The article talks about eye safety a bit in section 4.

> a stuck mirror

This is one of the advantages of using an array of low power lasers rather than steering a single high power laser. The array physically doesn't have a failure mode where the power gets concentrated in a single direction. Anyway, theoretically, you would hope that class 1 eye-safe lidars should be eye safe even at point blank range, meaning that even if the beam gets stuck pointing into your eye, it would still be more or less safe.

> 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.

In the article, I point out a small nuance: If you have many lidars around, the beams from each 905 nm lidar will be focused to a different spot on your retina, and you are no worse off than if there was a single lidar. But if there are many 1550 nm lidars around, their beams will have a cumulative effect at heating up your cornea, potentially exceeding the safety threshold.

Also, if a lidar is eye-safe at point blank range, when you have multiple cars tens of meters away, laser beam divergence already starts to reduce the intensity, not to mention that when the lidars are scanning properly, the probability of all of them pointing in the same spot is almost impossible.

I was always curious about this, it's impossible to find any safety certifications or details about the lidars used by e.g. Waymo. Are we supposed to just trust that they didn't cut corners, especially given the financial incentives to convince people that lidar is necessary (because there's a notable competitor that doesn't use it).

To date most class-1 lasers have also been hidden/enclosed I think (and there is class 1M for limited medical use), so I'm not convinced that the limits for long-term daily exposure have been properly studied.

Until I see 3rd party studies otherwise, I plan to treat vehicle lidar no different than laser pointers and avoid looking directly at them. If/when cars become common enough that this is too hard to do, maybe I'll purchase NIR blocking glasses (though most ones I found have an ugly green tint, I wonder if it's possible to make the frequency cutoff sharp enough that it doesn't filter out visible reds).

A quick note about units -- you correctly quote the limits as an energy-per-pulse limit. The theory behind this is that pulses are short enough that rotation during a pulse is negligible, so they tend to hit a single point (on the retina, at focusable frequencies; the cornea itself for longer wave lengths), and the absorption of that energy is what causes damage. But LiDAR range is determined not by energy per pulse, but by power. This drives a desire for minimum-time pulses, often < 10 ns -- if you can halve your pulse length, you can increase your range substantially while still being eye-safe. GaNFETs are one of the enabling technologies for pulsed lidar, since they're really the only way out there to steer tens of amps in single-digit nanoseconds. Even once you've solved generating short pulses, though, you still need to interpret short responses. Which drives either a need for very fast ADCs (gigasample+), or TDCs, which are themselves fascinating components.

> There are two wavelengths of interest used

Ouster uses (or at least used to use, not sure if they still do) 840 nm. Much higher quantum efficiency for standard silicon receivers, without having to play games with stressed silicon and stuff; but also much better focusing by the retina, so lower power permitted.

200m range seems adequate for passenger vehicle use. Even at 100kph that's over 7 seconds to cover the distance even if you aren't trying to slow down. I think there is diminishing returns with chasing even longer ranges. Even fully loaded trucks are expected to stop in about 160m or so.

>we had about an inch of separation between our laser diodes and our photodiodes

Why can't you place them further away from each other using an additional optical system (i.e. a mirror) and adjusting for the additional distance in software?

> My question is this: at what point, if at all, will self-driving get good enough to make automotive lidar redundant?

By 2018, if you listen to certain circa-2015 full self-driving technologists.

There are unquestionably some cases where Lidar adds actual data that cameras can't see and is relevant to driving accuracy. So the real question is whether there are cases where Lidar actually hurts. I think that is possible but unlikely to be the case.

Many humans do a really bad job at driving, so I'm not sure we should try to emulate that.

And it is certain that in India they use sound sound for echolocation.

A flash lidar is simply a 2D array of detectors plus a light source that's not imaged. It's mentioned super briefly at the start of section 3 but you're right, I should have gone into more detail given how common and important they are.

For pulsed emitters, indeed adding random jitter in the timing would avoid the problem of multiple lidars being synced up and firing at the same time. For some SPAD sensors, it's common to emit a train of multiple pulses to make a single measurement. Adding random jitter between them is a known and useful trick to mitigate interference. But in fact it isn't super accurate to say that interference is a problem for continuous-wave emitters either. Coherent FMCW lidar are typically quite robust against interference by, say, using randomized chirp patterns.