CN112945805A - Microstructure fiber grating series connection device and liquid density measurement method - Google Patents

Microstructure fiber grating series connection device and liquid density measurement method Download PDF

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CN112945805A
CN112945805A CN202110115416.8A CN202110115416A CN112945805A CN 112945805 A CN112945805 A CN 112945805A CN 202110115416 A CN202110115416 A CN 202110115416A CN 112945805 A CN112945805 A CN 112945805A
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fiber grating
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田野
马占宇
柴全
廉宇航
于浪
谭滔
段超
张建中
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Harbin Engineering University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
    • G01N13/02—Investigating surface tension of liquids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
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Abstract

The invention belongs to the technical field of liquid density measurement, and particularly relates to a microstructure fiber grating series connection device and a liquid density measurement method based on the device. According to the invention, the microstructure fiber grating series connection device is vertically inserted into liquid, reflection spectra of two microstructure fiber gratings before and after the microstructure fiber grating series connection device is inserted into the liquid are compared, liquid level heights of liquid inside and outside the edge hole fiber are measured, stress of the liquid inside and outside the edge hole fiber is contrastively analyzed, and density and surface tension coefficient of the liquid to be measured are calculated. The invention effectively utilizes the sensing measurement technology of the side hole fiber grating on the liquid level, combines the fiber polishing technology, and prepares the D-shaped fiber grating with polished side surface, thereby being convenient for measuring the liquid level of the external liquid. The invention realizes the simultaneous measurement of the density and the surface tension coefficient of the liquid. Based on the miniaturization advantage of the optical fiber microstructure device, the invention has the advantages of small amount of liquid required for measurement and convenience for clinical detection of blood density and density of trace biological samples.

Description

Microstructure fiber grating series connection device and liquid density measurement method
Technical Field
The invention belongs to the technical field of liquid density measurement, and particularly relates to a microstructure fiber grating series connection device and a liquid density measurement method based on the device.
Background
The liquid density is an important physical quantity for representing the characteristics of the liquid, the control of raw material components in production can be effectively realized through the measurement of the liquid density, the physical property analysis in chemical component detection is completed, and the method has important research significance particularly in the fields of petrochemical industry and biomedicine, for example, whether the AIDS is suffered or not can be judged through accurately measuring the blood density.
The liquid density measuring and sensing technology mainly comprises a float type, a capacitance type, a resonance type, a ray type, an ultrasonic type, an optical fiber sensing type and the like. People in the last century generally use a float type, the structure is simple, the cost is relatively low, but the test precision is relatively low. Researchers have improved on the basis of the float type, and have proposed the capacitance type, namely, the liquid density is measured by the change of the distance between two polar plates of the capacitor connected with the float, but the measurement accuracy is still limited. The resonant mode is also called vibration mode, the liquid density measurement is realized mainly by changing the resonant frequency of the elastic element of the vibrator through the liquid, the performance of the liquid density measurement is influenced by the elastic element, and the required liquid volume is relatively large. The ray type has great harm to the health of operators and has higher requirements on working occasions. The ultrasonic wave type and the optical fiber sensing type are currently researched on a lamb wave sensor, the lamb wave sensor is relatively smaller in size and higher in sensitivity, but the manufacturing process of the ultrasonic probe is relatively stricter and more complex. The existing liquid density measuring device applying optical fiber sensing comprises an optical fiber grating, an optical fiber ring and the like, and the amount of liquid required by measurement is large.
Disclosure of Invention
The invention aims to provide a microstructure fiber grating series connection device.
The purpose of the invention is realized by the following technical scheme: the fiber grating comprises a side hole fiber grating, a single mode fiber grating and a single mode fiber; the cladding diameters of the side-hole fiber grating, the single-mode fiber grating and the single-mode fiber are the same, and the fiber core diameters of the side-hole fiber grating, the single-mode fiber grating and the single-mode fiber are the same; the side surface of the single-mode fiber grating is polished, the section of a cladding of the single-mode fiber grating is D-shaped, and the polished surface is parallel to the axial direction of a fiber core of the single-mode fiber grating; the side hole of the side hole fiber grating is an axial cylindrical air hole arranged on one side of the fiber core, and the center wavelength of the side hole fiber grating is different from that of the single-mode fiber grating; the side hole fiber grating, the single-mode fiber grating and the single-mode fiber are connected in series and welded, fiber cores of the side hole fiber grating, the single-mode fiber grating and the single-mode fiber are connected in series to form a whole in an aligned mode, and the side hole of the side hole fiber grating and the polishing surface of the single-mode fiber grating are respectively arranged on two axial sides of the fiber core, so that the side hole of the side hole fiber grating is in a semi-closed state with the upper end sealed and; the single-mode fiber grating is externally fixed with equal-length capillaries, and a semi-closed sleeve structure with a sealed upper end and an open lower end is formed on the periphery of the single-mode fiber grating.
