New lidar chip design cuts interference for wider solid-state scanning

MIT engineers have developed a silicon-photonics lidar chip design that can steer a precise light beam across a wider view while avoiding much of the interference that has limited earlier chip-based systems. MIT said the work could help shrink lidar sensors and remove moving parts used in many systems for autonomous vehicles, drones and industrial monitoring.

The research, published in Nature Communications, focuses on integrated optical phased arrays, or OPAs, which steer light electronically rather than by rotating a mechanical scanner. According to MIT, lidar uses pulses of infrared light to measure distance and build 3D maps of nearby surroundings, a core function for machines that must detect objects and respond quickly.

Many conventional lidar units are large, expensive and dependent on moving components that can wear down, MIT said. Chip-scale lidar based on silicon photonics offers a path to more compact hardware, but MIT said existing versions often see only a narrow angular range or lose accuracy when designers try to widen that range.

Why antenna spacing matters

MIT said the main obstacle is crosstalk between neighboring antennas on the chip. If antennas sit close together, they can interfere with each other and distort the outgoing light; if they are spread farther apart, the array can create extra copies of the beam, known as grating lobes.

Those unwanted beam copies can make it harder for the sensor to identify the main beam and can generate false detections, according to MIT. Andres Garcia Coleto, an MIT electrical engineering and computer science graduate student on the project, said wider spacing limits the angular range visible to an autonomous vehicle.

The MIT team addressed the tradeoff by replacing identical antenna elements with a repeating set of three differently shaped antennas. MIT said the researchers changed antenna widths and the size and placement of small corrugations that scatter light out of the chip.

Because each antenna geometry changes how light travels through it, neighboring antennas interact far less, according to the researchers. Garcia Coleto said the different propagation properties mean that, when placed close together, each antenna effectively does not couple strongly with its neighbor.

Tests show lower coupling

MIT said the design challenge was to make the antennas different enough to reduce crosstalk while still forcing them to emit light with matching behavior. Lead author Henry Crawford-Eng said antennas with different shapes typically behave differently, making that balance difficult.

The researchers built their design from electromagnetic theory, tested it in computer simulations and then fabricated an OPA with the reduced-crosstalk antennas, MIT said. In experiments, the chip kept the antennas much closer together than a conventional design while producing a single clean beam.

Under the tested conditions, MIT said a typical OPA would have shown coupling of about 100 percent. The new antenna design reduced coupling to about 1 percent while steering the beam across a broad field of view without grating lobes, according to the researchers.

Jelena Notaros, an MIT associate professor of electrical engineering and computer science and senior author of the paper, said the demonstrated function addresses a basic problem for integrated optical phased arrays and points toward higher-performance lidar sensors. The research team also included Benjamin M. Mazur, Daniel M. DeSantis and Tal Sneh, according to MIT.

Joyce Poon, a University of Toronto professor and director at the Max Planck Institute of Microstructure Physics who was not involved in the work, said the antenna design tackles the need for both dense spacing and high beam quality in chip-scale beam steering. MIT said the team next plans to extend the method to cover an even wider field of view.

This story draws on original reporting from ScienceDaily.