Research On Two-dimensional OCDMA Based On Time-hopping Spread-spectrum And The Performance

To break through the limitation of “electronic bottle-neck” to the performance of the traditional network,OCDMA(Optical Code Division Multiple Access)is proposed.OCDMA is a novel technology combining CDMA(Code Division Multiple Access)applied in wireless communication field with optical fiber communications.Based on some of the precedents' works,the thesis mainly operated the simulation analysis and in-depth discussion for the incoherent OCDMA system.Firstly the development and the present status of optical communication were investigated.Comparing OCDMA with OTDMA(Optical Time Division Multiple Access)and OWDMA(Optical Wavelength Division Multiple Access).Then some key technologies of incoherent OCDMA system including optical addressing code and encoder/decoder were described in details.A series of simulation analysis were carried out for the incoherent OCDMA system.Three kinds of incoherent OCDMA system based on different encoder/decoder were built on simulation software OptiSystem and analyzed.The results indicate that the performance of OCDMA system was deteriorated due to the multiple access interference(MAI)when multiple users existed.To suppress MAI effectively,optical hard limiter introduced at the receiving end of system were proposed.The influence of some system parameters such as optical fiber dispersion parameter and user signal rate on system performance was also discussed.To enhance the security of OCDMA system,the thesis further studied all-optical logic Exclusive OR(XOR)based on semiconductor optical amplifiers(SOA).The simulations and performance analysis of logic XOR/reverse XOR schemes based on SOA in Mach-Zehnder interferometer(SOA-MZI)and cross-gain modulation(SOA-XGM)were operated respectively.The experimental results indicate that proper injection current of SOA made XOR encryption more ideal.A new system is proposed to introduce all-optical XOR encyption/decryption module based on SOA-MZI into two-dimensional incoherent OCDMA system.The simulation results show that the confidentiality of the new system is significantly enhanced when communication standards were met.