A slight movement of the ground is detected. A cable, which includes an optical fiber, is provided to have friction with the ground in such a way that the optical fiber is expanded and contracted in accordance with the movement of the ground. An optical output unit outputs a monitoring light to the optical fiber. A partial reflection unit is provided on a path of the optical fiber in the cable and partially reflects the monitoring light. An optical reception unit receives a reflection light reflected by the partial reflection unit. A calculation unit measures the length of the optical fiber to the partial reflection unit based on a round-trip propagation time of the reflection light that has been received and monitors its changes over time.

Embodiments relate to a Brillouin distributed optical fiber sensor including a first light source to output a first light having a modulated intensity at a preset frequency, an optical modulation unit to generate Brillouin probe light and Brillouin pump light using the first light and apply the Brillouin probe light and the Brillouin pump light to one end and the other end of a test optical fiber, respectively, a second light source to apply a second light with a frequency that is different from a frequency of the first light to one end of the test optical fiber in a direction opposite to the Brillouin pump light, and an optical detection unit to detect Brillouin scattered light generated by interaction between the Brillouin pump light and the Brillouin probe light in the test optical fiber.

Disclosed herein is a method comprising injecting light of a first wavelength λ.sub.1 into a wavelength division multiplexer; injecting light of a second wavelength λ.sub.2 into the wavelength division multiplexer; combining the light of the first wavelength λ.sub.1 and the light of the second wavelength λ.sub.2 in the wavelength division multiplexer to produce light of a third wavelength λ.sub.3; and reflecting the light of the third wavelength λ.sub.3 in a dual-Brillouin peak optical fiber that is in communication with the wavelength divisional multiplexer; wherein the dual-Brillouin peak optical fiber has at least two Brillouin peaks, such that an amplitude A.sub.1 of at least one of said Brillouin peaks is within 50% to 150% of an amplitude A.sub.2 of another Brillouin peak 0.5A2≤A.sub.1≤1.5A.sub.2; wherein the dual-Brillouin peak optical fiber generates a Brillouin dynamic grating that reflects an improved back-reflected Brillouin signal of the combined light.

A method and system for determining deformation in a cable, where a sensing optical fiber arrangement is applied along the cable. The method includes injecting a forward pulse pump signal in the optical fiber in a forward direction of the optical fiber and injecting a reverse probe signal in the optical fiber in a reverse direction of the optical fiber. A stimulated Brillouin backscattering is measured and, based on the Brillouin backscattering measurement, information is provided about a deformation of the cable. The forward pulse pump signal is provided as a sum of a stationary signal component and an interrogation pulse component, the stationary signal component has an energy below a Brillouin activation level and the interrogation pulse signal component has an energy which results in that the sum of the stationary signal component and the interrogation pulse signal component exceeds the Brillouin activation level.

A distributed acoustic system (DAS) method and system. The system may comprise an interrogator and an umbilical line comprising a first fiber optic cable and a second fiber optic cable attached at one end to the interrogator. The DAS may further include a downhole fiber attached to the umbilical line at the end opposite the interrogator and a light source disposed in the interrogator that is configured to emit a plurality of coherent light frequencies into the umbilical line and the downhole fiber. The method may include generating interferometric signals of the plurality of frequencies of backscattered light that have been received by the photo detector assembly and processing the interferometric signals with an information handling system.

In some examples, a temperature distribution sensor may include a laser source to emit a laser beam that is tunable to a first wavelength and a second wavelength for injection into a device under test (DUT). A first wavelength optical receiver may convert a return signal corresponding to the first wavelength with respect to Rayleigh backscatter or Raman backscatter Anti-Stokes. A second wavelength optical receiver may convert the return signal corresponding to the second wavelength with respect to Rayleigh backscatter or Raman backscatter Stokes. Bending loss associated with the DUT may be determined by utilizing the Rayleigh backscatter signal corresponding to the first wavelength and the Rayleigh backscatter signal corresponding to the second wavelength. Further, temperature distribution associated with the DUT may be determined by utilizing the Raman backscatter Anti-Stokes signal corresponding to the first wavelength and the Raman backscatter Stokes signal corresponding to the second wavelength.

The present invention is to provide a backscattered light amplification device, an optical pulse test apparatus, a backscattered light amplification method, and an optical pulse test method for amplifying a desired propagation mode of Rayleigh backscattered light with a desired gain by stimulated Raman scattering in a fiber under test having the plurality of propagation modes. The backscattered light amplification device according to the present invention is configured to control individually power, incident timing, and pulse width of a pump pulse for each propagation mode when the pump pulse is incident in a plurality of propagation modes after the probe pulse is input to the fiber under test in any propagation mode.

Aspects of the present disclosure describe systems, methods, and structures for distributed temperature sensing that employ joint wavelet denoising to achieve desirable signal-to-noise ratio(s) over extended sensor fiber distances.

In some examples, optical fiber identification and distance measurement may include utilizing a reflectometer and optical fiber connection device that includes a Rayleigh wavelength pass filter to pass, in one direction, an optical reflectometer signal to an optical fiber. The reflectometer and optical fiber connection device may include a Raman wavelength pass filter to filter out, in another direction, Rayleigh backscattering from the optical reflectometer signal. Further, the Raman wavelength pass filter may pass, in the another direction, a Raman Anti-Stokes signal from the optical fiber.

An optical fiber characteristic measurement device (1) includes a light detector (16) configured to detect Brillouin scattered light (LS) obtained by causing light to be incident on an optical fiber (FUT); a signal processor (18b) configured to obtain, on the basis of a detection signal (S1) which is output from the light detector, a first Brillouin gain spectrum (B1) which is a spectrum of the Brillouin scattered light obtained in a case where a spectral width of the light incident on the optical fiber is a first width and a second Brillouin gain spectrum (B2) which is a spectrum of the Brillouin scattered light obtained in a case where the spectral width of the light incident on the optical fiber is a second width larger than the first width; and a measurer (18c) configured to measure characteristics of the optical fiber on the basis of the first Brillouin gain spectrum and the second Brillouin gain spectrum.