Method and system using wavelength division multiplexing for eliminating and reducing light diffusion and light reflection interference in interference path

Patent metadata

Field	Value
Publication number	US-10024697-B2
Application number	US-201415028865-A
Country	US
Kind code	B2
Filing date	Oct 10, 2014
Priority date	Oct 12, 2013
Publication date	Jul 17, 2018
Grant date	Jul 17, 2018

Abstract

A method using wavelength division multiplexing for reducing light diffusion and light reflection interference in an interference path, comprising: connecting a wavelength division multiplexer (10) serially at an end of a sensing optical fiber (6); using the wavelength division multiplexer (10) to extract a wavelength component from a working path for measuring an interfering signal caused by light diffusion and light reflection; using the signal as a reference to extract an effective signal component that has been interfered by light diffusion and light reflection, and obtaining a pure effective signal. Because the device connected at the end of the sensing optical fiber (6) is passive and requires no power, the system is easy to implement and is particularly suitable for situations in which power provision is difficult at the end of the sensing optical fiber (6). The method is suitable for long distance pipeline monitoring and a wide-range optical of fiber perimeter security. Also provided is a system using wavelength division multiplexing for reducing light diffusion and light reflection interference in an interference path.

First claim

The invention claimed is:

1. A method using wavelength division multiplexing for eliminating and reducing light diffusion and light reflection interference in an interference path, the method comprising:
connecting a wavelength division multiplexer (“WDM”) in series between an end of a sensing optical fiber and a feedback device in an interference optical path structure;
providing the WDM with a multiplexed port, a first splitting port, and a second splitting port, corresponding wavelengths of light from the first and second splitting ports being λ1 and λ2, respectively;
connecting the multiplexed port with the end of the sensing optical fiber; and
connecting the first splitting port with the feedback device and not using the second splitting port, wherein
an interference optical path structure is configured such that:
light with wavelength λ2, when transmitted along the interference path, obtains an interference signal produced by one or more scattering points and reflecting points that are along the interference path, and
light with wavelength λ1, when transmitted along the interference path, obtains both an effective signal of a disturbance point and the interference signal.

2. The method according to claim 1 , wherein,
when light with the wavelength λ1 is transmitting along the sensing optical fiber to an end of the feedback device:
a part of the light is scattered by scattering or reflected by a reflection point and returns in advance, and
the remaining light passes through the WDM, reaches the feedback device, and then returns along the same route such that a signal P 1 formed by wavelength λ1 is expressed as:

P
1

=

P
eff

+

∑
i

⁢

⁢

p
S

⁡

(

λ
1

,
i

)

(
1
)

wherein, P eff is a signal formed by light reflected by the feedback device, p S (λ 1 ,i) is a signal formed by the light with wavelength λ1 caused by an i-th scattering point or reflecting point of the sensing optical fiber, and

∑
i

⁢

p
S

⁡

(

λ
1

,
i

)

is a sum of all scattering and reflecting points along the sensing optical fiber before the WDM, and

when light with wavelength λ2 is transmitting along the sensing optical fiber to the end of the feedback device:
a part of the light is scattered by the scattering point or reflected by the reflecting point and returns in advance, and
the remaining light passes through the WDM and leaks from the second splitting port such that a signal P 2 formed by wavelength λ2 is expressed as:

P
2

=

∑
i

⁢

⁢

p
S

⁡

(

λ
2

,
i

)

(
2
)

wherein, p S (λ 2 ,i) is a signal formed by the light with wavelength λ2 caused by an i-th scattering point or reflecting point of the sensing optical fiber, and

the method further comprising:
using signal processing to make λ1 close to λ2 such that:

p
S

⁡

(

λ
1

,
i

)

≈

p
S

⁡

(

λ
2

,
i

)

(
3
)

∑
i

⁢

⁢

p
S

⁡

Assignees

• Univ Fudan

Inventors

• Xiao Qian
• Jia Bo
• Bian pang

Classifications

• G02B6/2861

  using fibre optic delay lines and optical elements associated with them, e.g. for use in signal processing, e.g. filtering (delay lines in general H03H, H01P9/00; optical computing devices G06E) · CPC title

• G08B13/124

  with the breaking or disturbance being optically detected, e.g. optical fibers in the perimeter fence · CPC title

• G01M5/0091

  by using electromagnetic excitation or detection · CPC title

• G01D5/35358

  using backscattering to detect the measured quantity · CPC title

• G01M5/0025

  of elongated objects, e.g. pipes, masts, towers or railways (G01M5/0058 takes precedence) · CPC title