Voice diaphragm drives heliograph mirror
Lens focuses signal onto moving strip of photographic medium
Medium is developed and becomes for etching a pattern into wax, metal, or other material
Pattern is "played" by a phonographic needle, reproducing original sound
Could this be made to work?
(To stimulate your thinking, investigate talking balloons
In order to get "real time" sound reproduction, one might be able to use some thermally sensitive material. The receiving station would have to focus the beam onto a narrow edge so that as the beam moves its temperature changes. Of course I know of no material that responds that rapidly.
Then again, I'm a software guy. If it cannot be done with bits, I'm often at a loss as to how to do it :-)