Inline coherent optical amplifier with noise figurelower than 3 dB quantum limit

Abstract
The first demonstration of an inline coherent optical amplifier with a noise figure which is lower than the 3 dB quantum limit is presented. The amplifier is based on optical phase-sensitive amplification using a nonlinear fibre Sagnac interferometer pumped by an injection-locked semiconductor laser with a compensation phase-locked loop. A noise figure of 2.0 dB with a high signal gain of 16 dB has been successfully obtained.