Patent ID: 11920962
Assignee: NEC CORPORATION
Field: Measurement (Instruments)
Classification: CPC G  H | IPC G  H

Claim 13:
14. A surveying system comprising:
a cable that includes a first optical fiber and is provided so as to have friction between the cable and the ground, the cable being provided in such a manner that the first optical fiber is expanded and contracted in accordance with a movement of the ground;
an optical output unit configured to output a monitoring light to the first optical fiber;
a partial reflection unit that is provided on a path of the first optical fiber in the cable and partially reflects the monitoring light;
an optical reception unit configured to receive a reflection light reflected by the partial reflection unit;
a calculation unit configured to measure the length of the first optical fiber to the partial reflection unit based on a round-trip propagation time of the reflection light that has been received and monitor its changes over time; and
an optical amplification repeater system comprising:
third and fourth optical fibers whose forward directions are opposite to each other;
an optical amplification repeater configured to amplify light that propagates through the third and fourth optical fibers and relay the amplified light; and
a path for branching a part of light that reaches the optical amplification repeater and propagates through the third optical fiber in a direction opposite to the forward direction and coupling the branched light to the fourth optical fiber,

a first communication apparatus connected to one end of each of the third and fourth optical fibers, the first communication apparatus transmitting a first optical signal having a third wavelength to the forward direction of the third optical fiber and receiving a second optical signal having the third wavelength that propagates through the fourth optical fiber in the forward direction of the fourth optical fiber;
a second communication apparatus comprising a first reception unit that is connected to the OTDR device and receives the first optical signal and a first transmission unit configured to transmit the second optical signal including results obtained in the OTDR device;
a first optical coupler that is provided on a path of the third optical fiber and wavelength-selectively branches the first optical signal that propagates through the third optical fiber in the forward direction of the third optical fiber to a first reception unit of the second communication apparatus; and
a second optical coupler that is provided on a path of the fourth optical fiber and wavelength-selectively couples the second optical signal output from a first transmission unit of the second communication apparatus to the fourth optical fiber in such a manner that the second optical signal propagates through the fourth optical fiber in the forward direction of the fourth optical fiber, wherein
the optical output unit, the optical reception unit, and the calculation unit form an Optical time domain reflectometer (OTDR) device.