マルチキャリア光源を用いた光ネットワーク

摘要

Optical networks using wavelength division multiplexing technology are potential solutions tothe dramatic increase in Internet traffic. However, as the number of wavelengths increases, more andmore distributed light sources such as laser diodes (LDs) have to be prepared and controlledindividually in conventional optical networks, which would increase network cost, powerconsumption, and control complexity. In addition, Internet traffic fluctuates over time and degradesnetwork resource (e.g. wavelength) utilization efficiency.The multi-carrier light source (MCLS), which can generate a large number of optical carrierswith excellent frequency accuracy and optical quality, promises to avoid the problems inherent todistributed LDs. However, to the best of our knowledge, so far no work has been reported on how toefficiently utilize MCLS when designing dynamic optical networks.This thesis presents our study about optical network based on centralized MCLS (C-MCLS) forregional/metro networks. We propose two optical network architectures based on C-MCLS fromdifferent application perspectives. We design the proposed networks from both hardware (networkimplementation) and software (network control and management) aspects to show their practicability.We evaluate the proposed networks in terms of network cost, power consumption, networkingperformance and optical performance.This thesis is organized as follows.Chapter 1 introduces the research background and motivations. The research approach as well asthesis organization are also described.Chapter 2 covers the technical background of the whole thesis. Optical components as well asoptical transmission systems are introduced. Optical regional/metro networks are reviewed and theproblems are stated through the traffic modeling. Research works about MCLS are surveyed andcompared.Chapter 3 presents our proposed optical broadcast-and-select network architecture with aC-MCLS for green-field network applications. A large number of optical carriers generated by theC-MCLS are broadcast to all network nodes, which select and modulate wavelengths to realizeupstream transmission. To utilize wavelengths efficiently, we introduce a framework for wavelengthallocation and selection. Both static and dynamic schemes are adopted and implemented.Numerical results show that the proposed network offers greatly reduced cost and powerconsumption compared to the conventional one when the number of required wavelengths becomeslarge. Blocking probabilities of static and dynamic schemes are analyzed to evaluate networkperformance. Simulation results show that by choosing appropriate design parameters, the dynamicscheme offers about 25% increase in admissible offered load under the specified blocking probability,compared to the static scheme. This indicates that the dynamic scheme makes the network morerobust against traffic fluctuations and improves networking performance.Chapter 4 presents the design and evaluation of a resilient star-ring optical network with aC-MCLS. To protect the optical carriers as well as data in the star part network, we introduce a fiberconnection automatic protection switching (FC-APS) architecture at each network node. Based onthe FC-APS architecture, we design a distributed failure recovery scheme to recover the carriers anddata affected by fiber failures. Numerical results show that the distributed scheme greatly reduces therecovery time compared to the centralized configuration in the recoveries of both single and multiplefiber failures.Chapter 5 presents our proposed optical drop-add-drop network architecture with a C-MCLSfrom the network migration or upgrade perspective. Optical carriers generated by the C-MCLS aredropped at the source nodes by the reconfigurable optical add/drop multiplexer (ROADM) and usedfor uplink transmission, which eliminates the distributed LDs needed by the conventional network.Dynamic network operations are enabled by configurations of ROADM. Numerical results show thatit offers significantly lower network cost and power consumption compared to the conventionalnetwork if the total number of used wavelengths in the network becomes large. We evaluate itsoptical performance through an optical signal-to-noise ratio (OSNR) analysis. Results show thatOSNR of optical carriers ranged from 35 dB to 40 dB are sufficient for typical size opticalregional/metro networks while keeping certain bit error rate performance.Chapter 6 summarizes the contributions of the thesis and explores the potential applications aswell as research topics.This research presents new networking concepts and technologies to design future high-capacity,cost-effective, energy-efficient, dynamic/reconfigurable and reliable/survivable optical networksbased on C-MCLS. For future practical applications of the proposed networks, the followingtechnical challenges and developments require further studies. The MCLS that can provide hundredsof optical carriers with 50 GHz channel spacing and 35-40 dB OSNR is expected to be developed innear future. The cost and power consumption of MCLS, optical band pass filter (BPF), opticalamplifier etc are further reduced with the development of technologies and increased number ofproducts in market. The tunable BPF requires improvement design considering parameters such astuning range and bandwidth to improve the performance of dynamic wavelength selection. TheROADM architecture is extended with the carrier-drop function. Optical switches with switchingtime less than 1 ms are required to achieve fast fiber failure recovery. The star-ring network needsfiber deployment cost reduction for practical applications. Further experiments as well as testbedimplementation as a proof-of-concept would provide more practical data to push our research resultsto network vendors and carriers for future applications.