Instructions for a Do-It-Youself 10MB, 0.5-1km point-to-point optical link are on the web. It uses an Ethernet card as the modulator/demodulator. LEDs are used as the light source and the detector is a PIN photodiode. With a larger lens, the range can be extended. http://atrey.karlin.mff.cuni.cz/~clock/twibright/ronja/ John