阅读说明：本技术 一种内嵌空气泡的聚合物填充型光纤温度传感器制备方法 (Preparation method of polymer-filled optical fiber temperature sensor embedded with air bubbles ) 是由 刘颖刚 黄亮 李博文 宋小亚 董婧斐 韩党卫 于 2021-09-03 设计创作，主要内容包括：一种内嵌空气泡的聚合物填充型光纤温度传感器制备方法,选择毛细管和单模光纤,使用切刀将毛细管和单模光纤的端面切割平整；将单模光纤的涂敷层剥去,把单模光纤用酒精擦拭干净,把去除了涂敷层的单模光纤从毛细管左侧插入；取一滴PDMS胶滴在毛细管和单模光纤接口处,通过毛细管力的作用沿缝隙流向SMF的端面,在SMF端面上形成胶腔；将单模光纤抽插一次但不要拔出,在光纤端面与胶腔之间形成一个气腔；将结构静置一段时间,等到光纤端面与气腔之间再次形成一个胶腔,形成复合F-P腔后,放入温箱中进行固化,得到内嵌空气泡的聚合物填充型光纤温度传感器。本发明能够实现传感器结构对温度的高灵敏度响应,且该结构具有制作难度小,成本低的优势。(A method for preparing a polymer filled optical fiber temperature sensor embedded with air bubbles comprises the steps of selecting a capillary tube and a single-mode optical fiber, and cutting the end faces of the capillary tube and the single-mode optical fiber to be flat by using a cutter; stripping a coating layer of the single-mode optical fiber, wiping the single-mode optical fiber with alcohol, and inserting the single-mode optical fiber without the coating layer from the left side of the capillary; taking a drop of PDMS glue to be dropped at the interface of the capillary and the single-mode fiber, and flowing to the end face of the SMF along the gap under the action of capillary force to form a glue cavity on the end face of the SMF; the single-mode optical fiber is drawn and inserted once but not pulled out, and an air cavity is formed between the end face of the optical fiber and the rubber cavity; and standing the structure for a period of time, waiting until a glue cavity is formed between the end face of the optical fiber and the air cavity again, forming a composite F-P cavity, and then putting the composite F-P cavity into a warm box for curing to obtain the polymer-filled optical fiber temperature sensor embedded with the air bubbles. The invention can realize the high-sensitivity response of the sensor structure to the temperature, and the structure has the advantages of small manufacturing difficulty and low cost.)

1. A preparation method of a polymer filled optical fiber temperature sensor embedded with air bubbles is characterized by comprising the following steps;

the method comprises the following steps: selecting a section of capillary tube and a section of single-mode optical fiber, and cutting the end faces of the capillary tube and the single-mode optical fiber to be flat by using a cutter;

step two: stripping off a coating layer at one end of the single mode optical fiber, and inserting the end with the coating layer stripped off into the capillary;

step three: standing the prepared PDMS glue for a period of time, taking a drop of PDMS glue to be dropped at the interface of the capillary and the single-mode optical fiber after bubbles disappear completely, and flowing to the end face of the SMF along the gap under the action of capillary force to form a glue cavity on the end face of the SMF;

step four: the single-mode optical fiber is drawn and inserted once but not pulled out, and in the process, an air cavity is formed between the end face of the optical fiber and the rubber cavity by compressing air in the capillary;

step five: and standing the structure for a period of time, allowing PDMS (polydimethylsiloxane) glue dripped at the interface of the capillary and the single-mode optical fiber to continuously flow to the end face of the SMF along the gap by virtue of the force of the capillary, waiting until a glue cavity is formed between the end face of the optical fiber and the air cavity again, and curing in a warm box after a composite F-P cavity is formed to obtain the polymer-filled optical fiber temperature sensor embedded with the air bubbles.

