Ultrasonic levitation-based contactless actuation for reflective optical beam steering

High-performance optical beam steering requires large deflection angles, high optical throughput, fast response, and long operational lifetimes-criteria that remain challenging to satisfy simultaneously using mechanical scanners, MEMS mirrors, or integrated optical phased arrays (OPAs). Here, we introduce a contactless beam-steering mechanism in which a freely levitated reflective element is mechanically actuated by acoustic radiation forces rather than by conventional bearings, flexures, or electro-optic effects. A dual-array ultrasonic standing-wave field forms a stable three-dimensional potential well that traps and controllably tilts a lightweight aluminum mirror, enabling reflective beam steering without mechanical contact, friction, or wear. The present prototype achieves an optical throughput of approximately 75%. Experimentally, five discrete and repeatable steering states spanning ∼±8° optical deflection are demonstrated with settling times on the order of tens of milliseconds. Using the experimentally validated acoustic model, numerical studies of idealized phase-controlled drive suggest that the same architecture could, in principle, support smooth, continuous steering up to ∼8.8° of mirror tilt (∼17.6° optical deflection), potentially extending beyond the angular ranges of existing non-contact steering technologies such as OPAs and electro-optic deflectors. These results highlight acoustic radiation-force actuation as a previously underexplored route to wide-angle, high-efficiency, and wear-free optical beam steering, opening new opportunities for reconfigurable free-space photonics.