CN111272330B - Optical fiber gas pressure sensor and preparation method thereof - Google Patents
Optical fiber gas pressure sensor and preparation method thereof Download PDFInfo
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- CN111272330B CN111272330B CN202010101071.6A CN202010101071A CN111272330B CN 111272330 B CN111272330 B CN 111272330B CN 202010101071 A CN202010101071 A CN 202010101071A CN 111272330 B CN111272330 B CN 111272330B
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- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
- G01L11/02—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means
- G01L11/025—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means using a pressure-sensitive optical fibre
Abstract
An optical fiber gas pressure sensor and a preparation method thereof relate to a gas pressure sensor and a preparation method thereof. The invention solves the problems that the existing film for plugging the FPI optical fiber gas sensor is difficult to prepare and weak in structural strength, and the optical fiber and the film material for plugging have thermo-optic coefficients and thermal expansion coefficients and have temperature crosstalk. The optical fiber gas pressure sensor is an FPI optical fiber gas sensor; the optical fiber gas pressure sensor comprises a hollow optical fiber, a single-mode optical fiber and a film, wherein one end of the hollow optical fiber is welded with the single-mode optical fiber, and the other end of the hollow optical fiber is blocked by the film; the film is a polydimethylsiloxane film. The preparation method comprises the following steps: firstly, preparing a primary structure; dipping PDMS liquid; thirdly, adjusting the thickness of the film; fourthly, curing.
Description
Technical Field
The invention relates to a gas pressure sensor and a preparation method thereof.
Background
Optical fiber sensing has been practically applied to various fields such as biomedicine, health monitoring, artificial intelligence, and environmental monitoring. Among them, the gas pressure measurement of the optical fiber sensor has been the focus of attention, and commonly includes Fiber Bragg Gratings (FBGs), mach-zehnder interferometers (MZIs), fabry-perot interferometers (FPIs), and the like. In recent years, FPI sensors have attracted much attention from people due to their advantages of strong anti-electromagnetic interference, remote sensing capability, high resolution, fast response speed, small size, etc.
A typical FPI structure consists of two parallel plates and optical interference between the plates. Generally, there are two modes of operation of FPI fiber gas sensors: firstly, the pressure intensity is measured by changing the refractive index of a medium in a cavity; and secondly, the pressure is measured by changing the length of the FPI microcavity. However, the response of microcavities of different shapes to gas pressure is also different, and therefore the shape of the microcavities and the nature of the reflective film determine the sensitivity of the sensor. The sensitivity of a gas pressure sensor manufactured by replacing one plate in an FPI structure with a film with certain reflectivity and elastic deformation, such as a polymer, graphene, silicon or a water film, can be improved. The gas pressure sensor reported by Wangtongning et al in 2014 utilizes one end of a hollow optical fiber to be welded with a single-mode optical fiber and the other end of the hollow optical fiber to be welded with a molten ball, so as to form a closed air microcavity; the structure is simple to manufacture, but the sensitivity is only 1.036nm/MPa when the wall thickness of the probe end face reaches 320 nm. Wang et al in 2017 welded a single-mode fiber and a hollow fiber to form an air cavity, blocked by a 170nm quartz film to form a rectangular closed air microcavity, and the quartz film forms a second reflecting surface to form an FPI structure, so as to obtain high sensitivity 341 nm/Mpa; however, the gas pressure sensor has the defects of difficult preparation of the quartz film, low structural strength and the like. Cui et al adopted a peeled ultrathin graphene atomic layer as a reflecting surface in 2019 to form an FPI structure, and obtained high sensitivity of 1.28nm/mmHg (9600.79 nm/Mpa); however, the sensor still has the defects of difficult preparation method of the graphene film, weak structural strength and the like.
Disclosure of Invention
The invention provides an optical fiber gas pressure sensor and a preparation method thereof, aiming at solving the problems that the existing FPI optical fiber gas sensor plugging film is difficult to prepare and weak in structural strength, and the optical fiber and the plugging film material have thermo-optic coefficients and thermal expansion coefficients and have temperature crosstalk.
