When Google unveiled its first autonomous cars in 2010, the spinning cylinder mounted on the roofs really stood out. It was the vehicle’s light detection and ranging (LiDAR) system; together with cameras and radar, LiDAR mapped the environment to help the cars avoid obstacles and drive safely. Since then, inexpensive, chip-based cameras and radar systems have moved into the mainstream for collision avoidance and autonomous highway driving. Yet LiDAR navigation systems remain unwieldy mechanical devices that cost thousands of dollars.
That may be about to change, thanks to a new type of high-resolution LiDAR chip developed by researchers led by Ming Wu, professor of electrical engineering and computer sciences. Their LiDAR is based on a focal plane switched array (FPSA), a semiconductor-based matrix of micrometer-scale antennas that gathers light.
Mechanical LiDAR systems have powerful lasers that visualize objects hundreds of yards away, even in the dark. Yet putting these capabilities on a chip has stymied researchers for more than a decade, with the most imposing barrier involving the laser. But the FPSA — consisting of a matrix of tiny optical transmitters, or antennas, and switches that rapidly turn them on and off — can channel all available laser power through a single antenna at a time.
Switching, however, poses problems. Almost all silicon-based LiDAR systems use thermo-optic switches, which are both large and power-hungry. Jam too many onto a chip and they will generate too much heat to operate properly. The team’s solution replaces them with microelectromechanical system (MEMS) switches that physically move the waveguides from one position to another. Compared with thermo-optic switches, they are much smaller, use far less power, switch faster and have very low light losses.
The result is 16,384 pixels on a 1-centimeter-square chip — dwarfing the 512 pixels or less found on FPSAs until now. Equally significant, the design is scalable to megapixel sizes using the same complementary metal-oxide-semiconductor (CMOS) technology used to produce computer processors. This could lead to a new generation of powerful, low-cost 3D sensors for autonomous cars as well as for drones, robots and even smartphones.