U-shaped humidity-sensitive optical fiber sensor and manufacturing method thereof
Technical Field
The invention relates to a hydrogen sensor, in particular to a U-shaped humidity-sensitive optical fiber sensor and a manufacturing method thereof.
Background
Humidity is an important parameter affecting the safe operation of an electrical control cabinet, a communication machine room and the like. In order to maintain the humidity of the power distribution room in the normal allowable relative humidity working range of the device (the maximum allowable relative humidity is 75% RH), prolong the service life of the device and ensure the safe operation of the device, the humidity in the power distribution room must be monitored in real time.
At present, a plurality of sensors for humidity measurement are available, wherein the optical fiber sensor has the advantages of electromagnetic interference resistance, chemical corrosion resistance, long-distance transmission, high response speed, high sensitivity and the like, and is widely applied. In the optical fiber humidity sensor, compared with a quartz optical fiber humidity sensor, the plastic optical fiber humidity sensor has the advantages of low price, large diameter, large numerical aperture, good flexibility, easy molding and the like. Despite the advantages of the plastic optical fiber humidity sensor, the reported plastic optical fiber humidity sensor faces a critical problem: the sensitivity is low.
In order to improve the sensitivity of the optical fiber humidity sensor, plastic optical fiber humidity sensors with different structural types, such as U-shaped, D-shaped, tapered optical fiber sensors and the like, are developed. Although the sensitivity can be improved by optimizing the shape of the sensitive area of the sensor, the optical fiber humidity sensors still select communication plastic optical fibers as the light transmission and sensing media. The optical transmission in the communication plastic optical fiber is based on a fiber core-cladding film, light beams are mainly limited to be transmitted in the optical fiber, the light radiation intensity on the surface of the optical fiber is low, the action intensity of light and measured parameters is low, and the sensitivity of the sensor is low. Therefore, it is necessary to construct a new optical fiber for enhancing the light radiation intensity on the surface of the optical fiber, and couple the new optical fiber with the selective humidity sensitive material to improve the plastic optical fiber humidity sensor.
Disclosure of Invention
The invention aims to provide a U-shaped humidity-sensitive optical fiber sensor and a manufacturing method thereof.
The technical scheme of the invention is as follows: a manufacturing method of a U-shaped humidity-sensitive optical fiber sensor is characterized by comprising the following steps: the method comprises the following steps:
step A, fiber grating pretreatment: the protective layer of the middle section of one optical fiber is removed, then the middle section of the optical fiber is ground to 200 and 91500 mu m, and the ground optical fiber is bent into a U shape.
Step B, preparing the U-shaped optical fiber with the sensitization film:
and step B1, firstly dissolving the light guide material polysulfone in a dimethyl sulfoxide solution, then adding germanium dioxide into the solution, wherein the germanium dioxide plays a role in light scattering and refractive index modulation, and stirring uniformly to obtain the polysulfone germanium dioxide sol.
And step B2, dissolving the tackifier Canadian resin in dimethylbenzene to obtain Canadian resin sol.
And step B3, mixing the polysulfone germanium dioxide sol with the Canadian resin sol to obtain the sensitization sol.
B4, coating the sensitization sol on the surface of the U-shaped area of the optical fiber, drying the sensitization sol in a vacuum drying oven, and forming a sensitization membrane after drying the sensitization sol to obtain the U-shaped optical fiber with the sensitization membrane, wherein the sensitization membrane is formed by mixing polysulfone, Canadian resin and germanium dioxide; the refractive index of the obtained sensitization film U-shaped optical fiber is larger than that of the optical fiber core, and light which is transmitted in the optical fiber and is scattered on the surface of the optical fiber core can be coupled into the sensitization film so as to improve the light intensity transmitted in the sensitization film; while germanium dioxide GeO2The light will be scattered and the intensity of the radiation on the surface of the sensitization film will be increased to further provide the sensitivity of the sensor.
