| 摘要 |
An OTDR measurement device employs optical heterodyne wave detection to perform measurement on optical fibers. Optical pulses are incident on a measuring optical fiber, which in turn outputs backward scattering light. The device performs heterodyne wave detection on the backward scattering light as well as probe light whose frequency is set in proximity to a frequency of the backward scattering light, thus producing a detection voltage. The device provides a differential amplifier which performs amplification on a difference between the detection voltage and a reference voltage to produce a difference signal. An A/D converter converts the difference signal to a digital signal. Square addition is performed on the digital signal to produce a mean square signal representing property of the measuring optical fiber. Herein, calculations are performed on the mean square signal to produce a reference signal, which is then converted to the reference voltage. Herein, the reference signal is produced based on a reference value which is determined in advance such that the difference signal corresponds to an intermediate value of a voltage conversion range of the A/D converter under a state where only the probe light is incident on the device. Moreover, the reference signal is automatically changed to correct a shift of the reference voltage due to disturbance factors such as variations of temperature.
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