Optical transmission system and carrier monitoring apparatus

A carrier monitoring device that adjusts respective signal intensities of a first optical signal and a second optical signal that are included in a multiplexed signal input to an amplifier for amplifying the first optical signal and the second optical signal, the first optical signal being an optical signal having a first wavelength that is obtained as a result of first frequency-multiplexed multi-channel signals being converted by means of FM batch conversion and that is to be transmitted to a first optical receiving unit, the second optical signal being an optical signal having a second wavelength different from the first wavelength that is obtained as a result of second frequency-multiplexed multi-channel signals being converted by means of FM batch conversion and that is to be transmitted to a second optical receiving unit, the carrier monitoring device comprising:

• a first acquisition unit for acquiring the first optical signal;
• a second acquisition unit for acquiring the second optical signal;
• a first measurement unit for measuring a signal intensity of the first optical signal acquired by the first acquisition unit;
• a second measurement unit for measuring a signal intensity of the second optical signal acquired by the second acquisition unit;
• an adjustment amount calculation unit for calculating respective adjustment amounts for the signal intensity of the first optical signal acquired by the first acquisition unit and the signal intensity of the second optical signal acquired by the second acquisition unit, based on a measurement result of the measurement performed by the first measurement unit and a measurement result of the measurement performed by the second measurement unit, such that the signal intensity of the first optical signal received by the first optical receiving unit is larger than or equal to a first predetermined value, the signal intensity of the second optical signal received by the second optical receiving unit is larger than or equal to a second predetermined value, and a signal intensity of the multiplexed signal output from the amplifier is larger than or equal to a third predetermined value;
• a signal intensity adjustment unit for adjusting the signal intensity of the first optical signal acquired by the first acquisition unit and the signal intensity of the second optical signal acquired by the second acquisition unit based on the respective adjustment amounts calculated by the adjustment amount calculation unit, and outputting the first optical signal and the second optical signal that have been subjected to the signal intensity adjustment;
• and a carrier monitoring function unit for obtaining an amount of frequency deviation of each carrier signal included in the first optical signal or the second optical signal, calculating a minimum optical sensitivity at the first optical receiving unit or the second optical receiving unit based on the amount of frequency deviation, and updating the first predetermined value or the second predetermined value based on the minimum optical sensitivity.