| Optical code division multiplex access (OCDMA) is a novel kind of technologies which combines with the features of wireless CDMA and optical fiber communications and has strongly technical advantages and widely applied perspectives. It is one of the possible resolutions for future all optical communication network, which is a hot topic in optical communication research. Compared with other multiplex technologies, it is still at the state of infancy.The design of optical address code is one of key technologies in OCDMA system. One special address codeword which is a"0/1"sequence of certain code-length is assigned to each user in advance. A special address codeword produced by optical encoder at the side of transmission and data information are modulated on optical carrier and transferred. The data from different users are transmitted through optical fiber. The information belonging to local user is demodulated by the special optical decoder while optical signals carrying other users'information are filtered as noise. Optical orthogonal code (OOC) among optical address code is mostly investigated, so the main research of this paper is focused on the construction of OOC.Firstly, the basic principle of OCDMA, the basic theory of OOC and the key technologies of OCDMA are introduced. The development, research status and trends of OCDMA technologies are also summarized. Combining with other multiplexing technologies and using fiber gratings as the encoder/decoder are the trends of OCDMA system.The construction of OOC is investigated in the second section. The construction methods of OOC are summarized. Furthermore, the algorithm based on difference matrix together with the algorithm based on extended set are investigated, then, these are corrected as for existing problem. Finally, the properties of time convergence about these algorithms are compared by simulation, then, the advantages and disadvantages are pointed out.The improved algorithm of construction of OOC based on finite field is... |
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