Reconfigurable Optical Add/drop Multiplexers Architectures Research Articles

Impact of the reconfigurable optical add-drop multiplexer architecture on the design of multi-band C+L+S optical networks

The main advantage of multi-band (MB) networks is to provide more capacity than C-band networks by using other unused bands like the L- and S-bands and, in this way, postpone the announced optical network capacity crunch. However, MB nodes have a more complex structure than C-band nodes, impacting their cost and enhancing their induced physical layer impairments (PLIs). The main goal of this paper is to analyze the impact of several MB node architectures (namely baseline, common-band and compact MB node architectures) on the total network capacity and total network cost-per-bit, using a routing, modulation format, and spectrum assignment (RMSA) network planning tool based on a Monte–Carlo simulation that also incorporates the impact of network PLIs. When the PLIs are neglected, the common-band architecture presents the lowest cost-per-bit compared to the remaining MB architectures, since only lower cost C-band components are used. However, with the PLIs impact, the common-band architecture leads to the lowest total network capacity and highest cost-per-bit due to additional noise coming from all-optical wavelength converters. In particular, the common-band total network capacity is less than half the baseline and compact total network capacities for a blocking probability of 1%, considering the best channel launch power. Also, the common-band cost-per-bit is almost twice the baseline and compact cost-per-bit due to the PLIs-induced degradation.

Networking assessment of ROADM architecture based on a photonics integrated WSS for 800G multi-band optical transport

The capacity of the optical transport network must be expanded to support the increasing demand due to bandwidth-intensive applications. Multi-band transmission solutions can achieve this goal by exploiting the low-loss optical spectrum windows while maintaining the same existing fiber infrastructure, increasing the network’s capacity, and minimizing the operator capital expenditure (CAPEX) by limiting the need for a new fiber deployment. In the context of multi-band transmission, this work proposes a novel reconfigurable optical add–drop multiplexer (ROADM) architecture using a modular photonic integrated multi-band wavelength selective switch (WSS) that operates over multi-bands (S + C + L). This study focuses on conducting a comprehensive network performance analysis of different settings, enabling operation from 400G up to 800G using the proposed multi-band WSS on two real network topologies: German and Italian. The results provide the potential benefits of transitioning from traditional C-band transmission to multi-band transmission based on overall network performance.

CDC ROADM design tradeoffs due to physical layer impairments in optical networks

In this work, we assess the impact of several physical layer impairments (PLIs) on the performance of optical networks based on colorless, directionless and contentionless reconfigurable optical add/drop multiplexers (ROADMs), through Monte-Carlo simulation, and considering polarization division multiplexing 4 and 16 quadrature amplitude modulation (QAM) signals, at 28 GBaud, for 37.5 GHz optical channels. The PLIs taken into account are the amplified spontaneous emission noise, optical filtering, in-band crosstalk and nonlinear interference noise caused by Kerr effect. A detailed model of the ROADM node is built considering two typical ROADM architectures, broadcast and select (B&S) and route and select (R&S), and two different add/drop structures, multicast switches (MCSs) and wavelength selective switches (WSSs), resulting in four different ROADM node scenarios. Our results have shown that for 16QAM signals, the B&S ROADMs with WSSs-based add/drop structures is the scenario that has the best relation cost/performance, foreseeing its use in metro networks, while for 4QAM signals, the R&S ROADM with WSSs-based add/drop structure scenario allows a larger ROADM cascade at an expectable lower cost anticipating its implementation in long-haul networks.

Low-Cost CDC ROADM Architecture Based on Stacked Wavelength Selective Switches

A highly flexible, stacked, switch module is proposed, wherein multiple independent 1 × N wavelength selective switches (WSSs) can be realized on a single 4k liquid crystal on silicon device. The stacked WSS module can be configured in different ways for application at either the transit side or the add/drop side of a colorless, directionless, and contentionless (CDC) reconfigurable optical add/drop multiplexer (ROADM). TwoROADMarchitectures are proposed based on the stacked WSS modules. Their costs are analyzed for both a 4-deg network node and a larger 8-deg node. The first proposed ROADM architecture with full CDC features is shown to realize a cost reduction of at least 35% in these two test network nodes, when compared with the conventional CDC ROADMarchitecture based on the standalone WSSs and multicasting switches (MCSs). The second ROADM architecture proposed has a small probability of wavelength contention, which could be prevented by a local wavelength assignment algorithm. According to our cost estimation, we are able to aggressively reduce the number of components at the add/drop side and make an overall cost reduction of >70% and >80% in the 4- and 8-deg network nodes, respectively.

Demonstration of Quasi-Contentionless Flexible ROADM Based on a Multiport WXC

Colorless, directionless, and contentionless (CDC) are considered to be three important features for next-generation reconfigurable optical add/drop multiplexer (ROADM) nodes. However, CDC-ROADMs have not been widely deployed due to their relatively higher cost and complexity. In this paper, a compact and multiport wavelength cross connect (WXC) is proposed and demonstrated. Based on the developed WXC, we introduce two novel quasi-contentionless ROADM architectures, which provide considerable reduction of traffic blocking ratio when compared with colorless/directionless (CD)-ROADM architectures. Meanwhile, compared to conventional CDC-ROADMs, the proposed architectures show advantages on cost, intrafiber connection, and system complexity. Experiments are carried out to demonstrate the ability to add/drop two or more identical wavelengths simultaneously in a static network and the flex-grid wavelength routing characteristic of the proposed ROADM nodes. These results indicate that the proposed ROADM solution is a practical and promising trade-off for future elastic optical networks.

