Bio-inspired four-degree-of-freedom AlN micromirror for visual tracking and accommodation

Simultaneous realization of large-angle beam steering and dynamic focusing within a single micro-electromechanical system (MEMS) remains a significant challenge. Inspired by the human eyes, we propose an aluminum nitride (AlN) piezoelectric micromirror that integrates tip, tilt, piston, and varifocal capabilities into a single device. The micromirror consists of a 1.0 × 1.0 mm varifocal plate driven by four decoupled actuating beams. Experimentally, the device exhibits an optical scanning angle of 12°/7.5° at the resonant frequency of 2.6 kHz, effectively covering the primary human visual field with rapid spatial tracking. The resonant piston displacement of 48 µm at 1.68 kHz facilitates high-speed phase modulation and active optical stabilization. Meanwhile, it demonstrates a focal tuning range from 39 mm to 45 mm under static (DC) operation. Remarkably, the micromirror achieves a dynamic varifocal response time of 1.7 ms, providing instantaneous focal transitions that are approximately 100 times faster than the biological accommodation of the human eye. Combining a human-like field of view with ultra-fast actuation speeds, this low-cost, compact AlN micromirror holds great potential as a core component for biomimetic machine vision and wearable optics.