CN102393272B - Fiber bragg grating hydraulic pressure sensing method based on conical fiber - Google Patents

Abstract

The invention discloses a fiber bragg grating hydraulic pressure sensing method based on a conical fiber. The existing method has the defects of low sensitivity, overlength of sensing optical fiber and the like. The method provided by the invention comprises the following steps: firstly determining the fiber bragg grating of a broadband light source, a triport light coupler, an optical spectrum analyser and a conical optical fiber; then connecting the devices according to a measurement scheme; and finally putting the fiber bragg grating of the conical optical fiber in an environment which requires measurement hydraulic pressure, and determining the hydraulic pressure applied to the fiber bragg grating through measuring the central wavelength drifting of the fiber bragg grating of the conical fiber. The method provided by the invention has the advantages of capability of being free from electromagnetic interference, low cost, compact structure, high sensitivity and the like.

Description

Fiber Bragg grating hydraulic sensing method based on tapered optical fiber

Technical Field

The invention belongs to the technical field of optical fiber sensing, and relates to a tapered optical fiber-based hydraulic sensing method for fiber Bragg gratings.

Background

The invention of the optical fiber brings revolutionary development of the communication field and promotes the birth of the information society. On the other hand, the invention of the optical fiber also brings revolutionary development of the sensing technology and becomes an indispensable part of the development of the technology of the internet of things. The optical fiber can be used as a transmission medium of light waves, and when the light waves are transmitted in the optical fiber, the amplitude, the phase, the polarization state, the wavelength and the like of characteristic parameters of the optical fiber can be indirectly or indirectly changed due to external factors such as temperature, pressure, strain, a magnetic field, an electric field, displacement and the like, so that the optical fiber can be used as a sensing element to detect physical quantities. The optical fiber sensing technology is a technology for converting an external physical quantity into a signal which can be directly measured by utilizing the characteristic that an optical fiber is sensitive to certain physical quantity. The optical fiber sensing technology is one of the most important sensing technologies in the optical field, and has been widely applied to the fields of biology, medicine, aerospace, aviation, machinery, petrifaction, building, high-speed rail, bridges, national defense industry and the like.

The fiber bragg grating is one of the most mature devices in the fiber sensing technology, and the sensing of physical quantities such as temperature, stress, refractive index and the like can be realized by utilizing the fiber bragg grating. At present, hydraulic sensing can be realized by the fiber Bragg grating based on the common optical fiber, but the technical scheme has the defect of low sensitivity because the fiber Bragg grating is insensitive to hydraulic influence. In addition, the current report about the special optical fiber hydraulic sensing technology mainly utilizes the existing commercial photonic crystal optical fiber to realize hydraulic sensing, and has the defects of low sensitivity, overlong sensing optical fiber and the like. Therefore, the invention has important significance in providing the hydraulic sensing method with low price, compact structure and high sensitivity.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a fiber Bragg grating hydraulic sensing method based on a tapered optical fiber.

The method of the invention comprises the following steps:

selecting a broadband light source with output wavelength covering 1500nm to 1600nm, a three-port optical fiber coupler, an optical fiber Bragg grating of a tapered optical fiber and a spectrum analyzer with working wavelength covering 1500nm to 1600 nm;

step (2) connecting an output port of a broadband light source with an input port of an optical fiber coupler through an optical fiber; connecting an output port of the optical fiber coupler with the optical fiber Bragg grating of the tapered optical fiber in an optical fiber fusion mode, wherein an output port of the optical fiber coupler is connected with an input port of the optical spectrum analyzer in an optical fiber mode;

and (3) placing the fiber Bragg grating of the tapered optical fiber into a liquid environment needing to measure hydraulic pressure. The fiber Bragg grating of the tapered optical fiber is manufactured by the following steps: 1) intercepting a section of common single-mode optical fiber with the length of more than 10 centimeters and the diameter of D (120-130 micrometers), and drawing the optical fiber into a tapered optical fiber by adopting the existing mature technology, wherein the diameter D (25-50 micrometers) of the waist part of the tapered optical fiber and the length L (2-10 centimeters) of the waist part of the tapered optical fiber are obtained; 2) writing fiber Bragg grating on the waist of the tapered fiber, wherein the technology is the existing mature technology; 3) the waist of the tapered optical fiber is coated with curing glue, so that the mechanical strength of the fiber Bragg grating of the tapered optical fiber is enhanced, and the sensitivity of the sensor is increased.

