Synchronization of Commonly Driven Semiconductor Laser in Chaos

Abstract

Chaos theory is a concept over a century old. Chaotic processes are dynamic, deterministic, and very sensitive to initial conditions. Semiconductor lasers have been around for about half a century now. Using a semiconductor laser in chaos to generate random bits was a brilliant and novel idea first proposed by Dr. Atsushi Uchida in 2008. Not only is random bit generation using optical methods really fast, using a physical process is also much more secure than using pseudo-random algorithms. This project is based on numerically modeling the modified Lang- Kobayashi laser equations to achieve random bit stream synchronization. Chaos is created in two identical semiconductor laser systems by optical injection using feedback from fiber Bragg gratings. Although the emission intensities of the two ideal injected lasers are correlated, the correlation is drastically degraded for practical noisy lasers. To overcome this internal noise, the two lasers are commonly driven with a signal modeled as Additive White Gaussian Noise. The resultant intensities have much better (nearly perfect) correlation. These intensities are then used to generate random bits. A synchronization of the generated bit streams with low BER is successfully demonstrated.