OPTICAL TRANSMISSION LINE MONITORING DEVICE AND OPTICAL TRANSMISSION LINE MONITORING METHOD

1 . An optical transmission line monitoring device that specifies a polarization fluctuation position representing a position where polarization fluctuation occurs in an optical transmission line between a first terminal node and a second terminal node, the optical transmission line monitoring device comprising:

a processor configured to

acquire a delay measurement value representing a result of delay measurement between nodes for each of a plurality of spans constituting the optical transmission line,

calculate, for each of the plurality of spans, a refractive index of an optical fiber laid in the span based on a span length representing the length of the span and the delay measurement value,

calculate a propagation time of light between the first terminal node and the polarization fluctuation position based on timing information indicating timing at which polarization fluctuation generated on the optical transmission line is detected in each of the first terminal node and the second terminal node, and

calculate a distance between the first terminal node and the polarization fluctuation position based on the propagation time and the refractive index calculated for each of the plurality of spans.

2 . The optical transmission line monitoring device according to claim 1 , wherein

when the delay measurement is performed a plurality of times for each of the plurality of spans, the processor calculates, for each of the plurality of spans, a refractive index of an optical fiber laid in the span based on a span length of the span and a minimum value of a plurality of delay measurement values obtained by the delay measurement performed a plurality of times.

3 . An optical transmission system comprising:

a plurality of optical transmission devices provided on an optical transmission line between a first terminal node and a second terminal node; and

an optical transmission line monitoring device that specifies a polarization fluctuation position representing a position where polarization fluctuation occurs in the optical transmission line, wherein

the optical transmission line is configured of a plurality of spans,

each optical transmission device includes a delay measurement unit that measures a delay time of a span with an adjacent node, and

the optical transmission line monitoring device includes a processor configured to

acquire, for each of the plurality of spans, a delay measurement value representing a result of delay measurement between nodes from a corresponding optical transmission device,

calculate, for each of the plurality of spans, a refractive index of an optical fiber laid in the span based on a span length representing the length of the span and the delay measurement value,

calculate a propagation time of light between the first terminal node and the polarization fluctuation position based on timing information indicating timing at which polarization fluctuation generated on the optical transmission line is detected in each of the first terminal node and the second terminal node, and

calculate a distance between the first terminal node and the polarization fluctuation position based on the propagation time and the refractive index calculated for each of the plurality of spans.

4 . The optical transmission system according to claim 3 , wherein

the optical transmission line transmits a data signal by using a first wavelength, and

the delay measurement unit

transmits a delay measurement frame to an adjacent node through the optical transmission line by using a second wavelength different from the first wavelength,

receives the delay measurement frame from the adjacent node via the optical transmission line, and

measures a delay time of a span with the adjacent node based on a transmitting time of the delay measurement frame and a reception time of the delay measurement frame.

5 . The optical transmission system according to claim 4 , wherein

the processor corrects the calculated refractive index for each of the plurality of spans based on a difference between the first wavelength and the second wavelength.

6 . The optical transmission system according to claim 4 , wherein

the processor corrects the calculated refractive index for each of the plurality of spans based on a difference between the first wavelength and the second wavelength and a type of an optical fiber laid in the span.

7 . The optical transmission system according to claim 4 , wherein

the processor corrects the calculated refractive index for each of the plurality of spans based on a difference between the first wavelength and the second wavelength and a wavelength dispersion characteristic of an optical fiber laid in the span.

8 . An optical transmission line monitoring method for specifying a polarization fluctuation position representing a position where polarization fluctuation occurs in an optical transmission line between a first terminal node and a second terminal node, the method comprising:

acquiring a delay measurement value representing a result of delay measurement between nodes for each of a plurality of spans constituting the optical transmission line;

calculating, for each of the plurality of spans, a refractive index of an optical fiber laid in the span based on a span length representing the length of the span and the delay measurement value;

calculating a propagation time of light between the first terminal node and the polarization fluctuation position based on timing information indicating timing at which polarization fluctuation generated on the optical transmission line is detected in each of the first terminal node and the second terminal node; and

calculating a distance between the first terminal node and the polarization fluctuation position based on the propagation time and a refractive index calculated for each of the plurality of spans.