LiDAR Chip Gets a Boost From MEMS Switching to Hit a “Record” Resolution
New research from UC Berkeley leverages micro-electromechanical system (MEMS) in LiDAR focal plane switch arrays (FPSAs) to achieve "record resolution." What challenges did they overcome to reach this record?
Most companies pursuing autonomous vehicles (AVs) currently use LiDAR in some capacity. LiDAR has become a crucial sensor due to its ability for high resolution at long range and its immunity to environmental conditions such as lighting or weather.
However, LiDAR is far from perfect, and many different forms of LiDAR compete to be the future of the technology.
Examples of LiDAR technology and applications. Image used courtesy of Yole Développement
Adding to this competition, recently, researchers from the University of California Berkeley published a new research paper describing a new, MEMS-based FPSA LiDAR system that claims impressive performance specs.
This article will discuss FPSA technology, the challenges it faces, and how Berkeley researchers aim to solve these problems.
One of the major technologies being researched in pursuit of solid-state LiDAR is the FPSA.
FPSA is a technology that works by having each LiDAR pixel consisting of a single optical antenna, a thermo-optic phase shifter, or a switch. These pixels are arranged in a matrix with one pixel being driven at a time, where the pixel’s switch controls the power delivery to each antenna.
Like a camera’s optical system, each angle within the FPSA’s field of view (FOV) gets mapped back to a pixel, gathering light and creating a 3D map of the illuminated area.
A focal plane switch array beam scanner. Image used courtesy of Zhang et al
The idea behind FPSA technology is that, by driving each pixel at a time, each pixel can receive all of the driving laser’s available power, meaning further range and higher resolution.
Along with range and resolution, FPSAs could be promising candidates for solid-state LiDAR because they allow electronic scanning without mechanical moving parts.
Further, the small number of components allows for many of these pixels to be integrated into a single chip.
FPSA LiDAR Challenges
FPSA LiDAR, while offering many benefits, has one glaring drawback: it is limited in scale.
The major challenge with achieving large-scale FPSA LiDAR is that the thermo-optic switches are susceptible to temperature.
The switches work by converting applied electric fields to changes in temperature, which modify the silicon waveguide's refractive index. The effective refractive indexes help control the direction of the incident light and effectively navigate the FPSA laser to the desired pixel.
However, the shortcoming of this approach is that the switches are very power-hungry and generate a lot of heat. This drawback limits the ability to densely integrate many pixels in a single FPSA, as the cumulative heat eventually leads to failures.
To this point, FPSAs have been limited to a maximum of 512 pixels.
Berkeley's Approach for MEMS FPSA LiDAR
Hoping to push beyond the limits for FPSA LiDAR, researchers from Berkeley describe a new approach to FPSA that aims to resolve the challenges mentioned above.
To sidestep the thermal challenges in FSPA LiDAR, the researchers opted to use MEMS switches instead of thermo-optic switches.
In this scheme, the FSPA array selects a given pixel by physically moving a waveguide in the correct orientation, directing all of the laser's incident light to the given pixel's antenna. The chip can take a 360-degree scan of its environment by switching across the entire array.
Fabrication of the new FSPA technology. Image used courtesy of Zhang et al
All in all, the researchers claim that the benefits of this new approach for FPSA LiDAR technologies were tremendous, as the MEMS switches were lighter, smaller, and far less power-hungry than their thermo-optic counterparts.
The resulting device created a 128x128 array of pixels onto a 1 square cm solid-state chip. The researchers claim that the 16,348 pixels on this chip far exceed the previous maximum amount achieved, making this the highest resolution solid-state FPSA chip on the market.
This array was able to achieve a 70-degree FOV, with each pixel accounting for 0.6 degrees.
With more research pouring into newer and better LiDAR systems and technology, it will be interesting to see what gets picked up or adapted for actual market use.