| 摘要 |
PROBLEM TO BE SOLVED: To suppress deterioration of the optical S/N characteristic of a signal light and a transmission characteristic by allowing a 2nd amplifying part, having a reflecting mirror of 1st and 2nd amplifying parts having excitation light sources and optical fibers for amplification to have a bandpass filter making signal light pass through between an optical circulator and the optical fibers for amplification. SOLUTION: First and 2nd amplifying parts input excitation light from excitation light sources 1 and 5, and 11 and 15 to both ends of optical fibers 3 and 13 of amplification via optical demultiplexers 2 and 4, and 12 and 14 and amplify input signal light. The 2nd amplifying part leads an output of the 1st amplifying part from the ports P1 and P2 of an optical circulator 16 to a reflecting mirror 18 via a bandpass filter 17 and the fiber 13. Reflected signal light of the mirror 18 is made to pass through the fiber 13 and the filter 17 again and to be emitted from ports P2 and P3 of the circulator 16. Thus, unwanted spontaneously emitted light in outward and backward paths is suppressed, and the deterioration of the transmission characteristic of the optical amplifier can be suppressed. |
