| 摘要 |
At a post stage of an amplifying optical fiber, such a means is provided that detects a level of light having a center wavelength of the amplified signal light, and also a level of light having a wavelength different from that of this center wavelength, and further another means is provided which compares the level of the light having these wavelengths, and controls an output of a pumping light source based on this comparison result. To detect the intensity of the light having these two wavelengths, two light branching devices, and light receiving devices are arranged via the respective light band-pass filters for passing therethrough the light having the above-described wavelengths at the post stage of the amplifying optical fiber. When the light intensity ratio of both the light having the wavelengths is larger than a preset value, the output of the pumping light source is maintained. Conversely, when this light intensity ratio is smaller than this preset value, the output of the pumping light source is interrupted by assuming that the input signal light is interrupted. The adverse influences caused by the light surge can be avoided without increasing the noise figure. |
