Optical Switch Matrix Research Articles

Large‐Scale High‐Density Multimode Optical Switch Matrix

AbstractOptical switching technology is emerging as a solution to the limitations of traditional electronic switching. Combining optical switching with mode‐division multiplexing effectively overcomes the limitations of expanding switching capacity solely by increasing the number of ports. This paper introduces a compact four‐mode 2 × 2 optical switch and a four‐mode reconfigurable non‐blocking 4 × 4 optical switch matrix based on the Beneš architecture. The multimode 2 × 2 switch achieves an extinction ratio larger than 15 dB for all modes in the wavelength range of 1530–1590 nm. The multimode 4 × 4 switch matrix has an extinction ratio exceeding 9 dB for all modes and states in the C‐band, with a compact size (1.46 × 0.23 mm2) and low power consumption (0–154 mW). It supports high‐integrity 50 Gbaud PAM4 signal transmission with a bit error rate below the forward error correction limit. These devices pave the way for enhanced integration density and capacity in optical switching systems.

Flexible waveband routing node architecture for spatial-division and multi-band optical networks [Invited

We propose a network architecture named flexible waveband routing (FWR) that adopts flexible path bundling and bundled path routing. This two-stage routing scheme can be implemented by a combination of small degree wavelength selective switches (WSSs) and optical matrix switches. As the optical-cross-connect (OXC) scale depends on just that of the matrix switches adopted, large-scale OXC nodes are realized by introducing recently developed high-port-count switches. FWR supports spatial division multiplexing efficiently through its introduction of spatially joint switching at WSSs. Multi-band transmission can also be supported by the use of WSSs handling different frequency bands. Numerical simulations and transmission experiments confirm its validity.

Disaggregated optical-layer switching for optically composable disaggregated computing [Invited

Disaggregated computing has been widely investigated to support the continuous progress in computing performance and overcome the slowdown of Moore’s law. It involves a flexible and optimal interconnection of heterogeneous compute nodes, such as the CPU, GPU, xPU, memory, and storage, to offer an efficient computing environment for various applications. Such a scheme inherently requires high network performance, including low latency, high capacity, determinism, and energy efficiency, all of which are simultaneously achieved through the introduction of optical-layer switching. This paper presents the application of optical-layer-switching architectures to disaggregated computing. Networks associated with disaggregated computing are classified into intra- and interserver networks. Focusing on the intraserver network, a holistic concept of optically composable disaggregated computing (OCDC) is discussed, along with its technological direction toward future digital infrastructure (i.e., the computing continuum). To realize OCDC, scalable and flexible optical switch technologies, as well as their dynamic and automatic control and management mechanisms, are indispensable. Previous studies have reported 32 × 32 silicon photonic switches that can form a nine-stage Clos topology with a radix of 131,072 and a machine-processable function description model for optical-layer switching, called the functional block-based disaggregation model (FBD model) that is capable of automating the operation, administration, and management of any optical physical topology in cooperation with upper-layer operating systems. This study examines their applicability to OCDC. The superior energy performance and scaling of an OCDC system equipped with optical matrix switches, such as silicon photonic switches, with respect to the conventional one big electrical packet-switching approach based on the reported wall-plug power consumption is also presented. The potential applicability of the FBD model as an essential control and management system for the optical layer of OCDC is evaluated through numerical experiments.

High-speed optical sampling system combined with cavity-less pulse source

High-speed optical sampling can overcome the limitation faced by electronic systems, such as bandwidth and precision. In this work, a 4-fold optical sampling time-parallelization is combined with a cavity-less 10GHz pulse source. The 4-fold sampling time-parallelization is based on a 1x4 optical switching matrix. Three dual-outputs Mach-Zehnder modulators (D-MZM) in cascaded configuration are included. Instead of a 10GHz repetition mode-locked laser (MLL), a cavity-less 10GHz pulse source is designed and used to provide the 10GHz modulated pulse as used in the switching matrix, which consists of a Mach-Zehnder amplitude modulator (MZM), a phase modulator (PM) and a highly dispersive optical fiber. We demonstrate a 4-fold sample time-parallelization with a high repetition rate up to 10GHz and 2.5GHz per channel, also with a signal-to-noise ratio (SNR) of 30dB, and combined with a 10GHz cavity-less pulse source with a pulsewidth of 9ps, which can be used into the advancements in radar and telecommunication systems.

Efficient layout-aware statistical analysis for photonic integrated circuits.

