Integrated Acousto-optic Beam Steering for Advanced Free Space Optical Applications

Abstract

Optical beam steering underpins numerous technologies, including light detection and ranging (LiDAR), biomedical imaging, remote sensing, and utility-scale quantum computing with optically addressed qubits. However, established beam-steering approaches are constrained by slow response times, system complexity, and limited control over beam dynamics, preventing their widespread deployment in practical, high-performance optical systems. This thesis introduces integrated acousto-optic beam steering (AOBS), a solid-state beam-steering technology based on enhanced light–sound interactions in thin-film lithium niobate (TFLN). Gigahertz surface acoustic waves (SAWs), generated piezoelectrically and controlled by RF signals, produce moving refractive-index gratings that dynamically reshape the phase front of guided light. When the acoustic and optical modes satisfy the phase-matching condition, the guided light is efficiently scattered into free space, enabling agile beam steering on chip. The first part of the thesis establishes the principles and device-design considerations for AOBS on TFLN. I examine the piezoelectric and acoustic properties of lithium-niobate-on-insulator (LNOI), which form the foundation for efficient SAW generation. I then present theoretical models and simulation frameworks for acousto-optic interactions, identifying the key mechanisms that govern scattering efficiency and guiding the design of high-performance AOBS devices. The second part demonstrates LiDAR and multi-beam free-space communication enabled by the unique properties of AOBS. The Brillouin scattering process not only allows the steering angle to be controlled by the acoustic frequency using a single transducer, but also imprints a distinct frequency shift on each steered beam. This enables frequency–angular resolving (FAR) LiDAR, in which a single coherent receiver extracts the angular position of a target directly from the frequency of the returned signal. The coherent nature of the process further supports simultaneous transmission of microwave-encoded data streams at different acoustic frequencies to spatially separated targets, enabling multiple-input multiple-output (MIMO) free-space optical communication. In the final part, I show that co-confining acoustic and optical modes in micrometer-scale rib waveguides not only boosts the efficiency and agility of AOBS, but also enables seamless integration within broader photonic integrated circuits (PICs). This opens the door to compact, high-performance, and multifunctional free-space optical systems that combine acousto-optic, electro-optic, and nonlinear photonic functionalities on a single TFLN platform.