Chaotic time delay feature cancellation and bandwidth enhancement in cascaded-coupled nanolasers

Abstract

As an important part of optical sources, nanolasers have a prominent impact in photonic circuit integration, and their nonlinear dynamics has become one of the hotspots of research in recent years. In this paper, we investigate the time-delay signature and bandwidth characteristics in a cascade-coupled nanolaser system. In which the master nanolaser is connected to an external feedback cavity and injected into the intermediate nanolaser and the slave nanolaser sequentially. The 0-1 chaos test is introduced to quantify the dynamics of the nanolaser, which can accurately distinguish whether the laser is in a chaotic state or not, and the autocorrelation function is used to analyze the time-delay characteristics in the laser output signal. This type of calculation has the advantages of fast operation speed, high accuracy and anti-noise robustness. The lower the autocorrelation value, the more difficult it is to extract useful information from the chaotic random sequence. The bandwidth is defined as the value where the range between DC and frequency contains 80% of the spectral power, which is only applicable to chaotic states. In the simulation, we compare and analyze the two cases for whether the intermediate nanolaser carries an obvious peak of the time-delay signature or not. The research results show that by selecting appropriate system parameters, the slave nanolaser can always output a broadband chaotic signal without obvious time-delay signature. Under the condition of a certain injection intensity, by changing the frequency detuning parameter, the intermediate nanolaser has obvious time-delay signature, and then the slave nano-laser can output chaotic signals which can suppress time-delay signature and enhance bandwidth in a small parameter interval. When the time-delay signal of the intermediate nanolaser is completely hidden, the slave nanolaser can achieve the suppression of the time-delay signature in a larger parameter plane, meanwhile the bandwidth is significantly enhanced. In addition, by plotting the two-dimensional spatial distribution diagram and bandwidth line diagram of the output from the nanolaser under frequency detuning and injection intensity, it was determined that the nanolaser can simultaneously suppress the delay characteristics and enhance the bandwidth under chaotic signals. This provides an important theoretical basis for the realisation of secrecy-enhanced chaotic optical communication applications.