Method for determining distributed birefringence variations in a polarization-maintaining optical fiber

Patent metadata

Field	Value
Publication number	US-12529623-B2
Application number	US-202318362145-A
Country	US
Kind code	B2
Filing date	Jul 31, 2023
Priority date	Jul 31, 2023
Publication date	Jan 20, 2026
Grant date	Jan 20, 2026

Abstract

System and method for determining distributed birefringence variations in a polarization-maintaining optical fiber (PM fiber). The method includes causing a pump signal to be sent into the PM fiber to generate a Brillouin dynamic grating (BDG) therein, causing a first chirped probe optical pulse to be sent into the PM fiber, receiving a first reflected signal, the first reflected signal being a first portion of the first chirped probe optical pulse reflected by the BDG, receiving a second reflected signal, the second reflected signal being a second portion of the first chirped probe optical pulse reflected by the BDG, and determining a variation of birefringence of the PM fiber indicative of a variation of physical disturbance of the PM fiber between times of reflections on the BDG of the first and second reflected signals.

First claim

What is claimed is:

1 . A method for determining distributed birefringence variations in a polarization-maintaining optical fiber (PM fiber), the method being executed by a computer-implemented system comprising a controller, the method comprising:
causing a pump signal to be sent into the PM fiber at a first moment in time to generate a Brillouin dynamic grating (BDG) in the PM fiber along a first polarization direction at an interaction region of the PM fiber, the pump signal being polarized in the first polarization direction; causing a first chirped probe optical pulse to be sent into the PM fiber at a second moment in time subsequent to the first moment in time, the first chirped probe signal being polarized in the second polarization direction, the second polarization direction being orthogonal to the first direction; receiving a first reflected signal at a third moment in time, the first reflected signal being a first portion of the first chirped probe optical pulse reflected by the BDG; receiving a second reflected signal at a fourth moment in time, the second reflected signal being a second portion of the first chirped probe optical pulse reflected by the BDG at the interaction region of the PM fiber; and determining a variation of birefringence of the PM fiber at the interaction section based on the second, third and fourth moments in time, the variation of birefringence being indicative of a variation of physical disturbance of the PM fiber between times of reflections on the BDG of the first and second reflected signals.

2 . The method of claim 1 , wherein:
causing the first chirped probe optical pulse to be sent comprises producing a first chirped pulse having a linear frequency profile.

3 . The method of claim 1 , wherein:
causing the first chirped probe optical pulse to be sent comprises producing a first chirped pulse having a uniform optical power profile.

4 . The method of claim 1 , wherein:
generating the BDG in the PM fiber comprises injecting the pump signal into the PM fiber via a first end; and causing the first chirped probe optical pulse to be sent comprises injecting the first chirped probe optical pulse into the PM fiber via a second end, the second end being different from the first end.

5 . The method of claim 1 , wherein a wavelength profile of the pump signal is centered at 1550 nm.

6 . The method of claim 1 , wherein determining the variation of birefringence (ΔB) of the PM fiber at the interaction section comprises determining:

Δ
⁢
B

=

Δ
⁢

ϑ
C

·

n
gy

W
·

ϑ
P

·
Δ

⁢
t

where Δϑ C is a frequency chirping range of the chirped probe optical pulse,
n gy is a refractive index of a y-axis of the PM fiber,
W is a pulse width of the first chirped probe optical pulse,
ϑ p is a frequency of the pump signal, and
Δt=(T 4 −T 3 ) where:
T 3 is the third moment in time of receiving the first reflected signal, and
T 4 is the fourth moment in time of receiving the second reflected signal.

7 . The method of claim 1 , further comprising:
sending a second chirped probe optical pulse in the PM fiber at a fifth moment in time subsequent to the third moment in time, the second probe signal being polarized in the second polarization direction; receiving a third reflected signal at a sixth moment in time, the third reflected signal being a third portion of the second chirped probe optical pulse reflected by the BDG at the interaction section of the PM fiber; and determining a second variation of birefringence of the PM fiber at the interaction section based on the second, third, fifth and sixth moments in time, the second variation of birefringence being indicative of a variation of physical disturbance of the PM fiber between times of reflections on the BDG of the first and third reflected signals.

8 . The method of claim 1 , wherein the pump signal is a continuous wave pump signal.

9 . The method of claim 1 , wherein the pump signal is a pulsed pump signal.

10 . The method of claim 1 , wherein the first polarization direction is a direction of a slow axis of the PM fiber, and the second polarization direction is a direction of a fast axis of the PM fiber.

11 . A system for determining distributed birefringence variations in a polarization-maintaining optical fiber (PM fiber), the system being optically connected to the PM fiber, the system comprising:
a controller; a detector communicatively connected to the controller; and a probe signal generating module, the system being configured to:
cause a pump signal to be sent into the PM fiber at a first moment in time to generate a Brillouin dynamic grating (BDG) in the PM fiber along a first polarization direction at an interaction region of the PM fiber, the pump signal being polarized in the first polarization direction;
cause a first chirped probe optical pulse to be sent into the PM fiber at a second moment in time subsequent to the first moment in time, the first chirped probe signal being polarized in the second polarization direction, the second polarization direction being orthogonal to the first direction;
receive, at the detector, a first reflected signal at a third moment in time, the first reflected signal being a first portion of the first chirped probe optical pulse reflected by the BDG receive, at the detector, a second reflected signal at a fourth moment in time, the second reflected signal being a second portion of the first chirped probe optical pulse reflected by the BDG at the interaction region of the PM fiber; and
determine a variation of birefringence of the PM fiber at the interaction section based on the second, third and fourth moments in time, the variation of birefringence being indicative of a variation of physical disturbance of the PM fiber between times of reflections on the BDG of the first and second reflected signals.

12 . The system of claim 11 , further comprising a pump laser source optically connected to the PM fiber and configured to generate the pump signal and stimulate the Brillouin dynamic grating along the first polarization direction in the PM fiber.

13 . The system of claim 12 , wherein the pump laser source is a narrow linewidth laser source.

14 . The system of claim 12 , wherein the pump laser source is configured to emit a continuous wave pump signal.

15 . The system of claim 12 , wherein the pump laser source is configured to emit a pulsed pump signal.

16 . The system of claim 11 , wherein the probe signal generating module comprises:
a distributed feedback (DFB) laser source; and a pulse generator operatively connected to the DFB laser source, the pulse g

Assignees

• Huawei Tech Co Ltd
• Huawei Tech Canada Co Ltd
• Univ Ottawa

Inventors

• Bao Xiaoyi
• Wang Yuan

Classifications

• G01K11/322

  using Brillouin scattering · CPC title

• G01N2021/638

  Brillouin effect, e.g. stimulated Brillouin effect · CPC title

• G02B6/02109

  having polarization sensitive features, e.g. reduced photo-induced birefringence · CPC title

• G01M11/37 Primary

  in which light is projected perpendicularly to the axis of the fibre or waveguide for monitoring a section thereof · CPC title