Reconfigurable Add-drop Multiplexers Research Articles

Low Power Consumption Hybrid-Integrated Thermo-Optic Switch with Polymer Cladding and Silica Waveguide Core

Taking advantage of the large thermo-optical coefficient of polymer materials, a hybrid-integrated thermo-optic switch was designed and simulated. It is also compatible with the existing silica-based planar light-wave circuit (PLC) platform. To further reduce the power consumption, we introduced the air trench structure and optimized the structural parameters of the heating region. This scheme is beneficial to solving the problem of the large driving power of silica-based thermo-optic switches at this stage. Compared with the switching power of all-silica devices, the power consumption can be reduced from 116.11 mW (TE) and 114.86 mW (TM) to 5.49 mW (TE) and 5.96 mW (TM), which is close to the driving power of the reported switches adopting polymer material as the core. For the TE mode, the switch's rise and fall times were 121 µs and 329 µs. For the TM mode, the switch times were simulated to be 118 µs (rise) and 329 µs (fall). This device can be applied to hybrid integration fields such as array switches and reconfigurable add/drop multiplexing (ROADM) technology.

Performance evaluation of data-driven techniques for the softwarized and agnostic management of an N×N photonic switch

The emerging Software Defined Networking (SDN) paradigm paves the way for flexible and automatized management at each layer. The SDN-enabled optical network requires each network element’s software abstraction to enable complete control by the centralized network controller. Nowadays, silicon photonics due to its low energy consumption, low latency, and small footprint is a promising technology for implementing photonic switching topologies, enabling transparent lightpath routing in re-configurable add-drop multiplexers. To this aim, a model for the complete management of photonic switching systems’ control states is fundamental for network control. Typically, photonics-based switches are structured by exploiting the modern technology of Photonic Integrated Circuit (PIC) that enables complex elementary cell structures to be driven individually. Thus PIC switches’ control states are combinations of a large set of elementary controls, and their definition is a challenging task. In this scenario, we propose the use of several data-driven techniques based on Machine Learning (ML) to model the control states of a PIC N×N photonic switch in a completely blind manner. The proposed ML-based techniques are trained and tested in a completely topological and technological agnostic way, and we envision their application in a real-time control plane. The proposed techniques’ scalability and accuracy are validated by considering three different switching topologies: the Honey-Comb Rearrangeable Optical Switch (HCROS), Spanke-Beneš, and the Beneš network. Excellent results in terms of predicting the control states are achieved for all of the considered topologies.

Performance Evaluation of Data-DrivenTechniques for Softwarized and AgnosticManagement of N×N Photonic Switch

The emerging Software Defined Networking (SDN) paradigm paves the way for flexible and automatized management at each layer. The SDN-enabled optical network requires each network element’s software abstraction to enable complete control by the centralized network controller. Nowadays, silicon photonics due to its low energy consumption, low latency, and small footprint is a promising technology for implementing photonic switching topologies, enabling transparent lightpath routing in re-configurable add-drop multiplexers. To this aim, a model for the complete management of photonic switching systems’ control states is fundamental for network control. Typically, photonics-based switches are structured by exploiting the modern technology of Photonic Integrated Circuit (PIC) that enables complex elementary cell structures to be driven individually. Thus PIC switches’ control states are combinations of a large set of elementary controls, and their definition is a challenging task. In this scenario, we propose the use of several data-driven techniques based on Machine Learning (ML) to model the control states of a PIC N×N photonic switch in a completely blind manner. The proposed ML-based techniques are trained and tested in a completely topological and technological agnostic way, and we envision their application in a real-time control plane. The proposed techniques’ scalability and accuracy are validated by considering three different switching topologies: the Honey-Comb Rearrangeable Optical Switch (HCROS), Spanke-Beneš, and the Beneš network. Excellent results in terms of predicting the control states are achieved for all of the considered topologies.

