Researchers at MIT’s Photonic Microsystems Group are developing a LiDAR-on-a-chip system that is smaller than a dime, has no moving parts, and could be mass produced at a very low cost to be used in self-driving cars, drones, and robots. An article describing the new system is published in IEEE Spectrum.
Most LiDAR systems—like the ones commonly seen on autonomous vehicles—use discrete free-space optical components like lasers, lenses, and external receivers. In order to have a useful field of view, this laser/receiver module is mechanically spun around, often while being oscillated up and down. This mechanical apparatus limits the scan rate of the LiDAR system while increasing both size and complexity, leading to concerns about long-term reliability, especially in harsh environments. Today, commercially available high-end LiDAR systems can range from $1,000 to upwards of $70,000, which can limit their applications where cost must be minimized.
Applications such as autonomous vehicles and robotics heavily depend on LiDAR, and an expensive LiDAR module is a major obstacle to their use in commercial products. Our work at MIT’s Photonic Microsystems Group is trying to take these large, expensive, mechanical LiDAR systems and integrate them on a microchip that can be mass produced in commercial CMOS foundries.
Our LiDAR chips promise to be orders of magnitude smaller, lighter, and cheaper than LiDAR systems available on the market today. They also have the potential to be much more robust because of the lack of moving parts, with a non-mechanical beam steering 1,000 times faster than what is currently achieved in mechanical LiDAR systems.—Christopher V. Poulton and Michael R. Watts
The device is a 0.5 mm x 6 mm silicon photonic chip with steerable transmitting and receiving phased arrays and on-chip germanium photodetectors. The laser itself is not integrated into the chips; however, there are on-chip lasers that could be integrated in the future.
In the current version of the LiDAR chip, thermal phase shifters directly heat waveguides through which the laser propagates. Silicon’s index of refraction—which changes the speed and phase of light passing through it—depends on its temperature. As the laser passes through the waveguide, it encounters a notch fabricated in the silicon, which acts as an antenna, scattering the light out of the waveguide and into free space. Each antenna has its own emission pattern, and where all of the emission patterns constructively interfere, a focused beam is created without a need for lenses.
The current on-chip LiDAR system can detect objects at ranges of up to 2 meters; the researchers are hoping to achieve a 10-meter range within a year. They said there is a clear development path towards technology that can reach 100 meters, with the possibility of going even farther.
The MIT team is producing the LiDAR chips on 300-millimeter wafers, making their potential production cost on the order of $10 each at production volumes of millions of units per year.