Last year at my university someone did an audio transmitter that used modulated laser for transmission. If memory serves, they did it by literally cutting apart a normal cheapo laser pointer and connecting their circuit where the batteries would contact... + side to a positive rail, and - side through an NPN or NMOS transistor to ground, then they could modulate the laser by driving the transistor gate. you'd have to experiment with amplitude and biasing point if you're looking to modulate with an analog signal, or if you are going to just modulate with a logic square wave then it's even easier, but either way it shouldn't involve more than a transistor and a few discretes, plus whatever drive circuit you choose.