Abstract
In order to deliver extremely high bandwidth in a single fiber, the vision for future optical communication is to build a WDM-based all-optical network, in which the large-scale optical switches are the most important constituent elements. In essence, a large-scale optical switch can handle network traffic of thousands of input/output ports, allowing any input signal to be routed to the desired output port. Micro-mirrors realized by MEMS technology are intended to replace the conventional optical-electrical-optical conversion by routing light signals using direct reflection. The purpose is to reduce the required power and overall cost. In order to reduce the transmitting light path and the signal insertion loss in this large-scale optical switching application, the 3D-rotating angle of each micro-mirror has to be increased. In this design, we choose closed-loop control to realize a stable large rotation for the 3D micro-mirrors. Based on issues such as design area, power consumption and ease of fabrication, most research efforts on large-scale optical switches adopt open-loop parallel-plate electrostatic actuation. We expect to use feedback control to extend the travelled range of a parallel-plate actuator beyond one-third of the initial gap. Extended travelled range by charge control has been reported to overcome the pull-in limit. However this method has to use complex circuit to overcome leakage current and charge injection without guaranteed long-term stability. The applied closed-loop control can also perform sensitivity in face of external disturbance reduction. A linear controller and a position sensor are used in the closed-loop system. The controller is used to stabilize the extended position beyond the pull-in, and a capacitive sensor is used to detect the position. The fabrication of the mirror is based on the CMOS-MEMS process in order to minimize signal attenuation due to the parasitic capacitance. This theses includes the analysis and simulation of the actuator、the sensor and the servo-controller. The measurements of wet etching and dry etching, posting the CMOS process, verify the released structures.