Innovative speckle noise reduction procedure in optical encryption

Encrypting techniques are currently of interest in the optical domain. A common issue when using coherent techniques is speckle noise which influences the final results. Most efforts to solve this issue were directed towards processing the output of the systems. Instead, we present an alternative approach where we seek to control the input to enhance the performance of these techniques. In particular, we analyze an encoding procedure with a joint transform correlator architecture as a case study. We first demonstrate the dependence of the output noise on the spatial distribution of the input, showing the existence of a neglected random correlation noise which contributes to the degradation of the output. We then propose a rearrangement of the input that results in a reduction of the noise level in the outcome. This rearrangement consists of separating the pixels of the input by introducing black pixels between them, keeping the usual remaining procedure unaltered. Our experimental approach opens up new possibilities for the applications of optical security techniques beyond the limitations imposed by noise.