## 1 Introduction  
Optical switching offers several benefits over electronic switching in data communication applications. In data center, long-haul, and metro communications, the signal is already travelling through optical fiber and significant energy savings can be achieved by having the signal remain in the optical domain rather than undergoing an optical-to-electrical-to-optical (OEO) conversion cycle. Skipping the OEO conversion also reduces the latency time as the information is redirected literally at the speed of light. Finally, most of the optical switch technologies are rate and protocol agnostic, which makes them extensible for the next several generations of transceivers and modulation formats. Several devices have been proposed for optical switching, each based on different physical phenomena. Researchers have investigated acousto-optics modulators, electro-optics interferometers, thermo-optics devices, nonlinear photonics circuits, and semi-conductor optical amplifiers as possible candidates for optical switching [1, 2]. While these approaches are active research areas, these technologies have so far had a difficulty finding a commercial application due mainly to the high energy required to perform the switching operation, either due to the electrical or the optical power required. Energy consumption (typically measured in pJ/bit) is an extremely important criterion for the adoption of new data communication technology. Worldwide Internet traffic is forecasted to continue its exponential growth, doubling every 18 months until at least 2020 [3]. The dramatic increase in traffic has driven many content providers to increase both the number and size of data centers to meet the demand for instant access to information. Major content providers are adding new data centers every 6 months with each data center covering many acres, consuming more than 100 MW of electricity and responsible for releasing tons of CO\({}_{2}\) emissions [4]. In 2006, servers and data centers were estimated to consume 1.5% of the electricity in the USA (61 billion kWh), doubling from the year 2000. By 2014, data centers were consuming 5% of the entire United States' electrical energy production. The projected demand for electricity from US data centers alone will reach 400 TWhr by 2020 [5]. The problem may be even more acute than it appears due to the predicted demise of Moore's law which enabled the new generation of microchips to be more energy efficient per bit than the previous generation [6]. The current state-of-the-art optical switching technology is based on micro-electro-mechanical systems (MEMSs) where an array of micro mirrors is oriented to reflect the incident light toward specific output ports [7; 8; 9]. The first generation of these MEMSs was designed so the light is propagating along the plane of the devices, e.g., west-east. When a mirror initially laying flat on the surface was raised up, it intercepted the beam and reflected it at 90\({}^{\circ}\) in the north-south direction. Since the layout of this switch was within a plane, this configuration was named two-dimensional (2D) MEMS. A schematic representation is presented in Figure 1. The binary orientation of the mobile mirrors, flat or raised, simplified the electronic control. However, to obtain a strictly non-blocking switch with such an architecture, \(N^{2}\) number of mirrors are needed, with \(N\) being the number of accessible ports [10]. This quadratic increase of the number of active mirrors limited its adoption for large numbers of ports. The second generation of MEMS switches takes advantage of reflection away from the plane of the device. Dubbed three-dimensional (3D) MEMSs, they are composed of micro mirrors lying in the plane of the substrate and mounted on a gimbaled support. The orientation of the mirrors can be continuously adjusted over a range of tip and tilt angles so the reflection of the incoming light is directed to a specific output port.