Abstract

An experimental study of enhancement of interferometric sensitivity using squeezed vacuum fluctuations is described. By operating an interferometer at the dark fringe, large laser powers can be used for high sensitivity. It is possible to enhance the interferometric sensitivity beyond the shot-noise limit in the dark fringe arrangement by using an electrooptic modulator in the interferometer to vary the phase periodically away from the dark fringe. A detector at the dark output port can then operate at the shot-noise limit and detect phase imbalance at the sensitivity determined by power level at the bright output port.¹ This shot-noise limit can be reduced further by illuminating the dark input port with squeezed vacuum, as demonstrated recently in balanced output port experiments.^2,3 However, there are interesting limits to the sensitivity improvement expected in the dark fringe case.¹ The experimental arrangement includes a polarization interferometer illuminated with 100 mW of 1.064-μm wavelength light from a Nd:YAG cw laser. Squeezed vacuum is generated by a KTP optical parametric amplifier. Experimental progress is reported at sensitivities in the nanoradian polarization rotation range.

© 1988 Optical Society of America