US 9,404,856 B2Granted

Optical refractive index measuring system based on speckle correlation

AssigneeMacau University of Science and Technology

InventorsJianqing Li, Ben Xu, Yuanyuan Pan

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Abstract

An optical detection system for measuring a refractive index of a liquid analyte comprising a light transmitting assembly fiber, which includes a single-mode fiber, an optical fiber sensing module and a multi-mode fiber. The optical detection system is configured to emit a coherent light beam to one end of the assembly fiber; and a detector is configured to capture a specklegram from an exit end of the assembly fiber. When the optical detection system is in operation, the optical fiber sensing module is configured to be submerged into the liquid analyte. By analyzing the correlation between the specklegram corresponding to the liquid analyte and the reference specklegram, the refractive index of the liquid analyte can be obtained.

Claims18

Dependent claims

An optical detection system for measuring a refractive index of a liquid analyte comprising:

a light transmitting assembly fiber that includes a single-mode fiber, a no-core optical fiber sensing module and a multi-mode fiber, wherein said no-core optical fiber sensing module is sandwiched between said single-mode fiber and said multi-mode fiber;
a coherent light source that emits a coherent light beam to a first end of said assembly fiber located at said single-mode fiber;
a detector that captures a signal from a second end of said assembly fiber located at said multi-mode fiber;
and
a microcomputer programmed to compute a correlation value (r) between said signal and a reference speckleqram signal such that r is computed from:
r
=
∑
m
⁢
∑
n
⁢
(
A
mn
-
A
_
)
⁢
(
B
mn
-
B
_
)
(
∑
m
⁢
∑
n
⁢
(
A
mn
-
A
_
)
2
)
⁢
(
∑
m
⁢
∑
n
⁢
(
B
mn
-
B
_
)
2
)
wherein A is said signal and B is said reference speckleqram signal, m and n are coordinates of a pixel of a speckleqram, Amn and Bmn denote intensities of pixel (m, n) in A and B respectively, and Ā and B are average intensities of all pixels in A and B;
and
wherein said no-core optical fiber sensing module is submerged into said liquid analyte when said optical detection system is in operation.

61 more elements

A method for measuring a refractive index of a liquid analyte, said method comprising:

providing a light transmitting assembly fiber comprising a no-core optical fiber sensing module, a single-mode fiber and a multi-mode fiber, wherein said no-core optical fiber sensing module is sandwiched between said single-mode fiber and said multi-mode fiber;
submerging said no-core optical fiber sensing module into said liquid analyte;
directing a coherent light beam to a first end of said assembly fiber located at said single-mode fiber by a coherent light source;
generating a signal based on phase differences between excited modes;
capturing said signal at a second end of said assembly fiber located at said multi-mode fiber by a detector;
and
determining said refractive index of said liquid analyte based on the captured signal that is in a form of a specklegram signal by analyzing a correlation between said specklegram signal and a reference specklegram signal with a correlation function (r) defined by:
r
=
∑
m
⁢
∑
n
⁢
(
A
mn
-
A
_
)
⁢
(
B
mn
-
B
_
)
(
∑
m
⁢
∑
n
⁢
(
A
mn
-
A
_
)
2
)
⁢
(
∑
m
⁢
∑
n
⁢
(
B
mn
-
B
_
)
2
)
wherein A is said specklegram signal and B is said reference specklegram signal, m and n are coordinates of a pixel of a specklegram, Amn and Bmn denote intensities of pixel (m, n) in A and B, and Ā and B are average intensities of pixels in A and B.

61 more elements

Dependencies are inferred from the claim text.

Facts

Application: 13/907,993Filed 3 Jun 2013
Published: US 2014/0354979 A14 Dec 2014
Granted: 2 Aug 2016
Term ends: Not estimatedThe source records don’t support an estimate.

Classification4 codes

G01N 21/41
Systems in which incident light is modified in accordance with the properties of the material investigated: refractivity; Phase-affecting…
G01N 2021/433
Comprising optical fibres: with an unclad part on the fibre
G01N 2021/438
Sensing resonant reflection: with investigation of wavelength
G01N
Investigating or analysing materials by determining their chemical or physical properties