Gray scale effect on photorefractive dynamics

Abstract

Dynamic photorefractive memories are promising for digital optical computing and optical neural networks because of their large storage capacities and fast memory access.1 Scheduled recording and incremental recording schemes have been introduced to obtain uniformly multiplexed gratings. Recently, the dynamics of a selective erasure process was studied and applied for fast update of memory. However, all these schemes assume simple plane wave recording and neglect the effect of gray scale images on the recording dynamics. Recording gray scale images is common in many practical situations, e.g., gray scale data and Fourier transform of binary data. We analyzed the effect of gray scale images on the dynamics of scheduled and incremental recording as well as the selective erasure processes, assuming that the material response time is inversely proportional to the writing intensity. We found that multiplexing using scheduled recording failed to provide uniform recording of gray scale images. In contrast, incremental recording allows recording of gray scale images, but the required number of iteration cycles varies depending on the gray scale. Selective erasure time is also gray scale dependent, and the darkest region requires twice the time of the brightest region. We will also present the experimental results and compare them with the analysis.