Wavelength-Selective CDC ROADM Designs Using Reduced-Sized Optical Cross-Connects

As optical transport networks become more configurable, the need for reconfigurable optical add/drop multiplexers (ROADMs) that are colorless, directionless, and contentionless (CDC) increases. Either of the two major classes of ROADM architectures, i.e., broadcast-and-select and wavelength-selective, can provide the CDC properties. With broadcast-and-select ROADMs, this is generally accomplished by employing more costly or complex configurations or adding adjunct equipment. In contrast, the wavelength-selective class of ROADMs, where the central component is an optical cross-connect (OXC), inherently provides the CDC properties. However, this architecture is limited by the achievable size (i.e., port count) of the OXC. We present alternative wavelength-selective ROADM designs that require smaller OXCs while providing equivalent functionality.

Architecture on Demand Design for High-Capacity Optical SDM/TDM/FDM Switching

Reconfigurable optical add/drop multiplexers (ROADMs) are key elements in operators' backbone networks. The breakthrough node concept of architecture on demand (AoD) permits us to design optical nodes with higher flexibility with respect to ROADMs. In this work, we present a five-step algorithm for designing AoD instances according to some given traffic requests, which are able to support subwavelength time switching up to wavelength/superchannel/fiber switching. We evaluate AoD performancein terms of power consumption and number of backplane optical cross-connections. Furthermore, we discuss trade-offs involved in the migration from a fixed to a flexible grid with regard to the optical node size, capacity, and power consumption. We compare several ROADM architectures proposed in the literature with AoD in terms of power consumption and cost. We also study different technologies for enhancing the scalability of AoD. Results show that AoD can bring significant power savings compared to other architectures while offering a throughput of hundreds of terabits per second.

Optical network scaling: roles of spectral and spatial aggregation.

As the bit rates of routed data streams exceed the throughput of single wavelength-division multiplexing channels, spectral and spatial traffic aggregation become essential for optical network scaling. These aggregation techniques reduce network routing complexity by increasing spectral efficiency to decrease the number of fibers, and by increasing switching granularity to decrease the number of switching components. Spectral aggregation yields a modest decrease in the number of fibers but a substantial decrease in the number of switching components. Spatial aggregation yields a substantial decrease in both the number of fibers and the number of switching components. To quantify routing complexity reduction, we analyze the number of multi-cast and wavelength-selective switches required in a colorless, directionless and contentionless reconfigurable optical add-drop multiplexer architecture. Traffic aggregation has two potential drawbacks: reduced routing power and increased switching component size.

Evaluating Availability of Optical Networks Based on Self-Healing Network Function Programmable ROADMs

Due to the large transmission speeds and enormous volume of transferred data, network reliability performance and cost-efficiency are among the key concerns in optical network design. Reducing the number of used optical components with higher failure probability within nodes represents a promising approach for achieving reliable and cost-effective optical network operation as it reduces the correlated risk of connection failures and enables reusing idle components as redundancy for failure recovery. This can result in greater overall network availability and lower loss of data and related revenue. Recently introduced synthetic network function programmable optical nodes implemented by architecture on demand (AoD) support the aforementioned approach by offering high levels of flexibility, modularity, and scalability. In AoD nodes, an optical backplane (i.e., optical switch) hosts optical components and enables arbitrary node configurations by cross-connecting attached modules. As a result, each lightpath passing through the node uses only the components necessary for fulfilling the switching and processing requirements. AoD nodes can perform switching at the wavelength and waveband granularity and also support switching of lightpaths at the fiber level by connecting an input fiber directly to the targeted output, referred to as fiber switching (FS). The latter functionality is particularly beneficial for the availability aspect, as it helps decrease the number of failure-prone components traversed by each lightpath, allowing them to be reused as redundancy. In this paper we demonstrate and evaluate self-healing capabilities of AoD nodes arising from their flexibility and ability to employ idle components for failure recovery. To improve efficiency of self-healing by increasing the number of idle components within nodes, we propose a routing algorithm which obtains a targeted portion of lightpaths switched at the fiber level, called the enforced FS (EFS) algorithm. We study the impact of AoD on network availability at different traffic switching granularities and compare it to traditional hard-wired node architecture via simulation. The results show significant improvements of availability and recovery time due to node-level restoration, with reduced network outage time and operator revenue losses. Finally, to the best of our knowledge, for the first time we experimentally demonstrate two novel hard-wired and synthetic reconfigurable optical add–drop multiplexer architectures with redundancy and all-optical self-healing capabilities.

