"Corner cube" mirrors reflect light back the way it came no matter the angle of incidence (within limits). If you attach a "modulator" to the back of it, you can put a local signal on the light and thus send information back the way it came.

https://en.wikipedia.org/wiki/Modulating_retro-reflector

So, you could, in principle, send information back even without a ginormous power source on-board.

Of course, corner-cube mirrors are petty heavy compared to nano-machines, so... :-/

It's good that people are thinking about such things as going to the next star, but using them in our solar system might make much more sense.

Cheers,
Scott.