Opening up ROADMs: streaming telemetry [Invited

We present an implementation of streaming telemetry of optical metrics within open hardware reconfigurable add/drop multiplexers (ROADMs). Our key achievements are sub-second updates of high-resolution spectrum scans, and we demonstrate a sustained telemetry stream of the full C-band with a sub-GHz resolution. The telemetry streaming is implemented over a standard, Internet Engineering Task Force (IETF)-defined protocol (YANG Push) in collaboration with an open-source YANG software stack and device-specific code. As the telemetry collector, we used a common time series database (TSDB) along with a visualization dashboard. We also extended the Open Network Operating System (ONOS) software-defined network (SDN) controller to act as a telemetry receiver.

Asymmetric CDC ROADMs for Efficient Support of Bi-Directionally Asymmetric Traffic Demands

With the arrival of 5G era, Internet traffic is growing explosively. Meanwhile, the asymmetry of traffic in upstream and downstream directions is becoming more severe. Most current network architectures are designed based on the assumption of bi-directionally symmetric traffic demands. Network capacity in the direction that carries less traffic is largely wasted. To tackle this issue, we propose a new optical network architecture that can efficiently handle bi-directionally asymmetric traffic demands. Specifically, we design a novel asymmetric colorless, directionless, and contentionless (CDC) reconfigurable add/drop multiplexer (ROADM), which can adaptively configure numbers of ingress and egress 1 ×N wavelength selective switches (WSSs) in each direction asymmetrically according to actual traffic demands, thereby avoiding wastage of 1 ×N WSSs in the direction carrying less traffic. Also, we decouple each transponder into a pair of split transmitter (Tx) and receiver (Rx), and asymmetrically configure their numbers according to actual bi-directional traffic demands, significantly reducing the add/drop cost in a ROADM. To evaluate the benefit of the proposed asymmetric network architecture, we exploit the routing and spectrum assignment problem in an optical network. A novel analytical model to evaluate lightpath blocking performance with asymmetric numbers of opposite fibers on each link of an optical network is developed. Also, efficient heuristic algorithms to target asymmetric traffic are proposed. Simulation results show that the proposed asymmetric optical network architecture can achieve significantly better lightpath blocking performance than its counterpart symmetric architecture when their total system costs are close. Furthermore, the analytical model can accurately predict the blocking performance of an optical network based on the asymmetric architecture.

On-Chip Switch and Add/Drop Multiplexer Design With Left-Handed Behavior in Photonic Crystals

An integrated optical switch consisting of a Mach-Zehnder Interferometer with photonic crystals-based phase shifters is designed for telecom wavelength range. The phase modulation along the two arms of the interferometer comes from the photonic band-to-band transition on the photonic crystals that leads to a large effective index difference and results in a switching/modulation with a low-voltage, small optical interaction length, and a low insertion loss. Moreover, shifting along the same photonic band is utilized for constructing a fully reconfigurable add-drop multiplexer for tunable wavelength range with a broadband response.

Monolithically integrated reconfigurable add-drop multiplexer for mode-division-multiplexing systems.

An integrated reconfigurable optical add-drop multiplexer (ROADM) for mode-division-multiplexing systems is proposed and demonstrated for the first time, to the best of our knowledge. The present ROADM with four mode-channels is composed of a four-channel mode demultiplexer, four identical 2×2 thermo-optic Mach-Zehnder switches (MZSs), and a four-channel mode multiplexer, which are integrated monolithically on silicon. All the devices are designed for operation with TM polarization. The ROADM can add/drop any one of the mode channels freely by thermally turning on/off the corresponding MZS. For the added/dropped mode-channels, the excess loss is 1-5 dB, and the extinction ratio is 15-20 dB in the wavelength range of 1535-1565 nm.

Silicon Nanophotonic Integrated Devices for On-Chip Multiplexing and Switching

A review is given on our recent progresses in silicon nanophotonic integrated devices for multiplexing and switching, which are key elements in a multichannel multiplexed photonic networks-on-chip. On-chip (de)multiplexers include wavelength-division-multiplexing filters based on arrayed-waveguide gratings and microring resonators, polarization-division-multiplexing devices like polarizers, polarization-beam splitters and polarization rotators, mode-division-multiplexing devices, and some novel hybrid (de)multiplexers enabling more than one multiplexing technologies simultaneously. Thermal-switchable silicon photonic devices are also discussed regarding the increasing demands for reconfigurable photonic networks-on-chip, including high-performance optical switches and reconfigurable add-drop multiplexers.

