PHOTON NUMBER SQUEEZING OF SPECTRALLY FILTERED SUBPICOSECOND OPTICAL SOLITONS

Photon number squeezing of spectrally filtered optical solitons has be en observed in the sub-picosecond regime, where the Raman effect chang es the internal quantum structure of each pulse. 160 fs pulses were pr opagated down a 10 m optical fibre of anomalous group velocity dispers ion. At energies below the soliton energy subsequent spectral filterin g with an optical band-pass squeezed the directly detected photocurren t fluctuations to 3.2 +/- 0.1 dB (52%) below the shot-noise limit. Thi s implies 4.5 dB (65%) of soliton photon number squeezing, if detectio n losses are taken into account. Using a spectral edge filter the spec tral components of the pulses are shown to contribute asymmetrically t o the squeezing due to stimulated Raman scattering.