Xu Shao

Optimization of Spectrum-Sliced ASE Source for Injection-Locking a Fabry–PÉrot Laser Diode

We experimentally study the impact of filter bandwidth of a spectrum-sliced amplified spontaneous emission (ASE) source on the injection-locking of a Fabry-Perot laser diode (FPLD) for passive optical network application. Optimal bandwidth of a spectrum-sliced ASE source was found in terms of receiver sensitivity after transmission. We also investigate the impact of intensity noise (IN) of the spectrum-sliced ASE source and its suppression for a wavelength-locked FPLD using a semiconductor optical amplifier. Experiment results show that the output performance of a wavelength-locked FPLD is improved by IN suppression

Best Effort SRLG Failure Protection for Optical WDM Networks

With the increase in the size and number of shared risk link groups (SRLGs) in optical wavelength-division multiplexing (WDM) networks, the capacity efficiency of shared-path protection becomes much poorer due to the SRLG-disjoint constraint, and thus the blocking probability becomes much higher. Furthermore, due to severe traps caused by SRLGs, it becomes more difficult to find an SRLG-disjoint backup path with trap avoidance within reasonable computational complexity. As a result, in a mesh WDM network with a large number of SRLGs or a large SRLG size, 100% SRLG failure protection is no longer a practical protection scheme. To solve this problem, we present a new protection scheme called best effort SRLG failure protection, in which we try to provide an SRLG-disjoint backup path by choosing the backup path sharing the least number of SRLGs with the working path; this is to make the impact of SRLG failures as low as possible and accept as many as possible connection requests. As a result, the proposed best effort SRLG failure protection scheme manages to make a trade-off between blocking probability and survivability. 100% SRLG failure protection becomes a special case of best effort SRLG failure protection when the working path and backup path share zero SRLG. Due to the NP-completeness of this problem, we propose a heuristic to find the optimal result of the best effort SRLG-disjoint backup path under dynamic traffic. We formulate the connection survivability against SRLG failures and analyze the possibility of backup sharing under best effort SRLG failure protection. Analytical and extensive simulation results with various network topology and SRLG parameters demonstrate that, compared with 100% SRLG failure protection, the proposed best effort SRLG failure protection scheme offers much better capacity efficiency and much lower blocking probability while keeping survivability as high as possible. This can be explained by the fact that by slightly loosing the SRLG-disjoint constraint, shared-path protection will become more capacity efficient and more efficient in overcoming traps.

Best Effort Shared Risk Link Group (SRLG) Failure Protection in WDM Networks

With the increase of size and number of shared risk link groups (SRLGs), capacity efficiency of shared-path protection becomes much poorer due to SRLG-disjoint constraints and blocking probability becomes much higher due to severe traps. As a result, 100% SRLG failure protection is no longer a practical protection scheme. To solve this problem, we present a new protection scheme called best effort SRLG failure protection, in which we try to provide SRLG-disjoint backup path by choosing the backup path sharing the least number of SRLGs with the working path, so as to make the impact of SRLG failures as low as possible and accept as many as possible connection requests. 100% SRLG failure protection becomes a special case of best effort SRLG failure protection when the working path and backup path share zero SRLG. We propose a heuristic to find the best effort SRLG-disjoint backup path under dynamic traffic. The best effort SRLG failure protection scheme tries to make a trade-off between blocking probability and survivability. Analytical and simulation results show, compared with 100% SRLG failure protection, the proposed scheme offers much better capacity efficiency and much lower blocking probability while keeping survivability as high as possible.

Providing Differentiated Quality-of-Protection for Surviving Double-Link Failures in WDM Mesh Networks

Providing differentiated quality-of-protection (QoP) for surviving single-link failures in WDM mesh networks has been extensively studied in recent years. This paper investigates the problem of providing differentiated QoP for surviving arbitrary double-link failures by allowing a connection request to choose from several QoP classes. In this paper, we propose to use three classes, i.e., single shared-path protection (SSPP), single dedicated-path protection (SDPP), and double shared-path protection (DSPP) to provide differentiated QoP. We present two differentiated QoP schemes. Scheme 1 (conventional differentiated QoP) is a natural extension of conventional differentiated QoP for surviving single-link failures, which uses SDPP, SSPP, and SDPP separately to satisfy different QoP requirements. Scheme 2 (shared differentiated QoP) tries to share backup resources between SSPP and SDPP. Simulation results show that our proposed architecture of QoP can satisfy different QoP requirements for surviving double-link failures by making a balance between blocking probability and average QoP. Analytical and numerical results indicate that the proposed differentiated QoP scheme 2 are more efficient in improving not only blocking probability but also average QoP.

