Abstract: The interferometric range finding device with a grating external-cavity semiconductor laser is presented. By modulating the frequency of the laser with a triangular injection current, an optical beat is formed from a Michelson intererometer with unbalanced arms. The frequency of the beat is proportional to the difference between the two interferometer arms. The range finding is complemented by measuring the beat frequency. The spectral linewidth of the laser is greatly narrowed, i.e., the coherence length of the laser is greatly extended, by external optical feedback from the grating. So the measurable range is obviously extended and the effects of the laser phase noise on the ranging accuracy may be reduced distinctly. The experimental results show that the measurable range of the device is as long as 15 meters. The configuration of the device is described. Some experimental results and analysis are presented. The advantages of the ranging device are portable and quick-measuring. !8
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