Optical transmission line monitoring device and optical transmission line monitoring method

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.

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.