Photopolymer materials have received a great deal of attention because they are inexpensive, self-processing materials that are extremely versatile, offering many advantages over more traditional materials. To achieve their full potential, there is significant value in understanding the photophysical and photochemical processes taking place within such materials. This paper includes a brief review of recent attempts to more fully understand what is needed to optimize the performance of photopolymer materials for Holographic Data Storage (HDS) and Self-Written Waveguides (SWWs) applications. Specifically, we aim to discuss the evolution of our understanding of what takes place inside these materials and what happens during photopolymerization process, with the objective of further improving the performance of such materials. Starting with a review of the photosensitizer absorptivity, a dye model combining the associated electromagnetics and photochemical kinetics is presented. Thereafter, the optimization of photopolymer materials for HDS and SWWs applications is reviewed. It is clear that many promising materials are being developed for the next generation optical applications media.

Photopolymer materials can be used as recording media for self-written waveguides (SWWs) as they can exhibit a large refractive index change and high photo-sensitivity. In free radical photo-polymerization systems, the dyes, functioning as the photosensitizer, strongly influence the material properties. During photo-illumination the spatial and temporal evolution of the dye concentration is an important factor leading to nonlinear absorption. In this paper, based on an investigation of the photochemical mechanisms, we analyze the nonlinear photo-absorptive effect during the photo-initiation processes. The time varying exposing light distribution is calculated and used to iteratively estimate the evolving cross-sectional refractive index and loss coefficient values. The model enables a more accurate and physical description of the optically induced growth of SWWs in such systems. Then SWWs formed in dry acrylamide/polyvinyl alcohol (AA/PVA) based photopolymer samples, containing different initial dye concentrations, are experimentally examined. The nonlinear absorptive behavior is quantified by comparing the model predictions and the experimental results.

Recently, the vulnerability of the linear canonical transform-based double random phase encryption system to attack has been demonstrated. To alleviate this, we present for the first time, to the best of our knowledge, a method for securing a two-dimensional scene using a quadratic phase encoding system operating in the photon-counted imaging (PCI) regime. Position-phase-shifting digital holography is applied to record the photon-limited encrypted complex samples. The reconstruction of the complex wavefront involves four sparse (undersampled) dataset intensity measurements (interferograms) at two different positions. Computer simulations validate that the photon-limited sparse-encrypted data has adequate information to authenticate the original data set. Finally, security analysis, employing iterative phase retrieval attacks, has been performed.

Self-written waveguide (SWW) trajectories fabricated inside a dry photopolymer bulk material, acrylamide/polyvinyl alcohol (AA/PVA), are studied. Their production using both Gaussian and Laguerre–Gauss exposing (writing) light beams, output from optical fibers, is explored. The formation of the primary and secondary eyes is also discussed. Furthermore, the interactions that take place when two counterpropagating beams pass through the photopolymer material (both Gaussian and Laguerre–Gauss) are examined. In all cases experimental and theoretical results are presented. Good agreement between the predictions of the proposed model and experimental observations are demonstrated.

An experimental and theoretical investigation of the preparation and exposure of multilayer photosensitive materials is presented. It is shown how the recorded change in the refractive index in each layer depends on the dye (photosensitizer) concentrations in each layer. It is also shown how the photosensitive material properties in each layer can be controlled to optimize some recording characteristics for particular applications. To do so, a set of equations, predicting the amplitude of higher harmonics refractive index amplitudes induced in the material layers with depth during exposure, is derived. This results in a technique for varying the dye concentration in each layer of a multilayer, so as to optimize volume diffraction grating performance. In part I of this paper, the 3D nonlocal photopolymerization-driven diffusion (NPDD) model is applied to calculate the resulting combined multilayer absorption and polymerization processes. The NPDD describes the time-varying behaviors taking place during exposure in such photopolymer materials. Simulations are performed for an acrylamide/polyvinyl alcohol-based photopolymer containing erythrosine-B dye. It is predicted that, in general, non-uniform gratings are formed, with the resulting refractive index being distorted both from the ideal sinusoidal cross-sectional spatial distribution and also with depth. This agrees with previous results indicating that increasing the thickness of a single photopolymer layer does not in practice lead to ever-increasing angular selectivity. In part II of this paper, it is confirmed experimentally that a suitably modified multilayer can be used to increase grating angular selectivity, i.e., reduce the width of the off-Bragg replay curve.

The diffraction of a light beam as it propagates through a medium can be effectively compensated by self-trapping. A laser beam propagating through a nonlinear medium can generate a waveguiding action, i.e., a higher refractive index, along the direction of the light propagation. Experiments involving light beams illuminating the front surface of a solid bulk photopolymer sample are reported. The self-bending of parallel beams (input simultaneously but separated in space) during the resulting self-writing process is studied. It is shown that there is strong correlation between the initial beam input separation distance and the resulting waveguide trajectories taken during channel formation. Finite element-based simulations are performed, which predict the self-writing waveguide formation process, e.g., beam focusing, trapping, and the deviations of the waveguide trajectories caused by adjacent beams. The model is shown to be in good qualitative agreement with observed experimental results.