Many different techniques have been developed for precision measurements of sub-mm displacements. This paper will provide a brief overview of such techniques and compare relevant performance characteristics and limitations. The performance of a fiber-based sensor system that addresses many of the limitations of existing displacement measurement technologies will then be described. This research system is an optical fiber based, multi-channel interferometer system that combines high-accuracy displacement measurement capability with absolute distance measurement over a range of 500 μm, with a displacement measurement uncertainty (k=2) of 4 parts per million. The ability to determine the absolute distance of the target relative to the sensor datum provides a highly repeatable (～2-3 nm) position datum, e.g., for use in establishing a 'home' position. Such a system could be used in demanding applications requiring a multitude (～60) of thermally passive, electrically immune, extremely compact sensors and exceptional long-term drift performance.
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