Reconfigurable WDM Networks Research Articles

SiC pinpin photonic filters for linking the visible spectrum to the telecom gap

Expanding far beyond traditional applications at telecommunications wavelengths, the SiC photonic devices has recently proven its merits for working with visible range optical signals. Reconfigurable wavelength selectors are essential sub-systems for implementing reconfigurable WDM networks and optical signal processing. Visible range to telecom band spectral translation in SiC/Si can be accomplished using wavelength selector under appropriated optical bias, acting as reconfigurable active filters. In this paper we present a monolithically integrated wavelength selector based on a multilayer SiC/Si integrated optical filters that requires optical switches to select wavelengths. The selector filter is realized by using double pin/pin a-SiC:H photodetector with front and back biased optical gating elements. Red, green, blue and violet communication channels are transmitted together, each one with a specific bit sequence. The combined optical signal is analyzed by reading out the generated photocurrent, under different background wavelengths applied either from the front or the back side. The backgrounds acts as channel selectors that selects one or more channels by splitting portions of the input multi-channel optical signals across the front and back photodiodes. The transfer characteristics effects due to changes in steady state light, irradiation side and frequency are presented. The relationship between the optical inputs and the digital output levels is established.

Dynamic quality of transmission optimization and global impairments control in reconfigurable transparent WDM networks: schemes and demonstrations

Dynamic quality of transmission optimization and global impairments control in reconfigurable transparent WDM networks: schemes and demonstrations

Minimisation of end‐to‐end delay in reconfigurable WDM networks using genetic algorithms

AbstractA new genetic algorithm (GA) is proposed to design logical topologies for wavelength‐routed optical networks (WRONs) with the objective of minimising the end‐to‐end delay. Two versions of the algorithm, called D‐GALD (Delay‐optimised Genetic Algorithm for Logical topology Design), have been developed. The first one minimises the average end‐to‐end delay of the packets transported by the network, while the second one minimises the average delay of the most delayed traffic flow. By means of a simulation study, we show that the logical topologies designed by D‐GALD support more than 50 per cent higher traffic load—without causing network instability—than those ones designed by other heuristics. Moreover, the utilisation of D‐GALD leads to reductions of up to 15 per cent in the average end‐to‐end delay and around 30 per cent in the average end‐to‐end delay of the most delayed traffic flow. Copyright © 2008 John Wiley & Sons, Ltd.

Genetic algorithm to design logical topologies in reconfigurable WDM networks

A new method to design logical topologies based on genetic algorithms is presented. Not only does the algorithm determine which nodes should be connected by means of lightpaths with the aim of minimizing congestion, but it also solves the routing and wavelength assignment problem. In this way, the algorithm guarantees that the logical topology obtained can be embedded in the optical network subject to the available set of resources. The algorithm is effective in terms of both congestion and fairness. For instance, when compared with other work, the congestion is significantly reduced (from 20% to 75% depending on the matrix of traffic considered), and the fairness, when evaluated in terms of the Jain index, is generally higher than 0.94. Moreover, the algorithm brings advantages when employed in dynamic scenarios where the logical topology is frequently reconfigured, as it is fast and, in contrast to other algorithms previously proposed, the calculation process can be stopped at any time (if required) in order to give the best virtual topology found up to the moment.

Load balancing – node transfer trade-off in reconfigurable WDM networks

When the traffic demand changes in single-hop WDM broadcast and select networks, the load can become unbalanced. This situation leads to poor resource utilisation and the wavelength assignment (WLA) requires reconfiguring to maintain a balanced load. The problem of reconfiguring the wavelength assignment in single-hop WDM networks is considered here. Topologies used in the study are passive star and bus networks, and all nodes in the network are assumed equipped with fast tunable transmitters (FTTs) and slowly tunable receivers (STRs). When reconfiguring the WLA according to the new traffic demand, it is important to reduce the number of receivers that need to be retuned to provide low disruption to the network traffic and thus correspondingly reduce the periods when the network operation is suspended during the retuning. The trade-off here is thus between the number of node transfers and the degree of network load balance. A new WLA reconfiguration algorithm is introduced, the one direction transfer (1DT) algorithm, which provides a low number of retunings and an excellent load balance. The 1DT algorithm transfers a group of nodes from the highest loaded channels to the lowest loaded channels. A comparison between the proposed algorithm and previous algorithms found in the literature is carried out to demonstrate the efficiency of the proposed algorithm.

