Search

Time-delay signature (TDS) suppression of semiconductor lasers with external optical feedback is necessary to ensure the security of chaos-based secure communications. Here we numerically and experimentally demonstrate a technique to effectively suppress the TDS of chaotic lasers using quantum noise. The TDS and dynamical complexity are quantified using the autocorrelation function and normalized permutation entropy at the feedback delay time, respectively. Quantum noise from quadrature fluctuations of vacuum state is prepared through balanced homodyne measurement. The effects of strength and bandwidth of quantum noise on chaotic TDS suppression and complexity enhancement are investigated numerically and experimentally. Compared to the original dynamics, the TDS of this quantum-noise improved chaos is suppressed up to 94% and the bandwidth suppression ratio of quantum noise to chaotic laser is 1:25. The experiment agrees well with the theory. The improved chaotic laser is potentially beneficial to chaos-based random number generation and secure communication., 4 pages, 5 figures

Polarization switching in a long-wavelength vertical-cavity surface-emitting laser (VCSEL) under parallel optical injection is analyzed in a theoretical and experimental way. For the first time, to our knowledge, we report experimentally a state in which injection locking of the parallel polarization and excitation of the free-running orthogonal polarization of the VCSEL are simultaneously obtained. We obtain very simple analytical expressions that describe both linear polarizations. We show that the power of both linear polarizations depend linearly on the injected power in such a way that the total power emitted by the VCSEL is constant. We perform a linear stability analysis of this solution to characterize the region of parameters in which it can be observed. Our measurements qualitatively confirm the previous theoretical predictions., Ministerio de Economía y Competitividad (MINECO/FEDER) (TEC2015-65212-C3-1-P); Fonds Wetenschappelijk Onderzoek (FWO); Methusalem Foundation.