Wavelength Routing Switching Research Articles

Design and evaluation of a reconfigurable optical add-drop multiplexer with flexible wave-band routing in SDM networks

Space-division multiplexing (SDM) is expected to increase the capacity of photonic networks. Reconfigurable optical add-drop multiplexers (ROADMs) for SDM-based networks must have high scalability in terms of port count. However, the ROADM architecture adopted in present networks cannot support large numbers of ports due to the limited port count of wavelength-selective switches. In this paper, we propose a ROADM architecture composed of space switches and wavelength-routing switches. Space switches have lower per-port cost than wavelength-routing switches. However, space switches cannot route optical paths on a wavelength basis, unlike wavelength-routing switches. By combining these two types of switches, the ROADM port count can be cost-effectively expanded virtually unlimitedly. Numerical simulations show the routing performance of our ROADM; they elucidate that the maximum fiber increment penalty is about 5% compared to the reference scheme. Experiments detail the transmission performance of the ROADM, where 32 Gbaud DP-4QAM/8QAM/16QAM signals are aligned on a 50 GHz grid, are examined.

Design and Evaluation of Optical Circuit Switches for Intra-Datacenter Networking

With the rapid growth in intra-datacenter traffic, the high power consumption stemming from the huge number of electrical switches is becoming a critical issue. Hence, high-port-count optical circuit switches are urgently needed. In this paper, we overview recently developed optical circuit switch architecture based on two-dimensional switches, i.e., space switches and wavelength-routing switches. The attainable maximum switch port counts and hardware requirements are quantitatively evaluated through extensive computer simulations that consider 10-Gbps intensity modulation with direct detection systems, 43-Gbps differential quadrature phase-shift keying with self-coherent detection systems, and 128-Gbps dual-polarization quadrature phase-shift keying with coherent detection systems. The simulation results confirm the existence of switching architecture that can accommodate more than 1,000 ports with relatively light hardware requirements.

On-chip cyclic-AWG-based 12 × 12 silicon wavelength routing switches with minimized port-to-port insertion loss fluctuation

With the rapidly increasing bandwidth requirements of optical communication networks, compact and low-cost large-scale optical switches become necessary. Silicon photonics is a promising technology due to its small footprint, cost competitiveness, and high bandwidth density. In this paper, we demonstrate a 12×12 silicon wavelength routing switch employing cascaded arrayed waveguide gratings (AWGs) connected by a silicon waveguide interconnection network on a single chip. We optimize the connecting strategy of the crossing structure to reduce the switch’s footprint. We develop an algorithm based on minimum standard deviation to minimize the port-to-port insertion loss (IL) fluctuation of the switch globally. The simulated port-to-port IL fluctuation decreases by about 3 dB compared with that of the conventional one. The average measured port-to-port IL is 13.03 dB, with a standard deviation of 0.78 dB and a fluctuation of 2.39 dB. The device can be used for wide applications in core networks and data centers.

Multicast-Enabling Optical Switch Design Employing Si Buffering and Routing Elements

We demonstrate experimentally an optical switch architecture that employs $\mu \text{m}$ -silicon-on-insulator (SOI)-based circuitry for both buffering and routing purposes and operates with 10-Gb/s optical packets in both uni- and multi-cast switching forwarding modes. It comprises a hybrid broadcast-and-select (BS)/wavelength-routed architecture, with the BS layout being responsible for identifying the desired cluster of outgoing ports, while the wavelength-routed switch part forwards then the data to the specific outgoing port. Contention resolution at the BS switch part is offered through an $\mu \text{m}$ -SOI integrated optical delay line bank and wavelength-routing is realized by means of a $\mu \text{m}$ -SOI $3\times 3$ echelle grating router, while semiconductor optical amplifier Mach-Zehnder interferometers are employed for wavelength conversion purposes. The switch architecture has been experimentally validated with 10-Gb/s optical data packets for both uni- and multicasting operation, revealing error-free performance with <5-dB power penalty.