The invention also aims to provide a liquid density measuring method based on the microstructure fiber grating series device.
The purpose of the invention is realized by the following technical scheme: the method comprises the following steps:
step 1: installing a light source, an optical fiber coupler, a micro-structure fiber grating series device and a spectrometer, enabling continuous optical signals emitted by the light source to enter the micro-structure fiber grating series device through the optical fiber coupler, reflecting optical signals under corresponding central wavelengths after sequentially passing through a single-mode fiber grating and a side-hole fiber grating, and enabling the reflected optical signals to be received and detected by the spectrometer in real time after passing through the optical fiber coupler again;
step 2: calibrating the initial state of the single-mode fiber grating and the edge hole fiber grating;
vertically fixing the microstructure fiber grating series connection device in the air, and recording the reflection spectra of the edge hole fiber grating and the single-mode fiber grating through a spectrometer when the initial test is not carried out;
and step 3: inserting the microstructure fiber grating serial device into liquid to ensure that the edge hole fiber grating is just completely immersed into the liquid, and the liquid enters the capillary and the edge hole of the edge hole fiber grating; after the liquid level is stable, recording the reflection spectra of the edge hole fiber grating and the single-mode fiber grating;
and 4, step 4: comparing the reflection spectrum changes in the step 2 and the step 3 to obtain the height H of the liquid level in the side hole of the side hole fiber bragg grating1And the liquid level height H inside the capillary2；
And 5: calculating the density rho of the liquid and the surface tension coefficient alpha of the liquid according to an equation system;
P0+Pα1+PH＝Pp1+PG1
P0+Pα2＝Pp2+PG2
wherein, P0Is known to be ambient atmospheric pressure; pα1Liquid in the side hole of the side hole fiber grating is at the liquid level pressure PHSurface tension, P, under influenceα1＝2παr1/S1；S1Is the cross-sectional area of the side hole, S1＝πr1 2，r1Is the radius of the side hole; pH＝ρgL1，L1The height of the side hole fiber grating; pp1Is the gas pressure in the side hole, Pp1＝P0L1/(L1-H1)；PG1Is the gravity of the liquid in the side hole, PG1＝ρgH1；Pα2Surface tension, P, to which the liquid in the capillary is subjectedα2＝2παr4/S5；S5The cross-sectional area of the liquid in the capillary; r is4The capillary tube is used as the outer diameter of the semi-closed sleeve structure; pp2＝P0L2/(L2-H2)，L2Is the height of the single mode fiber grating; pG2Is the liquid gravity in the capillary, PG2＝ρgH2。
The invention has the beneficial effects that:
aiming at the limitations of other existing liquid density measurement methods, the invention provides a micro-structure fiber grating series connection device and a liquid density measurement method based on the micro-structure fiber grating series connection device. According to the invention, the microstructure fiber grating series connection device is vertically inserted into liquid, reflection spectra of two microstructure fiber gratings before and after the microstructure fiber grating series connection device is inserted into the liquid are compared, liquid level heights of liquid inside and outside the edge hole fiber are measured, stress of the liquid inside and outside the edge hole fiber is contrastively analyzed, and density and surface tension coefficient of the liquid to be measured are calculated. The invention effectively utilizes the sensing measurement technology of the side hole fiber grating to the liquid level, combines the fiber polishing (or called grinding) technology to prepare the D-shaped fiber grating with polished side surface, and is convenient for measuring the liquid level of the external liquid. The invention realizes the simultaneous measurement of the density and the surface tension coefficient of the liquid. Based on the miniaturization advantage of the optical fiber microstructure device, the invention has the advantages of small amount of liquid required for measurement and convenience for clinical detection of blood density and density of trace biological samples.
Drawings
Fig. 1 is a schematic diagram of a microstructure fiber grating tandem device according to the present invention.
