A fiber-optic displacement sensor with subnanometer resolution is described. The sensor is based on a highly sensitive detection of power change at a 'zero' working point in light reflected from an object surface to be measured when the surface is subject to a small displacement. The sensor consists of a He-Ne laser source, a directional fiber coupler as a beam splitter, a small-diameter (less than 5 mm) optical-fiber probe, and a photodetector setup. Measurements by this sensor are not sensitive to the power fluctuation of the light source. The sensor has high accuracy, stability, and wide working range, is simple, and can be manufactured at low cost.
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