Fabrication variability significantly impacts the performance of photonic integrated circuits (PICs), which makes it crucial to quantify the impact of fabrication variations before the final fabrication. Such analysis enables circuit and system designers to optimize their designs to be more robust and obtain maximum yield when designing for manufacturing. This work presents a simulation methodology, Reduced Spatial Correlation Matrix-based Monte-Carlo (RSCM-MC), to efficiently study the impact of spatially correlated fabrication variations on the performance of PICs. First, a simple and reliable method to extract physical correlation lengths, variability parameters that define the inverse of the spatial frequencies of width and height variations over a wafer, is presented. Then, the process of generating correlated variations for MC simulations using RSCM-MC methodology is presented. The methodology generates correlated variations by first creating a reduced correlation matrix containing spatial correlations between all the circuit components, and then processing it using Cholesky decomposition to obtain correlated variations for all circuit components. These variations are then used to conduct MC simulations. The accuracy and the computation performance of the proposed methodology are compared with other layout-dependent Monte-Carlo simulation methodologies, such as Virtual wafer-based Monte-Carlo (VW-MC). A Mach-Zehnder lattice filter is used to study the accuracy, and a second-order Mach-Zehnder filter and a 16x16 optical switch matrix system are used to compare the computational performance.

Spatial Channel Cross-Connect Architectures for Spatial Channel Networks

A spatial channel network (SCN) is a novel optical network architecture targeting the space division multiplexing (SDM) era where the optical layer is explicitly evolved into the hierarchical SDM layer and wavelength division multiplexing layer, and an optical node is decoupled into a spatial channel cross-connect (SXC) and a wavelength cross-connect to form a hierarchical optical cross-connect. In this article, we discuss a wide variety of SXC architectures based on optical matrix switches (MSs) and newly proposed core selective switches (CSSs) from the viewpoints of connection flexibility and architectural complexity. After briefly reviewing the architecture and functionalities of an SCN and its building-block optical devices, novel SXC architectures based on sub-MSs and CSSs are described and formulas are derived for each SXC architecture that give the required number of optical devices, switching mirrors, and internal fiber connections. Based on the formulations, these architectures are compared with traditional SXC architectures based on a high-port count full-MS pair and a Clos network from the viewpoints of the freedom of connection functionalities, operational benefits, and potential node costs associated with the architectural complexity in order to obtain insights regarding which network application is suited to each SXC architecture.

Fast Polarization-Insensitive Optical Switch Based on Hybrid Silicon and Lithium Niobate Platform

We propose and demonstrate a polarization-insensitive and high speed optical switch unit based on a silicon and lithium niobate hybrid integration platform. The presented device exhibits a sub nano-second switching time, low drive voltages of 4.97 V, and low power dissipation due to electrostatic operation. The measured polarization dependence loss was lower than 0.8 dB. The demonstrated optical switch could provide as a building block for polarization-insensitive and high-speed optical matrix switches.

Silicon nitride based polarization-independent 4 × 4 optical matrix switch

A polarization-independent 4 × 4 optical matrix switch based on a 580-nm-thick silicon nitride platform is designed and experimentally demonstrated. The switch is composed of four 2 × 2 Mach-Zehnder interferometers, with each integrated with a pair of Ti/Pt resistive micro-heaters. Polarization-independent performance can be realized with the power consumption for a single switching operation of less than 130 mW. The measured rise/fall time of the switch upon electrical tuning is about 24.5/30.5 μs, corresponding to a maximum switching speed of about 20 kHz. The insertion loss is about 7.2 dB for transverse electric light or 5.7 dB for transverse magnetic wave, with a polarization dependent loss of about 0.65 dB. The device performance can be further optimized and even large-scale silicon nitride polarization-insensitive electro-optical matrix switches can be expected for future optical communication applications.

Low-loss broadband 5 × 5 non-blocking Si3N4 optical switch matrix

An integrated 5×5 non-blocking optical switch matrix is proposed and experimentally demonstrated based on the silicon nitride (Si3N4) platform. The proposed optical switch matrix is designed with the Spanke–Benes architecture having 10 balanced Mach–Zehnder interferometers, each of which operates as a 2×2 switching unit enabled by an on-chip thermo-optic phase shifter. Over an 80 nm bandwidth (from 1520 to 1600 nm), the optical switch matrix is characterized with intriguing specifications, including the average extinction ratio larger than 25 dB, the excess loss less than 5 dB for both “all-cross” and “all-bar” states, and the leaked power lower than −48 dB. To the best of our knowledge, this is the first non-blocking optical switch matrix based on a Si3N4 platform with leading comprehensive performance in extinction ratio, excess loss, leaked power, and bandwidth. It will provide enabling building blocks for massive switch networks of optical communications and microwave photonics.

Fluorinated photopolymer cascaded MMI-based integrated optical waveguide switching matrix with encoding functions.

