Chaotic time-delay signature suppression in semiconductor lasers with dispersive feedback

Abstract

The project aims to investigate the ultimate limit of suppressing Time-Delay Signature (TDS) in the chaotic waveform by adding dispersion. Since the semiconductor laser requires feedback to act as an oscillator to generate laser light, therefore, normally the mirror feedback will be chosen. However, the mirror feedback will lead to the similar intensity pattern after a round-trip time. With the help of the autocorrelation function (ACF), the obvious TDS will appear. To hide the time delay information, the dispersive feedback can be used to arrange different dispersion coefficients to different frequencies of light, as a result, the TDS of the autocorrelation function will be reduced and will no more be so obvious to let others to trace the time delay of the feedback through the figure. The ultimate limit of the TDS is to be found numerically, by using different feedback strengths and dispersion coefficients, different sets of TDS magnitude of autocorrelation function and coherence function, Intensity-time graph, histogram of the distribution of intensity, optical spectrum and power spectrum can be found. The best situations of chaos with dispersive feedback, the chaos with mirror feedback and the Gaussian noise with same bandwidth are compared. The results show that TDS can be sufficiently suppressed to below the noise flow when the dispersion is increased.