All first-generation large-scale gravitational wave detectors are operated at the dark fringe and use a heterodyne readout employing radio frequency (RF) modulation-demodulation techniques. However, the experience in the currently running interferometers reveals several problems connected with a heterodyne readout, of which phase noise of the RF modulation is the most serious one. A homodyne detection scheme (DC-readout), using the highly stabilized and filtered carrier light as local oscillator for the readout, is considered to be a favourable alternative. Recently a DC-readout scheme was implemented on the GEO 600 detector. We describe the results of first measurements and give a comparison of the performance achieved with homodyne and heterodyne readout. The implications of the combined use of DC-readout and signal-recycling are considered.
@article{arxiv.0811.3242,
title = {DC-readout of a signal-recycled gravitational wave detector},
author = {S. Hild and H. Grote and J. Degallaix and S. Chelkowski and K. Danzmann and A. Freise and M. Hewitson and J. Hough and H. Lueck and M. Prijatelj and K. A. Strain and J. R. Smith and B. Willke},
journal= {arXiv preprint arXiv:0811.3242},
year = {2009}
}