The optical fiber gas pressure sensor is an FPI optical fiber gas sensor;
the optical fiber gas pressure sensor comprises a hollow optical fiber, a single-mode optical fiber and a film, wherein one end of the hollow optical fiber is welded with the single-mode optical fiber, and the other end of the hollow optical fiber is blocked by the film; the film is a polydimethylsiloxane film.
The optical fiber gas pressure sensor is prepared by the following steps:
firstly, welding a single mode fiber with a hollow fiber, and then cutting the single mode fiber into required length to form a primary structure of the fiber gas pressure sensor;
dipping one end of a hollow optical fiber of the primary structure of the optical fiber gas pressure sensor with polydimethylsiloxane liquid;
thirdly, if the initial thickness of the polydimethylsiloxane film dipped in the initial structure is larger than the preset film thickness, dipping redundant polydimethylsiloxane liquid by using a clean single-mode optical fiber; if the initial thickness of the polydimethylsiloxane film dipped in the primary structure is smaller than the preset film thickness, contacting the end of the hollow-core optical fiber of the primary structure with an optical fiber adhered with polydimethylsiloxane liquid until the thickness of the polydimethylsiloxane film in the primary structure reaches the preset film thickness;
and fourthly, curing the polydimethylsiloxane film to obtain the optical fiber gas pressure sensor.
Polydimethylsiloxane (PDMS) is prepared from OSi (CH)3)2The elastomer polymer formed by the crosslinking structure of the group repeating unit has the advantages of low cost, good adhesive force, good chemical inertia and the like. The invention selects PDMS as the film preparation material due to the low Young modulus, which causes high elasticity, hydrophobicity, simple preparation process and other factors.
The sizes of the single-mode optical fiber and the hollow-core optical fiber in the primary structure are unified, and the length and the time of the primary structure extending into liquid when being dipped in polydimethylsiloxane liquid are unified, so that the optical fiber gas pressure sensor prepared by the method has extremely high repeatability; and the thickness of the dipped film is adjusted in the third step, so that the optical fiber gas pressure sensor prepared by the invention has uniform product standard and specification, and the consistency of the product structure is ensured.
The invention can manufacture the gas pressure sensors with different sensitivities by controlling the thickness of the PDMS film of the optical fiber gas pressure sensor. The optical fiber gas pressure sensor has the advantages of simple manufacture, high sensitivity, high mechanical strength, small volume, low cost and the like, so the optical fiber gas pressure sensor has good application prospect in the fields of physics, biology, chemistry and the like in the future.
Drawings
FIG. 1 is a schematic diagram of the construction of a fiber optic gas pressure sensor of the present invention;
FIG. 2 is a diagram of an experimental apparatus for measuring gas pressure in the examples;
FIG. 3 is a graph of the spatial frequency spectrum of the fiber optic gas pressure sensor of the present invention;
fig. 4 is a graph of experimental results of PDMS film thickness versus pressure sensitivity, where (4a) is a reflection spectrum at H-3 μm and (4b) is a linear fit of Dip wavelength and intensity at H-3 μm to gas pressure; fig. 4c is a reflectance spectrum for H22 μm, and fig. 4d is a linear fit of Dip wavelength and intensity to gas pressure for H22 μm; fig. (4e) is a reflection spectrum at H44 μm and fig. (4f) is a linear fit of Dip wavelength and intensity at H44 μm to gas pressure; fig. (4g) is a reflectance spectrum at H71 μm, and fig. (4H) is a linear fit of Dip wavelength and intensity at H71 μm to gas pressure;
FIG. 5 is a diagram showing the results of Comsol simulation in example 1;
FIG. 6 is a graph of gas pressure sensitivity comparison experiments for PDMS films of different thickness;
fig. 7 is a graph showing the results of temperature response experiments for PDMS films of different thicknesses, where (7a) is a graph fitted with data for Dip points with H ═ 3 μm, (7b) is a graph fitted with data for Dip points with H ═ 22 μm, (7c) is a graph fitted with data for Dip points with H ═ 44 μm, and (7d) is a graph fitted with data for Dip points with H ═ 71 μm;
FIG. 8 is the response of the fiber-optic gas pressure sensor structure of the present invention to pressure and temperature, with FIG. 8a being a reflection spectrum at different gas pressures, FIG. 8b being a graph of the variation of air microcavity length and the variation of Dip2 intensity at different gas pressures, FIG. 8c being a reflection spectrum at different temperatures, and FIG. 8d being a graph of the variation of air microcavity length and the variation of Dip2 intensity at different temperatures;
FIG. 9 is a schematic view of step two;
FIG. 10 is a schematic representation of the operation of step three wherein the initial thickness of the polydimethylsiloxane film is greater than the predetermined film thickness;
FIG. 11 is a schematic diagram of the operation of the polydimethylsiloxane film in step three with an initial thickness less than the predetermined film thickness.