FIG. 2 is a schematic diagram of the process of liquid density measurement and parameter labeling in the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The invention provides a micro-structure fiber grating series device and a liquid density measuring method based on the micro-structure fiber grating series device, aiming at the limitations of other existing liquid density measuring methods. The two sections of microstructure fiber gratings comprise a section of single-side hole fiber grating and a section of single-mode fiber grating with a flat side surface, so that the liquid level can be conveniently measured. The microstructure fiber grating series connection device is vertically inserted into liquid, reflection spectrums of two microstructure fiber gratings before and after the microstructure fiber grating series connection device is inserted into the liquid are compared, liquid level heights of liquid inside and outside the edge hole optical fiber are measured, stress of the liquid inside and outside the edge hole optical fiber is contrastively analyzed, and density and surface tension coefficient of the liquid to be measured are calculated. The invention effectively utilizes the sensing measurement technology of the side hole fiber grating to the liquid level, combines the fiber polishing (or called grinding) technology to prepare the D-shaped fiber grating with polished side surface, and is convenient for measuring the liquid level of the external liquid.
A microstructure fiber grating series device comprises a side hole fiber grating 1, a single mode fiber grating 2 and a single mode fiber 3; the diameters of the cladding 11 of the edge hole fiber grating, the cladding 21 of the single mode fiber grating and the cladding of the single mode fiber are the same; the fiber core 12 of the side-hole fiber grating, the fiber core 22 of the single-mode fiber grating and the fiber core of the single-mode fiber have the same diameter; the side surface of the single-mode fiber grating is polished, the section of a cladding of the single-mode fiber grating is D-shaped, and the polished surface is parallel to the axial direction of a fiber core of the single-mode fiber grating; the side hole 13 of the side hole fiber grating is an axial cylindrical air hole arranged on one side of the fiber core, and the center wavelength of the side hole fiber grating is different from that of the single-mode fiber grating; the side hole fiber grating, the single-mode fiber grating and the single-mode fiber are connected in series and welded, fiber cores of the side hole fiber grating, the single-mode fiber grating and the single-mode fiber are connected in series to form a whole in an aligned mode, and the side hole of the side hole fiber grating and the polishing surface of the single-mode fiber grating are respectively arranged on two axial sides of the fiber core, so that the side hole of the side hole fiber grating is in a semi-closed state with the upper end sealed and; the single-mode fiber grating is externally fixed with equal-length capillaries 4, and a semi-closed sleeve structure with a sealed upper end and an open lower end is formed at the periphery.
A liquid density measurement method based on a microstructure fiber grating series device comprises the following steps:
step 1: installing a light source 6, an optical fiber coupler 5, a microstructure fiber grating series device and a spectrometer 7, enabling continuous optical signals emitted by the light source to enter the microstructure fiber grating series device through the optical fiber coupler, reflecting optical signals under corresponding central wavelengths after sequentially passing through a single-mode fiber grating and a side-hole fiber grating, and enabling the reflected optical signals to be received and detected by the spectrometer in real time after passing through the optical fiber coupler again;
step 2: calibrating the initial state of the single-mode fiber grating and the edge hole fiber grating;
vertically fixing the microstructure fiber grating series connection device in the air, and recording the reflection spectra of the edge hole fiber grating and the single-mode fiber grating through a spectrometer when the initial test is not carried out;
and step 3: inserting the microstructure fiber grating serial device into liquid to ensure that the edge hole fiber grating is just completely immersed into the liquid, and the liquid enters the capillary and the edge hole of the edge hole fiber grating; after the liquid level is stable, recording the reflection spectra of the edge hole fiber grating and the single-mode fiber grating;
and 4, step 4: comparing the reflection spectrum changes in the step 2 and the step 3 to obtain the height H of the liquid level in the side hole of the side hole fiber bragg grating1And the liquid level height H inside the capillary2；
And 5: calculating the density rho of the liquid and the surface tension coefficient alpha of the liquid according to an equation system;
P0+Pα1+PH＝Pp1+PG1
P0+Pα2＝Pp2+PG2
