Optical Cross-connect Architecture Research Articles

Performance of Dynamic Optical Path Networks with Large-scale WBSS-based Optical Cross-connects

In this paper, we have proposed a generalized large-scale optical cross-connect (OXC) architecture utilizing waveband selective switches (WBSS) for realizing future cost-effective, bandwidth-abundant and flexible optical networks. The developed architecture implements multiple WBSSs for each incoming fiber and small size wavelength selective switches (WSSs) for dropping optical paths while simply deploying 1´2 WSSs or 1´2 optical couplers for realizing the adding function. Thanks to the use of WBSSs, which are more cost-effective and simpler devices, the developed architecture enables a significant hardware scale reduction. The WBSS-based OXC, however, suffers from a limited routing capability, which relies on the inner node parameter (i.e., the WBSS number per input fiber) and the waveband granularity of WBSSs. We, therefore, evaluate the hardware scale requirement of our developed architecture in comparison with that of conventional WSS-based OXC. It is verified that a substantial hardware scale reduction can be achieved by using the proposed architecture, especially for high port count OXCs or when applying coarser granular WBSSs. Moreover, we also assess the performance of dynamic optical networks based on the proposed OXC. Numerical simulations show that the network offers a substantial necessary hardware scale reduction at the cost of a small performance offset comparing to that of the network using conventional WSS-based OXC.

Spectrum Utilization Efficiency of Elastic Optical Networks Utilizing Coarse Granular Routing

In this paper, we have investigated an elastic optical network that uses coarse granular routing based on our recently developed coarse granular node architecture. The developed coarse granular optical cross-connect (OXC) architecture that enables routing bandwidth-flexible lightpaths coarse-granularly is based on coarser granular selective spectrum switches. The network takes the advantages of both elastic optical networking and coarse granular routing technologies to cope with the trade-off between the link cost and the node cost in order to build a spectrum-and-cost efficient solution for future Internet backbone networks. We have evaluated the hardware scale requirement and the spectrum utilization efficiency of the network with typical modulation formats under various network and traffic conditions. We also compared the spectrum utilization of our network to that of corresponding traditional WDM network and conventional elastic optical network. Numerical results verified that, similar to conventional elastic optical network, the proposed network offers a substantial spectrum saving comparing to traditional WDM network.

Highly reliable and large-scale subsystem-modular optical cross-connect.

To create reliable high-capacity photonic networks, we propose a novel optical cross-connect (OXC) architecture that offers failure resiliency and port scalability, simultaneously. The proposed OXC employs the subsystem-modular structure to attain the port scalability, where the use of 1xM wavelength selective switches (WSSs) or MxM WSSs is considered. Furthermore, by introducing an intra-node protection mechanism suited to each OXC architecture, our proposed scheme offers high reliability while retaining the port scalability. Through computer simulations, we evaluate the total number of WSSs needed in a network and the annual path downtime due to WSS failures. The proposed OXC architecture can drastically decrease the annual path downtime with just a small number of WSSs.

Criteria for Selecting Subsystem Configuration in Creating Large-Scale OXCs

We investigate in detail the performances of different subsystem-based modular optical cross-connect (OXC) architectures that can be expanded to cover large port counts. They include ring, linear, and main/junction types, all of which are proved to substantially reduce total hardware scale compared to the conventional architecture. The reduction in necessary number of wavelength selective switches (WSSs) can be more than 70% for OXCs with about 50 x 50 ports, where the accepted traffic offset is about 2%. The maximum number of WSSs traversed by optical paths is also reduced by more than 50% for Pan-European (26 nodes) and 5 x 5 regular mesh networks.