Detailed Description
The technical solution of the present invention is not limited to the following specific embodiments, but includes any combination of the specific embodiments.
The first embodiment is as follows: the present embodiment will be described with reference to fig. 1, in which the optical fiber gas pressure sensor of the present embodiment is an FPI optical fiber gas sensor;
the optical fiber gas pressure sensor is composed of a hollow optical fiber 2, a single-mode optical fiber 1 and a film 3, wherein one end 2 of the hollow optical fiber is welded with the single-mode optical fiber 1, and the other end of the hollow optical fiber is blocked by the film 3; the film is a polydimethylsiloxane film.
The optical fiber gas pressure sensor of the present embodiment has three reflecting surfaces, which are named surface 1, surface 2 and surface 3, respectively. The three surface-binding structures are divided into two FPI structures, one formed by surface 1 and surface 2, and the other formed by surface 1 and surface 3. However, the surface 3 is susceptible to dirt in direct contact with the external environment, resulting in a roughened surface and a reduced reflectivity. Thus, the FPI consisting of surface 1 and surface 2 plays a dominant role in the sensor of the present invention.
The second embodiment is as follows: the present embodiment differs from the first embodiment in that: the thickness of the polydimethylsiloxane film is 1 to 71 μm. Other steps and parameters are the same as those in the first embodiment.
The thickness of the polydimethylsiloxane film is the middle thickness of the film.
The third concrete implementation mode: the present embodiment is different from the first or second embodiment in that: the thickness of the polydimethylsiloxane film was 3 μm. The other is the same as in the first or second embodiment.
The fourth concrete implementation mode: the present embodiment is different from one of the first to third embodiments in that: and a closed air microcavity is formed between the welding position of the single-mode optical fiber and the hollow optical fiber and the blocking film, and the length of the closed air microcavity is 50-60 mu m. The others are the same as in one of the first to third embodiments.
The fifth concrete implementation mode: the present embodiment is different from one of the first to fourth embodiments in that: and a closed air microcavity is formed between the fused joint of the single-mode fiber and the hollow fiber and the blocking film, and the length of the closed air microcavity is 55 microns. The other is the same as one of the first to fourth embodiments.
The sixth specific implementation mode: the optical fiber gas pressure sensor of the embodiment is prepared by the following steps:
firstly, welding a single mode fiber with a hollow fiber, and then cutting the single mode fiber into required length to form a primary structure of the fiber gas pressure sensor;
dipping one end of a hollow optical fiber of the primary structure of the optical fiber gas pressure sensor with polydimethylsiloxane liquid 4;
thirdly, if the initial thickness of the dipped polydimethylsiloxane film in the initial structure is larger than the preset film thickness, using a clean single-mode optical fiber 5 to dip redundant polydimethylsiloxane liquid (as shown in figure 10); if the initial thickness of the polydimethylsiloxane film dipped in the initial structure is smaller than the preset film thickness, contacting the end of the hollow-core optical fiber of the initial structure with the optical fiber 6 adhered with the polydimethylsiloxane liquid 6-1 until the thickness of the polydimethylsiloxane film in the initial structure reaches the preset film thickness (as shown in figure 11);
and fourthly, curing the polydimethylsiloxane film to obtain the optical fiber gas pressure sensor.
In the second step of the embodiment, a capillary phenomenon is utilized, and a Polydimethylsiloxane (PDMS) liquid is adsorbed at one end of the hollow optical fiber with the primary structure, so that a part of air can be blocked in the hollow optical fiber (between the welding position of the single-mode optical fiber and the hollow optical fiber and the blocking film), and a closed air microcavity is formed.
