A novel high-resolution confocal measurement of nanometric displacement that uses a simple 2×1 optical fiber coupler is presented. The basic principle is to detect interferometrically the change in the phase difference between two adjacent input fibers of the coupler that results from the nonuniform wave-front curvature of the reflected light. Measurement of subnanometer axial modulation, which permits high-resolution displacement sensing by optical means, is demonstrated.
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