Free-Space Optical Link
In 1965 Tony Davis built a free-space optical link (for the CEGB).
Its purpose was to transmit electrical current measurements from a high voltage power line, down to the ground.
It used a GaAs LED at the transmitter and a Silicon PIN Photodiode at the receiver.
Pulse Width Modulation was used, providing a channel bandwidth of several MegaHertz, sufficient for Video (B&W).
It had a range of 200 feet.
This same system was later modified by myself (R. Epworth) to transmit through a specially constructed fibre bundle, utilising~80 large core step-index, multimode optical fibres made by Schott Glass.
My 1965/6 final year project (with Paul Sinclair) at Manchester University was also a free space link, using a Ferranti Mesa GaAs LED driven by a distributed amplifier at the transmitter, and a Silicon PIN Photodiode at the receiver. 1 Mbit/Sec