'Best-case' noise performance of feedback interferometers, potential for micromachine applications

We present a theoretical analysis of the noise performance of phase measuri ng feedback interferometers. We first analyse the operation of this kind of instrument and note that under certain circumstances bistability can occur . The bistable region should be avoided if possible when using feedback int erferometry for high-accuracy measurement with low-input powers, as it can give rise to very high-noise levels. We then go on to investigate the effec ts of shot noise (on the interferometer output signal) and thermal noise (i n the feedback loop), and relate these to the phase measurement accuracy of the interferometer, A 'best-case' calculation indicates that phase noise o f about 0.005 lambda is possible at input powers in the nanowatt region. In practice, we expect that noise levels will be higher than predicted (parti cularly at high-input powers) due to the effects of vibration and air turbu lence. (C) 2000 Elsevier Science Ltd. All rights reserved.