Suppression of time-delayed signature in chaotic signals based on optoelectronic hybrid feedbacks

A novel approach to suppressing the time-delayed signature (TDS) in chaotic signals from the semiconductor laser (SCL) is proposed and experimentally demonstrated based on the optoelectronic hybrid feedback. Through combining the distributed feedback in the chirped fiber Bragg grating (CFBG) with the nonlinear optoelectronic feedback provided by the microwave photonic link, a low-TDS chaotic oscillation is successfully built up in the SCI cavity. Thanks to the employment of the nonlinear optoelectronic feedback, the proposed scheme can generate low TDS chaotic signals by using a CFBG with a much smaller grating dispersion coefficient of about 22.3 ps/nm compared with the scheme relying solely on the distributed feedback (i.e., 2000 ps/nm). In addition, different from the broadband optoelectronic oscillator, there is almost no stringent requirement of the extremely high net gain of the microwave photonic link. In the proof-of-concept experiment, the chaotic signal generated by the proposed scheme has a much lower TDS of about 0.05, a higher PE of 0.9978, and a better spectral flatness of 8 dB, compared with the conventional distributed feedback laser.