Chaos Time Delay Signature Suppression and Bandwidth Enhancement by Electrical Heterodyning
Chih-Hao Cheng1*, Yi-Cheng Chen1, Fan-Yi Lin1
1Institute of Photonics Technologies, National Tsing Hua University, Hsinchu, Taiwan
* presenting author:鄭致灝,
We numerically investigated the chaos time delay signature (TDS) suppression and bandwidth enhancement by electrical heterodyning. Semiconductor lasers with optical feedback are often used for chaos signal generation owing to its simple and low-cost configuration. However, the power spectra of the chaos signals generated have distinct loop frequency peaks, corresponding to the reciprocals of the time delays. Besides, the power spectra usually have weaker power in the low frequency region relative to the strong power around the relaxation oscillation frequency. Such periodicity and non-uniform power distribution degrade the randomness and reduce the effective bandwidth of the chaos signals. By electrically heterodyning the chaos signal with a single frequency local oscillator, the power in the chaos spectrum can be redistributed to smooth out the loop frequency peaks and elevate the dip in the low frequency region. Compared with the chaos directly generated from a semiconductor laser subject to optical feedback, the amplitudes of the TDS measured at different feedback strengths can be suppressed up to 63% and the effective bandwidths can be enhanced up to 46% in average after the electrical heterodyning is applied. The proposed electrical heterodyne technique has great advantages in generating high-quality broadband chaos for applications including high-resolution low-ambiguity chaos ranging and fast random bit generation.

Keywords: Chaos Signal Generation, Time Delay Signature Suppression, Bandwidth Enhancement, Electrical Heterodyning, Nonlinear Dynamics of Semiconductor Lasers