This circuit I built for fun and to see if it could be done. I have seen other ways of making audio transfer via light. Other projects seem to have extra parts or insufficient parts; photocells did not work for me (had to use solar panel).
Step 1: Transmitter
I spent the time to solder all of the parts but it is not needed.
This project is built with a power source (3-9 volts work for me), LED diode (laser; for more distance), and mono male audio jack.
Step 2: Receiver
This part is simple. Solar panel attached to a male mono audio jack. I did not need to supply power to the line but I did plug into a Bluetooth portable speaker; I assume it does not inject power on the line either.