Experimental demonstration of gridless spectrum and time optical switching

An experimental demonstration of gridless spectrum and time switching is presented. We propose and demonstrate a bit-rate and modulation-format independent optical cross-connect architecture, based on gridless spectrum selective switch, 20-ms 3D-MEMS and 10-ns PLZT optical switches, that supports arbitrary spectrum allocation and transparent time multiplexing. The architecture is implemented in a four-node field-fiber-linked testbed to transport continuous RZ and NRZ data channels at 12.5, 42.7 and 170.8 Gb/s, and selectively groom sub-wavelength RZ channels at 42.7 Gb/s. We also showed that the architecture is dynamic and can be reconfigured to meet the routing requirements of the network traffic. Results show error-free operation with an end-to-end power penalty between 0.8 dB and 5 dB for all continuous and sub-wavelength channels.

Compact Matrix-Switch-Based Hierarchical Optical Path Cross-Connect with Colorless Waveband Add/Drop Ratio Restriction

We propose a compact matrix-switch-based hierarchical optical cross-connect (HOXC) architecture that effectively handles the colorless waveband add/drop ratio restriction so as to realize switch scale reduction. In order to implement the colorless waveband add/drop function, we develop a wavelength MUX/DMUX that can be commonly used by different wavebands. We prove that the switch scale of the proposed HOXC is much smaller than that of conventional single-layer optical cross-connects (OXCs) and a typical HOXC. Furthermore, we introduce a prototype system based on the proposed architecture that utilizes integrated novel wavelength MUXs/DMUXs. Transmission experiments prove its technical feasibility.

Cost-effective heuristics for planning GMPLS-based transport networks

With the ever-increasing traffic in WDM transport networks, the development of GMPLS (or multi-granular) transport networks becomes essential to avoid the cost explosion of OXCs. Much work has been devoted to the development of Multi-Granular Optical Crossconnect (MG-OXC) architectures and network design and planning methods. Extending these efforts here, we address a new problem of planning the GMPLS-based transport network by (1) considering the whole traffic hierarchy defined in GMPLS; and (2) allowing the bifurcation of multi-granularity traffic demands among different physical routes. We call such a problem the Routing and Multi-Granular Paths Assignment (RMGPA). The objective of the problem is to minimize the total weighted port count in the transport network. Due to the computational complexity of the problem, only very small-sized planning problems can be solved exactly through Mixed Integer Linear Programming (MILP) optimization. In this paper, we propose efficient heuristics that are capable of solving large-sized planning problems in a reasonable amount of time.

Multi-Granular Optical Cross-Connect: Design, Analysis, and Demonstration

A fundamental issue in all-optical switching is to offer efficient and cost-effective transport services for a wide range of bandwidth granularities. This paper presents multi-granular optical cross-connect (MG-OXC) architectures that combine slow (ms regime) and fast (ns regime) switch elements, in order to support optical circuit switching (OCS), optical burst switching (OBS), and even optical packet switching (OPS). The MG-OXC architectures are designed to provide a cost-effective approach, while offering the flexibility and reconfigurability to deal with dynamic requirements of different applications. All proposed MG-OXC designs are analyzed and compared in terms of dimensionality, flexibility/reconfigurability, and scalability. Furthermore, node level simulations are conducted to evaluate the performance of MG-OXCs under different traffic regimes. Finally, the feasibility of the proposed architectures is demonstrated on an application-aware, multi-bit-rate (10 and 40 Gbps), end-to-end OBS testbed.

A novel dynamic RWA algorithm with intelligent granularity regulation in multi-granular all-optical networks

With the great advances of DWDM technology, optical cross-connects have to deal with much more wavelengths. Accordingly, the size of optical cross-connects become larger and larger; also the management cost is much higher. To simplify the architecture of cross-connects for low-complexity maintenance, waveband switching (WBS) in conjunction with several optical cross-connect architectures have been proposed and attracted much attention recently. The main concept of WBS is to group multiple wavelengths into a single waveband and what it concerns includes cross-connect cost and port count reduction. In this paper, we investigate the dynamic RWA problem (MG_DRWA) in WBS networks comprising of all-optical switches based on a cost-effective multi-granular optical cross-connect (MG-OXC) architecture. With this reconfigurable architecture, an optical cross-connect can switch at either fiber level, waveband level, or wavelength level according to its configuration. In order to effectively accommodate dynamic traffic demand, we propose a new MG_DRWA algorithm. Numerical results reveal that the proposed algorithm can achieve significantly better blocking performance as compared to a previously proposed algorithm named MILB under various traffic loads.