Large-Scale Optical Switch Utilizing Multistage Cyclic Arrayed-Waveguide Gratings for Intra-Datacenter Interconnection

We develop a design method for creating a large-scale optical switch consisting of two sub-switch parts, i.e., delivery-and-coupling switches and wavelength-routing switches based on cyclic arrayed-waveguide gratings, where the available optical-power budget is optimally allocated to the two sub-switches to maximize the entire switch scale. The power budget necessary for each sub-switch is quantitatively evaluated via extensive computer simulations. The simulation results show that a 1000 × 1000 switch scale can be realized when the available optical-power budget is 23 dB. The simulation results are verified via proof-of-concept experiments.

Application of artificial neural networks for optimal design of OADM for DWDM applications

For greater flexibility and connectivity, optical add/drop multiplexers (OADMs) with wavelength routing devices and switches play a crucial role in DWDM optical networks. OADM can act as access node (AN) in any DWDM network. They can add or drop signals as per our requirement. A DWDM system is modeled using different number of channels, data rates and spacing between channels in terms of bit error rate (BER), optical signal to noise ratio (OSNR), Jitter and Dispersion. These parameters are then optimized and classification of signals analyzed by using Artificial Neural Networks. Comparison was performed between FBG/OADM and OFDM in respect of transmitted and received signal powers.

Large-Scale Optical-Switch Prototypes Utilizing Cyclic Arrayed-Waveguide Gratings for Datacenters

We propose novel large-scale optical-switch architectures that utilize delivery and coupling (DC) switches and wavelength routing (WR) switches based on the cyclic arrayed-waveguide gratings (AWGs). To suppress the passband-frequency deviation inherent in cyclic AWGs, we propose two-stage WR structures in which multiple small-scale cyclic AWGs are cascaded to create a large-scale WR switch. We introduce two configurations for constructing a WR switch; the degrees of the first- and second-stage cyclic AWGs are coprime or not. We fabricate both types of optical switches with planar lightwave circuit technologies. A 270 × 270 switch comprised of coprime cyclic AWGs and a 180 × 180 switch comprised of cyclic AWGs whose degrees have a common divisor are compactly fabricated. Transmission experiments confirm their excellent performance.

Low-loss wavelength routing optical switch consisting of small matrix switch and cyclic arrayed-waveguide gratings for colorless add/drop

We describe a new wavelength routing switch architecture that uses matrix switches and cyclic arrayed-waveguide gratings (AWGs). By devising connections between them, we construct a large port count optical switch using small port count matrix switches and AWGs. An 80 × 8 switch that consists of 8 × 8 matrix switches and 10 × 1 cyclic AWGs exhibits an insertion loss of only 4–7 dB. This switch enables us to make add/drop ports colorless in the existing reconfigurable optical add/drop multiplexer nodes.

A large-scale wavelength routing optical switch for data center networks

Intra-data-center traffic is estimated to be about four times global Internet traffic and is continuously increasing. Applying optical switching to data center networks will increase network bandwidth and reduce power consumption while meeting the traffic requirements. One of the major attributes of the optical switch must be scalability. The wavelength routing switch is a promising technology for the development of 1000 × 1000 scale large port count optical switches. Recent advances are demonstrated.

Monolithically Integrated Wavelength-Routing Switch Using Tunable Wavelength Converters with Double-Ring-Resonator Tunable Lasers

We present an 8×8 wavelength-routing switch (WRS) that monolithically integrates tunable wavelength converters (TWCs) and an 8×8 arrayed-waveguide grating. The TWC consists of a double-ring-resonator tunable laser (DRR TL) allowing rapid and stable switching and a semiconductor-optical-amplifier-based optical gate. Two different types of dry-etched mirrors form the laser cavity of the DRR TL, which enable integration of the optical components of the WRS on a single chip. The monolithic WRS performed 1×8 high-speed wavelength routing of a non-return-to-zero signal at 10Gbit/s. The switching operation was demonstrated by simultaneously using two adjacent TWCs.

