| 摘要 |
PROBLEM TO BE SOLVED: To prevent degradation in reception sensitivity and misalarming by precisely matching the wavelength of an optical filter which removes naturally emitted light from amplified signal light with the wavelength of the signal light. SOLUTION: In addition to an optical fiber amplifier including an optical fiber 1 for amplification, an exciting light source 2 which outputs excited light, and an optical multiplexer 3 which inputs the excited light to the optical fiber amplifier and a variable wavelength optical filter 7 which outputs passing amplified signal light by selectively transmitting light of specific wavelength of the amplified signal light with a wavelength control signal, a signal light output level control part 6 which detects the signal light output level of the passing amplified signal light and controls the excited light output level to hold the passing amplified signal light output level constant and a wavelength control part which outputs a wavelength selects signal to the variable wavelength optical filter 7 so that the excited light output level becomes minimum are provided. The signal light output level control part 6 controls the excited light source to vary the transmission wavelength of the variable wavelength optical filter 7 while holding the level of the amplified signal light constant, thereby setting the optical filter to the wavelength at which the output of the excited light becomes minimum. |
