The erbium-doped fibre amplifier

technology

A short length of optical fibre doped with erbium ions, pumped by a laser at a shorter wavelength, which amplifies a passing signal in the 1.55 µm band directly in the optical domain. Two groups demonstrated a practical low-noise device at almost the same moment in 1987 — R. J. Mears, L. Reekie, I. M. Jauncey and David Payne at the University of Southampton's optoelectronics group, and a team including Emmanuel Desurvire and Randy Giles at AT&T Bell Laboratories — and the invention is what turned intercontinental fibre from an expensive replacement for coaxial cable into the medium of a global network. Before it, a transoceanic system needed electronic regenerators that received the light, recovered the bits electrically and retransmitted them, which fixed the cable's capacity at the moment it was laid and put a complex, fault-prone circuit on the seabed every few tens of kilometres. An optical amplifier is indifferent to what the light is carrying. That single property is why a cable laid in one decade can be re-terminated with newer equipment on shore in the next and carry many times its original design traffic, and it is the reason the capacity of the ocean floor has grown far faster than the number of cables lying on it.

A technology is not a place. Drawing it on a map would assert something about the world that no stored fact supports.