In the third step of this embodiment, an electron microscope may be used to detect the thickness of the polydimethylsiloxane film in the initial structure.
The seventh embodiment: the present embodiment is different from the sixth embodiment in that: and step three, the diameter of the part of the single-mode optical fiber extending into the primary structure and used for dipping the redundant polydimethylsiloxane liquid is smaller than the inner diameter of the hollow optical fiber. The rest is the same as the sixth embodiment.
The specific implementation mode is eight: the present embodiment is different from the sixth or seventh embodiment in that: in the third step, the optical fiber stuck with the polydimethylsiloxane liquid contacts the upper edge or the lower edge of the end of the hollow optical fiber of the primary structure by the polydimethylsiloxane liquid on the optical fiber. The others are the same as the sixth or seventh embodiments.
In the embodiment, PDMS liquid can flow in along the upper edge or the lower edge of the end of the primary structure hollow optical fiber, the thickness of the polydimethylsiloxane initial film of the optical fiber gas pressure sensor is increased, and the optical fiber adhered with the polydimethylsiloxane liquid can be taken away when the thickness of the polydimethylsiloxane film reaches the preset value.
The specific implementation method nine: this embodiment is different from the sixth to eighth embodiments in that: the polydimethylsiloxane fluids were mixed from Sylgard 184-A and Sylgard 184-B in a 10:1 ratio. The rest is the same as the sixth to eighth embodiments.
Sylgard 184-A and Sylgard 184-B are Dow Corning Sylgard 184 silicone rubber two-component.
The detailed implementation mode is ten: this embodiment is different from one of the sixth to ninth embodiments in that: and step four, the curing temperature is 70 ℃, and the curing time is 6 hours. The others are the same as in one of the sixth to ninth embodiments.
The concrete implementation mode eleven: the present embodiment is different from one of the sixth to tenth embodiments in that: the length of the air micro-cavity is 50-60 mu m. The others are the same as in one of the sixth to tenth embodiments.
The specific implementation mode twelve: this embodiment is different from one of the sixth to eleventh embodiments in that: the length of the air microcavity was 55 μm. The others are the same as in one of the sixth to eleventh embodiments.
The specific implementation mode is thirteen: this embodiment is different from the sixth to twelfth embodiment in that: the predetermined thickness of the polydimethylsiloxane film is 1 to 71 μm. The rest is the same as in one of the sixth to twelfth embodiments.
The specific implementation mode is fourteen: this embodiment is different from one of the sixth to thirteenth embodiments in that: the predetermined thickness of the polydimethylsiloxane film was 3 μm. The others are the same as in one of the sixth to thirteenth embodiments.
The optical fiber gas pressure sensor of the present embodiment has an interference valley wavelength and a gasPressure linear relation Y52.143X +1527.143, gas pressure sensitivity of 52.173nm/Mpa, linearity of 99.86%, and low temperature cross sensitivity of 2.51X 10-3Mpa/℃。
Example 1
The optical fiber gas pressure sensor is prepared by the following steps:
firstly, a single-mode optical fiber (Corning SMF28) is welded with a hollow optical fiber (Polymicro Technologies TSP080135 with the inner diameter of 80 microns and the outer diameter of 135 microns), and then the hollow optical fiber is cut into required length to form a primary structure of the optical fiber gas pressure sensor;
dipping one end of a hollow optical fiber of the primary structure of the optical fiber gas pressure sensor with polydimethylsiloxane liquid; the polydimethylsiloxane liquid is uniformly mixed by Sylgard 184-A and Sylgard 184-B according to the proportion of 10:1, and bubbles in the polydimethylsiloxane liquid are eliminated;
thirdly, if the initial thickness of the dipped polydimethylsiloxane film in the primary structure is larger than the preset film thickness, dipping redundant polydimethylsiloxane liquid by using a clean single-mode optical fiber, wherein the diameter of the part of the clean single-mode optical fiber extending into the primary structure is smaller than the inner diameter of the hollow optical fiber; if the initial thickness of the polydimethylsiloxane film dipped in the primary structure is smaller than the preset film thickness, the polydimethylsiloxane liquid on the optical fiber adhered with the polydimethylsiloxane liquid is used for contacting the upper edge or the lower edge of the end of the hollow optical fiber of the primary structure until the thickness of the polydimethylsiloxane film in the primary structure reaches the preset film thickness;
fourthly, curing the polydimethylsiloxane film at the temperature of 70 ℃ for 6 hours to obtain the optical fiber gas pressure sensor.
