Towards a stable low-voltage torsional microscanner

Torsional micromirrors emerged recently as an effective means of light manipulation. Their fast response, low wavelength sensitivity, and easy mass production have made them an attractive technology to implement optical switching and scanning applications. In this work, we developed a rigorous model of an electrically-actuated torsional micromirror. We verified the model against experimental data and conducted a convergence analysis to determine the minimum size of a reduced-order model (ROM) capable of representing the microscanner response accurately. We used the optimal ROM to study the dynamics of a microscanner. We found that the microscanner response exhibits a softening-type nonlinearity whose magnitude increases as the magnitude of the bias voltage increases. This nonlinearity results in multiple stable solutions at excitation frequencies close to but less than the natural frequency of the first mode. Operating the mirror in this region can cause abrupt jumps in the mirror response, thereby degrading the scanner performance. Furthermore, for a certain voltage range, we observed a two-to-one internal resonance between the first two modes. Due to this internal resonance, the mirror exhibits complex dynamic behavior, which degrades the microscanner's performance. We formulated a simple design rule to avoid this problem.