Large Port Count Optical Switches Research Articles

Optical switching will innovate intra data center networks [Invited Tutorial

Reflecting the recent slow-down in Moore’s law and the proliferation of artificial intelligence/machine learning workloads, the performance and energy consumption of networks are becoming barriers in high-performance computing (HPC) and data centers. Optical switches are expected to break these barriers, and indeed their introduction has recently commenced in data centers. This paper discusses how optical switching technologies can innovate future intra data center networks. Hyperscale data centers are much bigger in scale, and network requirements are slightly different from those of HPC. This paper focus on data center networks, since the impact of optical technologies will be more significant in data centers than in HPC. In addition to the scale issue, important metrics to be considered for network design are traffic characteristics and latency, both of which are highlighted in this paper. For hybrid (electrical packet and optical circuit) switching networks, the target latency for the optical circuit switch network (connection setup/teardown time) is shown to be around 10 µs, and the needed technologies are clarified and verified by experiments. The optical switch can simplify the present multi-tier switching network above tier-1 switches into a single tier configuration, which is possible with the development of efficient large port count optical switches. Among the different switching architectures, combining the different dimensions of space and wavelength is shown to be one of the best solutions. Fast switching needs fast device response time. Si photonics devices using Mach–Zehnder interferometers or ring-resonator-based switches and tunable filters are the most promising candidates; they offer cost-effective mass-production and fast operation and so are excellent candidates for the optical switches envisaged. Another critical technology to maximize the benefits of optical switches is a simple and low-latency control mechanism. Different approaches have been suggested as summarized in this work. Among them, harnessing optical switch parallelism is a unique technique that matches recent advances in electrical switch chips. A fast control network is realized by using a fully decentralized and asynchronous control mechanism. A hyperscale data center offers a wide variety of services, and no one system fits all needs. Optimization of parameters is an important task for maximizing the impact of optical switching in different kinds of data centers.

Bi-Directional Benes With Large Port-Counts and Low Waveguide Crossings for Optical Network-on-Chip

We propose a new variant of the Benes network using a merge-replace-fold approach. It is to realize a large port-count optical switch with low waveguide crossings. A bidirectional switch is built instead of a unidirectional switch. Compared to the classical Benes, it requires the same number of switches but far fewer intersections. The novel designs enable a 24-percentage reduction in waveguide intersections. Moreover, it has a worst-case insertion loss of 12.01 dB and a comparable crosstalk level of −13.67 dB between the neighbouring paths. Thus, it offers an energy-efficient way to solve the optical on-chip design problem in a bidirectional manner.

Realization and Application of Large-Scale Fast Optical Circuit Switch for Data Center Networking

Applying optical switching to data center networks can greatly expand network bandwidth and reduce electrical power consumption, both of which are needed to meet the explosive traffic increase. The optical switch offers large bandwidth switching capability, and so eliminates the multistage switch network architecture needed with electrical switching. Furthermore, the single stage architecture of the optical switch greatly simplifies operating costs, which include cabling, while substantially reducing the number of transponders needed. Data center networks place very different demands on optical systems than communication networks. Grasping the right direction to proceed is of paramount importance. To realize the full potential of optical switches, such as scalability and cost effectiveness, we analyze the role of large-scale optical circuit switches and discuss the realization technologies that combine the two dimensions of space and wavelength. Our recent advances in large port-count optical switches are presented.

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.

Scalable, Low-Energy Hybrid Photonic Space Switch

A scalable monolithically integrated photonic space switch is proposed which uses a combination of Mach-Zehnder modulators and semiconductor optical amplifiers (SOAs) for improved crosstalk performance and reduced switch loss. This architecture enables the design of high-capacity, high-speed, large-port count, low-energy switches. Extremely low crosstalk of better than -50 dB can be achieved using a 2 × 2 dilated hybrid switch module. A “building block” approach is applied to make large port count optical switches possible. Detailed physical layer multiwavelength simulations are used to investigate the viability of a 64 × 64 port switch. Optical signal degradation is estimated as a function of switch size and waveguide induced crosstalk. A comparison between hybrid and SOA switching fabrics highlights the power-efficient, high-performance nature of the hybrid switch design, which consumes less than one-third of the energy of an equivalent SOA-based switch. The significantly reduced impairments resulting from this switch design enable scaling of the port count, compared to conventional SOA-based switches.

Large Port Count High-Speed Optical Switch Fabric for Use Within Datacenters [Invited

This paper reviews advances in the technology of integrated semiconductor optical amplifier based photonic switch fabrics, with particular emphasis on their suitability for high performance network switches for use within a datacenter. The key requirements for large port count optical switch fabrics are addressed noting the need for switches with substantial port counts. The design options for a 16 × 16 port photonic switch fabric architecture are discussed and the choice of a Clos–tree design is described. The control strategy, based on arbitration and scheduling, for an integrated switch fabric is explained. The detailed design and fabrication of the switch is followed by experimental characterization, showing net optical gain and operation at 10 Gb/s with bit error rates lower than 10−9. Finally improvements to the switch are suggested, which should result in 100 Gb/s per port operation at energy efficiencies of 3 pJ/bit.

Physical-parameter design in 2-D MEMS optical switches

Free-space micromachined optical switching technology has emerged as a promising candidate for the transparent optical cross connects that are needed in next-generation optical transport networks. This paper deals with the system design of two-dimensional (2-D) microelectromechanical system (MEMS)-based cross connects. In particular, we propose a method, applicable to any kind of 2-D MEMS switching architectures, which finds the best choices of the basic geometrical parameters of the device (such as mirror radius and beam-waist size) allowing the achievement of given insertion-loss and differential-loss target values for the overall switching matrix. Our proposal is based on a widely used model of the loss mechanisms in a 2-D MEMS switch, keeping Gaussian-beam divergence and free-space/fiber mode mismatching into account. By adopting the proposed design technique, we compare various 2-D MEMS architectures recently proposed in the technical literature in terms of cost and feasibility of large port count optical switches.

Design and nonlinear servo control of MEMS mirrors and their performance in a large port-count optical switch

In this paper, we demonstrate full closed-loop control of electrostatically actuated double-gimbaled MEMS mirrors and use them in an optical cross-connect. We show switching times of less than 10 ms and optical power stability of better than 0.2 dB. The mirrors, made from 10-/spl mu/m-thick single-crystal silicon and with a radius of 400-450 /spl mu/m, are able to tilt to 8/spl deg/ corresponding to 80% of touchdown angle. This is achieved using a nonlinear closed-loop control algorithm, which also results in a maximum actuation voltage of 85 V, and a pointing accuracy of less than 150 /spl mu/rad. This paper will describe the MEMS mirror and actuator design, modeling, servo design, and measurement results.