In this example, 4 types of fiber gas pressure sensors were prepared, in which the thicknesses of the PDMS films were 3 μm, 22 μm, 44 μm and 71 μm, respectively, and the lengths of the air micro-cavities were 55 μm.
The basic principle of FPI is multi-beam interference, and for the fiber gas pressure sensor structure of this embodiment, the surface 1 and the surface 2 mainly interfere, and since the refractive indexes of SMF, PDMS and air are 1.455, 1.399 and 1RI, respectively, and since the beam propagation of the fiber gas pressure sensor structure of this embodiment can be regarded as normal incidence, the reflectivity of the surface 1 and the surface 2 can be obtained by formula (1).
Wherein R is the reflectivity, n1And n2The effective refractive indices of the media on either side of the reflecting surface, respectively, can be found to be about 3.5% for surface 1 and about 2.8% for surface 2. For a reflective surface with a relatively low reflectivity, its high-order reflection capability is very weak and almost negligible, and thus can be approximated as a two-beam interference, i.e., an FPI formed by the interference between two reflected lights generated by the surface 1 and the surface 2. Having an interference intensity of
Wherein I1And I2Respectively representing the intensity of light reflected by surface 1 and surface 2, ncIs the refractive index of the gas in the air micro-cavity, L is the length of the air micro-cavity, lambda is the central wavelength of the interference valley,
is the initial phase. When it is satisfied with
Interference fringes occur, where m is an integer. The wavelength of the corresponding interference valley is
Central wavelength lambda for two adjacent interference valleys1And λ2Is called the free spectral range (FSR, formed by the interference of surface 1 and surface 2 is FSR)12The interference of the surface 1 and the surface 3 is FSR13) Which is represented by formula (4)
Since PDMS has high elasticity due to its low Young's modulus, it is easily deformed under the action of the external gas pressure, thereby causing the change of cavity length L, as shown in formula (5)
Wherein v is 0.49 Poisson's ratio, E is 7.5 x 105pa is Young's modulus, H is the thickness of PDMS film, R is the radius of the hollow-core optical fiber, and R is 40 μm; as can be seen from the equations (3) and (5), when the gas pressure P changes, the wavelength λ changes. Therefore, the sensitivity of the structure of the optical fiber gas pressure sensor of the embodiment is
From the formula (6), the sensitivity of the fiber gas pressure sensor structure of the present embodiment is only related to the thickness H of PDMS. As H decreases, the sensitivity S increases.
An experimental setup for gas pressure testing of the fiber gas pressure sensor of the present embodiment is shown in fig. 2. The light source used in the experimental setup was a broadband light source (BBS) with a wavelength ranging from 1300nm to 1600nm, which was connected to the a branch of the fiber optic circulator. The optical signal is transmitted to the optical fiber gas pressure sensor of the present embodiment along the optical fiber, and the optical fiber gas pressure sensor of the present embodiment is placed inside a gas pressure calibration (Air pressure calibration) table, and seals the gas pressure calibration table. The fiber gas pressure sensor then reflects a portion of the optical signal back into the fiber circulator through the C-channel into the Optical Spectrum Analyzer (OSA). The resolution of the OSA detection reflection spectrum is 0.02 nm.
FIG. 3 is a spatial frequency spectrum diagram of the fiber gas pressure sensor of the present embodiment, in which an inset graph is a measurement spectrum of the FPI structure sensor, and the FSR is 20.5 nm; thus according toThe length L of the air microcavity of the fiber gas pressure sensor structure of this embodiment at normal temperature and normal pressure can be calculated by formula (4). On the space spectrogram, two peaks exist, and the positions of the peaks are 0.0488nm-1The other at 0.0976nm-1To (3). The occurrence of the second peak may be due to two reasons, one being the interference of the surface 1 with the surface 3 and the other being the second harmonic of the first peak. From the formula (7), it can be seen that
N in the formula (7)PDMSRefractive index of PDMS, about 1.4; h is a PDMS thickness of about 3 μm, and the spectral peak obtained by interference between the surface 1 and the surface 3 can be found to be 0.0524nm-1And the second peak is 0.0976nm-1So the second is not formed by the interference of surface 1 and surface 3, but is the second harmonic of the first peak. This means that there is only one FPI in the fiber gas pressure sensor structure of this embodiment, i.e. the interference formed between surface 1 and surface 2.
