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10 Platform one Engineers at the University of California, Berkeley, have used MEMS switches to dramatically increase the resolution of chip- based Lidar sensors (writes Nick Flaherty). The Lidar is based on a focal plane switch array (FPSA), a semiconductor- based matrix of antennas that gathers light in a similar way to an optical camera sensor. The resolution, of 16,384 pixels, is far higher than the current 512 pixel resolution on current FPSAs, said Ming Wu, professor of electrical engineering and computer sciences, and co-director of the Berkeley Sensor and Actuator Center at Berkeley. The design is scalable to megapixel sizes using standard CMOS chip- making process technology for low- cost Lidar sensors in all types of autonomous vehicles. “We want to illuminate a very large area,” said Prof Wu. “But if we try to do that, the light becomes too weak to reach a sufficient distance. So, as a design trade-off to maintain light intensity, we reduce the areas that we illuminate with our laser light.” The FPSA consists of a matrix of tiny optical antennas, and switches them rapidly on and off to channel all available laser power through a single antenna. However, this switching poses problems. Almost all silicon-based Lidar systems use thermo-optic switches that rely on large changes in temperature to produce small changes in the refractive index and bend or redirect laser light from one waveguide to another. These are both large and power- hungry. Instead, a MEMS switch physically moves the waveguides from one position to another, allowing each pixel to share one or more Lidar ranging units, reducing the size and power consumption of the overall system. This is the first time MEMS switching has been applied to Lidar, and allows the 16,384 pixels on a 10 x 11 mm chip. When the switch turns on a pixel, it emits a laser beam and captures the reflected light. Each pixel is equivalent to 0.6 º of the array’s 70 º FoV. By cycling rapidly through the array, the FPSA builds up a 3D picture. Mounting several of them in a circular configuration would produce a 360 º view around a vehicle. “While the optical antennas are hard to make smaller, the switches are still the largest components, and we think we can make them a lot smaller,” Prof Wu said. The sensor currently has a range of only 10 m, limited by the power of the LED laser and the power through the MEMS switch. “We are certain we can get to 100 m though, and believe we could get to 300 m with continual improvement,” he said. The footprint of the current pixel (55×55µm 2 ) can be reduced by optimising the design of the MEMS switches and switch couplers. It is feasible to shrink the pixel to 10×10µm 2 for megapixel Lidar with a 1×1 cm 2 FPSA, which will provide an angular resolution of 0.11. MEMS boost for Lidars Lidar 3D images are obtained by sequentially turning on the switches in the array April/May 2022 | Unmanned Systems Technology If we try illuminating a very large area, the light becomes too weak to reach a sufficient distance so we reduce the areas we illuminate with the laser light