well its a laser communicator.You transmit sound in the form of light through a laser pointer.The laser is attached to an audio device ,as shown in the transmitter circuit, and the reciver is simply a solarcell connected to an audio amplifier .Now the music is played on the audio device the changing voltage changes the laser light falling the solercell which in turn genrates chaninging electricity that flows through the audio amplifier and hence we hear the same music we're playing on the audio device.heres the link to this project **broken link removed**