Control circuit, control method, and transmission system

A control method for a transmission system in which signal light transmitted from a transmission-side apparatus via a transmission path to a reception-side apparatus is subjected to Raman amplification by inputting excitation light from the reception-side apparatus to the transmission path, the control method comprising:

• detecting a change amount of an optical loss of the transmission path, caused by a state change of the transmission path, on the basis of a difference between a difference at a first time point and a difference at a second time point following the first time point;
• detecting a backscattered light amount of the excitation light;
• and
• controlling an intensity of the excitation light input by the reception-side apparatus to the transmission path on the basis of the detected change amount of the optical loss and the detected backscattered light amount.

A transmission system comprising:

• a transmission-side apparatus configured to transmit signal light via a transmission path;
• a reception-side apparatus configured to receive the signal light transmitted by the transmission-side apparatus and perform Raman amplification on the signal light by inputting excitation light to the transmission path;
• and
• a control circuit configured to control an intensity of the excitation light input by the reception-side apparatus to the transmission path on the basis of a change amount of an optical loss of the transmission path caused by a state change of the transmission path and a backscattered light amount of the excitation light, the change amount of the optical loss being detected on the basis of a difference between a difference at a first time point and a difference at a second time point following the first time point.