Measurement of absolute displacement by a double-modulation technique based on a Michelson interferometer

A novel method is presented for of measuring absolute displacement with a s ynthesized wavelength interferometer. The optical phase of the interferomet er is simultaneously modulated with a frequency-modulated laser diode and o ptical path-length difference. The error signal originating from the intens ity modulation of the source is eliminated by a signal processing circuit. In addition, a lock-in technique is used to demodulate the envelope of the interferometric signal. The displacement signal is derived by the self-mixi ng technique. (C) 1999 Optical Society of America OCIS codes: 120.0120, 120 .3180.