Controlling correlative chaos in dual-color laser for cryptographic communication

Abstract

Chaotic fluctuation of light, which is being intrinsically different from deterministic chaos in lasers, arises from quantum-optic stochastic processes, and it therefore cannot be artificially replicated. When the fluctuation is correlative, however, it will be of more use in practical applications such as cryptographic communications. Throughout various experiments, it was found that a double-ring laser having a common semiconductor gain medium with strong saturation characteristics can produce a stable light beam consisting of negatively correlative dual-color components. Although each component decomposed by chromatic beam splitting is chaotic, their combination regenerates a stable light beam. This means that the photon-number states can be controlled by using an optical processing scheme for a correlative dual-color chaotic beam. How such a beam is generated is explained by a simple numerical simulation using a finite Markov chain model that assumes strong short-term intensity correlation between the components. A possible cryptosystem is presented based on the controllability of the photon-number state.