Study On The Key Technologies Of The Spectral-amplitude-coding (SAC) Optical CDMA Systems

Optical code division multiple access (OCDMA) is a novel kind of technologies which combines with the features of CDMA and optical communications. It has been a hot topic in the field of optical communication research because of its technical advantages as asynchronously access, high level of security, soft capacity, etc. Theoretical analysis of optical CDMA systems has shown that multiple access interference (MAI) is the main reason for performance degradation, especially when large numbers of users are involved. The scheme of spectral-amplitude-coding (SAC) optical CDMA system is one of the important breakthroughes in the field of optical CDMA and now receving widely attentions because the MAI can be canceled when code sequences with fixed in-phase cross correlation. For SAC-OCDMA, it is still at the stage of infancy, the main technical problems are the construction of optical address code, the design of optical encoder/decoder, and the manufactureal technics of optoelectronical apparatus, etc.This thesis mainly discussed the key techniques of SAC-OCDMA. Firstly, the basic principle of OCDMA and SAC, system schemes and the key technologies of SAC-OCDMA are summarized. Secondly, researching works have been done about the address-code- designing for SAC-OCDMA systems. A new code structure for spectral-amplitude-coding optical CDMA system based on modifying LSOOC (MLSOOC) is proposed. Characteristic analysis of the new code has been done. The results reveal that the new code has quite large capacity and an ideal in-phase cross correlation and reaches the upper bound for SAC-OCDMA. A new WDM/SAC code structure based on combining with WDM was proposed. It can solve the problem about the lack of codes capacity by combining with existing codes. Thirdly, researching works have been done about the optical encoder/decoder for SAC-OCDMA. It proposed two kinds of structure for spectral encoder/decoder based on tunable Fiber Bragg gratings. The results reveal that the two kinds of structure are easy to modulate, encode and decode. Researching works have been done about the other two kinds of structure for spectral encoder/decoder based on gratings arrayed waveguide gratings (AWG) and diffractive gratings- phasic mask. Fourthly, Principle analysis and computer emulational analysis of SAC-OCDMA systems have been done. It made a analysis of SNR and BER by taking into account the effects of phase-induced intensity noise (PIIN), shot noise, thermal noise and dark current noise. The results reveal that MAI can be canceled at an ideal source and channel and the new code can effectively suppress the PIIN when the noise is taken into account. For a stated BER (BER=10^-9), the total active synchronous users are increase greatly than using Hadamard.Lastly, the summarization of the paper is given and some application prospects of SAC-OCDMA are introduced.