We analyze in details experimental measurements of high frequency laser dynamics and chaos generated by a laser diode subjected to phase-conjugate feedback realized using nonlinear wave mixing in a SPS photorefractive crystal in a CAT configuration. In addition to the typical figure of merit, ie, chaos bandwidth, the corresponding spectral flatness and permutation entropy at delay is analyzed. The experiments reveal that chaos, with a bandwidth up to 30 GHz, a spectral flatness up to 0.75, and a permutation entropy at delay of up to 0.99 can be generated. These optimized performances are observed over a large range of parameters and have not been achieved in the conventional optical feedback configuration. Interestingly, when the pump current is reduced, the chaos bandwidth is also reduced while keeping the spectral flatness and the permutation entropy. Our experimental findings are in qualitative agreement with the presented numerical simulations produced using the Lang-Kobayashi model. Such chaotic laser diodes can be used in chaotic cryptography, high-rate random number generation and optical metrology with the enhancement of lidar resolution.
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