Random bit generation using chaotic dynamics of an optically injected semiconductor laser

Abstract

Fast generation of random bits is of great importance in applications such as numerical simulation, encryption, and secure communications. Recently, semiconductor lasers in chaotic oscillations have been utilized for random bit generation at output rates exceeding gigabits per second. However, among the previously proposed schemes, optical feedbacks were usually utilized to invoke chaotic dynamics in the lasers. Such optical feedbacks often led to undesirable autocorrelations at the feedback round-trip time. In this thesis, an optically injected semiconductor laser in chaos is investigated for random bit generation. Due to the absence of optical feedback, the autocorrelation is free from any problematic side peaks. By oversampling the chaotic waveform, the approach relaxes the bandwidth requirements of the detection electronics. The detected output from the chaotic laser subject to the continuous-wave optical injection has a bandwidth of about 10 GHz. It is then digitized by an 8-bit analog-to-digital converter with a front-end bandwidth of only 2.5 GHz. By retaining only the 4 least significant bits per sample and performing exclusive-OR operation on consecutive samples, random bit generation is successfully demonstrated at 40 Gbps. The randomness is verified by the standard statistical tests in Special Publication 800-22 of National Institute of Standards and Technology. Furthermore, to efficiently utilize the chaos spectrum, two heterodyne detection schemes are investigated. The first scheme adopts optical heterodyne detection using the injecting laser as the local oscillator, which increases the output bit rate to 100 Gbps. The second scheme adopts electrical heterodyne detection using three local microwave oscillators at different frequencies, which lead to random bit generation at 200 Gbps. These random bit generation techniques offer opportunities in high-speed secure communications and statistical computations.

Date of Award	15 Jul 2013
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Sze Chun CHAN (Supervisor)