Chaos synchronization and communication between two semiconductor lasers separated by a distance of 40 Km

A 40 Km fiber bidirectional chaotic communication system, composed of a driving chaotic semiconductor laser and twin semiconductor lasers, is proposed. We experimentally observe synchronization between the twin lasers driven by a chaotic signal, generated by the driving laser and after being transported in a pair of 20 Km single mode fibers. Based on the high-quality synchronization between the twin lasers, a bidirectional public cryptographic scheme is developed after introducing an additional optical path between the twin lasers as public message channel. Two GHz messages, encrypted into chaotic carriers, can be decrypted effectively in principle.