Lidar technology utilizes infrared light pulses to gauge distance and create detailed 3D maps, enabling self-driving cars to swiftly respond to obstacles. However, traditional lidar sensors are costly and cumbersome, with numerous moving parts that wear down over time, restricting their deployment. MIT researchers have introduced a breakthrough that could lead to the development of next-generation lidar sensors that are compact, robust, and feature no moving parts. The innovation centers on a unique design for a silicon-photonics chip that manipulates light instead of electricity.<\/p>\n
Silicon-photonics chip-based systems usually have a limited field of view, meaning a silicon-photonics-based lidar cannot scan peripheral angles effectively. Current solutions to this limitation tend to increase noise and reduce precision. To overcome these challenges, MIT researchers created an array of integrated antennas that minimizes crosstalk between them. This advancement allows a lidar chip to scan a broader field of view while maintaining lower noise compared to other silicon-photonics-based methods.<\/p>\n
This new approach could propel the development of advanced lidar sensors for critical applications such as navigation for autonomous vehicles, aerial surveys, and monitoring construction sites. “The functionality we demonstrated in this work solves a fundamental problem for integrated optical-phased-array technology, enabling future lidar sensors that can achieve significantly higher performance than we could demonstrate previously,” states Jelena Notaros, the Robert J. Shillman Career Development Associate Professor of Electrical Engineering and Computer Science at MIT and the senior author of the study published in Nature Communications.<\/p>\n
Traditional lidar systems map environments using a large spinning box that sends out light in various directions. The reflected light from nearby objects is then used to reconstruct the surroundings. In contrast, silicon-photonics-based lidar sensors utilize an integrated optical phased array (OPA) to non-mechanically scan an emitted light beam in multiple directions. The core of an OPA is an array of integrated antennas with small periodic perturbations along their length, allowing light to scatter from an input source out of the photonic chip.<\/p>\n
By adjusting the light phase directed to each antenna, researchers can alter the angle at which the light exits the array, steering the beam without moving parts. However, placing antennas too closely can lead to coupling, resulting in jumbled emissions. While spacing them further apart avoids this, it can cause the array to emit multiple copies of the beam at different angles, complicating field of view limitations and power wastage.<\/p>\n
The MIT team addressed this issue by designing a set of reduced-crosstalk antennas that can be placed in close proximity without significant coupling effects. Unlike standard OPAs, where antennas are identical and strongly couple when close together, their design involves three antennas with varied geometries. Each antenna’s unique propagation coefficient determines light travel, preventing coupling. “Because the antennas have very different propagation coefficients, when we put them close together, essentially each antenna doesn\u2019t \u2018see\u2019 the antenna next to it. Therefore, it won\u2019t couple with its neighbor,” explains Andres Garcia Coleto.<\/p>\n
Even with different propagation coefficients, the antennas must emit light uniformly. The researchers achieved this by ensuring each antenna emits the same light amount, at the same angle for a given wavelength, and uniformly changes emission angles across the array. “We have this challenge where we require the antennas to have different geometries to reduce the crosstalk, but we need to simultaneously design the antennas to have the same emission characteristics,” notes Henry Crawford-Eng, the lead author.<\/p>\n
They developed electromagnetic theory to guide antenna design and simulation, fabricating an OPA with reduced-crosstalk antennas placed closer than in traditional designs. Experimentation showed their OPA reduced coupling to about 1 percent, maintaining a single, precise beam and accurate beam steering across a wide field of view without grating lobes. Future plans involve enhancing the technique for an even wider field of view and exploring new solutions discovered during theory development. “This work addresses a longstanding challenge in integrated optical phased arrays,” says Joyce Poon, a professor at the University of Toronto, highlighting the significance of the researchers’ antenna design.<\/p>\n