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How the LIDAR tech GM just bought probably works

arstechnica.com

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Re: How the LIDAR tech GM just bought probably works

#31

Post by joshvm »

Animats wrote: post #9

Interesting. Frequency-modulated continuous-wave LIDAR is easy to do as a one-point device. Many such devices have been built. But they're usually short range, such as the discontinued Swiss Ranger, and don't reject ambient light as effectively as pulse systems. Being both eye-safe and sunlight-tolerant is hard. Eye-safe is easier if you can increase the diameter of the outgoing beam. Eye safety is measured based on…

The Mesa Imaging SwissRanger is an amplitude modulated system, not frequency modulated. It's also not really LIDAR, as it uses LED illumination, but AMCW LIDAR is more or less the same principle. A better comparison might be laser tape measures - these often use phase modulated LIDAR rather than direct ToF. You can also buy phase shift scanning systems from people like Leica Geosystems.

In a ToF camera (at least some of them - see lock-in pixels), each pixel is sampled four times per cycle to detect the phase offset from the outgoing illumination. The SwissRanger was one of the first time of flight cameras. The reason it suffers short range is because of phase ambiguity - the lasers are modulated at around 30MHz which gives a wavelength of 10 m or so. The ambiguity distance is half this (5 m). LIDAR systems historically got round this by using multiple modulation frequencies for different distance scales.

This tech is now everywhere thanks to Microsoft buying Canesta.

Re: How the LIDAR tech GM just bought probably works

#32

Post by joshvm »

deepnotderp wrote: post #10

I have a genuine question to all the LIDAR experts here: all the optical phased array research I've seen, such as the MIT, UCB and DARPA "SWEEPER" work only has a range of something like 2 meters, and 10 meters after lots of work. All the research papers I've seen also mention that accurate and high power phase shifters are a challenge as well as getting the optical phased array to a high enough output power. On the…

The Quanergy system looks like it's doing conventional pulsed time of flight (maybe FMCW, but I don't know). They're operating in a frequency band that lets them put out a lot of power without risking eye safety, which means long range. Pulsed LIDAR is basically limited only by signal to noise, so provided you get some photons back and you know they're 'yours', you can measure long distances.

Re: How the LIDAR tech GM just bought probably works

#33

Post by Cerium »

mseebach wrote: post #29
jacksmith21006 wrote: post #27

Earlier quoted context omitted.

People will not be buying for a long time. Use will come through ride sharing services.

That's irrelevant. 7 cents per mile in LIDAR costs is expensive, regardless of how the vehicle is owned and it's use charged.

7 cents per mile on LIDAR would be reasonable in a truly driver-less system. Uber costs like $2.8/mile and vehicle cost estimates are usually around $0.5/mile, leaving a healthy overhead for a driver-less system to live in.

Re: How the LIDAR tech GM just bought probably works

#35

Post by iamleppert »

Wondering why no one has thought of using a Acousto-optic modulator? https://en.wikipedia.org/wiki/Acousto-optic_modulator

It's solid state, has a very fast response time, super cheap to manufacture, and can steer a beam with high precision. And they are very efficient, achieving a >90% first-order diffraction efficiency. The AOM material can be solid and thermally insulating (such as glass), so you can get very high power.

In the paper cited, they produced a device that had an effective power of 4 mW with active cooling. How are they going to scale this up, taking into consideration first order diffraction depends on the angle of incidence of the incoming beam? The steering mechanism is basically a tunable diffraction grating which means the active area is going to be tiny.

Most high power diffraction gratings work by expanding the surface area of the grating, it would still be very expensive to create a large tunable waveguide/grating (think how much it costs to make a CPU die), making the whole cost savings of solid state a moot point. You could make an array of the devices, but you're going to need a ton of them to get the necessary power and reasonable deflection angle range.

Re: How the LIDAR tech GM just bought probably works

#36

Post by deepnotderp »

joshvm wrote: post #32
deepnotderp wrote: post #10

I have a genuine question to all the LIDAR experts here: all the optical phased array research I've seen, such as the MIT, UCB and DARPA "SWEEPER" work only has a range of something like 2 meters, and 10 meters after lots of work. All the research papers I've seen also mention that accurate and high power phase shifters are a challenge as well as getting the optical phased array to a high enough output power. On the…

The Quanergy system looks like it's doing conventional pulsed time of flight (maybe FMCW, but I don't know). They're operating in a frequency band that lets them put out a lot of power without risking eye safety, which means long range. Pulsed LIDAR is basically limited only by signal to noise, so provided you get some photons back and you know they're 'yours', you can measure long distances.

The DARPA SWEEPER was also pulsed lidar, and it only had a range of 2 meters. And the problem really isn't the regulations for power output at the wavelength, but rather that the optical phased array itself can't put out the necessary power, regulations notwithstanding.

Re: How the LIDAR tech GM just bought probably works

#37

Post by baybal2 »

deepnotderp wrote: post #30
baybal2 wrote: post #28

I genuinely don't understand obsession with LIDARs in the autonomous vehicle community, a millimetre wave radar is late seventies tech, does the job many times better, for less money, and can be made by an electronics engineering undergrad from radio shack parts. Commies had them in such abundance that they put millimetre wave imagers (and that was in seventies) on thing as cheap as vision aids for tank drivers, fiel…

Resolution?

Theoretical one is lower than that of lidar, but in practice a well made mm-wave radar, currently, has superior resolution to commercially available lidars

Re: How the LIDAR tech GM just bought probably works

#38

Post by randyrand »

JoblessWonder wrote: post #25
generj wrote: post #2

One of the advantages for solid-state LIDAR has to be an increase in reliability. Nobody wants to buy a car which requires a new LIDAR to be installed after 100,000 miles for the sum of $7,000. Hopefully once production starts and yield rates increase the unit costs can shrink small enough to being becoming feasible for integration into lower-end products like cell phones or laptops. I think there are a lot of cool a…

It will probably lead to the advent of the "car as as service" sales model. Although the pushback from traditional dealers will be huge.

For cities yes. For suburbs and rural areas, not as much.

Re: How the LIDAR tech GM just bought probably works

#39

Post by icebraining »

olegkikin wrote: post #22
mrfusion wrote: post #15

Earlier quoted context omitted.

Don’t forget you can also drive reasonably well with one eye closed. The stereo stuff isn’t buying you much for driving.

Humans tend to move their heads, which is why one-eyed depth perception still works.

Humans can also drive RC cars, airplanes, quadcopters, etc using a single unmovable camera.

Re: How the LIDAR tech GM just bought probably works

#40

Post by Symmetry »

baybal2 wrote: post #28

I genuinely don't understand obsession with LIDARs in the autonomous vehicle community, a millimetre wave radar is late seventies tech, does the job many times better, for less money, and can be made by an electronics engineering undergrad from radio shack parts. Commies had them in such abundance that they put millimetre wave imagers (and that was in seventies) on thing as cheap as vision aids for tank drivers, fiel…

Normally with radar you get very precise range and radial velocity measurements but very slopping phi and theta.
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