wherein, P0Is known to be ambient atmospheric pressure; pα1Liquid in the side hole of the side hole fiber grating is at the liquid level pressure PHSurface tension, P, under influenceα1＝2παr1/S1；S1Is the cross-sectional area of the side hole, S1＝πr1 2，r1Is the radius of the side hole; pH＝ρgL1，L1The height of the side hole fiber grating; pp1Is the gas pressure in the side hole, Pp1＝P0L1/(L1-H1)；PG1Is the gravity of the liquid in the side hole, PG1＝ρgH1；Pα2Surface tension, P, to which the liquid in the capillary is subjectedα2＝2παr4/S5；S5The cross-sectional area of the liquid in the capillary; r is4The capillary tube is used as the outer diameter of the semi-closed sleeve structure; pp2＝P0L2/(L2-H2)，L2Is the height of the single mode fiber grating; pG2Is the liquid gravity in the capillary, PG2＝ρgH2。
The side-hole fiber is realized by a side-hole fiber which is distributed with axial cylindrical air holes 13 at one side of a fiber core 12. The two microstructure fiber gratings have different central wavelengths, so that the detection of a spectrometer is facilitated. The side surface of the single-mode fiber grating 2 is polished, the section of the cladding 21 is D-shaped, and the polished surface is parallel to the axial direction of the fiber core, so that the measurement of the liquid level of external liquid is facilitated. The fusion splicing process of the single-mode fiber grating 2 polished on the side surface and the side-hole fiber grating 1 ensures that the side hole and the polished surface are respectively arranged on two axial sides of the fiber core, so that the side hole of the side-hole fiber grating 1 is in a semi-closed state. The capillary 4 with the same length is fixed on the outer side of the single-mode fiber grating 2 polished on the side surface, the top end of the capillary is fixed by glue, and the lower end of the capillary is opened to form a semi-closed structure.
The liquid stress analysis is mainly realized by aiming at the liquid inside the side-hole fiber grating 1 and the liquid inside the fiber outer capillary 4, including the external atmospheric pressure, the internal atmospheric pressure, the surface tension and the gravity of the liquid, and the density of the liquid and the surface tension coefficient of the liquid are calculated.
The invention realizes the simultaneous measurement of the density and the surface tension coefficient of the liquid. Based on the miniaturization advantage of the optical fiber microstructure device, the invention has the advantages of small amount of liquid required for measurement and convenience for clinical detection of blood density and density of trace biological samples.
Example 1:
the invention provides an optical fiber optical path device for measuring a trace liquid density value and an acquisition method thereof aiming at the limitation of the existing liquid density measurement method, and designs a novel micro-structure fiber grating series device by utilizing the sensitivity characteristics of two devices, namely a side-hole fiber and a capillary tube, on the surface tension of a liquid.
The fiber grating inscription technology is developed more mature now, liquid level sensing is realized by writing grating on the side hole fiber in 2019, and particularly, liquid level change is measured by utilizing grating reflection spectrum.
The optical fiber polishing (or called polishing) technology is originally derived from the polishing processing of an optical fiber end face, structures such as a cone, a wedge-shaped cone, a four-corner cone, an inclined end face and the like of the optical fiber end are prepared, the polishing of the side face of the optical fiber can be effectively realized by controlling the polishing direction and a holding device of the optical fiber, and a D-shaped optical fiber structure is prepared. Based on the technical means, the invention realizes the side surface polishing of the single-mode fiber grating, so that the cladding of the single-mode fiber grating is D-shaped, and the external liquid level can be conveniently measured.
Firstly, preparing and building a side-hole optical fiber series micro-structure device, writing gratings on a single-mode optical fiber and a side-hole optical fiber, wherein the central wavelengths of the gratings are different; polishing the side surface of the single-mode fiber grating along the axial direction of the optical fiber to enable the cladding of the single-mode fiber grating to be D-shaped; the optical fiber grating manufacturing method comprises the steps of intercepting the grid area parts of two microstructure optical fiber gratings by using an optical fiber cutter, utilizing an optical fiber fusion splicer to connect edge hole optical fiber gratings 1, a single-mode optical fiber grating 2 and a single-mode optical fiber 3 which are polished on the side surface in a series fusion mode, fixing equal-length capillaries 4 by using glue outside the single-mode optical fiber grating 2 which is polished on the side surface, forming a semi-closed sleeve structure with an upper end sealed and a lower end opened on the periphery, manufacturing a microstructure optical fiber grating series connection device, connecting an optical fiber light path, and comprising a wide-spectrum light source 6, a 1 x 2 optical fiber coupler 5, a microstructure optical fiber grating series connection device and a spectrometer 7, wherein the central wavelengths of the.
