Design optimization of a dynamically flat resonating micro-mirror for pico-projection applications

One of the main design limitations of resonant micro-mirrors, intended for visual projection display applications, is inertia-driven dynamic deformation. In order to achieve high scan angles, micro-mirrors used for high frequency (20–30 kHz) laser beam scanning are typically operated at resonance and in the region of their torsional modal frequency. Although the optical resolution of the projected image is defined by the micro-mirror dimensions, the scanning frequency and the maximum scan angle, significant dynamic deformation (> 1/10 of the incident wavelength) can develop and give rise to a loss in contrast between adjacent projected spots. A design optimization scheme for a one directional resonant micro-mirror intended for laser projection with XGA optical resolution is performed and presented in this study. The minimization of dynamic deformation is considered as one of the main objectives but other parameters related to micro-mirror optical performance, structural reliability and gas damping characteristics are also investigated. The optimization scheme is performed using Design of Experiments and response surface methodologies. The design process demonstrates the technical feasibility of including features, such as a gimbal structure, that improve the dynamic mirror flatness without compromising the target scanning frequency, mode separation, maximum shear stress and power consumption.