Suppression of noise and cross-talk in brillouin fiber sensors

Patent metadata

Field	Value
Publication number	US-11473983-B2
Application number	US-202117383263-A
Country	US
Kind code	B2
Filing date	Jul 22, 2021
Priority date	Jul 23, 2020
Publication date	Oct 18, 2022
Grant date	Oct 18, 2022

Abstract

A dynamic Brillouin fiber sensor that is immune to fluctuations in the power, frequency, or polarizing state of the pump and probe beams is described herein. A new measurand that combines information from the complex Stokes and anti-Stokes interactions is provided to extract the absolute Brillouin frequency shift while rejecting the majority of noise sources that may limit the performance of current slope-assisted Brillouin optical time domain analysis systems.

First claim

What is claimed is:

1. A method for suppressing noise and cross-talk in a Brillouin fiber sensor, the method comprising:
injecting a pump into a first end of the fiber sensor;
transmitting a plurality of co-propagating probe beams into a second end of the fiber sensor;
measuring photocurrent produced by interactions of the transmitted probe beams;
determining a measurand based on the measured photocurrent, the measurand being configured to extract a Brillouin frequency shift while suppressing noise and cross-talk originating from fluctuations in power or frequency of the pump or the probe beams; and
detecting a change in a parameter of interest along a length of the fiber sensor based on the measurand.

2. The method of claim 1 , further comprising:
dividing a narrow-linewidth laser into a pump path and a probe path; and
modulating light directed along the pump path to generate the pump.

3. The method of claim 2 , wherein modulating light directed along the pump path to generate the pump comprises at least one of:
modulating the light to generate a pulsed pump; or
modulating the light in a manner to enable distributed measurements at a plurality of positions along the fiber.

4. The method of claim 2 , wherein the probe beams are generated by modulating light along the probe path with a pair of modulators to generate four probe beams that comprise a Stokes probe, a Stokes local oscillator sideband, an anti-Stokes probe, and an anti-Stokes local oscillator sideband.

5. The method of claim 4 , wherein the measurand comprises a dual probe gain to phase ratio and is determined based on measurements of both Stokes and anti-Stokes interactions.

6. The method of claim 4 , wherein the measurand provides a linear response to changes in Brillouin frequency while removing any dependence on fluctuations in pump power or in frequency of the pulsed pump or probe beams.

7. The method of claim 1 , wherein the photocurrent produced by the interactions of the probe beams is measured via a pair of photodetectors.

8. The method of claim 1 , wherein the parameter of interest comprises at least one of a strain or temperature measurement.

9. A fiber optic sensor system comprising:
an optical source configured to output a first optical signal into a first end of an optical fiber and a second optical signal into a second end of the optical fiber, the second optical signal being modulated into a plurality of co-propagating probe beams prior to being transmitted into the optical fiber;
a pair of photodetectors configured to measure photocurrent produced by interactions of the transmitted probe beams; and
a processing unit configured to
determine a measurand based on the measured photocurrent, the measurand being configured to extract a Brillouin frequency shift while suppressing noise and cross-talk originating from fluctuations in power, frequency or polarization state of the pulsed pump or the probe beams, and
detect a change in a parameter of interest along a length of the optical fiber based on the measurand.

10. The system of claim 9 , wherein the first optical signal is modulated prior to being injected into the first end of the optical fiber.

11. The system of claim 9 , further comprising:
a pair modulators configured to generate the plurality of co-propagating probe beams that comprise a Stokes probe, a Stokes local oscillator sideband, an anti-Stokes probe, and an anti-Stokes local oscillator sideband.

12. The system of claim 9 , wherein the pair of photodetectors comprise photodiodes.

13. The system of claim 9 , wherein the measurand comprises a dual probe gain to phase ratio and is determined based on measurements of both Stokes and anti-Stokes interactions.

14. The system of claim 9 , wherein the measurand provides a linear response to changes in Brillouin frequency while removing any dependence on fluctuations in pump power or in frequency of the pulsed pump or probe beams.

Assignees

• Us Gov Sec Navy
• The Government Of The Us Secretarv Of The Navy

Inventors

• Murray Joseph B
• Redding Brandon F

Classifications

• G01K11/322 Primary

  using Brillouin scattering · CPC title

• G01K3/00

  Thermometers giving results other than momentary value of temperature (G01K7/42 takes precedence) · CPC title