In the optical path transmission process, a continuous wide-spectrum optical signal is emitted by the wide-spectrum light source 6, enters the micro-structure fiber grating series device through the 1 × 2 fiber coupler 5, sequentially passes through the two micro-structure fiber gratings, reflects an optical signal under the corresponding central wavelength, passes through the 1 × 2 fiber coupler 5 again, and is received and detected by the spectrometer 7 in real time.
And secondly, calibrating the initial state of the reflection wavelength of the microstructure fiber grating for the built fiber optical path measuring device, namely vertically fixing the microstructure fiber grating series connection device in the air, and recording the reflection spectra of the two microstructure fiber gratings (the side hole fiber grating 1 and the single mode fiber grating 2) when the microstructure fiber grating series connection device is not tested initially through a spectrometer 7 so as to facilitate subsequent comparison.
And step three, inserting the microstructure fiber grating series connection device into the liquid until the side hole fiber grating 1 is just completely immersed, and recording the reflection spectrums of the two microstructure fiber gratings after the liquid level is stable.
Step four, comparing the reflection spectrum changes in the step three and the step two to obtain the liquid level height H in the side hole of the side hole fiber grating 11The liquid level inside the capillary 4 is H2。
And fifthly, performing stress analysis on the liquid in the side holes of the side-hole fiber bragg grating 1 and the liquid in the capillary 4 to calculate the liquid density and the surface tension coefficient.
The liquid in the side hole of the side hole fiber grating 1 is at the liquid level pressure PH(upward in direction) surface tension of Pα1Rise under (direction up) action:
PH＝ρgL1
Pα1＝2παr1/S1 (1)
where α is the surface tension coefficient, is an intrinsic parameter of the liquid, is to be measured, r1Is a known radius of the air holes of the edge-holed fiber, is a known quantity, and S1＝πr1 2。
The liquid in the capillary 4 is mainly driven to rise by the action of surface tension without the action of liquid level pressure. The liquid in the capillary 4 is subjected to a surface tension of Pα2(direction up):
Pα2＝2παr4/(S4-S3+S2) (2)
wherein S2Is the sectional area, S, of the side-ground part of the single-mode fiber grating3The sectional area of the single-mode fiber is r, the cladding radius of the single-mode fiber is the same as that of the edge hole fiber3Then, then
Figure BDA0002920256270000061
r4Is the inner radius of the capillary 4, and
Figure BDA0002920256270000062
are all known quantities.
Also includes internal air pressure and external atmospheric pressure, for external atmospheric pressure P0The air pressure in the air hole of the side-hole optical fiber can be controlled from an ideal gas state according to the known numerical valueThe process is obtained, namely:
PV＝nRT (3)
wherein P represents pressure, V represents volume of gas object to be analyzed, n is amount of substance, R is gas constant, and T is absolute temperature, because before and after the micro-structure fiber grating serial device is inserted into liquid, the amount of gas in the side hole fiber air hole and the capillary 4 is unchanged, the gas constant is unchanged, and the temperature is unchanged, therefore, the volume of the whole air hole is assumed to be V1The volume of the space in the optical fiber outer capillary 4 is V2Namely:
V1＝S1×L1
V2＝(S4-S3+S2)×L2 (4)
after the microstructure fiber grating serial device is inserted into the liquid, the volume of air inside the air hole is V'1The volume of air in the capillary (4) is V'2Namely:
V′1＝S1×(L1-H1)
V′2＝(S4-S3+S2)×(L2-H2) (5)
therefore, according to the equation (3), the constant relationship between the two times of insertion of the lower-edge hole optical fiber series microstructure into the liquid at different insertion depths can be obtained:
P0V1＝Pp1V′1＝nRT
P0V2＝Pp2V′2＝nRT (6)
substituting equations (4) and (5) into (6) can determine the gas pressure P in the air hole of the side-hole fiberp1And Pp2(downwards direction), i.e.:
Pp1＝P0L1/(L1-H1)
Pp2＝P0L2/(L2-H2) (7)
the liquid is also under the action of self gravity, and the gravity of the liquid in the side hole of the side hole fiber grating 1 is PG1(in the downward direction) the liquid in the capillary 4 has a weight PG2(downwards direction):
PG1＝ρgH1
PG2＝ρgH2 (8)
in conclusion, the liquid in the air holes of the side-hole optical fiber is stressed in a balanced manner, and the following steps are obtained:
P0+Pα1+PH＝Pp1+PG1
