Sun K X, Gustafson E K, Fejer M M, Byer R L
Opt Lett. 1997 Sep 1;22(17):1359-61. doi: 10.1364/ol.22.001359.
We describe a balanced heterodyne detection method for a Sagnac interferometer that uses a polarization-dependent beam splitter. The signal and the local oscillator are orthogonally polarized components of a single laser beam, permitting the detection of the signal by subtraction of two photocurrents produced in appropriate polarization projections. Using this scheme, we experimentally demonstrate a phase measurement with a sensitivity of 9x10(-10) rad/ radicalHz. The measurement is robust in the presence of laser frequency noise, as a result of preserving the common-path nature of the Sagnac interferometer, and of laser-amplitude noise, as a result of balanced detection.
