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Quantum limits of optical amplification

Prem Kumar, Renyong Tang, Paul L. Voss

Published Jan 1, 2004• 0 citations
Publisher

Abstract

Ideal phase-insensitive amplifiers have a 3 dB noise figure at high gains. We show through theory and experiment that fiber parametric amplifiers do not reach this limit due to coupling of noise via the Raman effect.
DOI
10.1364/oaa.2004.otua4

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We used a spatially broadband optical parametric amplifier for image amplification. In the phase-sensitive configuration of the amplifier, we observed noiseless amplification of input images. For a gain of $\ensuremath{\simeq}2.5$, we measured noise-figure values of ( $0.2\ifmmode\pm\else\textpm\fi{}0.6$) and ( $0.4\ifmmode\pm\else\textpm\fi{}0.5$) dB, respectively, for two amplifiers of different lengths. These experimental values agree with theory (for an ideal noiseless amplifier the noise figure is 0 dB) and are almost 2 dB lower than the quantum limit of an ideal phase-insensitive amplifier.
We experimentally demonstrate that a type-II pulsed optical parametric amplifier operated in a phase-insensitive configuration works as a near-perfect classical optical amplifier whose noise figure approaches 3 dB at high gains. We further demonstrate that, when operated in a phase-sensitive configuration, this amplifier works as a quantum-optical amplifier whose noise figure goes below 3 dB and approaches 0 dB at high gains. The noise figure of 1.45 ± 0.2 dB, measured for a gain of 9 dB, is clearly in the quantum regime.