Optical Fiber Communication Systems Based On Code Division Multiple Access

Due to advances in information technologies and the emerging of various bandwidth consuming services, we are seeing an ever increasing demand for faster and more secure internet connections. Optical code division multiple access (OCDMA) is considered as one of the attractive access technologies in both military and civil applications due to its advantages such as high capacity, simple networking protocol, and the potential of security enhancement for the physical layer. The main topic of this thesis is all optical OCDMA based on FBG en/decoders and electrical processed OCDMA systems and subsystems. Theoretical analysis as well as system simulations and experimentations are carried out.A large part of this work on all optical OCDMA systems and sub-systems based on FBG en/decoders is devoted to experimental demonstration and analysis. First, a novel optical thresholder based on nonlinear polarization rotation is proposed. Our proposed optical thresholder has the advantage of colorless operation over C-band without the utilization of custom-designed band-pass filters, which is crucial in the design of large-scale and cost-effective OCDMA-PON systems. A 4x2.5 Gb/s TPC-OCDMA system based on our proposed optical thresholder is experimentally demonstrated. Then, a hybrid 1D/2D en/decoding architecture is proposed and experimentally demonstrated for the first time. An ASE source is used for 2D WHTS-OCDMA link using cascaded FBG en/decoders, while ultra-short pulses from an mode-locked fiber laser is used as the source for the 1D TPC-OCDMA link with 127-code SSFBG en/decoders. After that, we analyze the performance of 10 Gb/s TPC-OCDMA systems using SSFBGs designed for 2.5 Gb/s applications, as the fabrication process poses a limitation on high-speed (short grating length),long-code SSFBGs. We show through simulation and experimentation that a～6-dB power penalty is expected when using 2.5 Gb/s (38.1 mm) SSFBGs in single user 10 Gb/s, and 180 km TPC-OCDMA systems.All optical OCDMA systems suffer from severe beat noise and multiple access interference (MAI). Additionally, practical deployment of all-optical OCDMA systems typically faces the challenges of high system costs due to the adoption of expensive optical units. To address these problems, we propose a novel CDM/SCM-PON based on spatial coding and subcarrier multiplexing, with code division multiplexing in electrical domain. We first demonstrate a 15×1 Gb/s CDM/SCM-PON with 20 km of standard single mode fiber transmission, through both simulation and experimentation. We show that error free operation assuming forward error correction (FEC) can be achieved when 15 simultaneous users are present. We then address the chromatic dispersion induced signal distortion for both DSB and SSB modulated CDM/SCM-PON systems, using electrical post chromatic dispersion compensation for SSB modulated systems, and electrical chromatic dispersion pre-compensation for DSB modulated systems. Both proposed schemes have been verified using VP1 and matlab co-simulation. In our last work, we analyzed the ADC impact on CDM/SCM-PON systems. Through system simulation we find that the system performance can be optimized using an ADC with at least 5-bits resolution, with a bandwidth of around 0.8 times signal bandwidth, and with a clipping ratio of around 3-5.