Friday, November 09, 2018

Ouster Discusses its LiDAR Principles

PRNewswire: Ouster unveils the details of its LiDAR technology. Several breakthroughs covered by recently granted patents have enabled Ouster's move toward state-of-the art, high volume, silicon-based sensors and lasers that operate in a near-infrared light spectrum.

Ouster's multi-beam Lidar is said to carry significant advantages over traditional approaches:

True solid state - Ouster's core technology is a two chip (one monolithic laser array, one monolithic receiver ASIC) solid state lidar core, which is integrated in the mechanically scanning product lines (the OS-1 and OS-2) and will be configured as a standalone device in a future solid state product. Unlike competing solid state technologies, Ouster's two chip lidar core contains no moving parts on the macro or micro scale while retaining the performance advantages of scanning systems through its multi-beam flash lidar technology.

Lower cost at higher resolution - Ouster's OS-1 64 sensor costs nearly 85% less than competing sensors, making it the most economical sensor on the market. In an industry first, Ouster has decoupled cost from increases in resolution by placing all critical functionality on scalable semiconductor dies.

Simplified architecture - Ouster's multi-beam flash lidar sensor contains a vastly simpler architecture than other systems. The OS-1 64 contains just two custom semiconductor chips capable of firing lasers and sensing the light that reflects back to the sensor. This approach replaces the thousands of discrete, delicately positioned components in a traditional lidar with just two.

Smaller size and weight - Because of the sensor's simpler architecture, Ouster's devices are significantly smaller, lighter weight and more power efficient, making them a perfect fit for unmanned aerial vehicles (UAVs), handheld and backpack-based mapping applications, and small robotic platforms. With lower power and more resolution, drone and handheld systems can run longer and scan faster for significant increases in system productivity.

In an article on the company's website, CEO Angus Pacala wrote, "I'm excited to announce that Ouster has been granted foundational patents for our unique multi-beam flash lidar technology which allows me to talk more openly about the incredible technology we've developed over the last three years and why we're going to lead the market with a portfolio of low-cost, compact, semiconductor-based lidar sensors in both scanning and solid state configurations."

The US10063849 "Optical system for collecting distance information within a field" and US9989406 "Systems and methods for calibrating an optical distance sensor." disclose LiDAR Tx side consisting of an array of VCSEL lasers and Rx side - an array of SPADs. The VCSEL lasers project an set of points on the subject, while each SPAD has a small FOV aligned with the projection point in order to cut the ambient light. Also, the Rx side optics has a 2nm-narrow spectral filter, again to cut more of the ambient light illumination. All this is placed on a rotating platform:

Angus Pacala also publishes an explanatory article in the Company's blog on Medium and gives an interview to ArsTechnica. Few quotes:

"While our technology is applicable to a wide range of wavelengths, one of the more unique aspects of our sensors is their 850 nm operating wavelength. The lasers in a lidar sensor must overcome the ambient sunlight in the environment in order to see obstacles. As a result lidar engineers often choose operating wavelengths in regions of low solar flux to ease system design. Our decision to operate at 850 nm runs counter to this trend.

A plot of solar photon flux versus wavelength at ground level (the amount of sunlight hitting the earth versus wavelength) shows that at 850 nm there is almost 2x more sunlight than at 905 nm, up to 10x more sunlight than at 940nm, and up to 3x more sunlight than 1550 nm — all operating wavelengths of legacy lidar systems.

We’ve gotten plenty of strange looks for our choice given that it runs counter to the rest of the industry. However, one of our patented breakthroughs is exceptional ambient light rejection which makes the effective ambient flux that our sensor sees far lower than the effective flux of other lidar sensors at other wavelengths, even accounting for the differences in solar spectrum. Our IP turns what would ordinarily be a disadvantage into a number of critical advantages:

  • Better performance in humidity
  • Improved sensitivity in CMOS: Silicon CMOS detectors are far more sensitive at 850 nm than at longer wavelengths. There is as much as a 2x reduction in sensitivity just between 850 and 905 nm. Designing our system at 850 nm allows us to detect more of the laser light reflected back towards our sensor which equates to longer range and higher resolution.
  • High quality ambient imagery
  • Access to lower power, higher efficiency technologies

...the flood illumination in a conventional flash lidar, while simpler to develop, wastes laser power on locations the detectors aren’t looking. By sending out precision beams only where our detectors are looking, we achieve a major efficiency improvement over a conventional flash lidar.

Our single VCSEL die has the added advantage of massively reducing system complexity and cost. Where other lidar sensors have tens or even hundreds of expensive laser chips and laser driver circuits painstakingly placed on a circuit board, Ouster sensors use a single laser driver and a single laser die. A sliver of glass no bigger than a grain of rice is all that’s needed for an OS-1–64 to see 140 meters in every direction. It’s an incredible achievement of micro-fabrication that our team has gotten this to work at all, let alone so well.

The second chip in our flash lidar is our custom designed CMOS detector ASIC that incorporates an advanced single photon avalanche diode (SPAD) array. Developing our own ASICs is key to our breakthrough performance and cost, but the approach is not without risk. Ouster’s ASIC team has distinguished themselves time and again and they’ve now delivered seven successful ASICs — each more powerful, more reliable, and more refined than the previous."


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