Time-delay signature suppression in a chaotic semiconductor laser by fiber random grating induced random distributed feedback
We demonstrate that a semiconductor laser perturbed by distributed feedback with random time delays from a large number of scattering centers along a fiber random grating can emit light chaotically without the time-delay signature (TDS). A theoretical model is developed based on the modified Lang–Kobayashi model to numerically explore the chaotic dynamics of the laser diode subjected to random feedback. It is predicted that the random distributed feedback destroys the phase-correlated mode condition and hence suppresses the TDS. The fiber random grating is fabricated with random index modulation periods through point-by-point inscription, which introduces large numbers of phase-uncorrelated cavity modes into the semiconductor laser, leading to high dimensional chaotic dynamics and thus the concealment of the TDS. The experimentally obtained TDS value is negligible with a minimum of 0.0088, which is the smallest to date.