2. The method of claim 1, wherein the capillary has a length of 10mm-15mm, an outer diameter of 250 μm and an inner diameter of 150 μm, the single-mode fiber is Corning SNF-28, the inner diameter is 8.2 μm, the cladding diameter is 125 μm, and the cutter is FITEL S326.

3. The method for preparing an air bubble-embedded polymer-filled optical fiber temperature sensor according to claim 1, wherein the step two single-mode optical fibers are inserted from the left side of the capillary tube by a length of about 5 mm.

4. The method for preparing an air bubble-embedded polymer-filled optical fiber temperature sensor according to claim 1, wherein in the step four, when the air cavities are formed, the single-mode optical fiber is manually inserted and pulled out once, so as to ensure that the air cavities are necessarily formed during the operation, and when the air cavities are pulled out, the single-mode optical fiber is placed for a period of time and then slowly inserted back, so that the air cavities can be formed by compressing the air in the capillary, and the process is completed within 5 seconds, thereby avoiding multiple times of inserting and pulling, otherwise, multiple air cavities may be formed in the structure.

5. The method for preparing an air bubble-embedded polymer-filled optical fiber temperature sensor according to claim 1, wherein in the step five curing process, the second glue cavity is closely attached to the end face of the single-mode optical fiber.

6. The method for preparing an air bubble-embedded polymer-filled optical fiber temperature sensor according to claim 1, wherein the time for the step five to form the second glue cavity is 5 min.

7. The method for preparing an air bubble-embedded polymer-filled optical fiber temperature sensor according to claim 1, wherein the curing is performed by continuously heating for 10h after the temperature is kept at 80 ℃ in the five-step incubator.

Technical Field

The invention belongs to the technical field of manufacturing and application of optical fiber sensing devices, and particularly relates to a preparation method of a polymer-filled optical fiber temperature sensor embedded with air bubbles.

Background

In recent years, optical fiber sensors have become a hot spot for research in the sensing field due to their unique advantages of electromagnetic interference resistance, high sensitivity, high integration, easy networking, and the like. However, the conventional all-fiber sensing structure is not sensitive to changes of external environmental parameters such as temperature, tilt angle, electric field, etc. due to the limitations of inherent properties of the fiber material, such as low thermo-optic coefficient, low thermal expansion coefficient, high young's modulus, etc. Although the performance of the optical fiber sensor can be improved by micromachining the optical fiber, the optical fiber sensor is not sensitive to some environmental parameters, and in order to meet the requirements of various fields on optical fiber sensing, people begin to try to add some materials sensitive to measurement parameters on the optical fiber, change the transmission condition of light in the optical waveguide by the reaction of the measurement parameters and the sensitive materials, and realize the measurement of the measurement parameters by analyzing the variable quantity in the optical fiber. The sensitive material is combined with the optical fiber microstructure, so that the sensitivity of the sensor is improved, and the application range of the sensor is expanded.

In addition, an interference type optical fiber sensor manufactured based on the optical fiber interference principle, such as an optical fiber Fabry-Perot interferometer (FPI), is widely applied to the field of optical fiber sensing detection due to the advantages of flexible and various structures, high precision, high reflectivity and the like. At present, the technology of measuring temperature by using a sensor based on an all-fiber FPI and a fiber grating is mature, but the response sensitivity is limited to the level of the fiber, the manufacturing cost is high, and the process is tedious. In addition, although the sensitivity of the optical fiber temperature sensor is remarkably improved, the optical fiber sensor structure made by compounding the known sensitivity enhancing material and the optical fiber microstructure has high manufacturing difficulty and extremely high cost.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a preparation method of a polymer filled optical fiber temperature sensor with an embedded air bubble.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for preparing a polymer filled optical fiber temperature sensor embedded with air bubbles comprises the following steps;

the method comprises the following steps: selecting a section of capillary tube and a section of single-mode optical fiber, and cutting the end faces of the capillary tube and the single-mode optical fiber to be flat by using a cutter;

