Study On Key Technologies Of The Passive Optical Network Based On Dense Wavelength Mutiplexing

With the rapidly development of computer technology and society informatization, various bandwidth-intensive services are continuously emerging. The currently deployed passive optical network(PON) cannot satisfy the needs of users. Dense wavelength division multiplexing passive optical network(DWDM-PON) system has regarded as one of the ultimate development direction for fiber access network, due to the advantages of large capacity, high security, transparent protocol and good scalability. In order to realize the smooth upgrade from current TDM-PON to DWDM-PON, as well as increase the user number and reduce the cost, DWDM/TDM-PON has become a research hotspot in access network technologies. This thesis conducts researches on the implementation technologies of DWDM-PON and DWDM/TDM-PON, aiming at reducing cost, improving system performance and optimizing resource scheduling algorithm. The detailed research works are divided into following parts. 1. Study of Key Technologies for DWDM-PON.The system cost is the most important problem in DWDM-PON system. In order to reduce the cost, two DWDM-PON architectures are proposed in this thesis. Moreover, this paper also studies a mutual protection mechanism to improve the network survivability.To suppress Rayleigh backscattering noise in re-modulation scheme, we proposed a DWDM-PON system based on shared light source and fiber interconnection structure. The shared light sources with 25-GHz channel spacing are generated in OLT based on the OCS technique. Colorless ONU is realized by re-modulating the downstream signal via a RSOA. Due to the simple interconnecting architecture at remote node(RN), the downstream and upstream signals in each feed fiber are carried on different channels. Therefore the Rayleigh Backscattering and back-reflection effects are significantly reduced.To reduce the system cost and improve the transmission reach, a 25-GHz spaced DWDM-PON system based on optical frequency comb and RSOA injection locking techniques is proposed. The comb generator is deployed in OLT to provide 25-GHz spaced multi-wavelength as the upstream and downstream seeding sources. RSOAs are employed both in OLT and ONU as signal transmitters. The optical seeding light generated by optical frequency comb source has narrow bandwidth, so that the intensity noise of RSOA is reduced. This DWDM-PON system can support large number of wavelengths and 80-km long reach with a simple architecture.DWDM-PON with dual-protection mechanism. A novel survivable DWDM-PON system with centralized dual-protection scheme is proposed based on shared light sources. The ONUs of two neighboring sub PONs are grouped to provide protection path for each other. By employing alternate path routing of sideband channels, the centralized protection scheme can provide reliable protection against any failure in feed fibers, remote node and distribution fibers. The number of redundant fibers is greatly reduced, and efficient utilization of wavelength resource is achieved. 2. Study of Key Technologies for DWDM/TDM-PON.DWDM/TDM-PON is one of the best solutions to upgrade the present network smoothly. In this thesis, the transmission performance of DWDM/TDM-PON is studied and a system architecture with high capacity and low cost is proposed.Study on transmission performances for different channel spacing in DWDM/TDM PON system. The experimental results show that, although the performance is deteriorated by the crosstalk, successful fiber transmission for 25-GHz spaced system is achieved, by using the low-cost 10-Gb/s NRZ modulation format with direct detection scheme. The experimental results are instructive for the improvement of wavelength efficiency and the upgrade of access capacity.100 Gb/s DWDM/TDM PON system based on directly modulated lasers(DMLs) with low cost and high modulation rate. The 100-Gb/s system is experimentally demonstrated, based on the DMLs modulated by 25-Gb/s NRZ signals. A bi-pass delay interferometer(DI) is deployed in the OLT to mitigate the signal distortion caused by the DML chirp and fiber chromatic dispersion. The experimental results show that with the DI, error free transmission is achieved over fiber transmission and a high power budget is obtained, which could support 1:1024 splitting ratio. 3. Study of Onling Resource Scheduling Scheme in DWDM/TDM-PONThe resource scheduling algorithm is significant in hybrid DWDM/TDM-PON. This thesis focuses on the performance of dynamic wavelength allocation scheme, and analysis the impact of wavelength switch latency on upstream transmission performance for the first time.Performance comparison between static and dynamic wavelength allocation schemes. The simulation is conducted to compare the network performance between two different wavelength allocation schemes. The results show that dynamic way has lower average latency and packet loss ratio, especially when network load is uneven.Online resource scheduling with wavelength switch latency(SL) consideration. The tunable optical devices deployed in ONU induce the SL inevitably. In this thesis, we investigate the influence of SL on the system performance firstly, based on the online scheduling scheme evolved from the classic WDM-IPACT algorithm. The simulation results show that the network performance is deteriorated by the SL with nonzero value.Online resource scheduling with SL tolerant algorithm. A tolerant scheduling algorithm is proposed to alleviate the performance degeneration caused SL in hybrid PON. OLT sends GATE message to the objective ONU at a time epoch adaptive to the network situation and SL value, so that the ONU will have more time to process its wavelength switching before the upstream wavelength becomes idle. The simulation results show that this scheme can reduce or even eliminate the delay caused by SL.