Abstract

The squeezing experiments in a fiber ring, using pulses from a modelocked Nd:YAG laser at 1.3 μm have shown noise reduction of 5 dB below the shot noise level.^[1] The thermally induced index fluctuations in fibers cause forward scattering of the optical wave (Guided Acoustic Wave Brillouin Scattering, or GAWBS) and are a source of phase noise that obscures the squeezing. This phenomenon was first discovered by the IBM group,^[2] who performed extensive measurements to characterize the effect using both cw and pulsed sources.^[3,4,5] The GAWBS spectrum of acoustic modes that couples to the optical mode extends from approximately 20 MHz to 1 GHz. There are about 25 such noise peaks, with the more pronounced ones at the lower part of the frequency range. We report detailed GAWBS measurements in our experimental setup and point to ways for partially suppressing them.

© 1992 IQEC