Experimental distinction of weak and strong chaos in delay-coupled semiconductor lasers

Semiconductor lasers subject to external perturbations often exhibit deterministic chaotic behaviour. Optical delayed self-feedback is a common way to induce chaotic laser emission. In recent years, chaotic semiconductor lasers have proven to be useful in a number of practical applications, ranging from chaos communications and secure key distribution to random bit generation or LIDAR systems [1]. In particular, chaos communications and secure key distribution rely on the synchronization or two or more lasers operating in the chaotic regime [2]. Thus, a high degree of synchronization is desired for practical applications.