Transmission line monitoring device and transmission line monitoring method

A transmission line monitoring device comprising:

• a memory;
• and
• a processor coupled to the memory and configured to:
• compensate an electric field signal alternately for a chromatic dispersion and a nonlinear distortion produced in an optical signal in each of virtual sections, the electric field signal indicating an optical electric field component of the optical signal input from a transmission line virtually divided into the virtual sections;
• evaluate a quality of the electric field signal that is compensated for the chromatic dispersion and the nonlinear distortion;
• set a first compensation quantity of the chromatic dispersion according to a length of each of the virtual sections to search for a second compensation quantity of the nonlinear distortion for each of the virtual sections when the quality satisfies a predetermined condition;
• and
• monitor a power distribution of the optical signal on the transmission line on a basis of a relationship between the first compensation quantity and the second compensation quantity,
• wherein the processor is further configured to, when searching for the second compensation quantity,
• select the virtual sections in sequence,
• set the first compensation quantity, and
• search for a third compensation quantity of the nonlinear distortion for a selected virtual section when the quality satisfies the predetermined condition under an assumption that no nonlinear distortion is produced in virtual sections other than the selected virtual section out of the virtual sections, and
• search for the second compensation quantity for each of the selected virtual section by setting an initial value of the second compensation quantity to the third compensation quantity.