| 摘要 |
PURPOSE:To obtain information on which channel is received by setting the frequency of local oscillation light so that the center frequency of a signal of an intermediate signal which is present in the lowest range is at a specific position. CONSTITUTION:The oscillation frequencies of the 1st, the 2nd, the 3rd, and the 4th light sources 1, 2, 3, and 4 are controlled by the 1st, the 2nd, and the 3rd control circuits 5, 6, and 7 to set the oscillation frequency difference among the light sources to a value suitable to frequency multiplexing. Then, those light signals are multiplexed optically and sent out from an optical transmission line and a reception part uses a local oscillation light source 18 to performs the optical heterodyne detection of the signal light, thereby demodulating a signal of a specific channel. The reception part while monitoring the center frequency arrangement in the intermediate frequency range of each signal channel set the center frequency interval DELTAf of said signal light to >=2B and sets the frequency of the local oscillation light so that the center frequency fIF of the signal of the intermediate frequency signal which is present in the lowest range is at the position shown by an expression. Then, the signal of the desired channel is extracted in a reception band and demodulated to monitor which signal channel the currently received signal corresponds to from the frequency arrangement. |
