Erbium-doped fiber amplifiers (EDFAs) were invented in 1987 at the University of Southampton. Erbium ions allow for amplification in the 1540nm band with low fiber loss. Erbium can be excited by 980nm or 1480nm pumps carried by fiber. EDFAs provide high gain, low noise figure, and bit rate transparency for wavelength division multiplexing. They require pump lasers but do not need high-speed electronics.