Quantum fluctuations in stimulated Raman scattering

Results from a study of quantum noise and its macroscopic manifestations in stimulated Raman scattering are presented. Shot to shot fluctuations in quantrum noise initiated Stokes spectra are considered. The strokes spectra were recorded experimentally using a Fabry-Perot interferometer. For comparison, numerically generated Stokes spectra were produced using the semi-classic model of stimulated Raman scattering with a numerically generated 'vacuum' input field. The amount of structure on each spectrum was quantified by calculating the spectrum's standard deviation from its mean frequency. It was found that ensembles with the noisy spectra removed had narrower distributions of mean frequencies than ensembles that included noisy spectra. The effect of these shot to shot spectral fluctuations on soliton formation in simulated Raman scattering are presented next. Experimentally, the solitons were formed by using a Pockels cell to put a pi phase shift on the input Stokes pulse to a Raman amplifier. Theoretical solitons were produced by numerically placing a pi phase shift in a Stokes field that was amplified using the semi-classical model of simulated Raman scattering. Experimentally, noisy input spectra were discarded to insure the pi phase shift was the dominant phase structure. Good agreement was found with the numerical model when the noisy spectra were removed from the ensemble. These results indicate that soliton decay is directly related to quantum noise are presented. The amount of noise added to a signal during amplification was studied by placing an amplifier in each leg of an interferometer. The noise added by the amplifier was deduced from the degradation of the output fringe pattern from the interferometer. This was done experimentally using Raman amplifiers and numerically using ideal, single mode amplifiers and Raman amplifiers. The results indicate that the amount of noise added by the Raman amplifiers corresponds to 1 photon per mode input to a noiseless amplifier. This is the lowest amount of noise allowed by quantum mechanics.