High-gain erbium-doped traveling-wave fiber amplifier

Abstract
Traveling-wave amplification of a λ = 1.53 μm signal with +22-dB gain is achieved at 295 K in an Er3+-doped single-mode fiber using a λ = 514.5 nm pump source. The optimum fiber length for maximum gain is determined experimentally. A limit in signal-to-noise ratio that is due to concurrent amplification of spontaneous emission is observed. By cooling the fiber to 77 K, the amplifier gain is increased to +29 dB as a result of depopulation of the lower laser level.