A Wavelength-Routed Multicast Packet Switch With a Shared-FDL Buffer

In this paper, we propose a wavelength-routed multicast packet switch using a set of fiber delay lines as a shared buffer for both unicast and multicast packets. To avoid multicast packet contention, a multicast packet could be replicated in multiple timeslots by means of multi-wavelength conversion in conjunction with the shared-FDL buffer. Moreover, a packet scheduling technique is designed to assist the operation of the newly proposed switch. We investigate the traffic performance and the complexity in terms of component counts of the newly proposed switch in comparison with our previously reported multicast switch and the broadcast-and-select switch by simulation. Performance evaluation shows that the proposed switch with assistance of the packet scheduling technique can effectively avoid the performance deterioration caused by the increase of multicast traffic, leading to a much better performance than our previously reported multicast switch. In addition, the results show that the proposed switch exhibits an efficient and cost-effective configuration for packet multicasting over other switch architectures.

All-Optical Packet Switching and Label Rewriting for Data Packets Beyond 160 Gb/s

In this paper, two different paradigms to realize a scalable all-optical packet switch with label swapping will be reviewed. The two paradigms are based on wavelength routing switch and space routing switch. All the functions required for switching the packets, namely, the label processor, the label rewriter, and the optical switch, are based on all-optical signal processing with no electronic control. This allows for very fast processing time and potential photonic integration of the systems. We report, for both techniques, experimental results showing the routing operation of the 160-Gb/s packets and beyond. We will discuss and compare both techniques in terms of devices and bit-rate scalability, power consumption, power penalty performance, and cascadability as key parameters for the realization of an all-optical packet switch.

All-optical wavelength-routing switch with monolithically integrated filter-free tunable wavelength converters and an AWG

We present a compact 4x8 wavelength-routing switch that monolithically integrates fast tunable wavelength converters (TWCs) and an arrayed-waveguide grating (AWG) for optical packet switching. The TWC consists of a double-ring-resonator-coupled tunable laser which allows rapid and stable switching, and an optical gate based on a parallel amplifier structure which prevents an input optical signal from being routed through the AWG (filter-free operation). A deep-ridge waveguide technology, employed for the AWG and ring resonators, facilitates the fabrication of the switch and makes the device compact. The filter-free TWCs achieve low crosstalk of the input optical signal of less than -22 dB. The wavelength routing operation of a non-return-to-zero (NRZ) signal at 10 Gbit/s is achieved with a switching time of less than 5 ns.

Wavelength-Routed Optical Multicast Packet Switch With Improved Performance

Optical packet switch with multicast capability enables a broad range of applications in next generation optical networks. In this paper, we propose a cost-effective scheme to enhance the traffic performance of our earlier reported optical wavelength-routed multicast packet switch by modifying rather than adding multicast modules in the switch. A packet scheduling technique is introduced to substantially reduce the output contention for the switch. The effectiveness of our proposed scheme in conjunction with the scheduling technique is analyzed and validated by evaluation of packet loss performance of the modified multicast packet switch through simulations. The simulation results show that the multicast packet loss probability of the modified multicast switch can be significantly reduced without increasing the number of multicast modules by our proposed scheme. This means that to achieve an acceptable level of the multicast packet loss probability, the modified multicast switch requires fewer multicast modules in comparison with our earlier reported switch.

Semiconductor Double-Ring-Resonator-Coupled Tunable Laser for Wavelength Routing

A monolithic widely tunable semiconductor laser based on a double-ring resonator is developed for use in a wavelength-routing switch. By using the double-ring resonator as a wavelength-selective filter, operation over a wide wavelength tuning range is achieved with a low tuning current. This low-tuning-current operation makes the laser very promising as a high-speed tunable light source for a wavelength-routing-based switch by effectively suppressing the thermal wavelength drift induced by current injection. In addition, the laser fabrication process is simpler compared to conventional distributed Bragg reflector tunable lasers. A tuning range of 50.0 nm, covering the entire C-band, is successfully demonstrated with an injection current of less than 5.2 mA. The wavelength drift caused by the thermal transients is less than 5 GHz.

An Optical Wavelength-Routed Multicast Packet Switch Based on Multitimeslot Multiwavelength Conversion

This letter presents a new scheme to realize multicast operation in a wavelength-routed optical packet switch by adding multicast modules. The proposed multicasting scheme is based on multitimeslot multiwavelength conversion in conjunction with wavelength selection to resolve the problem of output contention.

