Technology
Optical Phased Array Beam Steering in LiDAR Systems
Quick fact
Optical phased arrays are inspired by radio antenna arrays but work with light waves, where the phase shifters are just micrometers across, and the entire beam-steering chip can be smaller than a fingernail.
Why this is interesting
Imagine steering a laser beam without any moving parts—just by sending tiny electrical signals across a chip. How can that be possible? That's exactly what an optical phased array does, and it's set to transform LiDAR technology.
Read the full explanation
Understanding Optical Phased Array Beam Steering in LiDAR Systems
You're probably familiar with the idea of a LiDAR system that rotates to scan the environment—like the spinning sensors on top of some autonomous vehicles. But imagine a flat, solid-state chip that can sweep a laser beam back and forth without moving a single part. That’s the promise of an optical phased array. Think of a lake with a row of small paddles. If you move all the paddles in sync, you'll create a straight wavefront moving forward. If you introduce a delay between the paddles—say, each one moves a bit later than the one before—you'll tilt the wavefront, and the wave will travel in a different direction. An optical phased array works the same way, but with light. It uses an array of tiny light emitters on a chip. By precisely controlling the phase (or timing) of the light each emitter emits, the array creates a constructive interference pattern that forms a bright beam. By adjusting the phase differences, you can steer that beam to different angles without physically moving the chip. In essence, you're shaping the wavefront of light to point in a desired direction.
A deeper explanation
The core mechanism behind an optical phased array (OPA) is the precise control of the phase of light emitted from a set of coherent sources. The array is typically fabricated using silicon photonics, where waveguides carry light from a central source to an array of grating emitters on the surface. Each emitter is equipped with a phase shifter—often a thermal or electro-optic element that changes the effective refractive index, thereby altering the optical path length and the phase of the light passing through it. When light from each emitter propagates into free space, the phases of the emitted beams determine the far-field pattern. If all phases are equal, the beams constructively interfere at one angle, producing a main lobe. By applying a linear phase gradient across the array—meaning the phase increases from one emitter to the next by a fixed amount—the main lobe tilts to a different angle. The relationship between the phase gradient and the steering angle is analogous to the beamforming in radio-frequency phased arrays. The key advantage in LiDAR is the ability to steer a beam rapidly and randomly (true beam pointing) without inertia, enabling agile scanning patterns and fast point-cloud acquisition. This eliminates moving parts, reducing size, weight, and reliability issues. Moreover, OPAs can be integrated with other photonic components, enabling a complete solid-state LiDAR on a chip. However, achieving large steering angles and high beam quality is challenging. The spacing between emitters must be less than a wavelength to avoid grating lobes (additional strong sidelobes), yet fabricating thousands of emitters on a chip requires advanced nanofabrication. Phase calibration and controlling thermal cross-talk are also complex. Despite these hurdles, optical phased arrays are a leading candidate for future solid-state LiDAR, promising compact, cost-effective, and high-performance sensors for autonomous vehicles and robotics.