| Access network as the “last mile†entering the metro access network/backbonefor users is a very important part in transmission network. Over the past few years,as the IPTV, high definition video, and the high-bandwidth online gaming businessneeds increase rapidly, the access network technology has undergone tremendouschange. Passive optical network with its large capacity, long transmission distance,low cost, full-service support and other benefits has become a hot technology. Withthe maturity of PON technology, PON technology as the most important technologysolutions for FTTx, has become the world’s major telecom operators’ mostconcerned technical area. Through APON/BPON age of exploration, PONtechnology has gradually developed standard EPON and GPON, and they are widelyapplied with their respective advantages in the world. With IPTV, HDTV, and onlinegames increasing, the bandwidth per user is expected to increase for an order everyfive years. For PON, no matter the EPON or GPON, the bandwidth will face a newbottleneck. Therefore we need continue to explore the next-generation passiveoptical network (NG-PON) technology.For this reason, many hybrid passive optical network systems, such as WDM/TDM hybrid PON system, OCDM/TDM hybrid PON system, OCDM/WDM/TDM hybrid PON system and so on, are researched.These hybrid PON systemsprovide larger number of users, and higher transfer rates for the access network, butthere are also some new problems. Since each ONU must own the resources of two-dimensional to three-dimensional (time-domain, wavelength domain, and codeaddress domain), the cost of the system raises, and this is a great challenge for thecost-sensitive access network.This paper studies how to make the existing PON to inherit the originaltechnology and equipment as much as possible. Meanwhile we focus on how toapply the OCDMA technology into PON. We hope the new propose hybrid PON notonly accommodates more users and provides larger system capacity, but also achievethat the new one-dimensional resources is transparent to the existing PON system, sothe system cost can be reduced. This paper focuses on hybrid OCDMA PON and thekey technologies of OCDMA, and the main contribuctions are presented as follows:1.The research of hybrid PON based on OCDMA technology(1) The proposed OCDM/WDMA PONIn chapter2, the unique characteristic of CDMA technology in the opticaldomain is analized and the theoretical model is developed.Then, a hybrid WDMA/OCDM system is proposed, where the optical code isnot as the address of every ONU, but as a virtual fiber of hybrid PON. It’s the firstreport that single encoder/decoder with its single corresponding optical code isexploited to encode/decode multiple wavelength signals simultaneously. It makes theOCDM be transparent to the ONU and so we can upgrade the existing WDM PONeasily without redesigning the OLT and ONU, and also decreases the number ofEncoder/Decoder greatly. Experiment employs2pairs of encoder/decoder tocombine2WDM-PONs in one fiber, and simulation results confirm the feasibility ofthe proposed system.(2) The proposed SAC-OCDM/TDM system for upgrading the TDM PONseamlesslyIn chapter3, a SAC-OCDM/TDM PON for upgrading the traditional TDM-PON is proposed. It is the first report that the spectral domain and orthogonalcode domain are both employed and transparent to the ONU for the hybrid PON,which will upgrades the TDM PON seamlessly. Fewer encoder/decoders and cheaperoptical source under the condition of high bite rate and large ONU accommodationwill lead the system be cost-effective. For the experimental setup, a variety of SACcode’ structures and characteristics are analyzed, and the expended double weightcode (EDW) are employed as the address code of the experimental system.Thedownstream experiment is demonstrated, and experiment results verify that theproposed system is feasible.2. The research of SAC-OCDMA’s key technologies(1) The Design of SAC-OCDMA optical encoder/decoderIn chapter4, a tunable encoder and a complementary decoder based onpolarization modulation for the SAC-OCDMA PON are designed. Theencoder/decoder is constructed with liquid crystal material, and it is reconfigurableand with high blocking ratio of about40dB for unwanted spectral slices. Thedecoder can achieve decoding and complementary decoding simultaneously forbalanced detection in SAC-OCDMA system. The eye diagrams and bit error rate(BER) measurement show that it can eliminate the multiple access interference (MAI)at the high code weight.(2) The method of SAC-OCDMA system noise suppressionIn chapter5, the main noise source which impacts the performance ofSAC-OCDMA system is analyzed, and then we enhance the performance by opticalpower equalization in the SAC OCDMA PON. The method is to use the encoderproposed in the previous section for further development, so it is achieved in onedevice for encoding and power equalization, the experimental results show that thesystem BER and eye diagram are greatly improved. Since the method does not use additional devices in the condition, the system are lower complexity and systemcost-effective. |
