The nonzero response time of the Kerr [χ<sup>(3)</sup>] nonlinearity determines the quantum-limited noise figure of χ<sup>(3)</sup> parametric amplifiers. This nonzero response time of the nonlinearity requires coupling of the parametric amplification process to a molecular-vibration phonon bath, causing the addition of excess noise through Raman gain or loss at temperatures above 0 K. The effect of this excess noise on the noise figure can be surprisingly significant. We derive analytical expressions for this quantum-limited noise figure for phase-insensitive operation of a χ<sup>(3)</sup> amplifier and show good agreement with published noise-figure measurements.
© 2004 Optical Society of America
Paul L. Voss and Prem Kumar, "Raman-noise-induced noise-figure limit for χ(3) parametric amplifiers," Opt. Lett. 29, 445-447 (2004)