Mode-Unbundled ROADM and Bidirectional Mode Assignment for MDM Metro Area Networks

A mode-unbundled reconfigurable add/drop multiplexer (ROADM), composed of a fiber-based mode-multiplexer/demultiplexer pair and a multiport microelectromechanical systems switch, is proposed and experimentally characterized for higher data granularity in mode-division multiplexing (MDM) deployment of future metro area networks (MAN). For enabling mode-unbundling transmission, crosstalk reduction through bidirectional mode assignment is adopted. Finally, a 62-km MDM–MAN ring, composed of two mode-unbundled ROADMs and few-mode fiber spans, is experimentally demonstrated by taking advantage of bidirectionally mode assigned 40 Gb/s, 16-QAM signals.

Evaluating Internal Blocking in Noncontentionless Flex-grid ROADMs [Invited

In heterogeneous flex-grid networks, optical connections for different line rates, spectral widths, and modulations can coexist in the same infrastructure. Optical connections are transparently routed by reconfigurable add/drop multiplexers (ROADMs). Flex-grid ROADMs are enabled by state-of-the-art evolution from original wavelength-selective switches (WSSs), designed for fixed-grid applications, to WSSs that operate in flexible grids. Broadcast-and-select (B&S) flex-grid ROADMs are subject to the same internal blocking as their fixed-grid counterparts, and this internal blocking can also be reduced by augmenting the number of add/drop transponder banks. In this paper, we dimension the number of transponder banks C required in flex-grid ROADMs to make the internal blocking negligible. To this end, we present a graph transformation that takes a network topology based on B&S ROADMs and converts it into an equivalent network composed of contentionless ROADMs. Then, any conventional (non-contention-aware) algorithm can be applied to the transformed topology to make lightpath allocations. Our results show that often C=2, and in some cases C=1, transponder banks are enough to eliminate internal contention in practice. Interestingly, these results are similar to the ones obtained in the fixed-grid case. This is not an obvious conclusion, since spectrum fragmentation in flex-grid networks may amplify internal blocking. Results have been obtained using the Net2Plan 0.2.3 open-source tool. Algorithms’ source code and data are available in the Net2Plan public repository for reuse and validation.

100G Superchannel Transmission Using <inline-formula> <tex-math notation="LaTeX">$4\times 28$ </tex-math></inline-formula> Gb/s Subcarriers on a 25-GHz Grid

We demonstrate the transmission of a 100G superchannel, composed of 4 × 28-Gb/s duobinary subcarriers placed on a 25-GHz grid, over 580 km of SSMF with three 25-GHz reconfigurable add-drop multiplexer nodes. The directdetect 100G superchannel has moderate optical signal to noise ratio requirements and significant tolerance to the different optical impairments. The robustness, low-power consumption, cost effectiveness, and spectral efficiency of this 100G system makes it a very strong candidate for today's datacenterand metro-networks.

Analysis of reconfigurable multi-channel wavelength add drop multiplexer for intelligent optical networks

This paper presents design of an electro-optically tunable polymer multi-channel wavelength add drop multiplexer (WADM). The proposed WADM with trapezoidal waveguide geometry and poled electro-optical polymer material in the waveguide cores enables the wavelength tuning speed of WADM as 7.5 ps at the resonance wavelength of 1550 nm and coupling length of 1.5 mm. The device can be electro-optically tuned to add/drop multiple channels. Transmission spectra of the device with varying device parameters are simulated. The proposed WADM with high speed, small size and varying tuning capability makes this device, an important element in faster provisioning and routing of light paths in intelligent optical network.

Modeling WDM Wavelength Switching Systems for Use in GMPLS and Automated Path Computation

Network control planes have made an implicit assumption that the switching devices in a network are symmetric. In wavelength-switched optical networks even the most basic switching element, the reconfigurable add-drop multiplexer, is highly asymmetric. This paper presents a model of optical switching subsystems for use in generalized multiprotocol label switching (GMPLS), route selection, and wavelength assignment. The model covers a large class of switching subsystems without internal wavelength converters. The model is applied to a number of common optical technologies, and a compact encoding for use in the optical control plane is furnished along with a method for deriving a simplified graph representation.

