A simple, low-cost deformation mechanism and method produces submicrometer increments of motion, to precisely stretch and compress fibers containing optical gratings in order to achieve a desired length and period. Such a "tunable" fiber can be used to, for example, produce an optical filter or to "match" two fiber lasers, thus enabling their use in a coherent detection system. Two beams, parallel to and opposing each other, are joined at two places. A screw is positioned between the beams such that a force is exerted on both beams simultaneously when the screw is rotated, deforming both beams. Motion reduction is provided by sharing the screw's movement between the two beams, and is further enhanced by making one beam thicker than the other. Two fibers are secured into grooves provided on one of the beams. By rotating the screw to increase or decrease the deformation, the fibers and their respective gratings are stretched or compressed. Because the grooves are at different distances from the point where force is applied, the two fibers are subjected to different amounts of deformation as the screw is turned. When the fibers are used as lasers, the difference in the frequencies of the two lasers can be adjusted with the mechanism, and reduced to within the bandwidth of a photodetector. Once "matched," the fiber lasers and the mechanism can be used in a coherent detection system.