In order to investigate the response of different PDMS film thicknesses to the pressure sensitivity, 4 types of fiber gas pressure sensors, each having a PDMS film thickness of 3 μm, 22 μm, 44 μm, and 71 μm and an air microcavity length of 55 μm, were measured every 0.1Mpa, and an experiment was performed at normal temperature, and the experimental results are shown in fig. 4.
As can be seen from fig. 4, the reflection spectrum is red-shifted with increasing gas pressure, and the red-shift of the reflection spectrum corresponds to an increase in the air microcavity length L. The simulation results are shown in FIG. 5 after 4 models are established by the verification of Comsol simulation software. The deformation structure of the thinnest area of the sensitive film is mainly intercepted, and a graph (5a) shows the deformation quantity of the PDMS film with uniform thickness under the action of external pressure, so that the deformation of the structure is gradually intensified along with the increase of the external pressure, namely the length of an air microcavity is continuously shortened, the structure belongs to the gas pressure response phenomenon of an ideal film, and the blue shift of an interference spectrum is caused. FIG. 5b is a non-uniform graded film with a 3 micron thickness in the middle and slightly thinner on both sides; the film has abnormal deformation under the action of external pressure, namely the middle position of the film is protruded outwards, so that the length of the air microcavity is continuously lengthened, and the spectrum is red shifted in the test. If the film type is asymmetric, the abnormal deformation phenomenon is also caused, as shown in FIGS. 5c and 5 d. The PDMS film prepared by the method has no uniform equal thickness and symmetry, and the interference spectrum is red-shifted along with the increase of the gas pressure.
According to the formula (6), the gas pressure sensitivity of the optical fiber gas pressure sensor structure of the present invention increases with the decrease of the thickness of the PDMS film. As shown in fig. 6, as the thickness of the PDMS film is reduced, the gas pressure sensitivity is increased, and the experiment is substantially consistent with theory.
In order to investigate the temperature response of different PDMS film thicknesses, 4 fiber gas pressure sensors with PDMS film thicknesses of 3 μm, 22 μm, 44 μm and 71 μm and air microcavity lengths of 55 μm were measured, and the experimental results are shown in FIG. 7.
As shown in fig. 7, the reflection spectrum undergoes a red shift with increasing temperature when the PDMS film thickness is 3 μm, and undergoes a blue shift with increasing temperature when the PDMS film thickness is 22, 44 or 71 μm. The reason for this is that when the PDMS film is too thin, the thermal expansion of the PDMS affects the length of the air micro-cavity less than the thermal expansion of the air, which results in the length of the air micro-cavity being longer and the reflection spectrum being red-shifted. When the thickness of PDMS reaches a certain value, the result is vice versa.
As can be seen from FIGS. 4 and 7, the wavelength and intensity of the same Dip point are affected by the pressure and temperature, and the pressure and temperature have different effects on the wavelength and intensity, and when the thickness of the PDMS film is 3 μm, the temperature cross sensitivity is low, namely 2.51 x 10-3Mpa/c, and the temperature cross talk problem becomes more serious as the thickness of the PDMS film increases. The invention introduces a double-parameter demodulation method to eliminate the problem of temperature crosstalk. As shown in equation (8)
In the formula KλPSensitivity to Dip point wavelength variations, K, due to gas pressure variationsIPSensitivity to variation in Dip spot intensity due to variation in gas pressure, KλTSensitivity to variations in Dip point wavelength due to temperature variations, KITSensitivity to variation in Dip spot intensity due to temperature change, D ═ KλPKIT-KλTKIP。
As can be seen from fig. 4a and 4c, when the gas pressure sensitivity is too high and the FSR is small, the measurement range is limited by the FSR. The wavelength demodulation method of the Dip point is selected to be converted into the demodulation method of the air microcavity length L so as not to be limited by the size of the FSR. The structure of the optical fiber gas pressure sensor of the present embodiment with H of 3 μm was taken and subjected to an experiment, and the experimental result is shown in fig. 8.
