| 摘要 |
<p>The presence or absence of a fault between the near end of a light transmission line (2) being tested and the far end of the light transmission line (2) is detected by identifying whether the light reflected along the light transmission line (2) is reflected by a position farther away than a filter (10) ordinarily inserted at the far end of the light transmission line (2), or by the light transmission line, by a method of detecting the quantity of light reflected from the far end of the light transmission line. The method comprises the steps of separating, from the light coming from the far end of the light transmission line, light of a wavelength used for transmitting a signal from light of another wavelength used for monitoring, by introducing this light from the light transmission line into the filter; introducing the light of the wavelength used for transmitting the signal into the original light signal passage (3); transmitting the light of the wavelength used for monitoring back into the light transmission line (2) by reflecting it with a high reflectivity; and transmitting from the near end of the light transmission line toward the far end thereof the light of the wavelength used for monitoring.</p> |
