[Laser] modulated retroreflectors

[Tim Toast]

This talk about corner cubes got me wondering about passive optical repeaters using modulated corner cubes. Has anyone in here experimented with modulating a retro-reflector either homemade or not?

While googling the subject (mostly research papers) i saw that some are using an AOM technique to get AM or phase shifts or polarization effects on the beam. While others use a shutter to mechanically do it at lower frequencies. Or something as simple as the old Bell photophone type flexible mirror to modulate a beam with your voice.
 
Seeing how touchy the alignment is when making a good retroreflector from scratch, it's easy to see how a very small misalignment of one of the 3 mirrors can effect the whole reflection in a major way.

If the final mirror adjustment is left "close enough" and instead, a slight modulation is impressed on it by moving the mirror in and out of alignment, or on either side of the exact alignment, it could be modulated. This would only require a very slight movement of one mirror to fully modulate the beam, breaking it up into the 6? misaligned beams.

In a communication link consisting of two stations, each would have a modulated corner reflector pointed roughly at the other station. Alignment is each side directing its laser at the other till they get a reflection either visually or with a test signal. 

After this initial alignment is done, the transmitted light beams won't need to be modulated. The entire two way communication is or can be done with Unmodulated light sources... Kind of a strange concept at first maybe. Each receiving station is providing the carrier for the others transmitting station. One of the two stations would not even be required to have a light source at all if the other station can modulate its own light beam - to make up for the missing carrier from the other station. 

All this requires the beams to travel twice the distances they would have without the passive retroreflectors of course. So a path that is only barely good enough for a direct link would not be able to use this method. Maybe it is only good for about half the distances achieved in other ways.