One of the biggest obstacles to the commercialization of autonomous vehicles is the cost of sensors. Self-driving cars need multiple cameras and lidar sensors to navigate and avoid obstacles including pedestrians. Developers have spent years waiting for inexpensive lidar systems.

Despite the investments and engineering efforts in self-driving cars, today’s lidar sensors use complex mechanical parts to send the flashlight-sized infrared lasers spinning around like the old-fashioned lights atop police cars — at a cost of $8,000 to $30,000.

But now a Stanford University team led by electrical engineer Jelena Vuckovic is working on shrinking the mechanical and electronic components in a rooftop lidar down to a single silicon chip that she thinks could be mass-produced for as little as a few hundred dollars.

The project grows out of years of research by Vuckovic’s lab to find a practical way to take advantage of a simple fact: Much like sunlight shines through glass, silicon is transparent to the infrared laser light used by lidar.

Inverse design

In a study published in Nature Photonics, the researchers describe how they structured the silicon in a way that used its infrared transparency to control, focus, and harness the power of photons, the quirky particles that constitute light beams.

The team used a process called inverse design that Vuckovic’s lab has pioneered over the past decade. Inverse design relies on a powerful algorithm that drafts a blueprint for the actual photonic circuits that perform specific functions — in this case, shooting a laser beam out ahead of a car to locate objects in the road and routing the reflected light back to a detector. Based on the delay between when the light pulse is sent forward and when the beam reflects back to the detector, the lidar measures the distance between car and objects.

It took Vuckovic’s team two years to create the circuit layout for the lidar-on-a-chip prototype they built in the Stanford nano-fabrication facility. Postdoctoral scholar Ki Youl Yang and Ph.D. student Jinhie Skarda played key roles in that process, with crucial theoretical insights from City University of New York physicist Andrea Alù and CUNY postdoctoral scholar Michele Cotrufo.

Milestones for inexpensive lidar

Building this range-finding mechanism on a chip is just the first — though essential — step toward creating inexpensive lidar sensors. The researchers are now working on the next milestone, ensuring that the laser beam can sweep in a circle without using expensive mechanical parts. Vuckovic estimates her lab is about three years away from building a prototype that would be ready for a road test.

“We are on a trajectory to build a lidar-on-a-chip that is cheap enough to help create a mass market for autonomous cars,” Vuckovic said.

Other Stanford co-authors include electrical engineering professors Shanhui Fan and Amin Arbabian, postdoctoral scholars Avik Dutt and Dries Vercruysse, and graduate students Geun Ho Ahn and Mahmoud Sawaby.

About the author:

Tom Abate is associate director of communications at the Stanford University School of Engineering — External Relations.