Abstract

Estimates of the necessary sensitivity for detecting gravitation waves are 10²¹ or 10²² root Hertz. Three-phase fringe measurement techniques giving 1/1536 fringe sensitivity at a few MHz bandwidth have now been demonstrated, but even with kilometric baselines and multipass interferometry that resolution falls short by a factor of 100 or 1000, the same as for other schemes. The strategy of oversampling, mainly described in connection with sigma-delta modulating AD converters, whereby bandwidth is traded for resolution much faster than by the square root, is proposed to overcome the shortfall. Most of the ingredients for the oversampling strategy, such as low-pass prefiltering and digital integration, are already part of the three-phase technology. Either feedback or ordered dither now needs to be introduced and multistage higher-order processing is recommended for further reduction of quantization noise. Remaining considerations will be isolation from seismic noise and surmounting shot noise.

© 1991 Optical Society of America