Laser communication from rangefinders.

[ArcSin]

Hello.

I am pondering on the feasibility to hack the commercially available, of the shelf, laser rangefinder modules in to two way laser communication devices.
As I understand, the device itself has all the bits and pieces from the optical standpoint to support good 1 to 2 km communication, or more, considering communicators don't suffer from inverse square law both ways. The thing that is left is to change the circuit that is responsible for measuring in to something that can communicate and filter out its own signal reflections and environment noise while tracking its paired partner.  Tracking part could be done with additional optic (some sort of collimation with simplest form of 4 lobe diode or go full steam and do a single sensor IR seeker like system) and some sort of light source on different frequency (or same, using some sort of "beacon" signal inserted in to communication signal) so that function is not crucial for rangefinder to preform. However, am I totally in the woods with my idea or is this even remotely feasible?

[Andy Chee]

FYI, lasers are still affected by inverse square law.

https://www.modulatedlight.com/

[mikerj]

FYI, lasers are still affected by inverse square law.

https://www.modulatedlight.com/

Further than the Rayleigh length this is true.

[Marco]

FYI, lasers are still affected by inverse square law.

For power density.

You could argue he was referring to link budget. Practically the inverse square law pretty much always applies to link budget for RF but not so frequently for lasers. It's more practical to capture a large part of the beam and the part captured is what's important, not power density.

[ArcSin]

What I was trying to say was that the laser system don't need to bounce the laser back to measure the distance, instead it reads other modules laser and reads its data. If it can detect its own beam bounce from 1500m (on youtube there is cool video of fairly cheap unit pulling it off in sunlight), surely, it can detect laser sent directly at it from analogous unit theoretically at 3000m, if not more? (assuming line of sight and atmospherics are ok)

Idea is to use the detector on the instrument to listen signal from another rangefinder, that is sending data. And filter its own signal so it wont get confused by reflections in case of two way communication. This will need to be done software side, I know.

This way you could transfer bit stream in a fairly tight configuration, depending of how nuts you go with additional steps to prevent the beam divergence.