Generation of flat wideband chaos based on mutual injection of semiconductor lasers

In this Letter, we propose and demonstrate a method to improve the bandwidth and flatness of chaotic signals using a mutual injection structure with two distributed feedback lasers. The frequency detuning and coupling strength are investigated to produce wideband flat chaos. The chaotic signal that the spectrum covers is greater than 50 GHz, which is approximately 6.42 times when compared with the one generated by the optical feedback, with a flatness of 5.6 dB achieved when the coupling strength is 1.635 and the frequency detuning is -33.5  GHz.