Waveband Switching for Dynamic Traffic Demands in Multigranular Optical Networks

Waveband switching (WBS) in conjunction with multigranular optical cross-connect (MG-OXC) architectures can reduce the cost and complexity of OXCs. In this paper, we study the performance of different MG-OXC architectures under dynamic traffic. In the case with online incremental traffic, we compare two MG-OXC architectures in terms of the blocking probability of new lightpath requests and study the impact of port counts and traffic loads. We develop an online Integer Linear Programming model (On-ILP), which minimizes the number of used ports and the request blocking probability, given a fixed number of wavelengths and MG-OXC architecture. The On-ILP optimizes the routing of new lightpaths so as to maximize lightpath grouping and reduce the port count given that existing traffic cannot be rearranged. We also propose a new efficient heuristic algorithm, called Maximum Overlap Ratio (MOR) to satisfy incremental traffic and compare it with the On-ILP, first-fit, and random-fit algorithms. Our results and analysis indicate that using WBS with MG-OXCs can reduce the size (and, hence, the cost) of switching fabrics compared to using ordinary OXCs. Based on the results and observations in the incremental traffic case, we further study the performance of a particular MG-OXC architecture under fully dynamic or fluctuating traffic. Our simulations show that the proposed heuristic algorithm waveband assignment with path graph, which groups wavelengths to bands and uses wavelength converters efficiently under fluctuating traffic, significantly out-performs other heuristic algorithms.

IP over optical cross-connect architectures [Topics in Optical Communications

IP over optical network architectures have been extensively discussed within the research literature over the past few years. However, although signaling protocols between IP routers and optical cross-connect networks have been standardized, large IP backbones are not typically deployed over optical cross-connect networks with automatic reconfigurability features, such as automatic restoration or dynamic establishment of new IP links. One of the most important criteria in determining whether an IP backbone should be carried over such an optical cross-connect network is economic viability. In this article we analyze and explore four architectures for a typical large ISP backbone. In contrast with some other published claims, our results suggest it is more economically attractive to bypass an intermediate cross-connect network, given current equipment and IP backbone network design requirements. However, for ISPs who also provide a large volume of private line services, we propose an integrated architecture for IP over optical cross-connect networks that may provide an attractive alternative for providing rapid and cost-effective restoration from network failures

Optical cross-connect architectures with the ability to tailor transmission properties

Feature Issue on Photonics in SwitchingA type of optical cross connect that is new to the best of our knowledge is introduced, which employs tunable dispersion compensating devices as switching elements. Such an architecture is used to impose the optimum balance between chromatic dispersion and nonlinearity in a core optical network, wherein each link carries signals coming from several different paths, with dissimilar transmission characteristics. Two scenarios are shown: one with 80km spans followed by dispersion compensating fiber (DCF) and one with 40km spans without any DCF. The overall process not only facilitates wavelength switching but also considerably improves the physical performance.

Comparative study of existing OADM and OXC architectures and technologies from the failure behavior perspective

Feature Issue on Photonics in Switching Several optical add-drop multiplexers (OADM) and optical cross-connect (OXC) architectures and technologies have been proposed in the literature and are being used in existing networks. We present a comparison of these architectures and technologies from the failure behavior point of view, including power drop, in-band and out-band jamming, and wavelength misalignment.

