Optimal laser diode chaos properties for security applications

Under appropriate conditions the output of a laser diode may consist of a series of irregular, chaotic pulses. Such a broadband chaotic output is a physical source of entropy at high rate, hence enabling the rapid generation of physical keys for cryptography. In addition the broadened light spectrum improves the performances in so-called chaotic LIDARs, and the extreme sensitivity of deterministic chaos to system’s perturbations allows for developing high precision sensing. These applications require the development of chaotic signals with optimised bandwidth and high entropy, in a large range of system parameters. The present contribution will discuss about the use of two different approaches to optimise chaos performances. One is based on the use of a phase conjugation external mirror re-injecting light into a laser diode. The second one is based on the injection of an optical frequency comb into a laser diode. In both cases chaos bandwidths extending beyond 40 GHz and a permutation entropy close to 1 are found experimentally.