In this work, thermo-optic tunable 4 × 4 cascaded multimode interference based integrated optical waveguide switching matrices are designed and fabricated using photopolymer lightwave circuits. The materials of the waveguide core and cladding are fluorinated epoxy-terminated copolycarbonate and polymethylmethacrylate, respectively. The driving power that controls matrices for binary encoding of different optical switching states are simulated and analyzed. The measured insertion loss of the actual chip is < 7.1 dB and the maximum crosstalk in adjacent channels is <-30 dB. The switching time is approximately 220 μs and the extinction ratio is obtained as 21.5 dB. This flexible encoding technique can be applied for achieving optical code-division multiple-access network coders.

Reivew of silicon photonic switches

Silicon photonic switch is recognized as a cost-effective optical switching technology because it has many applications in long-haul telecommunication networks, short-reach data center and high-performance computing. In this paper, the research progress of various silicon photonic switch technologies is reviewed systematically. Firstly, the principles of three kinds of switch technologies including Mach-Zehnder interferometer (thermo-optic and carrier-injection types), micro-ring resonator (thermo-optic and carrier-injection types) and micro-electro-mechanical-system actuated waveguide coupler (electrostatic actuated type) are introduced. The switch technologies with the state-of-the-art insertion loss, crosstalk, switch time, footprint and power consumption are summarized and compared. Then the recent demonstrations of large-port silicon photonic matrix based on the above switch technologies are discussed. In this paper, we also investigate the key technologies such as topological architecture, passive components and optoelectronic packaging, which affect the performance of large-port optical switch matrix. Specifically, we study the scalability of various topologies, low-loss/broadband waveguide components, high-density optical/electrical packaging and control interface to improve the overall performance of the silicon photonic switch matrix. Finally, we discuss the critical technical challenges that might hamper the commercialization of silicon photonic switches and envision their future.

Silicon photonic microelectromechanical switch using lateral adiabatic waveguide couplers.

A silicon photonic waveguide switch using adiabatic couplers with lateral comb-drive actuators is designed, fabricated, and tested for microelectromechanical optical matrix switch. One of the waveguides of the adiabatic coupler is moved laterally by three actuators for varying the coupler gap, which enables to switch the path of the waveguides. The coupler waveguides with 250 nm thickness consist of a movable tapered waveguide from 400 nm to 500 nm in width and 50 μm in length and a straight waveguide of 400 nm in width. The three actuators are ultra-small electrostatic comb-drive and move the two movable tapered waveguides. The switch's transmission characteristics were measured as a function of the coupler gap. Around a coupler gap of 109 nm, the port isolation of 16.7 dB was obtained. The switch's insertion loss was roughly estimated to be less than 1 dB. The switching time was 36.7 μsec under the present experimental condition. Moreover, 64 switches were arrayed in a 125 μm period square mash waveguide and an 8 x 8 matrix switch was composed. The matrix switch was also tested.

Integrated Reconfigurable Silicon Photonics Switch Matrix in IRIS Project: Technological Achievements and Experimental Results

This paper reports the performances of a silicon photonics optical switch matrix fabricated by using large-scale three-dimensional (3-D) integration. The wavelength selective optical switch consists of a photonic integrated circuit (PIC), with 1398 circuit elements, interconnected in a 3-D stack with its control electronic integrated circuit (EIC). Each PIC element can be trimmed or reconfigured by using metallic heaters. The EIC is designed to drive the heaters and to read the signal of monitor photodiodes integrated into the PIC. Small footprint and high energy efficiency are achieved in the PIC and the EIC. Automatic wavelength alignment of the optical circuits in the PIC to the ITU grid and fine temperature tuning of each photonic element to optimize the switch insertion losses are obtained by an optimization routine. A fully packaged switch with input/output fibers is tested both for optical and electrical characteristics as well as for the system performances. Fiber-to-fiber insertion losses of about 20 dB and channel isolation of −35 dB are achieved. Bit error rate characteristics at 25 Gb/s are evaluated. Perspective applications of the optical switch in optical transport and intra-data center networks are discussed.

A 3D Photonic-Electronic Integrated Transponder Aggregator With $48\times 16$ Heater Control Cells

An electronic integrated circuit (EIC) and a silicon photonic integrated circuit (PIC) are 3D-integrated. The EIC using the complementary metal–oxide–semiconductor (CMOS) part of STMicroelectronics’ BCD8sp $0.16~\mu \text{m}$ technology controls all 768 switches in the PIC individually and monitors them with 84 transimpedance amplifiers. A scalable analog–digital approach with a cell size of $100\times 100\,\,\mu \text {m}^{2}$ for thermal control of optical ring resonator switch matrices is introduced. An electrical power consumption of 220 mW for all electronic control circuits of the optical switch matrix is resulting in 5.5% of the power needed by a constant-voltage control approach.

