Yunfeng Shen

Impairment-Aware Lightpath Routing and Regenerator Placement in Optical Transport Networks With Physical-Layer Heterogeneity

We develop a framework that supports impairment-aware lightpath routing and wavelength assignments in optical transport networks. Different from most existing studies, we consider a more generic optical transport network with physical-layer heterogeneity, including different fiber types, variable amplification span distances and attenuation coefficients. In addition, rather than a single amplifier type as in most of the existing studies, we consider multiple amplifier types for different amplification situations. Owing to the high cost of OEO regeneration, the total number of required regenerators is considered as the major objective for optimization. A signal-quality-aware routing algorithm is developed to find routes that are expected to require the fewest regenerators. The first-fit wavelength assignment algorithm is extended to assign wavelength(s) for lightpaths after placement of some regenerators which can freely function as wavelength converters. Simulation studies indicate that the proposed algorithm can significantly reduce the required number of regenerators compared to the simple shortest-path routing algorithm. Moreover, it is found that the signal-quality-aware algorithm shows stronger benefits when a network demonstrates higher physical-layer heterogeneity such as different fiber types and non-uniform span losses. The signal-quality-aware algorithm also demonstrates better performance when a network has a higher average nodal degree. Finally, the results indicate that multiple amplifier options are important for cost-effective optical transport network design. For a network with high physical-layer heterogeneity, multiple amplifier options can significantly reduce the required number of regenerators (up to 50%) over a single amplifier option.

Design of Polarization De-Multiplexer and PMD Compensator for 112 Gb/s Direct-Detect PDM RZ-DQPSK Systems

The design of a polarization de-multiplexer and a polarization mode dispersion compensator (PMDC) for direct-detect polarization division multiplexed (PDM) return-to-zero differential quadrature phase shift keying (RZ-DQPSK) systems are studied in detail. The impact of polarization dependent loss is studied in polarization de-multiplexers with different error detection configurations for both bit-aligned and bit-interleaved PDM systems. The level of the clock frequency of the combined pulse train of the two polarizations is proposed as the error signal for the PMDC. It enables the PMDC to work in the cancellation mode. Two separate control loops are proposed for the polarization de-multiplexer and the PMDC to allow them to work independently. The DGD tolerances for the one-stage and two-stage PMDC are measured and discussed. Finally the glitch problem in the polarization tuning algorithm is studied. An advanced dithering algorithm and the corresponding architecture of the polarization controller are proposed to solve the glitch problem.

Optimal Node Hardware Module Planning for Layer-One Optical Transport Networks

Most of the studies on traffic grooming focus on minimizing network link capacity and providing serving-relationship between client services and link capacity. Subsequent to this step, it is important to plan for adding/dropping client services over client service ports and setting up end-to-end lightpaths over network ports, which is however seldom investigated. We call such effort node hardware module planning. This is an industrially practical problem aiming to minimize node hardware cost since hardware modules are the most expensive components in a network. Based on a link-based traffic grooming result that provides information on end-to-end capacity units incident to nodes and aggregation relationship between client services and capacity units, we develop an Integer Linear Programming (ILP) model to optimally plan hardware modules. To overcome the computation difficulty of the ILP model under large-sized planning scenarios, we also develop a fast sub-optimal heuristic for hardware module planning. Simulation studies indicate that the heuristic is efficient to achieve a design close to an optimal solution obtained by the ILP model. Also, the evaluation of the impact of switch backplane size shows that given a certain set of network modules, an optimal switch backplane size exists, which achieves the lowest hardware cost.

Optimal WDM layer partitioning and transmission reach in optical networks

We investigate WDM layer network cost in typical North American networks and show that optical transparency at degree 2 and system reach between 1000-2000 km is sufficient for traffic loads between 1 -13 Tb/s.

Optimal hardware module planning and switch backplane configuration for layer-one traffic grooming

We present an automatic hardware module planning approach for optical transport networks. An optimal switch backplane size is identified that can achieve the most cost-effective hardware module planning.

Optimal node hardware module planning for layer-one Optical Transport Networks

Most of the studies on traffic grooming focus on minimizing network link capacity and providing serving-relationship between client services and link capacity. Subsequent to this step, it is important to plan for adding/dropping client services over client service ports and setting up end-to-end lightpaths over network ports, which is however seldom investigated. We call such effort node hardware module planning. This is an industrially practical problem aiming to minimize node hardware cost since hardware modules are the most expensive components in a network. Based on a link-based traffic grooming result that provides information on end-to-end capacity units incident to nodes and aggregation relationship between client services and capacity units, we develop an Integer Linear Programming (ILP) model to optimally plan hardware modules. To overcome the computation difficulty of the ILP model under large-sized planning scenarios, we also develop a fast sub-optimal heuristic for hardware module planning. Simulation studies indicate that the heuristic is efficient to achieve a design close to an optimal solution obtained by the ILP model. Also, the evaluation of the impact of switch backplane size shows that given a certain set of network modules, an optimal switch backplane size exists, which achieves the lowest hardware cost.

Polarization tracker and PMD compensator for 112Gb/s direct-detect RZ-DQPSK PDM systems

The design of a polarization tracker and a PMDC for direct-detect RZ-DQPSK PDM systems is reviewed. The error signals are analyzed and their application spaces are identified. Experimental results are demonstrated to verify the designs.