Semiconductors and Semimetals - Volume 22 - Lightwave Communications Technology - Part E: Integrated Optoelectronics

Preface: When American Indians transmitted messages by means of smoke signals they were exploiting concepts at the heart of modern optical communications. The intermittent puffs of smoke they released from a mountaintop were a digital signal; indeed, the signal was binary, since it encoded information in the form of the presence or absence of puffs of smoke. Light was the information carrier; air was the transmission medium; the human eye was the photodetector.