Efficient routing and wavelength assignment for reconfigurable WDM ring networks with wavelength converters

We consider the problem of wavelength assignment in reconfigurable WDM networks with wavelength converters. We show that for N-node P-port bidirectional rings, a minimum number of /spl lceil/PN/4/spl rceil/ wavelengths are required to support all possible connected virtual topologies in a rearrangeably nonblocking fashion, and provide an algorithm that meets this bound using no more than /spl lceil/PN/2/spl rceil/ wavelength converters. This improves over the tight lower bound of /spl lceil/PN/3/spl rceil/ wavelengths required for such rings given in if no wavelength conversion is available. We extend this to the general P-port case where each node i may have a different number of ports P/sub i/, and show that no more than /spl lceil//spl sigma//sub i/P/sub i//4/spl rceil/+1 wavelengths are required. We then provide a second algorithm that uses more wavelengths yet requires significantly fewer converters. We also develop a method that allows the wavelength converters to be arbitrarily located at any node in the ring. This gives significant flexibility in the design of the networks. For example, all /spl lceil/PN/2/spl rceil/ converters can be collocated at a single hub node, or distributed evenly among the N nodes with min{/spl lceil/P/2/spl rceil/+1,P} converters at each node.

Performance and testbed study of topology reconfiguration in IP over optical networks

With the widespread deployment of Internet protocol/wavelength division multiplexing (IP/WDM) networks, it becomes necessary to develop traffic engineering (TE) solutions that can effectively exploit WDM reconfigurability. More importantly, experimental work on reconfiguring lightpath topology over testbed IP/WDM networks is needed urgently to push the technology forward to operational networks. This paper presents a performance and testbed study of topology reconfiguration for IP/WDM networks. IP/WDM TE can be fulfilled in two fashions, overlay vs. integrated, which drives the network control software, e.g., routing and signaling protocols, and selects the corresponding network architecture model, e.g., overlay or peer-to-peer. We present a traffic management framework for IP over reconfigurable WDM networks. Three "one-hop traffic maximization"-oriented heuristic algorithms for lightpath topology design are introduced. A reconfiguration migration algorithm to minimize network impact is presented. To verify the performance of the topology design algorithms, we have conducted extensive simulation study. The simulation results show that the topologies designed by the reconfiguration algorithms outperform the fixed topology with throughput gain as well as average hop-distance reduction. We describe the testbed network and software architecture developed in the Defense Advanced Research Projects Agency (DARPA) Next Generation Internet (NGI) SuperNet Network Control and Management project and report the TE experiments conducted over the testbed.

Service-specific resource allocation in WDM networks with quality constraints

The need to establish wavelength-routed connections in a service-differentiated fashion is becoming increasingly important due to a variety of candidate client networks (e.g., IP, SDH, ATM) and the requirements for QoS-delivery within transport layers. The multiservice operation changes the way we deal with wavelength-routed paths, as they are now being characterized by manifold properties, such as transmission quality, restoration, network management, and policies. We propose a generic approach to service-differentiated connection accommodation in wavelength-routed networks where, for the network state representation, the supplementary network graphs are defined and referred to as service-specific wavelength-resource graphs. These graphs are used for the appropriate allocation of wavelengths on concatenated physical resources building a wavelength route, along which the necessary transmission quality is achieved and the required management and surveillance functions are provided. By considering twofold wavelength routing metrics, i.e., QoS metrics (service requirements) and resource metrics (quality constraints), these graphs can yield the solution to the QoS-routing problem, i.e., the provision of service-specific guarantees under quality constraints-a feature that is still missing from the existing architectures. The numerical analysis of dynamically reconfigurable multiservice WDM networks is presented for regular network operation as well as for optical network service restoration.

Precision-tuning wavelength addressable laser for reconfigurable WDM networks

In this letter, we demonstrate a precision wavelength addressable laser with a rapid wavelength setting function for reconfigurable wavelength routed wavelength-division-multiplexing networks using a broad-band tunable laser combined with a phased-array waveguide-grating-based integrated real time multichannel wavelength monitoring circuit. The addressable laser could be set to four International Telecommunication Union wavelengths with 0.8-nm (100-GHz) channel spacing, limited by its tuning range, and the wavelength resolution is better than 0.02 nm. The tunable laser also supports self-contained and self-learning functions.