step two: stripping off a coating layer at one end of the single mode optical fiber, and inserting the end with the coating layer stripped off into the capillary;

step three: standing the prepared PDMS glue for a period of time, taking a drop of PDMS glue to be dropped at the interface of the capillary and the single-mode optical fiber after bubbles disappear completely, and flowing to the end face of the SMF along the gap under the action of capillary force to form a glue cavity on the end face of the SMF;

step four: the single-mode optical fiber is drawn and inserted once but not pulled out, and in the process, an air cavity is formed between the end face of the optical fiber and the rubber cavity by compressing air in the capillary;

step five: and standing the structure for a period of time, allowing PDMS (polydimethylsiloxane) glue dripped at the interface of the capillary and the single-mode optical fiber to continuously flow to the end face of the SMF along the gap by virtue of the force of the capillary, waiting until a glue cavity is formed between the end face of the optical fiber and the air cavity again, and curing in a warm box after a composite F-P cavity is formed to obtain the polymer-filled optical fiber temperature sensor embedded with the air bubbles.

The capillary tube is 10mm-15mm long, the outer diameter is 250 μm, the inner diameter is 150 μm, the single-mode fiber is Corning SNF-28, the inner diameter is 8.2 μm, the cladding diameter is 125 μm, and the cutter is FITEEL S326.

The insertion length of the single-mode fiber from the left side of the capillary tube in the step two is about 5 mm.

When the air cavity is manufactured in the fourth step, the single-mode optical fiber is only manually drawn and inserted once, the air cavity is inevitably formed for ensuring the operation, when the single-mode optical fiber is drawn out, the single-mode optical fiber is kept still for a period of time and then slowly inserted back, so that the air cavity can be formed by compressing the air in the capillary, the process is completed within 5 seconds, the repeated drawing and inserting is avoided, and otherwise, a plurality of air cavities can appear in the structure.

In the curing process of the fifth step, the second glue cavity is tightly attached to the end face of the single-mode optical fiber.

And step five, standing for 5min to form a second glue cavity.

After the temperature of the fifth-step incubator is kept at 80 ℃, the heating is continuously carried out for 10 hours for curing.

The invention has the beneficial effects that:

according to the invention, the temperature-sensitive material is combined with the optical fiber microstructure, so that the limitation of the temperature sensitivity of the sensor due to the inherent property of the optical fiber material is broken, and the high-performance optical fiber temperature sensor structure is prepared. The invention relates to a composite closed F-P cavity which is manufactured by filling PDMS glue in a section of capillary. Because the thermal expansion coefficient of the PDMS is high, when the external environment temperature changes, the interference spectrogram of the sensor obviously moves along with the change of the external environment temperature. Therefore, compared with an all-fiber structure and a fiber grating, the temperature sensitivity of the sensor is obviously improved, and most importantly, the structure is low in manufacturing difficulty and low in cost.

The closed F-P cavity is formed by heating and curing a temperature-sensitive material PDMS (polydimethylsiloxane) adhesive, so that the problem that the temperature sensitivity is limited to an all-fiber structure is solved;

the PDMS adhesive has good stability in the temperature range of-55-200 ℃, and the temperature measurement range of the composition of the sensitive material and the optical fiber microstructure is expanded;

the sensor manufactured by the invention simplifies the process for manufacturing the composite F-P cavity and improves the temperature sensitivity of the sensor.

Drawings

FIG. 1 is a schematic view showing a capillary and a single-mode optical fiber cut by a cutter.

FIG. 2 is a schematic view of a single mode optical fiber with the coating removed and the single mode optical fiber inserted into a capillary.

FIG. 3 is a schematic illustration of the formation of a glue cavity on the SMF endface by dropping PDMS glue at the interface of the capillary and the single mode fiber.

FIG. 4 is a schematic diagram of an air cavity formed between the end face of a single mode fiber and a glue cavity after the single mode fiber is inserted.

