Fig. 1. Experimental setup for wideband chaotic signal generation based on dual-mode microsquare laser. OC, optical circulator; EDFA, erbium-doped fiber amplifier; OBPF, optical bandpass filter; PD, photodetector; PC, polarization controller; ESA, electric spectrum analyzer.

Fig. 2. (a) Microscopic image of the microsquare laser. (b) Representative lasing spectra of the microsquare laser. (c) Magnetic field distributions of the fundamental (zeroth-order) and first-order (1st-order) mode. (d) Lasing spectrum at 50 mA in a large scale to show the longitudinal mode characteristics and the function of the OBPF.

Fig. 3. RF spectra of the generated chaotic signal at different currents with fixed feedback strength of 7.3 dB.

Fig. 4. Intensity ratio between two lasing modes (blue squares) and standard bandwidth (red circles) of the chaotic signal versus the biased currents. Inset: flatness of the RF spectrum versus biased current.

Fig. 5. Lasing spectra of the microsquare laser with a fixed biased current of 51 mA and different feedback strengths.

Fig. 6. (a) Representative RF spectra with different feedback strengths at 51 mA. (b) Flatness in the standard bandwidth, standard bandwidth, and effective bandwidth as a function of the feedback strength, indicated by symbols of red circles, blue squares, and blue triangles.

Fig. 7. (a) RF spectrum with feedback strength of 10.3 dB at 51 mA. (b) Time series and (c) autocorrelation coefficient of the chaotic signal.