Multiple link failure recovery in survivable optical networks

Survivability is of critical importance in high-speed optical communication networks. A typical approach to the design of survivable networks is through a protection scheme that pre-determines and reserves backup bandwidth considering single/double link failure scenarios. In this article, a greedy algorithm is presented to reserve backup bandwidth considering multiple (F > 2) link (SRLG) failure scenarios. A bandwidth-saving joint selection scheme of working and protection paths is presented for protection against random multiple-link failures under dynamic traffic. Simulation shows that the algorithm can achieve maximum sharing of backup bandwidth for protection against random multiple-link failure with significant amount of bandwidth saving.

Backup Reprovisioning After Shared Risk Link Group (SRLG) Failures in WDM Mesh Networks

In this paper, we study the impact of shared risk link group (SRLG) failures on shared-path protection by examining the percentage of connections that are vulnerable after SRLG failures, investigate the benefits of backup reprovisioning after SRLG failures, and evaluate different policies for backup reprovisioning. Compared with single-link failures, SRLG failures leave many more connections unprotected and vulnerable to the next failures and make the network topology much sparser. The major challenge of backup reprovisioning after SRLG failures is how to find SRLG-disjoint backup paths for those unprotected connections with a recovery ratio that is as high as possible within reasonable computational complexity. We are motivated to consider three reprovisioning policies by considering different sequences of reprovisioning according to the degree of SRLG constraints. The first policy is to reprovision backup paths for connections whose working paths traverse more SRLGs first (Policy I), and the second policy is to reprovision backup paths for connections whose working paths traverse fewer SRLGs first (Policy II). The third policy is to do backup reprovisioning randomly, i.e., we pick up an unprotected working path randomly (random reprovisioning). Extensive simulation results show that 1) SRLG failures will leave more connections unprotected compared with single-link failures, and the percentage of connections left vulnerable tends to be proportional to the SRLG size; 2) the network performance based on the first reprovisioning policy always performs best in recovery ratio; and 3) the network performance based on Policy II even underperforms the random reprovisioning. These results can be explained by the fact that connections whose working paths traverse fewer SRLGs are more flexible in finding SRLG-disjoint backup paths, and thus priority given to connections whose working paths traverse more SRLGs in Policy I can significantly improve the recovery ratio.

Large-scale WDM passive optical network based on cyclical AWG

A large scale wavelength division multiplexed passive optical network is proposed and experimentally demonstrated. 124 bidirectional optical channels with 10-Gb/s downstream and 1.25-Gb/s upstream transmission are simultaneously distributed by a single 32*32 cyclic AWG. The effect of the extinction ratio and seeding power to BER performance are experimentally investigated. The selection of the subcarrier frequency is also analyzed by simulation.

Wavelength-agile hybrid passive optical networks with dynamic ONU re-grouping functionality

We propose a novel hybrid wavelength-division-multiplexed (WDM)/ time-division-multiplexed (TDM) passive optical network (PON) architecture for next-generation optical access networks. This PON is based on a novel virtual PON (VPON) mechanism that will allow wavelength channels to be flexibly allocated to specific ONUs in a dynamic fashion. Dynamic wavelength allocation (DWA) algorithms and dynamic bandwidth allocation (DBA) algorithms can be combined to optimize the use of bandwidth resources in such a wavelength-agile hybrid WDM/TDM network. We experimentally demonstrate the proposed architecture using a 10-Gb/s downlink and 1.25-Gb/s uplink transmission setup. The experiment results show that the proposed scheme has good transmission performances with dynamic ONU re-grouping functionality.

10-Gb/s WDM-PON transmission using uncooled, directly modulated free-running 1.55-μm VCSELs

We investigate 10-Gb/s uncooled, directly modulated free-running 1.55-mum VCSEL transmission for WDM-PONs. Wavelength variation with bias current and dispersion tolerance are evaluated for WDM-PON transmission. Errorfree transmission over 10-km SMF and 80-km SMF+DCF have been demonstrated.

iOPEN testbed for dynamic resource provisioning in metro Ethernet networks

We propose novel iOPEN (integrated OPtical EtherNet) architecture to support dynamic reconfiguration of lightpaths between Ethernet switches and study the network control and operation algorithms and their performance. The iOPEN network maintains the Ethernet frame forwarding features and takes advantage of current available optical network technologies, and extends the Ethernet network technology and services to the metro area. The frame forwarding mechanisms and network topology configurations adapt to changes in traffic conditions for guaranteed QoS and efficient resource utilization. The simulation results from simple network configuration indicate that the iOPEN architecture dynamically reconfigures logical topology of the Ethernet switches in response to traffic changes and utilizes resources more efficiently