P0+Pα2＝Pp2+PG2 (9)
by the simultaneous connection of the two equations in the equation (9), the liquid density ρ and the surface tension coefficient α of the liquid can be obtained.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (2)

1. A micro-structure fiber grating series device is characterized in that: the fiber grating comprises a side hole fiber grating, a single mode fiber grating and a single mode fiber; the cladding diameters of the side-hole fiber grating, the single-mode fiber grating and the single-mode fiber are the same, and the fiber core diameters of the side-hole fiber grating, the single-mode fiber grating and the single-mode fiber are the same; the side surface of the single-mode fiber grating is polished, the section of a cladding of the single-mode fiber grating is D-shaped, and the polished surface is parallel to the axial direction of a fiber core of the single-mode fiber grating; the side hole of the side hole fiber grating is an axial cylindrical air hole arranged on one side of the fiber core, and the center wavelength of the side hole fiber grating is different from that of the single-mode fiber grating; the side hole fiber grating, the single-mode fiber grating and the single-mode fiber are connected in series and welded, fiber cores of the side hole fiber grating, the single-mode fiber grating and the single-mode fiber are connected in series to form a whole in an aligned mode, and the side hole of the side hole fiber grating and the polishing surface of the single-mode fiber grating are respectively arranged on two axial sides of the fiber core, so that the side hole of the side hole fiber grating is in a semi-closed state with the upper end sealed and; the single-mode fiber grating is externally fixed with equal-length capillaries, and a semi-closed sleeve structure with a sealed upper end and an open lower end is formed on the periphery of the single-mode fiber grating.
2. The method for measuring the liquid density of the microstructure fiber grating series device according to claim 1, comprising the following steps:
step 1: installing a light source, an optical fiber coupler, a micro-structure fiber grating series device and a spectrometer, enabling continuous optical signals emitted by the light source to enter the micro-structure fiber grating series device through the optical fiber coupler, reflecting optical signals under corresponding central wavelengths after sequentially passing through a single-mode fiber grating and a side-hole fiber grating, and enabling the reflected optical signals to be received and detected by the spectrometer in real time after passing through the optical fiber coupler again;
step 2: calibrating the initial state of the single-mode fiber grating and the edge hole fiber grating;
vertically fixing the microstructure fiber grating series connection device in the air, and recording the reflection spectra of the edge hole fiber grating and the single-mode fiber grating through a spectrometer when the initial test is not carried out;
and step 3: inserting the microstructure fiber grating serial device into liquid to ensure that the edge hole fiber grating is just completely immersed into the liquid, and the liquid enters the capillary and the edge hole of the edge hole fiber grating; after the liquid level is stable, recording the reflection spectra of the edge hole fiber grating and the single-mode fiber grating;
and 4, step 4: comparing the reflection spectrum changes in the step 2 and the step 3 to obtain the height H of the liquid level in the side hole of the side hole fiber bragg grating1And the liquid level height H inside the capillary2；
And 5: calculating the density rho of the liquid and the surface tension coefficient alpha of the liquid according to an equation system;
P0+Pα1+PH＝Pp1+PG1
P0+Pα2＝Pp2+PG2
wherein, P0Is known to be ambient atmospheric pressure; pα1Is the edge of the edge hole fiber gratingLiquid in the hole at liquid level pressure PHSurface tension, P, under influenceα1＝2παr1/S1；S1Is the cross-sectional area of the side hole, S1＝πr1 2，r1Is the radius of the side hole; pH＝ρgL1，L1The height of the side hole fiber grating; pp1Is the gas pressure in the side hole, Pp1＝P0L1/(L1-H1)；PG1Is the gravity of the liquid in the side hole, PG1＝ρgH1；Pα2Surface tension, P, to which the liquid in the capillary is subjectedα2＝2παr4/S5；S5The cross-sectional area of the liquid in the capillary; r is4The capillary tube is used as the outer diameter of the semi-closed sleeve structure; pp2＝P0L2/(L2-H2)，L2Is the height of the single mode fiber grating; pG2Is the liquid gravity in the capillary, PG2＝ρgH2。
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