By Junko Yoshida for EETIMES – Argo AI this week teased a few details of its lidars based on Geiger-mode sensing, a relatively uncommon technology. The company will outfit its entire testing fleet (roughly 200 vehicles) with the new lidars before the end of this year.
The self-driving car developer (Pittsburgh, Penn) uses avalanche photodiode technology originally developed by Princeton Lightwave (Cranberry, NJ), which Argo acquired in 2017, complete with its IP, technology and its team of more than fifty engineers.
For years, Argo has kept a tight lid on the progress with the Princeton Lightwave deal. Argo’s lidar also proves that the automotive lidar market remains deeply in flux. None of the leading autonomous vehicle companies — including Waymo, Aurora, Cruise and Argo — is betting its future on off-the-shelf lidars. (Many, however, have been using Velodyne’s lidars, spinning on the rooftops of their test vehicles.)
Rather, they have opted to design lidars of their own. However, among the leading AV developers, lidar technologies are all over the map, in terms of lidar physics (e.g., linear time of flight, ToF with photon counting detectors, frequency-modulated continuous-wave), operating wavelengths (850nm – 940nm, 1400nm -1550nm), and field of view (flash versus scanning).
No single winning technology has yet emerged.
In an interview with EE Times, Zach Little, senior director of hardware and firmware development at Argo AI, described Argo lidar as “unique.” He cited three factors: the use of a wavelength above 1400nm, a single photon, and a 360-degree horizontal field of view.
A single photon generated by Argo’s Geiger-mode lidars is critical to sensing objects with low reflectivity, according to Argo. Operating at higher wavelength, above 1400nm, gives longer range and higher resolution.
A full field of view is also important, added Little. While Argo’s lidar is a ToF flash lidar, it sits on top of a mechanically rotating pedestal, giving it a 360-degree horizontal field of view.
To Argo’s credit, the company isn’t pitching its lidar as a panacea. Little acknowledged compromises are inherent in the technology. In his opinion, in developing lidars, it is vital that the self-driving car’s perception team know exactly the perception problems it wants a lidar to solve, as well as the tradeoffs necessary to the solution.
It turns out that detecting dark targets, like black cars, is a challenge for most lidars.
For example, if the target is a white car, 80 percent of the light hit by a lidar will come back. “But there are dark cars in the market that less than 1% of the light comes back,” said Little.
That got Argo thinking of what happens in an unprotected left turn and you want to see if there’s a car coming. “Being able to see a 10 percent target at 200 meters wouldn’t help you,” he said. In developing its lidar, Argo’s team determined that its lidar should be able to see dark targets even when those targets are still farther up the road.
Pierrick Boulay, market and technology analyst at Yole Développement (Lyon, France), told EE Times, “Reflectivity of object is key for all lidar manufacturers. This is linked to the detection range.” But using “single photon detection,” as in Argo’s lidar, could “improve the detection, even for low reflectivity objects,” he added.
A case in point is a demo carried out at the 2019 Frankfurt Motor Show. BMW painted its X6 “Vantablack” which has reflectivity around 1 percent, said Boulay. “Ouster tested its lidar on this car. The outcome [in its PR stunt] was that the lidar still saw the car, but the detection range was reduced.”
Why go above 1400nm?
The use of wavelength above 1400nm in Argo’s lidar also contributes to its ability to see dark targets. Higher wavelength is “the biggest knob you have to determine how much [light] you can get back off the target,” explained Little.
The majority of lidar makers are using 905nm, but 1550nm is “gaining momentum today,” observed Boulay.
Longer wavelengths are in the works at Luminar, AEye, Cruise, Baraja, Aurora (previously Blackmore), Scantinel Photonics (Ulm, Germany), Innovusion (Sunnyvale, Calif.), or SiLC (Monrovia, Calif.), he noted, although the list isn’t exhaustive. Boulay sees that 1550nm will be increasingly deployed for lidars using silicon photonics.
Yole’s Boulay added that one of the main advantages of long-wavelength lidar is “related to eye safety.” Since longer wavelength lidar solutions can safely emit more laser energy than short wavelength lidar, they can achieve longer sensing distances while still being eye-safe… Full article
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