We implement a digital fringe-counting technique to measure in real time the relative mirror displacement of a suspended Michelson interferometer with modulated optical path length for oscillations much larger than the laser wavelength (λ). This provides the proper error signal for a servo mechanism that reduces the relative displacement within λ/2. The implemented technique does not require extra optics or polarizers and thus can be used for interferometric gravitational wave detectors as a starting procedure to get the system locked.
© 1994 Optical Society of America
Fabrizio Barone, Enrico Calloni, Rosario De Rosa, Luciano Di Fiore, Francesco Fusco, Leopoldo Milano, and Guido Russo, "Fringe-counting technique used to lock a suspended interferometer," Appl. Opt. 33, 1194-1197 (1994)