Codec Technology. Optical Cdma Systems

Optical code division multiplexing access (OCDMA) is one of the possible resolutions for all optical communication network in the future, which is a hot topic in optical communication research. Compared with other multiplexing technologies, it is still at the state of infancy.The main research work of this thesis is focused on the encoding and decoding technologies in the optical code divison multiplexing access system. Opticl encoder and decoder are key components of OCDMA. In the transmiting port, optical encoder turns data bits into spread spectrum sequences, then, optical decoder retverts it to data bits with the theory of correlation decoding in the receiving port. The structure and property of optical encoder and decoder impact the performance of OCDMA system directly and judging whether the system could work practically. The main types of optical encoder and decoder are the fiber delay lines, the diffraction gratings and phase-mask boards, the arrayed waveguide gratings and Bragg fiber gratings. The researching work of this thesis is mainly about the encoding and decoding schemes of the arrayed waveguide gratings and the Bragg fiber gratings systems.Firstly, the basic principle, system schemes and the key technologies are introduced in section one. The development, research status and trends of OCDMA technologies are also summarized. By summarizing the encoding and decoding technology schemes of OCDMA system, researching works are done about two dimensions OCDMA system of the wavelength and time in the second section. The Simulation results show that the capacity of the two dimensions OCDMA system of 2D-OOC wavelength and time is better than that of the one dimension system.In section three, a complementary scheme of spectral coding and decoding is proposed. It makes full use of the broad band incoherent Gauss optical source and compensates the unflatness of sectrum of the source. Combining with the method of banlanced detecting, the multiple accsss interference of the multiple users is rejected in the decoding port.