Fig. 1. Numerical simulation results of chaotic laser at I=1.5I_th and κ=10 ns^-1. (a) Time traces; (b) power spectra (vertical dashed line indicates 80% frequency bandwidth)

Fig. 2. Numerical results at I=1.5I_th and κ=10 ns^-1. (a) ACF (vertical dashed line indicates τ=86.7 ns); (b) permutation entropy as a function of delay time

Fig. 3. Numerical results at various κ and bias current of 1.35I_th,1.5I_th, 1.75I_th and 2I_th. (a) C_P; (b) H(p)

Fig. 4. Schematic of the experimental setup for the suppressing of time-delay signature in chaotic lasers by filtering

Fig. 5. Experimental frequency spectra, time traces, autocorrelation function and permutation entropy of the chaotic laser signal before and after filtering at inject current of 1.5I_th and feedback strength of -7.5 dB. (a1)-(a4) Chaotic laser signal and TDS before filtering; (b1)-(b4) chaotic laser signal and TDS after 500 MHz filtering; (c1)-(c4) chaotic laser signal and TDS after 100 MHz filtering

Fig. 6. Experimental results for C_p and H(p) of the chaotic signal at various feedback intensity and bia current before and after filtering. (a1) (b1) Before filtering; (a2)(b2) after 500 MHz filtering; (a3)(b3) after 100 MHz filtering

Fig. 7. Experimental results for time series, intensity distribution and skewness of the chaotic signal before and after filtering. (a) Statistical distribution before filtering; (b) statistical distribution after 500 MHz filtering; (c) statistical distribution after 100 MHz filtering; (d) skewness of intensity distribution at various feedback strength at 1.5I_th (solid curve represents Gaussian fitting, and dashed line represents the mean of value time series)