Patent ID: 11936423
Assignee: NEC CORPORATION
Field: Telecommunications (Electrical engineering)
Classification: CPC H | IPC H

Claim 0:
1. A fault detection apparatus comprising:
a transmitter configured to transmit a first optical signal to an optical transmission path;
a receiver configured to receive a second optical signal from the optical transmission path in response to transmission of the first optical signal, and measuring a reception level of the second optical signal; and
a controller configured to specify a section where the second optical signal according to the first optical signal has been generated, calculating, based on the reception level, an optical level associated with a loss in the section, determining that a first fault has occurred in the section when the optical level of the section has changed from a first reference level by a first threshold value or more, setting a second reference level and a second threshold value after occurrence of the first fault, and determining that a second fault has occurred in the section when the optical level has changed from the second reference level by the second threshold value or more; wherein the optical transmission path is a submarine cable through which a plurality of optical repeaters are connected in cascade, the second optical signal is the first optical signal looped-back in each of the plurality of optical repeaters, and the controller specifies the section, based on a transmission time of the first optical signal, a reception time of the second optical signal, and a distance to each of the plurality of repeaters.