| Summary: | 碩士 === 國立中央大學 === 光機電工程研究所 === 95 === A wavelength-modulated heterodyne grating interferometer is proposed to measure the displacement. A wavelength-modulated light is divided into s and p polarized parts, and these two polarized beams propagate with difference optical path. After combining these two polarized beams, we have the heterodyne light source. Then the heterodyne light is sent to the grating interferometer (GI). The optical phase variation which is induced by the grating movement will be measured by the heterodyne detection. By means of the measured optical phase variation and grating pitch, the displacement of the grating is determined.
The experimental results demonstrate that the proposed system has measurement range up to 5 μm with 5 nm precision. The theoretical predication shows that the sensitivity is 1.728 °/nm and the maximum velocity measuring ability is 2.6 μm/s. The measurement errors, such as the environmental error, the geometric error and nonlinearity error, are also discussed
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