Fabrication of (Pb,La)(Zr,Ti)O3 thin-film arrayed waveguide grating

The design and fabrication of an 8-ch, 500 GHz-spacing arrayed waveguide grating on (Pb,La)(Zr,Ti)O3 has been successfully achieved for the first time. An insertion loss of 22.1 dB, including a 10 dB coupling loss, and an adjacent crosstalk of −23.1 dB have been obtained. The device is expected to be monolithically integrated into high-speed optical switches to form integrated chips such as a reconfigurable add-drop multiplexer.

Design tools for transparent optical networks

Optical technology promises to revolutionize data networking by providing enormous bandwidth for data transport at minimal cost. A key to cost reduction is to increase transparency, that is, to keep a data stream encoded as an optical signal for as long as possible. Wavelength switching increases transparency by allowing different data streams, each encoded in a different wavelength of light, to be independently routed through an optical network. We discuss Bell Labs-developed software tools that help design wavelength-switched optical networks. The software tools simultaneously minimize the cost of the designed network, reduce the time and cost to perform the design, and ensure compliance with engineering constraints. The tools span three levels of abstraction, from routing and reconfigurable add/drop multiplexer (ROADM) choice, to span engineering, to power dynamics simulation. Each level represents a different tradeoff between design scope and level of detail. For each class of tool, we briefly describe design philosophy, algorithms, performance, and resulting value for Lucent's customers.

On the reconfigurability of single-hub WDM ring networks

We study the benefit of reconfigurability for wavelength division multiplexed (WDM) ring networks with dynamic single-hubbed traffic. We show that the ability to reconfigure wavelength add-drop multiplexers helps to reduce the number of expensive line terminating equipment (LTEs) by a factor of W, where W is the number of wavelengths in the network. In addition, we show that for a general class of traffic, optical networks using reconfigurable wavelength add-drop multiplexers guarantee to be almost as bandwidth efficient as full wavelength add-drop networks, that is, opaque networks. For such traffic, we introduce several fast algorithms that achieve or approximate the optimal performance guarantees. The comparison between reconfigurable networks and opaque networks is quantified using a performance metric called capacity ratio, which captures the relative throughput performance of a reconfigurable network compared to the opaque network.

Partially reconfigurable optical add-drop multiplexers for dense WDM networks

We propose a new partially reconfigurable add-drop multiplexer (OADM) that allows dropping several fixed wavelength channels and at least one tunable wavelength channel. It consists of fixed and tunable fiber Bragg gratings (FBGs) and optical circulators (OCs). By properly assigning wavelengths to signals that are added/dropped at an OADM node, the requirement for tuning range of tunable FBGs could be made as small as the wavelength spacing of dense WDM channels. The proposed OADM has potentially low insertion loss for through-channels compared with other tunable OADMs. Operation and performance of this OADM are experimentally investigated.

High-performance operation of monolithically-integrated multipurpose reconfigurable optical add-drop multiplexer

WDM operation of a novel monolithically-integrated 16-channel reconfigurable add-drop multiplexer (ROADM), demonstrating high crosstalk suppression and cascadability to eight nodes for 10 Gbit/s NRZ signals, is reported. The device provides separate wavelength add/drop ports and a common wavelength-multiplexed add/drop port for high system functionality.

Bidirectional grating wavelength shifter with a broad-range tunability by using a beam of uniform strength

Bidirectional chirp-free tuning in Bragg reflection wavelength by as much as 12.52 mm has been achieved based on the principle of a beam of uniform strength. The experimental results are in good agreement with the theoretical analysis. The tuning device is simple in configuration, low cost, and easy to operate, which can be used in numerous applications, such as tunable fiber grating lasers and reconfigurable wavelength add-drop multiplexers, etc.

Reconfigurable multichannel add-drop multiplexer with improved performance

Reconfigurable multichannel add-drop multiplexers (RM-ADMs) may become key components in large-capacity interoffice WDM ring networks. The authors propose a new RM-ADM which is simpler, has lower insertion loss, and has better crosstalk performance than existing structures.