Recent applications of laser chaos, e.g. in random number generation, cryptography and sensing motivate the search for the widest band chaos while keeping the laser system relatively simple[1]. We analyze here the chaos bandwidth of a laser diode subjected to a phase conjugate feedback (PCF) both experimentally and theoretically. We demonstrate that a commercial laser diode whose frequency of relaxation oscillations is 3.9 GHz can, thanks to a single PCF, generate a chaotic signal with up to 18.5 GHz chaos. The chaos bandwidth is defined as the span of frequencies which contains 80 % of the frequencies of the chaos[2]. We report that the chaos bandwidth of a laser diode first increases linearly with the feedback strength but then saturates. Numerical simulations reproduce this observation and highlight the influence of the finite penetration depth in the phase-conjugate mirror.

© 2019 IEEE

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