| 摘要 |
PURPOSE: To prevent the occurrence of an optical surge when becoming a non- signal state without bringing on a loss of a signal beam and without increasing an increase index by monitoring two optical outputs with a photodetector and controlling excitation light with a light intensity ratio of light of both wavelengths. CONSTITUTION: An optical band-pass filter 10 transmits selectively through light of a wavelength λ1, and the optical band-pass filter 11 transmits selectively through the light of the wavelength λ2. At this time, the wavelength λ2 whose wavelength is selected to one in the vicinity of the wavelength λ1. The optical band-pass filter 11 is provided with a narrow wavelength band characteristic, and cuts off the light of the wavelength of λ1. The light intensity ratio of respective wavelengths λ1, λ2 light received by the photodetectors 12, 13 is changed according to the change of the input level of the input signal of the wavelength λ1, and the ratio is changed large under the non-signal state. Thus, when the light intensity ratio of respective wavelengths λ1, λ2 detected by the photodetectors 12, 13 becomes a prescribed reference value or below, the occurrence of the optical surge is suppressed by performing no amplification. |
