Hybrid Raman and Brillouin scattering in few-mode fibers

Patent metadata

Field	Value
Publication number	US-9599460-B2
Application number	US-201514842503-A
Country	US
Kind code	B2
Filing date	Sep 1, 2015
Priority date	Oct 16, 2014
Publication date	Mar 21, 2017
Grant date	Mar 21, 2017

Abstract

Methods and systems of sensing conditions in a fiber includes launching a light beam into a fiber. A first branch of scattered light is set to a mode other than a fundamental mode. A second branch of scattered light is optically filtered to remove unscattered input light. Brillouin scattered light is coherently detected on the first branch to produce a combined temperature/strain profile of the fiber. Raman scattered light on the second branch is directly detected to produce a temperature profile of the fiber. A strain profile of the fiber is determined, using a processor, based on the combined temperature/strain profile and the temperature profile.

First claim

The invention claimed is:

1. A hybrid Brillouin/Raman sensor, comprising:
a mode converter configured to convert Brillouin backscattered light from a fiber to a spatial mode other than a fundamental spatial mode;
an optical filter configured to separate Raman forward-scattered light from a fiber to remove unscattered input light;
a Brillouin receiver configured to coherently detect the Brillouin backscattered light output by the mode converter and to produce a combined temperature/strain profile of the fiber;
a Raman receiver configured to directly detect the Raman forward-scattered light output by the optical filter and to produce a temperature profile of the fiber; and
a processor configured to determine a strain profile of the fiber based on the combined temperature/strain profile and the temperature profile.

2. The sensor of claim 1 , wherein the Raman receiver comprises:
a photodiode;
a trans-impedance amplifier; and
an analog to digital converter.

3. The sensor of claim 1 , wherein the Brillouin receiver comprises:
a P-I-N photodiode;
a trans-impedance amplifier;
an electrical spectrum analyzer configured to produce a Brillouin scattered trace; and
an analog to digital converter.

4. The sensor of claim 1 , further comprising a polarization controller configured to set light input to the fiber to a single polarization.

5. The sensor of claim 1 , wherein the mode converter comprises one of the group consisting of a long-period fiber grating, a spatial light modulator, free-space phase plates, and a fused spatial mode coupler.

6. A hybrid Brillouin/Raman sensor, comprising:
a coupler configured to split backscattered light from a fiber into two paths;
a mode converter configured to convert backscattered light on a first path to a spatial mode other than a fundamental spatial mode;
an optical filter configured to separate backscattered light on a second path to remove unscattered input light;
a Brillouin receiver configured to coherently detect the Brillouin backscattered light output by the mode converter and to produce a combined temperature/strain profile of the fiber;
a Raman receiver configured to directly detect the Raman forward-scattered light output by the optical filter and to produce a temperature profile of the fiber; and
a processor configured to determine a strain profile of the fiber based on the combined temperature/strain profile and the temperature profile.

7. The sensor of claim 6 , wherein the Raman receiver comprises:
a photodiode;
a trans-impedance amplifier; and
an analog to digital converter.

8. The sensor of claim 6 , wherein the Brillouin receiver comprises:
a P-I-N photodiode;
a trans-impedance amplifier;
an electrical spectrum analyzer configured to produce a Brillouin scattered trace; and
an analog to digital converter.

9. The sensor of claim 6 , further comprising a polarization controller configured to set light input to the fiber to a single polarization.

10. The sensor of claim 6 , wherein the mode converter comprises one of the group consisting of a long-period fiber grating, a spatial light modulator, free-space phase plates, and a fused spatial mode coupler.

11. A method for sensing conditions in a fiber, comprising:
launching a light beam into a fiber;
mode controlling a first branch of scattered light to a spatial mode other than a fundamental spatial mode;
optically filtering a second branch of scattered light to remove unscattered input light;
coherently detecting Brillouin scattered light on the first branch to produce a combined temperature/strain profile of the fiber;
directly detecting Raman scattered light on the second branch to produce a temperature profile of the fiber; and
determining a strain profile of the fiber, using a processor, based on the combined temperature/strain profile and the temperature profile.

12. The method of claim 11 , wherein the first branch comprises light that is Brillouin backscattered from the fiber.

13. The method of claim 12 , wherein the second branch comprises light that is Raman forward-scattered from the fiber.

14. The method of claim 12 , wherein the second branch comprises light that is Raman backscattered from the fiber.

15. The method of claim 11 , further comprising controlling a polarization of the light beam to set the light beam to a single polarization before launching the light beam into the fiber.

16. The method of claim 11 , wherein mode controlling the first branch of scattered light comprises passing the first branch of scattered light through a mode converter that comprises one of the group consisting of a long-period fiber grating, a spatial light modulator, free-space phase plates, and a fused spatial mode coupler.

Assignees

• Nec Lab America Inc
• Nec Corp

Inventors

• Wang Ting
• Weng Yi

Classifications

• G01B11/168 Primary

  by means of polarisation · CPC title

• G01L1/246 Primary

  using integrated gratings, e.g. Bragg gratings · CPC title

• G01L1/242

  the material being an optical fibre · CPC title