ABSTRACT
Optical communication via line of sight has been a key feature of the natural world. The earliest humans used signal beacons, with a human acting as an optical receiver. Later, more sophisticated semaphore systems using the same principle were deployed and heliographs were also developed. At the transmitter, the diameter of the transmission aperture is usually set by eye safety considerations, in order to ensure that the optical power density at the aperture is below allowable limits. Data centers and warehouse-scale computing environments use optical fibers to connect racks together, and are beginning to deploy rack-level optical communications. This is because the speed of the electrical interconnect required between boards requires complex electronic transmission protocols, high-speed impedance matched lines with consequent high-power requirements due to terminations, and complex expensive multilayer printed circuit boards. Radiofrequency (RF) wireless systems have been immensely successful, and users now see Wi-Fi and mobile data services as a utility that will always be available.
