| 摘要 |
PURPOSE:To decide the mis-alignment of optical axes by emitting test light of a wavelength different from the wavelength of signal light from an optical fiber, measuring the output of a photodetecting element and utilizing the change of the measured value. CONSTITUTION:A condensing spot A2 of the signal light exists in a photodetecting surface 31 of the photodetecting element and a condensing spot B2 of the test light protrudes partly to the outside of the photodetecting surface 31 if it is assumed that the optical axis of a photodetector is displaced. Since the photodetecting sensitivity of the photodetecting element 3 is nearly uniform over the entire surface of the photodetecting surface 31, the mis-alignment cannot be decided even if the photodetecting outputs before and after the screening of the signal light are compared. The mis-alignment can be decided only by using the test light. Namely, the test light of the wavelength different from the prescribed wavelength is emitted from the optical fiber 1 and the output of the photodetecting element 3 is measured. The mis-alignment of the optical axis is decided from the change in the measured value thereof.
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