Fast dynamics of low-frequency fluctuations in a quantum-dot laser with optical feedback.

We experimentally investigate the complex dynamics of a multi-mode quantum-dot semiconductor laser with time-delayed optical feedback. We examine a two-dimensional bifurcation diagram of the quantum-dot laser as a comprehensive dynamical map by changing the injection current and feedback strength. We found that the bifurcation diagram contains two different parameter regions of low-frequency fluctuations. The power-dropout dynamics of the low-frequency fluctuations are observed in the sub-GHz region, which is considerably faster than the conventional low-frequency fluctuations in the MHz region. Comparing the dynamics of quantum-dot laser with those of single- and multi-mode quantum-well semiconductor lasers reveals that the fast low-frequency fluctuation dynamics are unique characteristics of quantum-dot lasers with time-delayed optical feedback.

Effect of bandwidth limitation of optical noise injection on common-signal-induced synchronization in multi-mode semiconductor lasers.

We investigate common-signal-induced synchronization in two multi-mode semiconductor lasers subject to a bandwidth-limited optical noise signal. Synchronization can be achieved when the number of longitudinal modes is matched between the two lasers. The peak wavelengths need to be matched between the two lasers to achieve synchronization. In contrast, small correlation is observed when the peak wavelengths are mismatched. The synchronization is degraded as the number of longitudinal modes in one of the lasers is decreased. However, large correlation is obtained if the overlapped modes are selected and compared. We discuss the possibility of an unauthorized user reproducing the synchronized waveforms. It is difficult to completely reproduce the synchronized waveforms using synchronization if the bandwidth of the noise drive signal is limited.