Reconfigurable WDM Research Articles

Selectable-FSR 10-GHz Granularity WDM Superchannel Filter in a Reconfigurable Photonic Integrated Circuit

We present a 10-GHz granularity reconfigurable WDM superchannel filter in a photonic integrated circuit. The filter uses a ring-resonator-assisted tapped-delay-line topology. An example configuration with two ring resonators and four tapped delay lines provides a spectral filter with a flat-top passband, a roll-off factor of 8%, a tunable central wavelength, and a selectable free spectral range, i.e., 2× or 4× the 3-dB passband bandwidth. The device was fabricated in a silicon nitride (Si3N4/SiO2) waveguide with a chip area of 0.36 cm2 and has a fiber-to-fiber insertion loss of 5 dB. We experimentally demonstrate the filter for selecting a subchannel from a WDM superchannel comprising 10-GHz subchannels with 10% and zero guard bands. Owing to the infinite impulse responses of ring resonators, this filter requires a significantly smaller area and fewer tuning elements compared with designs based on only tapped-delay-line finite-impulse-response filters. This paper contributes to the creation of chip-scale all-optical WDM superchannel transceivers and reconfigurable optical add/drop multiplexers (ROADMs).

Demonstration of flexible and reconfigurable WDM multicast scheme supporting downstream emergency multicast communication for WDM optical access network

Demonstration of flexible and reconfigurable WDM multicast scheme supporting downstream emergency multicast communication for WDM optical access network

Reconfigurable WDM–OFDM–PON employing wavelength selective switching with SSB and direct detection optical OFDM

A reconfigurable WDM–OFDM–PON employing a WSS as a remote node is proposed. The system, which employs an optical comb source at the transmitter, is shown to support both spectrally efficient SSB-OFDM and high bit rate DDO-OFDM. Transmission over 30km of SSMF is performed and we show that DDO-OFDM with a virtual carrier offers three times the data rate for similar receiver sensitivities and the same DAC. A raw data rate of 31.25Gb/s/λ is achieved in the case where DDO-OFDM is employed.

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.

Hybrid distributed Raman/EDFA amplifier with hybrid automatic gain control for reconfigurable WDM optical networks

Nowadays, optical amplifiers designs are induced by new requirements generated by optical networks. The introduction of WDM reconfigurable networks with increasing rate from 10-40 Gb/s to 100 Gb/s and beyond, demand new optical amplifiers development with improved gain spectral flatness and noise figure for all operational range of input powers and set-point gains. In this paper, it was developed a hybrid distributed Raman/EDFA amplifier with a novel hybrid gain control (HGC) scheme based on joint actuation. The HGC was firstly developed by numerical simulation and after experimentally, in a WDM system with 100 km SSMF fiber span and full C-band load. The Results shows an improved equivalent noise figure with flattened gain spectrum for all amplifier operation range in dynamic optical networks.

Benefits of implementing a dynamic impairment-aware optical network: results of EU Project DICONET

Dynamic optical networking allows operators to effectively maximize the capacity of their physical infrastructure and cope with the rapid growth rates of the Internet traffic. In the framework of the European DICONET project we proposed and developed a comprehensive solution that utilizes the dynamicity as well as the valuable physical layer information of a reconfigurable WDM core network to provide a smooth transition from the quasi-static networking of today to an intelligent reconfigurable and physical impairment-aware architecture. In this work we discuss the benefits of implementing the DICONET solution and present some of the major achievements of the project that support both the planning and operation phase of a core optical network.

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 Erbium-doped waveguide amplifier insensitive to power fluctuations

We describe an efficient erbium-doped waveguide amplifier insensitive to output power variation by means of optical gain clamping. Output power suitable for metro applications and gain flatness over full C-band are demonstrated. We also show that this technology is suitable for transparent WDM ring network. In fact the possible recirculation of amplified spontaneous emission noise or laser power leaking from mirrors will not impact the device performance making robust to transients for next generation reconfigurable WDM ring networks.

