Modeling Optical Chaos Generation in Multimode Semiconductor Lasers

Abstract

Optical chaos generation of an optically injected multimode semiconductor laser is numerically investigated. Optical chaos is generated by the nonlinear dynamics of laser using different perturbations such as injection and feedback. Application of optical chaos includes optical computing, optical chaos communications, and random number generation. Former researches of chaos in optics mainly focus on single mode lasers. This project aims to model a multimode semiconductor laser for investigating the chaotic waveforms of different modes. Instead of just observing one single mode as in previous studies, this project explores on the generation of chaotic light in different modes caused by optical injection, where the relationship among three different modes of the semiconductor laser is monitored. To explore the statistical properties of chaotic waveform, values of injection strength, detuning frequency, cavity decay rate, and linewidth enhancement factor are tuned in the modeling process. The curves of intensity time series, optical spectrum, power spectrum, and probability distribution are found to vary with the above parameters. The investigation shows that the intensity time series reaches the most chaotic level when detuning frequency equals 11 GHz, which is close to the relaxation resonance frequency of the laser. The signal powers of two side modes are also maximized at this injection detuning. For illustrating the potential application, random bits extracted by calculating the time difference between adjacent optical pulses. Autocorrelation function is used to test the randomness of the time series of individual bit of the digitized values. Using the 8th to the 16th bits, the expected output bit rate reaches 195 Mbps. The simulation opened up the exploration of the multimode chaotic phenomenon for guiding future experimental investigations.