Interferometric Measurement With Squeezed Light
Annual technical rept. 1 Feb 1993-31 Jan 1994
MASSACHUSETTS INST OF TECH CAMBRIDGE RESEARCH LAB OF ELECTRONICS
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The MIT effort in squeezing concentrates on the pulse excited Sagnac fiber loop reflector was first proposed in 1989. This scheme has the advantage of reusing the pump as the local oscillator. The first results on squeezing were achieved in a fiber with exceptionally low noise caused by Guided Acoustic Wave Brillouin Scattering GAWBS i.e. index fluctuations caused by thermally excited acoustic waves which change the phase of the wave propagating through the fiber. For some very narrowly defined parameters it is possible to distribute the acoustic resonances so that they do not convolve into the low- frequency range of the measurement window 40-90kHz, for pulses of 100 MHz repetition rate the rate generally produced by modelocked laser sources. It so happened that the fiber used met these exceptional conditions. Since these conditions are not easily met, it is important to develop techniques that suppress the GAWBS noise. The GAWBS spectrum rolls off before it reaches 1 GHz. Thus, if the pulse reception rate is 1GHz or higher, the convolution of the GAWBS noise into the low frequency measurement window can be avoided entirely.