Generation of broadband chaos with perfect time delay signature suppression by using self-phase-modulated feedback and a microsphere resonator

We propose and experimentally demonstrate a broadband chaos generation scheme by introducing self-phase modulation (SPM) in the feedback loop of an external-cavity semiconductor laser and propagating the chaos through a microsphere resonator (MR). Four chaos generation cases—conventional optical feedback (COF), COF+MR, individual SPM optical feedback (SPMOF), and the proposed SPMOF+MR—are experimentally discussed. The experimental results demonstrate that with respect to the other three cases, in the proposed scheme with the joint effects of SPMOF and MR, the relaxation oscillation effect in chaos can be eliminated and a flat RF spectrum with much more significant bandwidth enhancement can be achieved. Simultaneously, the time delay signature (TDS) in the chaos can be perfectly suppressed at a very low level close to 0 in a wide operation range of feedback. This work shows a novel scheme to generate broadband chaos with flat spectrum and perfect TDS suppression.