Secured optical communications
Lai, Wenn Jing
Date of Issue2005
School of Electrical and Electronic Engineering
Secured optical communication suggests the possibility of transmitting signals that are very difficult to intercept by eavesdroppers [7, 8, 9]. By using chaotic signals instead of the conventional sinusoidal carriers, we are able to hide the messages that ride on this noise-like carrier. In this project, we were interested to study the fundamentals of optical chaos. Literature on chaos theory has established the fact that some form of nonlinearity has to exist in a system in order to generate chaos. This nonlinearity is inherent in the Erbium Doped Fiber Ring Lasers (EDFRL) that we use in our research. We started by studying the basic rate equations that model the laser system. Then, we proceeded by performing simulations on a dual ring laser model. Our simulations show that it is possible to generate chaos with the proposed setup. We also proposed a novel method of achieving chaotic communication with an improved setup. The new setup is simpler because we only need to transmit one laser output to the receiver instead of two (as in the original setup). This makes it more suitable for practical applications. The signals produced were low in frequency as the system was operating close to its resonance frequency (relaxation oscillation frequency). Experiments were carried out in an attempt to generate chaos. We built the dual ring transmitter or master system and observed its behavior. After putting together the essential optical components, we were finally able to generate low frequency chaos as predicted from our simulations. We have analyzed the signals produced and confirmed that they are indeed chaotic. The latest theoretical methods were adopted to perform our mathematical analysis. Once we proved that our signals were chaotic, we continued to characterize the signal. Here we discovered that our system produces low dimensional chaos. We compared this with the signal produced from simulations and obtained a good agreement.
DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics