MEMS-based optical switches

Microring-based optical switches are promising for wavelength-selective switching with the merits of compact size and low power consumption. However, the large insertion loss, the high fabrication, and the temperature sensitivity hinder the scalability of silicon microring optical switch fabrics. In this paper, we utilize a three-dimensional (3D) microring-based optical switch element (SE) on a multi-layer Si3N4-on-SOI platform to realize high-performance large-scale optical switch fabrics. The 3D microring-based SE consists of a Si/Si3N4 waveguide overpass crossing in the bottom and the top layers, and Si3N4 dual-coupled microring resonators (MRRs) in the middle layer. The switch is calibration-free and has low insertion loss. With the 3D microring-based SEs, we implement an 8×8 crossbar optical switch fabric. As the resonance wavelengths of all SEs are well aligned, only one SE needs to be turned on in each routing path, which greatly reduces the complexity of the switch control. The optical transmission spectra show a box-like shape, with a passband width of ∼69 GHz and an average on-state loss of ∼0.37 dB. The chip has a record-low on-chip insertion loss of 0.52–2.66 dB. We also implement a non-duplicate polarization-diversity optical switch by using the bidirectional transmission characteristics of the crossbar architecture, which is highly favorable for practical applications. 100 Gb/s dual-polarization quadrature-phase-shift-keying (DP-QPSK) signal is transmitted through the switch without significant degradation. To the best of our knowledge, this is the first time that 3D MRRs have been used to build highly scalable polarization-diversity optical switch fabrics.

Optical cross-connect switches (OXC) are key components in advanced WDM networks. Integrated optical switches have been reported using several mechanisms and materials. We have demonstrated waveguide-type thermo-optic switches which employ silica-based planar lightwave circuits. The crosstalk of OXC, due to a number of reasons, is an important parameter which influences the system performance. One of the reasons is the coupling ratio (CR) of a 3 dB coupler in a switch unit. Due to fabrication limitations, it is hard to obtain the exact CR as designed. We propose a scheme to achieve low crosstalk even with variation of CR. The design of our optical switch fabric is a strictly non-blocking matrix switch using dilated double-layer architecture.

In this paper, we propose an analytical model to evaluate the power consumption in the switching fabric of a bufferless shared-per-wavelength (SPW) optical packet switch architecture in which one bank of wavelength converters (WC) is dedicated to each wavelength. We assume that both optical gates and WCs are realized in semiconductor optical amplifier technology. In our evaluation, we account for the power consumption of the current drivers needed to both controlling the used active devices and supplying the thermoelectric coolers. SPW allows for a complexity reduction of the spatial switching matrix that leads to reduced power consumption with respect to other switching architectures. Results show the effectiveness in terms of consumed power of the considered architecture with respect to the shared-per-node reference architecture, where a fully sharing strategy of WCs is adopted. The main results show that SPW allows us to reduce the power consumption in the order of 26% for offered traffic equal to 0.6. The obtained results also show how the fabric switching of the SPW optical packet switch consumes much less power per gigabits per second carried than the one of a typical commercial core router.

Current developments in optical components technologies enable wavelengths to be very narrowly spaced, transforming the optical fiber into a multi-terabit capacity medium. A new generation of cross-connects started to appear in the market leading to a number of advantages such as increased switching capacity, decreased overall network costs, scalability and transparency resulting in the capability to support any protocol. An additional advantage is the ability to configure the switching fabric and the wavelength converters in real-time. All-optical switches are made possible by a number of technologies that allow the managing and switching photonic signals without converting them into electronic signals. Only a couple of technologies appear ready to make the transition form the laboratory to the network, where they must support the basic feature set of a carrier-grade, scalable optical switches. Arguably, the leading technology for developing an economically viable, scalable all-optical , OOO switch is the 3D micro-electromechanical system (MEMS). 3D MEMS uses control mechanisms to tilt mirrors in multiple directions (3 dimensional). For the control of optical cross-connects, the MP Lambdas approach was proposed by IETF, according to which the MPLS traffic engineering control plane is used in optical cross connects. In this paper, evolution of architectures for optical cross-connects all optical switch are discussed with different switch fabrics such as micro-electro-mechanical all optical switch fabric and arrayed-wavelength-grating routers (AWGRs). The paper includes also an illustration of the major function of the multi protocol label switching MPLS optical router and the use of MP lambda switch to control the all optical switch.

The growing demands for telecommunications bandwidth, and the development of high-capacity optical networks, are creating a demand for large-port-count optical cross-connects. The initial cross-connect products currently being offered all utilize electronic switch fabrics, and while they are meeting the immediate needs for network operators, there is a growing consensus that transparent optical switch fabrics will be needed in the near future. The purpose of the paper is to review the requirements and architectures for optical switch fabrics, and to compare and evaluate the various optical switch technologies that are available to implement fabrics capable of meeting those requirements.

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.

Aiming at providing 100% throughput with bounded packet delay, we consider traffic scheduling in high-speed routers with optical switch fabrics. Because of the switch reconfiguration overhead, a speedup in the switch fabric is essential. For a given packet delay bound, our objective is to minimize the overall speedup S = S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">reconfigure</sub> times S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">schedule</sub> so as to lower the implementation cost. Leveraging on the existing ADAPTIVE and DOUBLE algorithms, we show the speedup can be reduced by improving scheduling efficiency. Specifically, following the traffic matrix decomposition in ADAPTIVE and DOUBLE, we shift some packets from the residue matrix R to the quotient matrix Q, while keeping the number of configurations required to cover each matrix the same. We reduce the number of time slots required to send the diminished residue matrix. In case of DOUBLE, this translates into a 12.5% cut in S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">schedule</sub> (from 2 to 1.75). We call the resulting algorithm Scheduling Residue First (SRF).

To accomplish high-bandwidth and low-latency communications among tens or even hundreds of nodes with low power consumption, dual radial and angular grating optical network (DRAGON), a new integrated high-radix strictly nonblocking optical switching fabric, is proposed in this paper. The topology and routing algorithms of DRAGON are discussed, and a formal proof for the strictly nonblocking property is presented. With the loss model developed, we show DRAGON has significantly lower worst-case loss as well as average loss compared with other widely studied integrated nonblocking switching fabrics. In addition, our crosstalk analysis also suggests a lower crosstalk of DRAGON. For example, for 32 wavelength division multiplexing channels, both the worst-case loss and average loss of ${\text{180}}\times {\text{180}}$ DRAGON are around 20 dB lower than crossbar of the same size, and 28 dB lower than ${\text{128}}\times {\text{128}}$ Benes. Furthermore, due to the strictly nonblocking property, DRAGON has advantages of smaller communication latency and larger throughput compared with Benes switching fabric.

MEMS optical switches and interconnects

Scheduling traffic for maximum switch lifetime in optical data center fabrics

Next-generation wavelength routing optical networks requiring optical cross connects (OXC) in the network have the ability to direct optical signals from any input interface to suitable output interfaces by configuring their internal embedded optical switch matrices. Microelectromechanical systems (MEMS) switches are regarded as the most promising technology to achieve such functionality. We consider the construction of a multistage MEMS switch network with single two-dimensional (2-D) MEMS switch blocks. A power loss model is developed that calls on a single MEMS block that is then used to develop the model for a three-stage Clos network. An effective model for maximum loss difference between calls is also developed. Based on these, the paper also proposes three connection patterns [Max + Min greedy (MMG), compressed extended generalized shuffle 1 (C-EGS-1), and compressed extended generalized shuffle 2 (C-EGS-2)] to connect outlet ports and inlet ports between two neighboring stages in a three-stage Clos network. These connection patterns are proved to be optimal and efficient enough to reach the minimums of both the maximum power loss of calls and the maximum loss difference between calls.

In this paper, we describe the design principles of serpentine springs with high reliability for the micro-electromechanical systems (MEMS) optical switches with large mirror mass. The most often seen failure mode of the MEMS optical switches under reliability tests is the breaking of these springs, which provide the restoring force for the MEMS actuators. The breaking points are usually at the turning corner of the serpentine springs when the MEMS optical switches are under a high G shock test or a vibration test. In order to overcome the difficulties, we redesigned the corner shapes of the springs with careful consideration. We will discuss the theoretical analysis and simulation modeling for the corner shapes of serpentine springs. MEMS optical switches with redesigned serpentine springs are fabricated and tested to prove the proposed design. The results show that the MEMS optical switches with new serpentine springs can pass rigorous reliability tests.

Arch shaped microelectromechanical systems (MEMS) have been used as mechanical memories, micro-relays, micro-valves, optical switches, and digital micro-mirrors. A bi-stable structure is characterized by a multivalued load deflection curve. Here, the symmetry breaking, the snap-through instability, and the pull-in instability of a sinusoidal shaped MEMS under static and dynamic electric loads have been studied. The electric load is a nonlinear function of the a priori unknown deformed shape of the arch, and is thus a follower type load. The nonlinear partial differential equation governing transient deformations of the arch is solved numerically using the Galerkin method and the resulting ordinary differential equations are integrated by using the Livermore solver for ordinary differential equations. For the static problem, the displacement control and the pseudo-arc length continuation methods are used to obtain the bifurcation curve of the MEMS displacement versus a load parameter. The displacement control method fails to compute asymmetric deformations of the MEMS, which are found by the pseudo-arc-length continuation method. Two distinct mechanisms of the snap-through instability for the dynamic problem are demonstrated. It is found that critical loads and geometric parameters for instabilities of an arch under an electric load with and without the consideration of mechanical inertia effects are quite different.

This doctoral thesis focuses on the theoretical studies and experimental implementations of three types of tunable lasers using the microelectromechanical systems (MEMS) technology. A discretely tunable laser is first developed, including new theoretical models for the extremely short cavity and discrete wavelength tuning, and a MEMS prototype fabricated by deep etching on a silicon-on-insulator wafer. It can be tuned over 13.5 nm within 1 ms. Secondly, a continuously tunable laser is developed, including a modified theory and a fabricated MEMS laser. A continuous tuning range of 30.3 nm is obtained. Finally, an injection-locked laser subsystem is developed by integration of single MEMS laser components. A new generalized theory is established and a MEMS injection-locked laser is demonstrated. Locking states with a SMSR > 50 dB and all optical switching up to 50 MHz are achieved. In summary, the developed MEMS lasers exhibit many advantages such as small size, fast tuning speed, and high mechanical stability, and would find wide applications in optical communications, biomedical studies, and military defense.

Current electronic broadband switch matrices employ discrete semiconductor devices or VLSI chips. Isolation between ON- and OFF-states degrades and crosstalk between input and output lines of these electronic switch matrices increases at high operation frequencies. These will limit electronic switch matrices to low-frequency or low-bit-rate operations. In addition, optical-to-electrical (electrical-to-optical) conversions at the input (output) ends are required for these switch matrices to be used in a fiber environment. One way to achieve broadband, low-crosstalk, and high-isolation switching and to eliminate E/O and O/E conversions is to use optical switches. This paper describes an optical broadband switching architecture using optical/optoelectronic logic gates. Input and output signals are optical. No E/O or O/E conversions are needed for this architecture. The optical/optoelectronic logic gates that can be employed in this architecture are reviewed. Performance of this architecture is evaluated by calculating the crosstalk, isolation, insertion loss, switch matrix size, drive power, and switching speed. Technologies needed for hybrid and monolithic implementations of this architecture are also identified.