Parallel desynchronized block matching: A feasible scheduling algorithm for the input-buffered wavelength-routed switch

The input-buffered wavelength-routed (IBWR) switch is a promising switching architecture for slotted optical packet switching (OPS) networks. The benefits of the IBWR fabric are a better scalability and lower hardware cost, when compared to output buffered OPS proposals. A previous work characterized the scheduling problem of this architecture as a type of matching problem in bipartite graphs. This characterization establishes an interesting relation between the IBWR scheduling and the scheduling of electronic virtual output queuing switches. In this paper, this relation is further explored, for the design of feasible IBWR scheduling algorithms, in terms of hardware implementation and execution time. As a result, the parallel desynchronized block matching (PDBM) algorithm is proposed. The evaluation results presented reveal that IBWR switch performance using the PDBM algorithm is close to the performance bound given by OPS output buffered architectures. The performance gap is especially small for dense wavelength division multiplexing (DWDM) architectures.

G+: Enhanced Traffic Grooming in WDM Mesh Networks using Lighttours

In this article, a new technique for grooming low-speed traffic demands into high-speed optical routes is proposed. This enhancement allows a transparent wavelength-routing switch (WRS) to aggregate traffic en route over existing optical routes without incurring expensive optical-electrical-optical (OEO) conversions. This implies that: a) an optical route may be considered as having more than one ingress node (all inline) and, b) traffic demands can partially use optical routes to reach their destination. The proposed optical routes are named "lighttours" since the traffic originating from different sources can be forwarded together in a single optical route, i.e., as taking a "tour" over different sources towards the same destination. The possibility of creating lighttours is the consequence of a novel WRS architecture proposed in this article, named "enhanced grooming" (G <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ). The ability to groom more traffic in the middle of a lighttour is achieved with the support of a simple optical device named lambda-monitor (previously introduced in the RingO project). In this article, we present the new WRS architecture and its advantages. To compare the advantages of lighttours with respect to classical lightpaths, an integer linear programming (ILP) model is proposed for the well-known multilayer problem: traffic grooming, routing and wavelength assignment The ILP model may be used for several objectives. However, this article focuses on two objectives: maximizing the network throughput, and minimizing the number of optical-electro-optical conversions used. Experiments show that G <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> can route all the traffic using only half of the total OEO conversions needed by classical grooming. An heuristic is also proposed, aiming at achieving near optimal results in polynomial time

Optical Packet and Burst Switching Technologies for the Future Photonic Internet

This paper reviews advanced optical burst switching (OBS) and optical packet switching (OPS) technologies and discusses their roles in the future photonic Internet. Discussions include optoelectronic and optical systems technologies as well as systems integration into viable network elements (OBS and OPS routers). Optical label switching (OLS) offers a unified multiple-service platform with effective and agile utilization of the available optical bandwidth in support of voice, data, and multimedia services on the Internet Protocol. In particular, OLS routers with wavelength routing switching fabrics and parallel optical labeling allow forwarding of asynchronously arriving variable-length packets, bursts, and circuits. By exploiting contention resolution in wavelength, time, and space domains, the OLS routers can achieve high throughput without resorting to a store-and-forward method associated with large buffer requirements. Testbed demonstrations employing OLS edge routers show high-performance networking in support of multimedia and data communications applications over the photonic Internet with optical packets and bursts switched directly at the optical layer

Optical networks research at UCL

New dynamic optical switching technologies and adaptive transmission techniques will allow increased capacity and flexibility in future core and metro networks. The Optical Networks Group at UCL has carried out research focused on these areas, in collaboration with industry and other university research groups, for over a decade. In this paper, the technical challenges to be overcome in implementing dynamic, high-capacity networks are discussed, and recent results of the group's work are presented. New network architectures based on wavelength-routing and optical burst switching have been proposed and analysed, and the experimental demonstration of burst switching using fast wavelength-tunable lasers is described. High-capacity dense wavelength division multiplexed transmission systems, using advanced regeneration and equalisation techniques, have been studied, both theoretically, and experimentally using a dynamically reconfigurable recirculating fibre loop. Research results on advanced optical signal formats, all-optical 3R regeneration at 40 Gbit/s channel rates, adaptive analogue and digital electronic processing techniques and optical finite impulse response equalisation are presented. Finally, the development of optical performance monitoring technology, a key component of future all-optical networks, is described. The paper concludes with a prediction of future trends in optical communications research.