Three-color laser-diode interferometer

The combined optical spectrum of a pair of multimode laser diodes is composed of a large number of welldefined wavelengths. This work reports the use of three of these wavelengths in a phase-modulated interferometer to measure absolute distance over 360-microm intervals with a resolution of 0.5 nm. The laboratory demonstration system is composed of a three-wavelength source coupled by single-mode fiber to a compact interferometric probe. This system has been used for displacement measurement and profiling of optical surfaces.