| 摘要 |
PURPOSE:To prevent saturation in a light receiving system without lowering S/N ratio in the light receiving system of a coherent OTDR, by making a coherent light incident into an optical fiber to be measured to combine this return light with a sufficiently intense locally generated light. CONSTITUTION:A continuous wave from a coherent light source 1 is branched into two with branch unit 2. One is turned to an optical pulse weigh an interruption type optical switch 3 and made incident into an optical fiber 5 to be measured through an optical coupler 4. The other one is turned to the locally generated light to be made incident into the coupler 4 through a switch 8 and combined with the return light from the fiber 5. At this point, to ensure the combination of the locally generated light with the return light from a desired observing position, an electric pulse generated with a generator 6 is delayed and controlled 9 in the pulse width and converted 10 into a switch driving signal to interrupt the optical switch 8. The combined light wave is converted into an electrical signal with a photodetector 11 and undergoes a signal processing such as amplification, filtering, logarithmic computation and A/D conversion with a signal processor 12. The results are displayed 13 on a CRT or the like. |
