Hsu, Magnus T LLittler, Ian C MShaddock, Daniel AHerrmann, JanWarrington, Richard BGray, Malcolm B2016-04-202016-04-200146-9592http://hdl.handle.net/1885/101071We present an all-digital phase meter for precision length measurements using heterodyne laser interferometry. Our phase meter has a phase sensitivity of 3 μrad/√Hz at signal frequencies of 1 Hz and above. We test the performance of our phase meter in an optical heterodyne interferometric configuration, using an active Sagnac interferometer test bed that is flexible and low noise. We demonstrate more than 70 dB of laser frequency noise suppression to achieve an optical phase sensitivity of 5 μrad/√Hz and a corresponding displacement sensitivity of 0.5 pm/√Hz at signal frequencies above 10 Hz. In addition, we demonstrate the ability of our phase meter to follow full fringe signals accurately at 100 Hz and to track large signal excursions in excess of 10(5) fringes without cycle slipping. Finally, we demonstrate a cyclic error of ≤1 pm/√Hz, above 10 Hz.© 2010 Optical Society of AmericaKeywords: Cycle slipping; Cyclic errors; Digital phase meter; Digital RF; Fringe signals; Heterodyne laser interferometry; Interferometric configuration; Large-signals; Laser frequency; Length measurement; Low noise; Optical heterodyne; Optical phase; Phase sensiti2010-12-1510.1364/OL.35.0042022016-06-14