As shown in fig. 8 (a), due to the limitation of FSR, the wavelength is severely overlapped, so that the measurement range is limited, and a two-parameter demodulation method of air microcavity length and gas pressure intensity is provided, and the air microcavity length L can be changed under the action of different temperatures or gas pressures. Through experiments, the FSR does not change along with the changes of the gas pressure and the temperature, the wavelengths lambda 1 and lambda 2 of the two Dip points change along with the changes of the gas pressure and the temperature, and the refractive index n of the air microcavitycSince no change occurs, the amount of change in the air microcavity length L due to changes in gas pressure and temperature can be determined by equation (4). Then introducing formula (9) for demodulation
In the formula KLPSensitivity to changes in air microcavity length due to changes in gas pressure, KIPSensitivity to Dip2 intensity variations due to gas pressure variations, KLTSensitivity to changes in air microcavity length due to changes in temperature, KITSensitivity to Dip2 intensity variations due to temperature variations，D＝KLPKIT-KLTKIP. Wherein it is noted that KIT＝0.0059*X-0.28，X＝20+△T。
The PDMS film thickness of the fiber gas pressure sensor of this embodiment is 3 μm, the linear relationship between the interference valley wavelength and the gas pressure Y is 52.143 × X +1527.143, the gas pressure sensitivity is 52.173nm/Mpa, the linearity is 99.86%, and the temperature cross sensitivity is low, 2.51 × 10-3Mpa/℃。
Claims (5)
1. The preparation method of the optical fiber gas pressure sensor is characterized in that the optical fiber gas pressure sensor is an FPI optical fiber gas sensor; the optical fiber gas pressure sensor consists of a hollow optical fiber, a single-mode optical fiber and a polydimethylsiloxane film, wherein one end of the hollow optical fiber is welded with the single-mode optical fiber, and the other end of the hollow optical fiber is blocked by the film; a closed air microcavity is formed between the welding position of the single-mode optical fiber and the hollow optical fiber and the blocking film; the optical fiber gas pressure sensor is prepared by the following steps:
firstly, welding a single mode fiber with a hollow fiber, and then cutting the single mode fiber into required length to form a primary structure of the fiber gas pressure sensor;
dipping one end of a hollow optical fiber of the primary structure of the optical fiber gas pressure sensor with polydimethylsiloxane liquid;
thirdly, if the initial thickness of the polydimethylsiloxane film dipped in the initial structure is larger than the preset film thickness, dipping redundant polydimethylsiloxane liquid by using a clean single-mode optical fiber; if the initial thickness of the polydimethylsiloxane film dipped in the primary structure is smaller than the preset film thickness, contacting the end of the hollow-core optical fiber of the primary structure with an optical fiber adhered with polydimethylsiloxane liquid until the thickness of the polydimethylsiloxane film in the primary structure reaches the preset film thickness;
and fourthly, curing the polydimethylsiloxane film to obtain the optical fiber gas pressure sensor.
2. The method for manufacturing an optical fiber gas pressure sensor according to claim 1, wherein the diameter of the portion of the single-mode optical fiber extending into the primary structure for dipping in excess polydimethylsiloxane liquid in step three is smaller than the inner diameter of the hollow-core optical fiber.
3. The method for manufacturing an optical fiber gas pressure sensor according to claim 1, wherein the optical fiber having the polydimethylsiloxane liquid adhered thereto in step three contacts the upper edge or the lower edge of the end of the hollow-core optical fiber of the primary structure with the polydimethylsiloxane liquid thereon.
4. The method of claim 1, wherein the polydimethylsiloxane liquid is mixed from Sylgard 184-a and Sylgard 184-B in a ratio of 10: 1.
5. The method for manufacturing an optical fiber gas pressure sensor according to claim 1, wherein the curing temperature in the fourth step is 70 ℃ and the curing time is 6 hours.
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