Construction of large scale switch matrix by interconnecting integrated optical switch chips with EDFAs

Large scale optical switches are essential components in optical communication network. We aim to build up a large scale optical switch matrix by the interconnection of silicon-based optical switch chips using 3-stage CLOS structure, where EDFAs are needed to compensate for the insertion loss of the chips. The optical signal-to-noise ratio (OSNR) performance of the resulting large scale optical switch matrix is investigated for TE-mode light and the experimental results are in agreement with the theoretical analysis. We build up a 64×64 switch matrix by use of 16×16 optical switch chips and the OSNR and receiver sensibility can respectively be improved by 0.6 dB and 0.2 dB by optimizing the gain configuration of the EDFAs.

N × N Reconfigurable Nonblocking Polymer/Silica Hybrid Planar Optical Switch Matrix Based on Total-Internal-Reflection Effect

We present a reconfigurable model for N × N non-blocking optical switch matrix (OSM) constituted by N(N-1)/2 2 × 2 thermo-optic polymer/silica hybrid total-internal-reflection switch elements. The number of the elements in the general model is reduced by about 50% compared to the reported all nonblocking OSM, in addition, the proposed model is more compact in footprint and more power-efficient. Each element consists of crossed multimode polymer/silica hybrid waveguides and a heater electrode at the switching node. A switching power of 53.9 mW is required at 1550-nm wavelength to drop the crosstalk below -28.0 dB. Measurements result in a rise time of 421.5/410.1 μs (O1/O2), a fall time of 534.2/464.6 μs (O1 /O2), and crosstalk of -27.6 and -29.1 dB under cross state and bar state, respectively. Subtracting coupling losses, propagation losses of the device under cross state and bar state are about 1.0 and 1.8 dB, respectively. The fabricated 3 × 3 and 4 × 4 reconfigurable non-blocking OSMs using three and six switch elements at sizes of 16.0 mm × 6.8 mm and 26.0 mm × 6.8 mm all show excellent switching performances, and the insertion losses are less than 3.6 and 7.2 dB, respectively.

School of Telecommunications Engineering, Xidian University, Xi'an 710071, China

In order to apply compressive sensing in wireless sensor network, inside the nodes cluster classified by the spatial correlation, we propose that a cluster head adopts free space optical communication with space division multiple access, and a sensor node uses a modulating retro-reflector for communication. Thus while a random sampling matrix is used to guide the establishment of links between head cluster and sensor nodes, the random linear projection is accomplished. To establish multiple links at the same time, an optical space division multiple access antenna is designed. It works in fixed beams switching mode and consists of optic lens with a large field of view (FOV), fiber array on the focal plane which is used to realize virtual channels segmentation, direction of arrival sensor, optical matrix switch and controller. Based on the angles of nodes' laser beams, by dynamically changing the route, optical matrix switch actualizes the multi-beam full duplex tracking receiving and transmission. Due to the structure of fiber array, there will be several fade zones both in the focal plane and in lens' FOV. In order to lower the impact of fade zones and harmonize multi-beam, a fiber array adjustment is designed. By theoretical, simulated and experimental study, the antenna's qualitative feasibility is validated.

Handover reduction using optical matrix switch for indoor LTE cell deployment

Handover reduction using optical matrix switch for indoor LTE cell deployment

Integrated Pulsewidth Modulation Control for a Scalable Optical Switch Matrix

A scalable pulsewidth control approach with 7-bit resolution for thermal control of optical ring resonator switch matrices in 0.16- $\mu\text{m}$ Bipolar-CMOS-DMOS (BCD) with a cell size of $79\ast 105 \mu\text{m}^2$ is introduced. One Gray counter at up to 1.2-GHz clock and pulsewidth modulation generation in each matrix cell leads to an electrical power consumption of 330 mW for all electronic control circuits of an optical 1000-switch-node matrix, resulting in a reduction of 11.1% of the power needed by a constant-voltage control approach.

Optical switch matrix based on a liquid-actuated mirror reflector

We demonstrate a 1×2 optical switch matrix based on a liquid-actuated mirror reflector. Three indium tin oxide (ITO) electrodes are fabricated on the bottom substrate. One droplet is placed in the middle of the liquid channel and surrounded by density-matched silicone oil. A mirror reflector is placed on the droplet. In its initial state, the light beam can pass through the device from the light hole. When we apply voltage to one side of the ITO electrode, the droplet carries the mirror reflector, stretching and moving toward this side of the substrate. Therefore, the light beam is reflected by the mirror reflector. The light beam can pass through the device again when the mirror reflector is carried away by the droplet. Out-1 and Out-2 alternately change the switch-on and off states. Therefore, the device can achieve the function of a 1×2 optical switch matrix. Because it uses a mirror reflector to block the light beam, the device can attain 100% intensity attenuation. Our experiments show that the switch time from Out-1 (Out-2) to Out-2 (Out-1) are 129 and 123 ms, respectively. The proposed optical switch has potential applications in variable optical attenuators, electronic displays, and light shutters.