Parametric amplification of a resonant MEMS mirror with all-piezoelectric excitation

We report a resonant torsional micro-mirror with all-piezoelectric driving and tunable spring stiffness. Stiffness modulation finds two practical applications. First is tuning of the resonance frequency, achieved by applying DC bias voltage to the stiffness modulating structures. A tuning rate was found to be 0.95 Hz V−1 with up to 20 Hz of usable frequency range. Second, when direct excitation of the torsional mode is combined with the harmonic modulation of the spring stiffness, an optical scan angle is shown to be increased by more than 4° through 2:1 degenerate parametric amplification. By varying the phase of the parametric pump with respect to the direct excitation, the Q-factor is tuned between 617 and 898, corresponding to the minimum and maximum parametric gain factors of 0.84× and 1.21×, respectively, achieved at a nominal unpumped optical scan angle of 16.3°. Increasing the pump amplitude shows a moderate increase in the amplifier's gain with clear saturation at 1.43× in the superthreshold pumping regime, indicating a presence of the third order stiffness nonlinearity. The results show potential to apply parametric amplification to future piezo-micro-electro-mechanical-system actuators for large frequency and large-stroke mechanical response achieved at ambient pressure.