Electrostatic torsional micromirror: Its active control and applications in optical network

Electrostatically actuated torsional micromirror fabricated using microelectromechanical systems (MEMS) technology is a fundamental building block for many optical network applications, such as optical wavelength-selective switch, configurable optical add-drop multiplexers and optical cross-connects. The major technical obstacle to achieve its full potentials in both functionalities and performance is the controllability and stability of its tilting angle. This paper presents the model for a micromirror fabricated using micragem silicon-on-insulator process. Closed-loop control approaches are proposed for the 1-degree of freedom (DOF) MEMS device assuming that the angle position can be measured. Compared with traditional open loop control approaches, the nonlinear proportional and derivative (PD) control and the gain scheduling approach improve the performance of the mirror switching, and enhance the robustness of the structures to any stochastic perturbations. Furthermore, the nonlinear PD control can achieve a larger controllable tilting angle than the pull-in angle resulting in significantly enhanced device performance and functionality. Applications of the electrostatic torsional micromirror to optical network are further discussed to underscore the significance and necessities of such methods.