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Long-range shape measurement with high accuracy is needed for precision manufacturing of large-scale parts such as turbines, compressors, and trains. We have developed a high-accuracy ranging system based on frequency-modulated continuous-wave (FMCW) technology. Our system has two unique features. First, it achieves high-accuracy range measurement by directly modulating a low-cost vertical-cavity surface-emitting laser (VCSEL) at high sweep rates. The nonlinearity of the optical frequency sweep is compensated for by resampling through a reference interferometer. Second, an optical fiber with multiple fiber Bragg grating (FBG) structures is used for distance calibration. Ranging accuracy better than 10 μm is achieved at 2 m distance. Three-dimensional (3D) imaging of 10-cubic-meter volume has been obtained by combining the FMCW ranging with a galvanometer scanner.

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