Experimental demonstration of a multiple-/spl lambda/ wavelength shifter for dynamically reconfigurable WDM networks

We demonstrate a multiple-/spl lambda/ wavelength shifter that is based on temporal interleaving and semiconductor optical amplifier cross-gain compression. Our multiple-/spl lambda/ wavelength shifter is transparent to both the nonreturn-to-zero (NRZ) and return-to-zero (RZ) input data-formats. We simultaneously wavelength shift two independent NRZ 1-Gb/s WDM channels from 1548 and 1552 nm to 1540 and 1569 nm, respectively, with low-power penalties.

Transport network involving a reconfigurable WDM network layer-a European demonstration

A reconfigurable WDM network, introduced as a new optical layer in present network hierarchy, has been demonstrated in the Stockholm Gigabit Network by the European RACE-MWTN consortium. New optical network elements, OXC and OADM, have been developed together with associated photonic technologies. The development also includes a management system that conforms to the standardized Telecommunication Management Network architecture.

All-optical data format conversions and reconversions between the wavelength and time domains for dynamically reconfigurable WDM networks

We demonstrate all-optical error-free 2 Gb/s data format conversions and reconversions between the wavelength and time domains. Conversion between these two domains is accomplished by performing single-stage TDM-to-WDM and WDM-to-TDM conversions. We also perform the function of converting back all-optically to the original domain by performing both WDM-to-TDM-to-WDM and TDM-to-WDM-to-TDM reconversions. All conversions and reconversions are realized by using the cross gain compression mechanism inherent in semiconductor optical amplifiers (SOA's). We first demonstrate our TDM-to-WDM converter by simultaneously time demultiplexing and wavelength shifting a four-channel 2 Gb/s TDM data stream into four 500 Mb/s WDM channels. Moreover, we extend this single-stage approach by demonstrating a two-stage TDM-to-WDM converter consisting of two cascaded single-stage TDM-to-WDM modules. This two-stage converter selectively time demultiplexes and wavelength shifts a four-channel 2 Gb/s TDM data stream into two 500 Mb/s WDM channels after the second stage. Furthermore, we demonstrate a WDM-to-TDM converter by simultaneously time multiplexing and wavelength shifting the data from two 1 Gb/s WDM channels into one 2 Gb/s TDM signal. Finally, we demonstrate reconversion between the wavelength and time domains for two channels by performing both WDM-to-TDM-to-WDM and then TDM-to-WDM-to-TDM reconversions. In order to demonstrate system robustness, we use 80 km of fiber and three EDFA's between the conversion and reconversion stages. We show that reconverting back to the TDM data format requires an interstage WDM channel wavelength range less than /spl sim/4 nm, due to the power penalty induced by the interstage relative phase shift between the channels. This constraint limits the operation of the TDM-to-WDM-to-TDM reconverter to data rates up to 10 Gb/s and interstage distances to /spl sim/100 km. All demonstrated conversion and reconversion processes are accomplished with low power penalties. These conversion and reconversion schemes could be useful in WDM switching nodes and may serve as key building blocks for all-optical WDM networks.

Demonstration of an all-optical data format transparent WDM-to-TDM network node with extinction ratio enhancement for reconfigurable WDM networks

We demonstrate a nearly penalty free, all-optical and robust WDM-to-TDM network node that converts two input WDM channels into one high-speed TDM signal. Our node incorporates the very useful functions of: 1) WDM input data-format transparency; 2) time multiplexing; 3) wavelength shifting; and 4) extinction ratio enhancement of the output TDM signal. We demonstrate the principle of this network node by converting two 1-Gb/s NRZ WDM channels at 1552 and 1548 nm into a 2-Gb/s NRZ TDM signal at 1558-nm, while incurring only a 0.2 dB power penalty.

All-optical TDM-to-WDM data format conversion in a dynamically reconfigurable WDM network

We demonstrate both single-stage and two-stage all-optical TDM-to-WDM data format convertors based on cross-gain compression in an SOA. Our method simultaneously time demultiplexes and wavelength shifts each channel's data within a TDM packet. We convert a 2-Gb/s 4-channel TDM data stream at 1552 mn into four 500-Mb/s WDM channels at 1535, 1537, 1540, and 1571 mm. Moreover, we extend this single-stage approach by demonstrating a two-stage TDM-to-WDM convertor that selectively time demultiplexes and wavelength shifts a 2-Gb/s TDM input data stream into two 500-Mb/s WDM channels after the second stage. We find that low power penalties (<2 dB) can be achieved by using this scheme for both the single- and two-stage cases. This conversion scheme may be quite useful in WDM switching nodes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>