The center wavelength of the fiber Bragg grating of the tapered optical fiber is

λ=2Λn_eff

Wherein Λ, n_effThe effective refractive index of the fiber bragg grating period and the tapered fiber, respectively. When the hydraulic pressure applied to the fiber Bragg grating of the tapered optical fiber is changed, the central wavelength of the fiber Bragg grating corresponds to a wavelength drift delta lambda, and the hydraulic pressure delta p and the wavelength drift delta lambda meet the following relation

Δp=K×Δλ

Wherein,

$K=1/({2n}_{\mathrm{eff}}\frac{\∂\mathrm{\Λ}}{\∂p}+2\mathrm{\Λ}\frac{{\∂n}_{\mathrm{eff}}}{\∂p})$

is a constant. Therefore, the hydraulic pressure applied to the fiber bragg grating can be determined by measuring the central wavelength drift of the fiber bragg grating of the tapered optical fiber.

The invention is mainly suitable for measuring the hydraulic pressure in liquid, utilizes the characteristic that the central wavelength of the fiber Bragg grating of the tapered optical fiber changes along with the hydraulic pressure, determines the hydraulic pressure value through the central wavelength drift, and realizes the hydraulic pressure sensing. The invention has the advantages of no electromagnetic interference, low price, compact structure, high sensitivity and the like because the fiber Bragg grating of the tapered optical fiber is used as the sensing medium.

Drawings

FIG. 1 is a schematic diagram of the structure of an optical device in the method of the present invention;

FIG. 2 is a schematic diagram of a fiber Bragg grating of a tapered optical fiber;

FIG. 3 is a schematic view of a tapered fiber waist coated with a curing glue;

FIG. 4 is a graph showing the results of measurements made using the method of the present invention.

Detailed Description

As shown in fig. 1, 2 and 3, the tapered fiber bragg grating hydraulic sensing device includes a broadband light source 1, a fiber coupler 2, a tapered fiber bragg grating 3 and a spectrum analyzer 4.

Connecting an output port of a broadband light source 1 with an input port of an optical fiber coupler 2 through an optical fiber; one output port of the optical fiber coupler 2 and the fiber bragg grating 3 of the tapered optical fiber are connected in an optical fiber fusion mode, and one output port of the optical fiber coupler 2 is connected with the input port of the optical spectrum analyzer 4 in an optical fiber connection mode. Drawing the tapered optical fiber into a tapered optical fiber through a section of common single-mode optical fiber with the length of more than 10 cm and the diameter of D (120-130 micrometers), wherein the diameter D (25-50 micrometers) of the waist part of the tapered optical fiber and the length L (2-10 cm) of the waist part are the same; writing the fiber Bragg grating 5 on the waist part of the tapered fiber; and coating curing glue on the waist of the tapered optical fiber to form the fiber Bragg grating 6 of the tapered optical fiber.

