All about automotive lidar

Adding a comment here with some info on LIDAR human safety, since many are asking.

There are two wavelengths of interest used:

  a) 905 nm/940 nm (roof and bumpers): 70–100 µJ per pulse max, regulated by IEC 60825 since this WL is focused on the retina
  b) 1550 nm systems (the Laser Bear Honeycomb): 8–12 mJ per pulse allowed (100x more photons since this WL stays the cornea)

20 cars at an intersection = 20 overlapping scanners, meaning even if each meets single-device Class 1, linear addition could offer your retina a 20x dose enough to push into Class 3B territory. The current regs (IEC 60825-1:2014) assume single-source exposure. There is no standard for multi-source, multi-axis, moving-platform overlay.

Additionally, no LIDAR manufacturer publishes beam-failure shutoff latency. Most are >50ms, which can be long enough for permanent injury

Having built a LiDAR system for an autonomy company in the past, this is a great write-up, but it omits what I found to be one of the more interesting challenges. For our system (bistatic, discrete edge-emitting laser diodes and APDs; much like a Velodyne system at high level), we had about an inch of separation between our laser diodes and our photodiodes. With 70 A peak currents through the laser diodes. And nanoamp sensitivity in the photodiodes. EMI is... interesting. Many similar lidars ignore the problem by blanking out responses very close to firing time, giving a minimum range sensitivity, and by waiting for maximum delay to elapse before firing the next salvo -- but this gives a maximum fire rate that can be an issue. For example, a 32 channel system running at 20 kHz/channel would be limited to ~200 m range (468 m round trip delay, some blanking time needed)... so to get both high rate (horizontal resolution) and high channel count (vertical resolution), you need to be able to ignore your own cross-talk and be able to fire when beams are in flight.

Some correction here. FMCW lidar does not need fiber lasers. In fact most fiber lasers are actually very difficult to frequency sweep internally. Typical lasers used in swept wavelength interferometry (which is really the same thing) are so-called external cavity lasers, which rely on photodiodes + external cavity e.g. through a wavelength selective feedback (still comparably expensive though).

Baraja selling point was AFAIK that they used a integrated swept laser source (they typically have lower coherence but you can work around that in DSP).

In the current state of self-driving tech, lidar is clearly the most effective and safest option. Yet companies like Tesla refuse to integrate lidar, preferring to rely solely on cameras. This is partially to keep costs down. But this means the Tesla self-driving isn't quite as good as Waymo, which sits pretty comfortably at level 4 autonomy.

But humans have no lidar technology. We rely almost solely on sight for driving (and a tiny bit on sound I guess). Hence in principle it should be possible for cars to do so too. My question is this: at what point, if at all, will self-driving get good enough to make automotive lidar redundant? Or will it always be able to make the self-driving 1% better than just cameras?

I learned a lot from this article. The breakdown of the different LiDAR types and how they fit into real automotive sensor stacks was especially helpful. Nice to see a clear explanation without the usual hype or ideology around cameras vs. LiDAR.

I am surprised that I didn’t see discussion about Audi’s lidar that’s been in use in production vehicles now. Yes, it’s on a different level, only used for ADAS, but it’s still lidar that’s actively used.

I do wonder what’s preventing a Lidar device from cross talking with other lidar devices. I remember talking to somebody about this and they told me that each signal is uniquely encoded per machine.

This seems like it will be a growing problem with increased autonomy on the roads

No mention of flash LIDAR, which really ought to be seen more for the short-range units for side and rear views.

Interference between LIDARs can be a problem, mostly with the continuous-wave emitters. Pulsed emitters are unlikely to collide in time, especially if you put some random jitter in the pulse timing to prevent it. The radar people figured this out decades ago.

The discrete array, must be accurate for them to be close like that and not get overlap (eg. receiver 1 gets beam from emitter 2)

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