Distributed dynamic strain fiber optics measurement by Brillouin optical time-domain reflectometry

1. A method for performing Brillouin optical time-domain reflectometry for distributed dynamic strain measurements of a structure, the method comprising:

splitting a continuous-wave laser output into a first and second branch;

modulating the first signal branch using electro optic modulation controlled by received pulses into a stimulated Brillouin scattered (SBS) signal;

wherein the continuous-wave laser output from said second branch comprises a continuous wave reference signal;

applying the stimulated Brillouin scattered (SBS) signal to an optical fiber attached or embedded in a structure;

simultaneously detecting the SBS signal from the structure and coupling this with the continuous-wave reference signal to a photodetector to produce an output signal;

processing the output signal using Brillouin optical time-domain reflectometry (BOTDR) comprising a small gain SBS based short-time Fourier transform (STFT) configured to provide a desired spatial sampling resolution along said optical fiber; and

measuring a distribution of the Brillouin frequency shifts (BFS) along the structure to calculate one or more of an applied strain or temperature change on the structure.

2. The method of claim 1 , wherein processing the output signal comprises rebuilding of the Brillouin frequency shift (BFS) with short-time Fourier transform (STFT).

3. The method of claim 1 , wherein the SBS signal comprises a stimulated Brillouin counter-propagating pulse signal.

4. The method of claim 1 , wherein the SBS signal comprises a small-gain SBS signal, and is not relying on spontaneous Brillouin scattering (SpBS).

5. The method of claim 1 , wherein the stimulated Brillouin scattered (SBS) signal and reference signal are split from a continuous wave light by a coupler into optical signals along said first branch and said second branch.

6. The method of claim 1 , wherein the reference signal comprises an optical local oscillator (OLO).

7. The method of claim 6 , wherein the OLO reference signal and the Brillouin scattered (SBS) signal are mixed on a photodetector to produce the output signal.

8. The method of claim 7 , wherein the output signal is downconverted, amplified, filtered and digitized prior to processing.

9. A Brillouin optical time-domain reflectometry (BOTDR) based distributed dynamic strain sensor, comprising:

(a) a continuous-wave light source configured for outputting an optical signal to a first and second branch, and a signal generator coupled to an electro optic modulator (EOM) configured for modulating the optical signal in said first branch into a stimulated Brillouin scattered (SBS) signal, and wherein the optical signal in said second branch comprises a continuous wave reference signal;

(b) applying the stimulated Brillouin scattered (SBS) signal to an optical fiber attached or embedded in a structure;

(c) a detector configured for simultaneously detecting the SBS signal from the structure and coupling this with the continuous-wave reference signal to a photodetector to produce an output signal;

(d) a processor for processing the output signal; and

(e) a non-transitory memory storing instructions executable by the processor;

(f) wherein said instructions, when executed by the processor, perform steps comprising:

(i) measuring a distribution of the Brillouin frequency shifts (BFS) along the structure by using Brillouin optical time-domain reflectometry (BOTDR) comprising a small gain SBS based short-time Fourier transform (STFT) configured to provide a desired spatial sampling resolution along said optical fiber;

(ii) calculating one or more of an applied strain or temperature change on the structure from the measured BFS distribution.

10. The sensor of claim 9 , wherein calculating one or more of an applied strain or temperature change on the structure is performed in response to a rebuilding of the Brillouin frequency shift (BFS) with short-time Fourier transform (STFT).

11. The sensor of claim 9 , wherein the SBS signal comprises a stimulated Brillouin counter-propagating pulse signal.

12. The sensor of claim 9 , wherein the SBS signal comprises a small-gain SBS signal, and is not relying on spontaneous Brillouin scattering (SpBS).

13. The sensor of claim 9 , further comprising:

a first optical coupler configured to split said continuous wave light into optical signals on said first branch and said second branch.

14. The sensor of claim 13 , wherein the reference signal comprises an optical local oscillator (OLO) comprising a polarization scrambler configured to provide random polarization to the reference signal.

15. The sensor of claim 13 , wherein the detector comprises a photodetector, and wherein the continuous wave reference signal and the Brillouin scattered (SBS) signal are mixed on a photodetector via a second optical coupler to produce the output signal.

16. The sensor of claim 15 , wherein the photodetector further comprises an oscillator to downconvert the output signal, an amplifier, and a band-pass filter to produce the output signal.

17. The sensor of claim 16 , further comprising a digitizer to digitize the output signal prior to processing by the processor.

18. The sensor of claim 13 , wherein the signal generator is configured for using a specified pulse repetition rate for controlling said electro optical modulator (EOM).

19. The sensor of claim 18 , further comprising a tunable erbium-doped fiber amplifier (EDFA) for amplifying the optical signal along said first pass which is then filtered by a band pass filter (BPF) and injected into a circulator prior to being applied to the optical fiber attached or embedded in the structure.

20. The sensor of claim 9 , wherein said continuous-wave light source comprises a narrow-line width external cavity laser.

21. An apparatus for performing Brillouin optical time-domain reflectometry for distributed dynamic strain measurements of a structure, the apparatus comprising:

(a) a continuous-wave light source configured for outputting an optical signal to a first branch and to a second branch, wherein the optical signals in said second branch comprises a continuous-wave reference signal;

(b) a signal generator and modulator configured for manipulating the optical signal in said first branch into a stimulated small-gain Brillouin scattered (SBS) signal directed into an optical fiber attached or embedded in a structure;

(c) a detector configured for simultaneously detecting the SBS signal from the structure and the continuous-wave reference signal to produce an electrical output signal;

(d) a processor for processing the electrical output signal; and

(e) a non-transitory memory storing instructions executable by the processor;

(f) wherein said instructions, when executed by the processor, perform steps comprising:

(i) measuring a distribution of the Brillouin frequency shifts (BFS) along the structure by using Brillouin optical time-domain reflectometry (BOTDR) comprising a small gain SBS based short-time Fourier transform (STFT) configured to provide a desired spatial sampling resolution along said optical fiber;

(ii) calculating one or more of an applied strain or temperature change on the structure from the measured BFS distribution, by rebuilding of the Brillouin frequency shift (BFS) with short-time Fourier transform (STFT).

22. The apparatus of claim 21 , wherein calculating one or more of an applied strain or temperature change on the structure comprises rebuilding of the Brillouin frequency shift (BFS) with short-time Fourier transform (STFT).

23. The apparatus of claim 21 , further comprising:

a first optical coupler configured to split said continuous wave light into optical signals on said first branch and said second branch.

24. The apparatus of claim 23 , wherein the continuous-wave reference signal comprises an optical local oscillator (OLO) comprising a polarization scrambler configured to provide random polarization to the reference signal.

25. The apparatus of claim 23 , wherein the detector comprises a photodetector, and wherein the continuous wave reference signal and the Brillouin scattered (SBS) signal are mixed on a photodetector via a second optical coupler to produce the output signal.

26. The apparatus of claim 23 , wherein the signal generator is configured for using a specified pulse repetition rate for controlling said electro optical modulator (EOM).