FIG. 5 is a schematic view of the sensor structure after curing after the structure is left to stand for a period of time to form a second glue cavity between the end face and the air cavity.

Figure 6 is an image under a microscope of a closed F-P chamber formed by PDMS gel inside a capillary.

Fig. 7 is a schematic diagram of a sensor structure.

FIG. 8 is a schematic view of a measurement experiment apparatus.

FIG. 9 is a graph of the response spectrum of the sensor to temperature.

FIG. 10 is a spectral analysis of a sensor versus temperature response spectrum.

FIG. 11 is a graph of a linear fit of sensor wavelength drift as a function of temperature.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

As shown in fig. 1-11: the technical scheme for preparing the sensor comprises the following five steps:

the method comprises the following steps: selecting a section of capillary tube (outer diameter 250 μm and inner diameter 150 μm) with length of 10mm-15mm and a section of single mode fiber (Corning SNF-28, inner diameter 8.2 μm, cladding diameter 125 μm), and cutting the end faces of the capillary tube and the single mode fiber flat by using a cutter (FITIEL S326), as shown in FIG. 1;

step two: stripping off the coating layer of the single-mode optical fiber, wiping the single-mode optical fiber with alcohol, and inserting the single-mode optical fiber with the coating layer removed from the left side of the capillary tube for a distance of about 5mm, as shown in fig. 2;

step three: uniformly mixing PDMS (polydimethylsiloxane) glue according to a proportion, standing for a period of time, taking a drop of PDMS glue to be dropped at the interface of a capillary and a single-mode fiber after bubbles completely disappear, flowing to the end face of an SMF (as a reflecting surface 1 in fig. 7) along a gap under the action of capillary force, and forming a glue cavity on the end face of the SMF, as shown in fig. 3;

step four: the single mode fiber is inserted once but not pulled out, and an air cavity is formed between the end face of the fiber and the glue cavity, as shown in FIG. 4;

step five: standing the structure for a period of time, waiting until a glue cavity is formed between the end face of the optical fiber and the air cavity again, placing the optical fiber into a warm box after a composite F-P cavity is formed, keeping the temperature at 80 ℃, and continuously heating for 10 hours for curing, as shown in figure 5;

the invention provides a preparation method for filling and manufacturing a composite closed F-P cavity in a capillary by using a PDMS material. The single mode fiber used was standard common single mode fiber, the material used to make the hermetic EFPI was high transparency, high strength PDMS glue (Dow Corning 184), the demodulation equipment used in the laboratory was SM125 demodulator.

The temperature sensitivity of the all-fiber sensor is limited by the fiber material, so that the temperature sensitivity of the fiber F-P cavity can be effectively improved by the composite sensitive material PDMS. The structure is packaged in the capillary tube, and a composite F-P cavity formed by the capillary tube can be protected, so that the sensor is more stable and firm; the optical fiber temperature sensor prepared by the invention has the advantages of simple structure, easy manufacture, extremely low cost and good spectral response characteristic.

The preparation process of the temperature sensor provided by the invention particularly needs to be noticed as follows: (1) the end face of the optical fiber inserted into the capillary is used as a first reflecting surface, and the flatness of the end face of the optical fiber needs to be ensured, so that when the single-mode optical fiber is in contact with the capillary, the end face of the optical fiber is prevented from being damaged; (2) when the air cavity is manufactured, the single-mode optical fiber is only inserted once, and the process is finished within about 5 seconds, so that multiple times of insertion and extraction are avoided to form multiple bubbles; (3) when the second glue cavity is formed by standing, the time is not too short, so that the glue cavity cannot play a role because of being too short; (4) during the curing process, care should be taken that the second glue cavity is in close contact with the end face of the single-mode optical fiber.