Impact of optical cross-connect architecture on the accumulation of intraband crosstalk in wavelength division multiplexing optical networks

Optical crosstalk imposes a major limit to the practical implementation of optical cross-connects (OXCs). Intraband crosstalk characteristics of OXCs based on the dilated Benes (DB) and generally modified DB (GMDB) networks are investigated and compared. Numerical simulation and experimental results confirm that OXCs based on GMDB networks can eliminate intraband crosstalk influence effectively compared with OXCs based on DB networks.

Single-layer multigranular optical cross-connect architecture with conversion capability and enhanced flexibility

Feature Issue on Waveband Switching, Routing, and GroomingThe rapid advances in WDM technology are expected to bring about tremendous growth in the size of optical cross connects (OXCs). In this context, multigranular OXCs (MG-OXCs) have been suggested as a means of reducing the amount of equipment required. Here we expand the concept of MG-OXCs to include optical packet granularity and review the key building blocks for the advent of MG-OXCs. A single-layer MG-OXC is suggested that offers enhanced flexibility with respect to other single-layer concepts, conversion capability, and good physical performance. Concatenation performance is analytically investigated.

Novel MEMS L-switching matrix optical cross-connect architecture: design and analysis-optimal and staircase-switching algorithms

Free-space optical cross connect (OXC) for optical switching has shown promise in replacing traditional electronic switching fabrics. Micromachined optical switches offer superior performance in terms of bit rate and protocol transparency, which make them futureproof; however, they suffer from nonuniformity in port-to-port optical losses, which limit their use in large-scale optical connects. Recent reports on a novel two-dimensional (2-D) OXC architecture, L-switching matrix, presented that it can significantly improve nonuniformity in optical losses among all output ports. The drawback of L-switching matrix is that it is rearrangeably nonblocking (RNB) and not strictly nonblocking. This paper presents solutions to optimize its switching algorithms. A staircase-switching algorithm is proposed to minimize the occurrence of internal blocking conditions.

Inband crosstalk analysis of optical cross-connect architectures

In this paper, inband crosstalk in several important classes of optical cross-connect (OXC) architectures is studied. We derive the expression for the power penalty imposed by crosstalk so that the various OXC architectures can be evaluated in a systematic way. This, in turn, enables us to study the relation between crosstalk and the component requirement.

Performance Evaluation of OXC Architectures Equipped with Limited-Range Wavelength Converters

In this letter, we evaluate the performance of Optical Cross Connect (OXC) architectures equipped with limited-range wavelength converters. Performance will be evaluated according to both an optimum and a random output wavelength assignment strategy. Analytical and simulation results show the possibility to reduce the conversion degree of the Wavelength Converters while keeping network performance high.

Optical cross-connect architecture using waveband conversion and a passive wavelength router

An optical cross-connect architecture based on wavelength routing is proposed. The design utilises an input waveband conversion stage followed by an arrayed waveguide grating (AWG) to enable optical switching and an output single wavelength conversion stage for wavelength assignment and regeneration. Arranging the AWG in feedback or foldback loop configuration the requirement for an output multiplexer is eliminated. The proposed solution supports wavelength switching granularity while offering reduced component requirements. Experimental and modelling results indicate very good system performance of the node as the output conversion stage offers regenerating characteristics.

Modular MEMS-based optical cross-connect with large port-count

We describe and demonstrate a modular microelectromechanical systems (MEMS)-based optical cross-connect (OXC) architecture. The OXC port count increases modularly by adding new optical modules, and a maximum cross-connectivity of /spl sim/ 350 /spl times/ 350 can be achieved in the current design. Each optical module has 16 ports with closed-loop servo-controlled MEMS mirrors. Using a prototype OXC system, mounted in a standard telecommunications equipment bay comprising optical modules, folding mirrors, and other optical elements, we demonstrate switching times of less than 10 ms, excellent optical power stability of less than /spl plusmn/ 0.15-dB variation, and immunity to stochastic vibrations. An automatic power peak-up process is performed when the power falls below 0.5-dB off the maximum coupled power for any connection.