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Lidar, optical distance and time of flight sensors

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Re: Lidar, optical distance and time of flight sensors

#11

Post by jlokier »

MezzoDelCammin wrote: post #5
jeffreygoesto wrote: post #3

Earlier quoted context omitted.

Non-scanning means your flash emits the equivalent of all the beams at the same time. Look at their flagship spec, you must master 160A next to the other electronics. Two board designs are more expensive and error prone, can't get 160 amps through a flex-cable easily. Then there is the opening angle, you need wide _and_ long, at least for front and rear facing and the optics for that are challenging. Another influenc…

Also there's the simple physics view of the same problem. The advantage of scanning is that you can focus all the laser pulse energy into one narrow beam. Non scanning means covering the whole field of view at once with that same laser pulse. Then you have a choice. Either somehow deal with the exponentially weaker return pulse (since it's spread over the whole field of view), or try to increase the pulse energy (and…

From a physics point of view, continuous transmission and correlation detection of a temporally- and spatially-diverse optical signal over the entire field of view addresses the problem of energy being spread out, and gets you better, more robust depth information for less emitted energy than scanning or full-field flashes.

But from an optical and electronics point of view, it's much harder to process the return signal that way, and probably uses a lot more energy due to the processing required (with current tech).

Re: Lidar, optical distance and time of flight sensors

#12

Post by rowanG077 »

amelius wrote: post #10

Slightly offtopic, why is it so difficult to find a cheap and compact laser interferometer that can do sub-micron measurements? This guy gets close: https://www.youtube.com/watch?v=MUdro-6u2Zg&t=770s But why isn't something cheap and small like this commercially available as an integrated system?

They are available cheaply. You can purchase a blu ray reader and hack it. The reason a ready packaged sensor is not available cheaply is simply because of economics and market size.

Re: Lidar, optical distance and time of flight sensors

#13

Post by jbay808 »

amelius wrote: post #10

Slightly offtopic, why is it so difficult to find a cheap and compact laser interferometer that can do sub-micron measurements? This guy gets close: https://www.youtube.com/watch?v=MUdro-6u2Zg&t=770s But why isn't something cheap and small like this commercially available as an integrated system?

It's mainly the laser itself that is the expensive part. If you only care about resolution it's easy, you just need a single-mode laser. But if you care about accuracy it's very difficult, because then the wavelength needs to be stable, and that requires a much more expensive laser. Most people looking for an interferometer are interested in accuracy, unless they're just measuring vibrations.

Re: Lidar, optical distance and time of flight sensors

#14

Post by rowanG077 »

jbay808 wrote: post #13
amelius wrote: post #10

Slightly offtopic, why is it so difficult to find a cheap and compact laser interferometer that can do sub-micron measurements? This guy gets close: https://www.youtube.com/watch?v=MUdro-6u2Zg&t=770s But why isn't something cheap and small like this commercially available as an integrated system?

It's mainly the laser itself that is the expensive part. If you only care about resolution it's easy, you just need a single-mode laser. But if you care about accuracy it's very difficult, because then the wavelength needs to be stable, and that requires a much more expensive laser. Most people looking for an interferometer are interested in accuracy, unless they're just measuring vibrations.

You can get pretty far with cheap diodes + current and temperature control. Unless you need coherence lengths in the meters range you can make do with cheaper lasers.

Re: Lidar, optical distance and time of flight sensors

#15

Post by amelius »

jbay808 wrote: post #13
amelius wrote: post #10

Slightly offtopic, why is it so difficult to find a cheap and compact laser interferometer that can do sub-micron measurements? This guy gets close: https://www.youtube.com/watch?v=MUdro-6u2Zg&t=770s But why isn't something cheap and small like this commercially available as an integrated system?

It's mainly the laser itself that is the expensive part. If you only care about resolution it's easy, you just need a single-mode laser. But if you care about accuracy it's very difficult, because then the wavelength needs to be stable, and that requires a much more expensive laser. Most people looking for an interferometer are interested in accuracy, unless they're just measuring vibrations.

Can't you solve the stable wavelength issue by using a beamsplitter and a separate reference arm?

Re: Lidar, optical distance and time of flight sensors

#16

Post by amelius »

rowanG077 wrote: post #12
amelius wrote: post #10

Slightly offtopic, why is it so difficult to find a cheap and compact laser interferometer that can do sub-micron measurements? This guy gets close: https://www.youtube.com/watch?v=MUdro-6u2Zg&t=770s But why isn't something cheap and small like this commercially available as an integrated system?

They are available cheaply. You can purchase a blu ray reader and hack it. The reason a ready packaged sensor is not available cheaply is simply because of economics and market size.

