Hi,

Most cheap laser pointers are too slow to modulate but by using the idea of a mechanical beam chopper will take care of that.

Then you need an OP-amp or 2. Make sure they are AC coupled and have a decent amplifiation. After this you put a LM567 which is a tonedecoder that will give a logical signal if the tone is present.

They ar cheap, easy to use and detect small signals. If you can modulate teh laser and have a HWPM you can connect the - side of the laser to the HPWM pin and the + side of the laser to the USART tx pin or the opposite if you like to use inverted mode.

Then from the tone detector's logical pin straight in on your usart RX in the other end.

Or as mentioned before... use an already made audio amplifier and put the tone detector after it. That will work if you have a low enough baudrate becuse you need some carrier FQ cycles per bit to give the LM567 enough to work with.

/me