Erbium-doped waveguide amplifier for reconfigurable WDM metro networks

Transient dynamic due to signal power fluctuations is the main impairment in reconfigurable transparent wavelength-division-multiplexing metro networks design. In this letter, we demonstrate an optical-gain-clamped erbium-doped waveguide amplifier using fiber Bragg grating filters. We show both theoretically and experimentally that it is virtually insensitive to signal transient and that it reduces overshoot by 10 dB compared to standard erbium-doped fiber amplifiers. The device modeling shows that short highly doped optical amplifiers are insensitive to input signal level transient and will outperform longer fiber-based identical operating condition amplifiers. In fact, erbium-doped waveguide optical amplifiers do not exhibit any transient dynamic effect that can be detrimental after accumulation along the amplifier chain. In addition, waveguide amplifiers will require less extra pump to stabilize optical clamping, thus reducing clamping implementation cost.

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.

Benefits of partial reconfigurability in circuit-switched WDM networks

We describe and study partially reconfigurable circuit-switched networks. These are dynamic networks in which partial, but not complete, flexibility of resource assignment is retained during the lifetime of a connection. In particular we analyse two examples of partially reconfigurable WDM networks with flexibility of wavelength assignment. In the first example, each connection in the network requires a main lightpath (whose wavelength must remain fixed) and a standby lightpath (whose wavelength may change). In the second example, the network contains two classes of connections with different service levels, one class reconfigurable and the other not. We propose two contrasting reconfiguration algorithms, and demonstrate that even a small amount of reconfigurability can yield significant performance gains, while a large amount of reconfigurability yields almost all the performance gain that would be attained by introducing complete wavelength conversion to the network.

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.

A management and visualization framework for reconfigurable WDM optical networks

As the phenomenal advance in optical WDM networking technologies continues, optical WDM network equipment has been deployed not only in backbone networks, but also in regional, metropolitan, and access networks. It is widely believed that a major component of the next-generation Internet will be an IP-based optical network employing WDM. WDM wavelength routing and signaling have become an active research field, and dynamic and adaptive wavelength routing and assignment algorithms have been proposed. However, there is less work on reporting network control and management system implementation efforts over testbed WDM networks. This article presents a network management and visualization framework aimed at guiding the development of management applications for reconfigurable WDM optical networks. A layered framework architecture including element and network management and visualization is provided, and an object-based information model representing the WDM network is introduced. Functional components on reconfiguration, software agent, and network visualization services are presented, and important issues related to optical lightpath generation are discussed. A network visualization service also provides WDM control and management APIs to applications and access networks such as an IP network management system. To illustrate the usage of the framework, we share our experience in implementing the MONET network control and management system, and present network visualization views obtained from the MONET WDM network to highlight the framework features.

Optical performance monitoring in reconfigurable WDM optical networks using subcarrier multiplexing

Optical performance monitoring (OPM) is an important approach to determine the quality of optical channels within an optical core network without passing data through optoelectronic regeneration at the monitor points. Using this approach, the quality or "health" of signals can be determined at arbitrary points in a network without knowledge of the transport history of the data or the details of the transmission path. We report experimental results on the use of subcarrier multiplexing (SCM) to perform a variety of monitoring functions including chromatic dispersion monitoring, wavelength registration, power monitoring, and signal-to-noise ratio (SNR) monitoring.

MOSAIC: a multiwavelength optical subcarrier multiplexed controlled network

The experimental demonstration of MOSAIC, a reconfigurable WDM add/drop network with subcarrier multiplexed control, is presented. The MOSAIC network implements the optical layer protocol to support bit-rate transparent multichannel lightpaths. Two types of add/drop multiplexers are implemented and combined in a three-node experiment. Multihop lightpaths are established giving an end-to-end bit error rate of better than 10/sup -9/ at 1.2 Gbps. The reconfigurable add/drop multiplexer is based on a novel dilated 2/spl times/2 acoustooptic filter switch crossconnect and an analog optoelectronic crossconnect that drives a ten-wavelength laser array transmitter up to 2.5 Gbps per wavelength. The fixed wavelength add/drop multiplexer utilizes a fast digitally tunable laser transmitter. Both add/drop multiplexers support bit-rate transparent 2R optoelectronic regeneration as well as wavelength translation. Subcarrier multiplexing on each wavelength is used to support channel state monitoring and channel equalization as well as transmission of digital network control information. Systems experiments demonstrate cascaded 2R optoelectronic regeneration with wavelength translation and cascaded multichannel optical switching with up to seven hops. It is shown that combining cascaded 2R optoelectronic regeneration with cascaded multichannel optical switching can be used to balance jitter accumulation and amplified spontaneous emission generated amplitude noise to yield high signal-to-noise ratio for lightpaths.