The hydraulic sensing method using the detection device comprises the following steps:

(1) selecting a broadband light source 1 with output wavelength covering 1500nm to 1600nm, a three-port optical fiber coupler 2, an optical fiber Bragg grating 3 of a tapered optical fiber and a spectrum analyzer 4 with working wavelength covering 1500nm to 1600 nm;

(2) connecting an output port 1 of a broadband light source with an input port of an optical fiber coupler 2 through an optical fiber; connecting an output port of the optical fiber coupler 2 and the optical fiber Bragg grating 3 of the tapered optical fiber in an optical fiber fusion mode, and connecting an output port of the optical fiber coupler 2 and an input port of the optical spectrum analyzer 4 in an optical fiber mode;

(3) the fiber Bragg grating 3 of the tapered optical fiber is placed in a liquid environment where hydraulic pressure needs to be measured. The broadband light source 1 is turned on, and the center wavelength of the fiber Bragg grating 3 of the conical optical fiber is

λ=2Λn_eff

When the hydraulic pressure applied to the fiber Bragg grating of the tapered optical fiber is changed, the central wavelength of the fiber Bragg grating corresponds to a wavelength drift delta lambda, and the hydraulic pressure delta p and the wavelength drift delta lambda meet the following relation

Δp=K×Δλ

Wherein,

$K=1/({2n}_{\mathrm{eff}}\frac{\∂\mathrm{\Λ}}{\∂p}+2\mathrm{\Λ}\frac{{\∂n}_{\mathrm{eff}}}{\∂p})$

is a constant. Therefore, the hydraulic pressure applied to the fiber bragg grating can be determined by measuring the central wavelength drift of the fiber bragg grating of the tapered optical fiber. The specific measurement results are shown in fig. 4.

The invention provides a new technical scheme of optical fiber hydraulic sensing by utilizing the tapered optical fiber manufacturing technology which is developed recently and the technology of writing the optical fiber Bragg grating on the tapered optical fiber and utilizing the characteristic that the central wavelength of the optical fiber Bragg grating technology is sensitive to hydraulic pressure. The invention adopts the fiber Bragg grating technology of the tapered optical fiber as the sensing medium, and has the advantages of no electromagnetic interference, low price, compact structure, high sensitivity and the like.

Claims (1)

1. The fiber Bragg grating hydraulic sensing method based on the tapered optical fiber is characterized by comprising the following steps of:

selecting a broadband light source with output wavelength covering 1500nm to 1600nm, a three-port optical fiber coupler, an optical fiber Bragg grating of a tapered optical fiber and a spectrum analyzer with working wavelength covering 1500nm to 1600 nm;

the fiber Bragg grating of the tapered optical fiber is prepared by the following specific steps:

1) intercepting a section of common single-mode optical fiber with the length of more than 10 centimeters and the diameter of 120-130 micrometers, and drawing the single-mode optical fiber into a tapered optical fiber, wherein the diameter of the waist part of the tapered optical fiber is 25-50 micrometers, and the length of the waist part is 2-10 centimeters;

2) writing fiber Bragg grating on the waist of the tapered fiber;

3) coating curing glue on the waist of the tapered optical fiber to strengthen the mechanical strength of the fiber Bragg grating of the tapered optical fiber and increase the sensitivity of the sensor;

step (2) connecting an output port of a broadband light source with an input port of an optical fiber coupler through an optical fiber; connecting an output port of the optical fiber coupler with the optical fiber Bragg grating of the tapered optical fiber in an optical fiber fusion mode, wherein an output port of the optical fiber coupler is connected with an input port of the optical spectrum analyzer in an optical fiber mode;

step (3) placing the fiber Bragg grating of the tapered optical fiber into a liquid environment needing to measure hydraulic pressure, starting a broadband light source, wherein the central wavelength of the fiber Bragg grating of the tapered optical fiber is

Wherein、

The effective refractive indexes of the fiber Bragg grating period and the tapered fiber respectively, when the hydraulic pressure applied to the fiber Bragg grating of the tapered fiber is changed, the central wavelength of the fiber Bragg grating corresponds to a wavelength drift

Hydraulic pressure of it

And wavelength drift

Satisfy the following relationships

Wherein,

is a constant; the hydraulic pressure applied to the fiber bragg grating can be determined by measuring the central wavelength drift of the fiber bragg grating of the tapered optical fiber.

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