efficiency control.…”