I'm not convinced by the market/economics argument. Cheap and small ToF sensors exist, even though the market initially was also small.

Re: Lidar, optical distance and time of flight sensors

#17

Post by mahirsaid »

jeffreygoesto wrote: post #3
Animats wrote: post #2

I was expecting flash LIDAR and MEMS mirror systems to dominate self-driving cars by now, but rotating machinery is still dominant in the US. The trend in China and Japan is a long-range forward-facing LIDAR coupled with three shorter-range units for side and rear coverage.[1] The long-range unit still costs around US$10,000. This should come down with volume. [1] https://www.robosense.ai/en/news-show-1908 [2] https:…

Non-scanning means your flash emits the equivalent of all the beams at the same time. Look at their flagship spec, you must master 160A next to the other electronics. Two board designs are more expensive and error prone, can't get 160 amps through a flex-cable easily. Then there is the opening angle, you need wide _and_ long, at least for front and rear facing and the optics for that are challenging. Another influenc…

While i was reading this article i did find another article (AD) that was showcasing a product of LidAR tech in a small package. It seems unpractical to be very useful a long sim module with its own processing unit and on board electronics. The require space for the module to be installed was above the windshield and the roof. Much like other products of the same category, however this was a lot more compact. Seems to be a push for further compact innovation in this category. i was under the impression there was no need for multiple LIdar module on one vehicle, all you needed was one along with cameras to further assist the LIdar module .I do know that under normal operation the LIdar and camera system are separate and have different responsibilities.

Re: Lidar, optical distance and time of flight sensors

#18

Post by Animats »

jeffreygoesto wrote: post #3
Animats wrote: post #2

I was expecting flash LIDAR and MEMS mirror systems to dominate self-driving cars by now, but rotating machinery is still dominant in the US. The trend in China and Japan is a long-range forward-facing LIDAR coupled with three shorter-range units for side and rear coverage.[1] The long-range unit still costs around US$10,000. This should come down with volume. [1] https://www.robosense.ai/en/news-show-1908 [2] https:…

Non-scanning means your flash emits the equivalent of all the beams at the same time. Look at their flagship spec, you must master 160A next to the other electronics. Two board designs are more expensive and error prone, can't get 160 amps through a flex-cable easily. Then there is the opening angle, you need wide _and_ long, at least for front and rear facing and the optics for that are challenging. Another influenc…

> 160A

For how long? Can't be continuous. What's average power. Yes, flash LIDAR has a power problem. How does their long-range LIDAR work?

> Another influence certainly is that the automated driving craze has been superseded by the AI craze and scaling won't come in the time frame that was predicted some years ago.

Huh. Good point. Want to think about that one.

We might max out at most taxis being self-driving, because that works and sells, but not make it to personal vehicles.

> P.S.: a QNX desktop is possible and actually alive again, but company politics... :/

I'm out of that now. The closed source/open souce/closed source/open source/closed source transitions angered too many people. There was once Netscape/Firefox for QNX.

Re: Lidar, optical distance and time of flight sensors

#19

Post by rowanG077 »

amelius wrote: post #16
rowanG077 wrote: post #12

Earlier quoted context omitted.

They are available cheaply. You can purchase a blu ray reader and hack it. The reason a ready packaged sensor is not available cheaply is simply because of economics and market size.

I'm not convinced by the market/economics argument. Cheap and small ToF sensors exist, even though the market initially was also small.

ToF sensors have huge applications. Initially ToF sensors also cost thousands of dollars. What huge applications do you see that should have driven the prices of over the counter integrable interferometers down? As I stated blu ray (and DVD, CD and laser disc before it) readers are tiny purpose build inferometers. And they are cheap.

Re: Lidar, optical distance and time of flight sensors

#20

Post by tubs »

MezzoDelCammin wrote: post #5
jeffreygoesto wrote: post #3

Earlier quoted context omitted.

Non-scanning means your flash emits the equivalent of all the beams at the same time. Look at their flagship spec, you must master 160A next to the other electronics. Two board designs are more expensive and error prone, can't get 160 amps through a flex-cable easily. Then there is the opening angle, you need wide _and_ long, at least for front and rear facing and the optics for that are challenging. Another influenc…

Also there's the simple physics view of the same problem. The advantage of scanning is that you can focus all the laser pulse energy into one narrow beam. Non scanning means covering the whole field of view at once with that same laser pulse. Then you have a choice. Either somehow deal with the exponentially weaker return pulse (since it's spread over the whole field of view), or try to increase the pulse energy (and…

Quadratically weaker, not exponentially.
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