Gravity-wave detection via an optical parametric oscillator

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Abstract
An active gravity-wave detector based on a two-arm optical parametric oscillator (OPO) is proposed and analyzed. The signal and idler waves of a nearly degenerate parametric oscillator are internally separated such that the signal beam propagates along one arm of the OPO and the idler beam along the orthogonal arm. By monitoring the signal-idler beat frequency, a sensitive measure is obtained of the differential path displacement in the two arms of this OPO interferometer. The phase noise of the output beat frequency is calculated and is shown to exhibit time-dependent squeezing. The detection sensitivity is limited by the signal-idler phase diffusion and photon shot noise, and is the same as that of the usual passive Michelson interferometer or active two-laser interferometer for a given apparatus size and detected optical power. Squeezed vacuum can, in principle, be used to improve the detection sensitivity.