Resonant Piezoelectric Varifocal Mirror with on-Chip Integrated Diffractive Optics for Increased Frequency Response

We report the design, fabrication, and characterization of a resonant varifocal micromirror excited with thin-film piezoelectric actuators. The mirror features a spiral suspension allowing both in-plane and out-of-plane motion which reduces the stress build up upon the membrane deformation and hence high shape fidelity. Driven at resonance, the mirror reaches an optical power of more than 27.5 diopters at 197 kHz and 7 VP-P excitation. The unique feature of the mirror is a combination of large optical power with the integration of a binary Fresnel zone plate (BFZP) onto the flexible membrane. The BFZP provides a virtual and real focusing point, which, when combined with the main mechanical mode provides four focusing points per harmonic cycle, effectively doubling the resonant frequency to 394 kHz. Compared to state-of-the-art devices, this device features the highest figure of merit ever reported.