Optical amplification at the quantum limit

In this paper we evaluate experimentally measured signal-to-noise ratio performance of different types of optical amplifiers [V. Josse, M. Sabuncu, N. Cerf, et al., Phys. Rev. Lett. 96 163602 ( 2006); Z. Y. Ou, S. F. Pereira and H. J. Kimble, Phys. Rev. Lett. 70 3239 ( 1993)]. We pay particular attention to the low gain regime where the quantum limit of the amplifier varies with gain. Independent of the amplifier type the noise performance is remarkably close to the quantum limit. Low gain optical amplifiers are of interest for quantum communication