The problems solved by the invention are as follows:

firstly, the limitation of the optical fiber material is broken, so that the sensitivity of the optical fiber FPI sensor structure is improved to a greater extent; secondly, the packaging process after the temperature-sensitive material and the sensing microstructure are compounded is simplified, and the packaging problem of the sensor structure is solved; and thirdly, the manufacturing process of the temperature sensor is optimized, the manufacturing cost is reduced, and the problems of complicated manufacturing process and high cost of the high-sensitivity optical fiber temperature sensor are solved.

The working principle of the sensor is as follows:

the basic working principle of the sensor is that when the temperature changes, the thermosensitive material PDMS has high thermal expansion coefficient and thermo-optic coefficient, the cavity length of the composite F-P cavity changes, so that the optical path difference changes, interference spectrum is influenced, and the spectral line of the composite F-P cavity shifts.

The optical fiber temperature sensor prepared by the invention is formed by curing temperature-sensitive material PDMS glue in a section of capillary by heating. The sensor structure has four reflecting surfaces, wherein the reflecting surface 1 is an interface M between an optical fiber end surface and PDMS (polydimethylsiloxane) glue₁The reflecting surface 2 being the interface M₂The reflecting surface 3 being the interface M₃. The reflecting surface 4 being an interface M₄The incident light is reflected by the reflecting surface 1 and part of the light continues to travel forward through the reflecting surface 1 and is reflected again at the reflecting surface 2 after passing through an air cavity having a refractive index of 1 and a cavity length of 112.06 μm, having a refractive index of about 1.41, and a cavity length of 46.99 μm, and is reflected at the reflecting surface 3. And a part of the light passes through a glue cavity with a refractive index of 1.41 and a cavity length of 66.88 μ M, in M₄Where reflection occurs. The optical path diagram is shown in fig. 7. The reflection of light by the sensor structure causes a phase delay due to the difference in optical path lengths, thus causing multi-beam interference. The interference intensity is approximately expressed as:

wherein I is interference light intensity; a. the₁、A₂、A₃And A₂The incident light amplitudes of the reflecting surface 1, the reflecting surface 2, the reflecting surface 3 and the reflecting surface 4, respectively;is interface M₁And M₂The phase difference of the section of glue cavity between the two sections of glue cavities,is interface M₁And M₃The phase difference of a composite cavity formed by the glue cavity and the air cavity,is interface M₁And M₄The phase difference of a composite cavity formed by the two end rubber cavities and the air cavity,is the phase difference of the air cavity,is interface M₂And M₄The phase difference of the composite cavity formed by the air cavity and the glue cavity,is interface M₃And M₄The phase difference of the glue cavity. Can be represented by the following formula

In the formula (2), L₁And L₃The cavity lengths of the first left rubber cavity and the second left rubber cavity are respectively, and the refractive indexes are n₁，L₂And n₂Is the cavity length and refractive index of the composite cavity consisting of the glue cavity and the air cavity.

The Free Spectral Range (FSR) in closed EFPI spectra can be expressed as:

as shown in fig. 8, one end of the SM125 demodulator with a measurement accuracy of 1pm is connected to a computer, and the other end is connected to a sensor. The sensor is arranged in a temperature measuring environment, and when the temperature changes, the spectrum change can be obtained on a computer through a demodulator.

When the temperature rises, the cavity length of the sealed EFPI changes, and the spectral line of the interference spectrum shifts towards the long wave direction, namely red shift. The response spectrum of the sensor to temperature is shown in fig. 9.

As shown in FIG. 10, the sensor proposed by the present invention is mainly M₁M₂、M₁M₃、M₁M₄The three cavities reflect the strongest light. Due to I₁>I₂>I₃>I₄Other cavities have smaller light intensity and smaller peak value on the spectrogram,

the temperature sensitivity of the sensor is 5.85 nm/DEG C and is much higher than the response sensitivity of the sensor with an all-fiber structure by performing linear fitting on the sensor at the wavelength of 30-40 ℃ along with the temperature change, and a fitting curve is shown in FIG. 11.