Techniques and apparatus for improved spatial resolution for locating anomalies in optical fiber
Methods of measuring an anomaly, any induced change in physical parameters such as strain, temperature, and so forth, in an optical fiber. One method may include launching a plurality of probe pulses from a probe source; recording a Brillouin scattering spectrum from a plurality of reflection signals generated in the optical fiber, responsive to the plurality of probe pulses; determining a relative motion between the optical fiber and the anomaly during the recording the Brillouin back-scattering spectrum; and dynamically adjusting the Brillouin back-scattering spectrum according to the relative motion, or performing an adjustment of the Brillouin back-scattering spectrum after acquisition of the Brillouin back-scattering spectrum.
1. A method of measuring an anomaly in an optical fiber, comprising:
launching a plurality of probe pulses from a probe source into the optical fiber;
recording a Brillouin back-scattering spectrum from a plurality of reflection signals generated in the optical fiber, responsive to the plurality of probe pulses;
determining a relative motion between the probe source and the anomaly during the recording of the Brillouin back-scattering spectrum; and
dynamically adjusting the Brillouin back-scattering spectrum according to the relative motion.
2. The method of claim 1 , wherein the recording the Brillouin back-scattering spectrum comprises performing Brillouin Optical Time Domain Reflectometry (BOTDR) or comprises performing Brillouin Optical Time Domain Analysis (BOTDA).
3. The method of claim 1 , wherein the Brillouin back-scattering spectrum comprises a Brillouin gain spectrum.
4. The method of claim 3 , wherein the probe source comprises a sensing fiber, wherein the anomaly comprises a change in temperature and/or strain (temperature/strain) in the optical fiber, and wherein measurement of a relative motion of the sensing fiber and a temperature/strain profile is synchronized with detection of the Brillouin gain spectrum.
5. The method of claim 4 , wherein the Brillouin gain spectrum comprises a plurality of backscatter traces, acquired at a plurality of instances, wherein after an initial backscatter trace of the plurality of backscatter traces, subsequent traces of the plurality of traces are shifted forward in space when the anomaly is moving away from the probe source, and wherein after an initial backscatter trace of the plurality of backscatter traces, subsequent backscatter traces of the plurality of backscatter traces are shifted backward in space when the anomaly is moving toward the probe source at one end of the optical fiber.
6. The method of claim 5 , wherein a given pulse of the plurality of pulses is launched at a frequency ν 0 , wherein a given backscatter trace along the optical fiber is detected by a heterodyne receiver at a frequency ν B , and wherein the plurality of backscatter traces span a predetermined frequency range.
7. The method of claim 6 , wherein a given Brillouin gain spectrum is characterized for a first trace at a first frequency step as −ΔνI 11 (−Δν, x)→I′ 11 (−Δν, x)=I 11 (−Δν, x), and for an N th trace at as Δν: I 1N (−Δν, x) →I′ 1N (−Δν, x)=I 1N (−Δν, x−d 1N ), wherein d 1N a distance moved away along the direction of a pulse launch since the 1 st trace at the 1 st frequency step.
8. The method of claim 7 , wherein a given Brillouin gain spectrum is characterized for a N th trace at −Δν+m×δν: I mN (−Δν+m×δν, x)→I′ mN (−Δν+m×δν, x)=I mN (−Δν+m×δν, x−d mN ), where d mN is a distance moved away along the direction of pulse launch since the 1 st trace scan at the 1 st frequency step, (−Δν, Δν) and δν being the frequency range and step, respectively.
9. A method of measuring an anomaly in an optical fiber, comprising:
measuring a relative motion between a probe source and the anomaly;
synchronizing a start of an acquisition of a Brillouin gain spectrum (BGS) and an anomaly motion detection, wherein the BGS comprises a plurality of backscatter traces, acquired at a plurality of instances; and
after completing of the acquisition of the BGS, correcting the BGS based on a position of the anomaly at a time when a given BGS trace of the plurality of BGS traces is acquired.
10. The method of claim 9 , wherein the BGS is acquired by Brillouin Optical Time Domain Reflectometry (BOTDR) or is acquired by Brillouin Optical Time Domain Analysis (BOTDA).
11. The method of claim 9 , wherein the probe source comprises a sensing fiber, wherein the anomaly comprises a change in temperature and/or strain (temperature/strain) in the optical fiber, and wherein measurement of a relative motion of the sensing fiber and a temperature/strain profile is synchronized with detection of the Brillouin gain spectrum.
12. The method of claim 11 , wherein after an initial backscatter trace of the plurality of traces, subsequent backscatter traces of the plurality of backscatter traces are shifted forward in space when the anomaly is moving away from the probe source, wherein after the initial backscatter trace of the plurality of backscatter traces, subsequent backscatter traces of the plurality of traces are shifted backward in space when the anomaly is moving toward the probe source.
13. The method of claim 9 , wherein a given pulse of the plurality of pulses is launched at a frequency ν 0 , wherein a given backscatter trace along the optical fiber is detected by a heterodyne receiver at a frequency ν B , and wherein the plurality of backscatter traces span a predetermined frequency range.
14. The method of claim 13 , wherein a given Brillouin gain spectrum is characterized for a first trace at a first frequency step as −ΔνI 11 (−Δν, x)→I′ 11 (−Δν, x)=I 11 (−Δν, x), and for an N th trace at as −Δν: I 1N (−Δν, x)→I′ 1N (−Δν, x)=I 1N (−Δν, x−d 1N ), wherein d 1N a distance moved away along the direction of a pulse launch since the 1 st trace at the 1 st frequency step.
15. The method of claim 14 , wherein a given Brillouin gain spectrum is characterized for a N th trace at −Δν+m×δν: I mN (−Δν+m×δν, x)→I′ mN (−Δν+m×δν, x)=I mN (−Δν+m×δν, x−d mN ), where d mN is a distance moved away along the direction of pulse launch since the 1 st trace scan at the 1 st frequency step, (−Δν, Δν) and δν being the frequency range and step, respectively.