Encompassing ROADM add/drop constraints in GMPLS‐based WSONs

ABSTRACTDifferent reconfigurable optical add/drop multiplexer (ROADM) architectures can be considered for the deployment of cost‐effective wavelength switched optical networks (WSONs). They impose add/drop constraints that might significantly affect the efficient utilisation of the overall WSON resources.In this paper, the most relevant ROADM architectures and related constraints are first reviewed and discussed. Then novel provisioning schemes are proposed to effectively handle different ROADM architectures and provide a preference on the utilisation of add/drop resources with limited flexibility. The schemes are specifically designed to exploit the recently introduced generalised multiprotocol label switching extensions for the advertisement of capacity and/or availability of ROADM add/drop resources. Simulation results show that the proposed schemes guarantee the effective utilisation of the add/drop ROADM resources under several WSON scenarios. Copyright © 2011 John Wiley & Sons, Ltd.

Dimensioning the Add/Drop Contention Factor of Directionless ROADMs

Reconfigurable Optical Add/Drop Multiplexers (ROADM) are the optical switching equipment of transparent optical networks. Directionless ROADMs permit the network carriers to change the direction of an added and/or dropped lightpath without the need of a technician on-site intervention in the lightpath end nodes. Colorless ROADMs provide the same versatility for changing the lightpath transmission wavelength. Cost-effective directionless ROADM architectures (colorless or colored) can be built if the maximum number of lightpaths that can be added/dropped using the same wavelength is limited. We name this limit as the node add/drop contention factor, and denote it as <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> . In this paper we investigate the network lightpath blocking performance as a function of this add/drop contention factor of the nodes. The scenarios considered are the static planning of a network (i) with unprotected traffic, (ii) with traffic 1+1 protected for single-link failures, and (iii) with traffic 1+1 protected for single-link or single-node failures. Since for these scenarios, the wavelength of an existing lightpath does not have to be dynamically reconfigured, the work in this paper applies to both colorless and colored nodes. An ILP model and an effective heuristic are presented to solve the so-called Add/Drop Contention Aware RWA (ADCA-RWA) planning of the network. Extensive results are reported. In all the cases, an add/drop factor <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> = 2 is sufficient to provide the same performance as contentionless nodes ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> = ∞). Furthermore, in all the tests a factor <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> = 1 was also sufficient, or produced a minor lightpath blocking performance degradation (below 0.5% in the unprotected cases, and below 2.5% in the 1 + 1 protected cases).

Wavelength-Routing Capability of Reconfigurable Optical Add/Drop Multiplexers in Dynamic Optical Networks

According to their underlying switching technologies, reconfigurable optical add/drop multiplexers (ROADMs) can be classified into three categories: Category I consists of a single large optical switch; category II is composed of a number of small optical switches aligned in parallel; and category III has a single optical switch and only one wavelength being added/dropped. To evaluate the wavelength-routing capability of ROADMs of various categories in dynamic optical networks, a theoretical routing-power model is developed, taking into account different ROADM architectures and dynamic traffic. Numerical simulations show that different category ROADMs differ considerably in their wavelength-routing capabilities, which are significantly dependent upon dynamic traffic. It is also observed that among these three ROADM architectures, category I (III) ROADMs offer the greatest (lowest) wavelength-routing capability and the lowest (highest) susceptibility to dynamic traffic. In particular, to maximize the ROADM-based network flexibility and connectivity, a set of practically applicable criteria is identified on designing/choosing optimum ROADMs for given dynamic optical networks

Planar lightwave circuit based reconfigurable optical add-drop multiplexer architectures and reusable subsystem module

We describe a wide range of reconfigurable optical add-drop multiplexer architecture designs that may be implemented in standard silica-on-silicon planar lightwave circuits. This proven, reliable technology offers high performance and cost-effective solutions for reducing complex service provisioning in reconfigurable optical networks. Recent advances enable very flexible wavelength routing devices for mesh- and ring-based networks to be implemented on a common subsystem integration platform. We show excellent system performance at 10 Gb/s.

Mach–Zehnder fiber-grating-based fixed and reconfigurable multichannel optical add-drop multiplexers for DWDM networks

Optical add-drop multiplexers (OADMs) will play an important role enabling greater connectivity and flexibility in dense wavelength-division multiplexing (DWDM) networks. In this paper, we first, to the best of our knowledge, utilize the Mach–Zehnder fiber Bragg grating (MZ-FBG) based devices with associated optical switches to construct large-dimension OADMs without the need for wavelength demultiplexers and multiplexers at the drop and add ports, respectively. The single- and cascaded-stage MZ-FBGs as the add-drop elements separately in a total of one fixed and two reconfigurable OADM architectures are considered. We investigate the required constitutive elements, and examine the relevant characteristics of system insertion loss and differential system loss for the added, dropped, and passed-through channels. The system power penalty induced by both inter- and intra-band crosstalks, and the required spectral characteristics for the MZ-FBG devices are analyzed. The add-drop dimension limits of these MZ-FBG-based OADMs are estimated. Other related issues such as multiwavelength amplification and bandwidth narrowing for the cascaded OADM chain in DWDM networks are also addressed. These proposed MZ-FBG-based OADMs may find important applications in DWDM systems and networks.