Chaotic External Cavity Laser Dynamics for Microwave Key Distribution

Description

Wireless technologies enabled by photonic microwave devices have been of growing importance over the past decade. Mobile communications is now ubiquitous as an integral part of the modern society. The capability of ensuring different levels of security for these technologies is foreseeably an aspect to be addressed. In recent years, researchers have developed an interesting approach of secure communications based on high-speed random number generation for optical fiber systems, while extensions to photonic microwave wireless systems can be expected in the near future. For secure key distribution, the generation of correlated random bits at ultrahigh speeds has attracted much attention through the nonlinear chaotic dynamics of semiconductor lasers, where the security stemmed from the fast broadband dynamics. Such approaches relied on the recently developed principle of bounded observability, while chaos signals of broad bandwidths and high dimensions are desired. Different laser dynamics with compound and cascaded feedback were reported, though the signals generated were mainly developed without involving any microwave subcarriers for transmission. These approaches of distributing random bits focused on fiber-based systems. In this proposal, the external cavity dynamics of semiconductor lasers is considered in a new region for wireless key distribution on microwave subcarriers. Through investigating the external cavity dynamics of lasers, an on-off switching behavior on a single-tone microwave oscillation was recently found. The on-off switching corresponds to variations of the oscillation envelope. The envelope was found to bifurcate from being regular to chaotic, resulting in chaotic bursting of microwave oscillations as wireless subcarriers, which can be used for distributing random bits. For the photonic microwave key distribution, the project will first experiment on the external cavity dynamics for microwave chaos bursting, which will be compared with the Lang-Kobayashi model regarding the external cavity mode interactions. Moreover, distribution of correlated random bits will be developed using the microwave oscillations as the subcarriers over wireless channels, where the bit rate will be maximized and bit errors will be minimized by optimizing the dynamics and postprocessing parameters. Fundamentally, the entropy extracted by the scheme will also be quantified through theoretical and experimental investigations, where the trajectory in the high-dimensional dynamics for amplifying the effect of noise will complement the statistical randomness testing. Success of the project will contribute to secure wireless applications through harnessing the microwave dynamics in lasers.