The Key Technology Research Of Optical Fiber Access System Based On OCDMA

With the development of new services based on Internet, we are seeing an ever increasing demand for faster, more capacity, more secure internet connections, etc. Optical code division multpile access (OCDMA) is considered as one of the attractive access technologies in optical access system due to its advantages such as vast bandwidth, truly random access, transparency protocol, high capacity, flexibility of controlling the quality of service, and the potential of sercurity enhancement for physical layer. The main topics of this thesis include design of optical orthogonal codes, electro-optic combinatorial codec, incoherent OCDMA system experiment, and transmission performance of OCDMA system.1. A new QCHC/SVWOOC, which is a two-dimensional frequency hopping/time spreading variable weight optical orthogonal code and employs QCHC as wavelength hopping patterns and strict VWOOC as time spreading patterns respectively, is proposed. The construction method of QCHC/SVWOOC is presented, and the analysis of its autocorrelation, cross-cocorrelation and performance is presented. QCHC/SVWOOC has a larger capacity and better BER performance than reported OCS/SVWOOC. In addition, a new three-dimensional optical orthogonal code, which employs LSOOC for as wavelength hopping patterns and TSAMLC as time/space spreading patterns respectively, namely LSOOC/TSAMLC is proposed. The collision probability between the code words is given, and the autocorrelation, cross-cocorrelation and performance are analyzed in detal. Compared with typical one-dimensional optical orthogonal code and two-dimensional optical orthogonal code, it has a larger capacity and better BER performance. Therefore, the proposed LSOOC/TSAMLC is very appropriate for high intensive communications.2. An electro-optic combinatorial codec, which is encoding in electrical domain and decoding in FBGs respectively, is proposed. The transmission performance of electro-optic combinatorial codec is analyzed by system simulation. Results show that system electro-optic combinatorial codec can encode and decode correctly, and the better performance is expcted when using longer code words as control scheme.3. An incoherent OCDMA over fiber system based on electrical domain encoding/decoding, and three users is proposed and experimentally demonstrated. Results show that users’signals with data rate of 100Mbit/s are successfully transmitted. In addition, an incoherent OCDMA over fiber system based on electro-optic combinatorial encoding/decoding, twe users, and direct detection is proposed and experimentally demonstrated. Preliminary analysis shows that the results can not indicate users’signals with data rate of 2.5Gbit/s and 155.52Mbit/s are successfully transmitted.4. The pulse shape evolution, pulse broadening properties in optical fiber are investigated and analyzed. In particular, the effects of group velocity dispersion, three-order dispersion and self phase modulation for optical fiber are included. A revised formula of BER, which considering the effects of dispersion and nonlinearity in three-dimensional OCDMA system, is proposed. The BER performance of two-dimensional OCDMA system and three-dimensional OCDMA system are discussed, and corresponding results reveal that the three-dimensional OCDMA system performs better than two-dimensional OCDMA system. The actual one-bit transmission system is analyzed. The BER formula with optical hard-limiter and the BER formula without optical hard-limiter are proposed. Through system simulation we find that the improvement of BER performance from using an optical hard-limiter is significant.