We describe a balanced-heterodyne postmodulated Sagnac interferometer signal extraction method that is suitable for gravitational wave detection. The method is simple to implement by placement of a polarization-selective modulator after the beam splitter in the dark port of the interferometer. The postmodulated Sagnac interferometer retains its common path advantage and exhibits insensitivity to laser frequency noise below, at, and above the heterodyne frequency. Balanced detection reduces sensitivity to laser amplitude noise. In this scheme mirror displacement signals were rf demodulated and observed from 0.2 to 10kHz.
© 1997 Optical Society of America
(000.2780) General : Gravity
(040.2840) Detectors : Heterodyne
(070.6020) Fourier optics and signal processing : Continuous optical signal processing
(120.3180) Instrumentation, measurement, and metrology : Interferometry
(350.7420) Other areas of optics : Waves
Ke-Xun Sun, Martin M. Fejer, Eric K. Gustafson, and Robert L. Byer, "Balanced heterodyne signal extraction in a postmodulated Sagnac interferometer at low frequency," Opt. Lett. 22, 1485-1487 (1997)