Effect of grating detuning in holographic storage

Organic photopolymers are becoming increasingly important in volume holographic storage. Unlike photorefractive crystals photopolymers are known to exhibit material shrinkage and a refractive index change during or after the hologram recording. An immediate result of the shrinkage is the grating detuning and the subsequent Bragg mismatch which may significantly decrease the diffraction efficiency, leading to a degradation of the signal to noise ratio. We have investigated the effect of index grating detuning due to anisotropic shrinkage in volume holographic storage systems. Analytical results on pixel displacement and Bragg mismatch due to a general anisotropic grating detuning and a refractive index change are obtained. Using the analytic results, we show that the pixel displacement and the Bragg mismatch can be minimized by using an appropriate combination of the horizontal and vertical shrinkage parameters.