Communications, Fiber Grating-based Security

With the development of the society and the improvement of our lives, the requirement of high-speed, large-capability and excellent-quality network is imperative under the situation. It is difficult for the traditional electronic network to enhance the quality of communication greatly because of the existence of "electronic bottle-neck". All-optical-network has been the most competitive candidate of the communication in the future, so that the technique of optical code division multiple access (OCDMA) based on fiber gratings become a hot area in the communication research because of its high-speed transmission, excellent anti-jamming ability, variable coding-mode and strong security.Fiber Bragg gratings(FBGs) have been applied broadly in OCDMA's coder and decoder because of their good optical reflected characteristic. Tunable FBGs have been studied and applied because the central reflected wavelength of a FBG can be changed with the variety of the stress and the temperature of the environment. The spreading sequences can affect not only the capacity of the users of the system, but also the system's bit error rate. The paper makes conclusions by summarizing, including and analyzing the main code sequences of the OCDMA systems: the OCDMA systems of the hybrid direct sequences/frequency hopping (DS/FH) have large capacity of the systems and the systems with bipolar spreading sequences will be the best systems in the future by the excellent cross correlation. Above concerned study is the base of my work.The contents of my work are listed as follows:A foundational optical communication system is described encoding/decoding information with arrays of fiber Bragg gratings. In the system a broadband pulse coming from an optical source will be split into a series of separated pulses when it reaches the encoding FBG array. Because it is difficult for an attacker to recover the original pulse if he doesn't know the exact structure of the encoding FBG array, one can say that the information from the optical source has been encrypted. Morecomplicated systems including N×N, N×1 and1×N based on bent sequences are designed and they have the more security and the larger capability.A new class of encoder/decoder based on shunt-wound structure of tunable FBGs has been proposed and that allows the OCDMA systems to vary code-weight in the communication at any time. Variable OCDMA can encrypt the information by more ways than the normal OCDMA. The analysis of the system shows that the variable OCDMA systems are more secure than the normal ones.An OCDMA system based on super structured fiber Bragg gratings(SSFBGs) arrays has been designed with the bipolar spreading sequences. Theories prove that the bipolar OCDMA communication systems with bent spreading sequences increase the difficulty for an unauthorized recipient to break the systems. Some simiulations of these above systems has been done, and the results support the probability of those systems.