Step C, preparation of humidity-sensitive optical fiber sensor
Step C1, adding the N-methyl pyrrolidone solution into a container, continuously stirring under the protection of nitrogen, adding 4,4 '-diaminodiphenyl ether powder, adding pyromellitic dianhydride particles after the 4, 4' -diaminodiphenyl ether powder is completely dissolved, and reacting for a certain time to obtain a polyamic acid solution; n-methylpyrrolidone is a solvent of 4, 4' -diaminodiphenyl ether powder; 4, 4' -diaminodiphenyl ether powder is an intermediate for synthesizing polyimide; pyromellitic dianhydride particles are used as raw materials for synthesizing polyimide; the pyridine solution is used for improving the thermal stability, mechanical property and processing property of the polyimide material; the propionic anhydride solution is used as a water removal agent to promote the low-temperature imidization of the polyamic acid; n-butanol is a solvent of polyether copolyamide PEBA 2533; the polyether copolyamide PEBA2533 is used for improving the water absorption performance of the polyimide film and the toughness and the elongation at break after water absorption.
Step C2, standing the prepared polyamic acid solution, adding the pyridine solution into the polyamic acid solution after bubbles in the solution disappear, and mutually dissolving the pyridine solution and the polyamic acid solution under magnetic stirring; wherein the pyridine solution is used for improving the thermal stability, the mechanical property and the processing property of the polyimide material.
Step C3, adding a propionic anhydride solution into the mixed solution obtained in the step C2, and continuously reacting under the stirring condition to obtain polyimide humidity sensitive sol; the propionic anhydride solution is used as a water remover to promote the low-temperature imidization of the polyamic acid.
Step C4, adding the polyether copolyamide into n-butanol, and continuously stirring by using a magnetic stirrer to obtain polyether copolyamide and n-butanol sol; the polyether copolyamide PEBA2533 is used for improving the water absorption performance of the polyimide film and the toughness and the elongation at break after water absorption.
Step C5, mixing the sol obtained in the step C3 and the step C4 with silicon dioxide to obtain humidity sensitive sol; the silica is used for enhancing the transmission of light beams in the humidity-sensitive sol and enhancing the mechanical property of the humidity-sensitive sol.
And step C6, coating the humidity sensitive sol obtained in the step C5 on the surface of the U-shaped area of the U-shaped optical fiber with the sensitization film obtained in the step B4, drying the humidity sensitive sol in a vacuum drying oven, and forming the humidity sensitive film after drying the humidity sensitive sol to obtain the U-shaped humidity sensitive optical fiber sensor with the humidity sensitive film and the sensitization film. At the interface of the humidity-sensitive film and the sensitivity-sensitive film, light radiated from the surface of the sensitivity-sensitive film is coupled into the humidity-sensitive film, after the humidity-sensitive film absorbs water molecules, the refractive index changes, the more water molecules are absorbed, the larger the refractive index change is, the stronger the light attenuation in the humidity-sensitive film is, finally, the smaller the light intensity output from the optical fiber is, and the measurement of the humidity is realized by detecting the change of the light intensity at the output end of the optical fiber.
The invention aims to improve the luminous intensity of the surface of the optical fiber, thereby improving the response sensitivity of the sensor to relative humidity; firstly removing a partial coating of an optical fiber and bending the optical fiber into a U shape, then coating a layer of polysulfone germanium dioxide sol on the surface of the U-shaped area, and finally coating a layer of selective humidity-sensitive material, namely a humidity-sensitive film, on the surface of the sensitization film, thereby constructing the high-sensitivity humidity-sensitive optical fiber sensor.
In the humidity sensitive film, polyimide is used for selectively absorbing water molecules to realize selective sensitivity in air, polyether copolyamide PEBA2533 can improve the water absorption performance, the toughness and the elongation at break after water absorption of the polyimide film, the service life of the polyimide film is prolonged, silicon dioxide enhances the transmission of light beams in the humidity sensitive sol and enhances the mechanical property of the humidity sensitive sol, the ground optical fiber has a rough surface, the light intensity in the humidity sensitive film can be increased by adopting a U-shaped structure and a sensitivity enhancing film, the higher the light intensity in the humidity sensitive film is, the more the light attenuation is, and the higher the sensitivity of the sensor is. Therefore, the plastic optical fiber humidity sensor of the invention has high sensitivity.
According to the preferable scheme of the manufacturing method of the U-shaped humidity-sensitive optical fiber sensor, germanium dioxide GeO is adopted in the step B12The mass of the polysulfone germanium dioxide sol is 0.5-5 percent of the total mass of the polysulfone germanium dioxide sol.
According to the preferable scheme of the manufacturing method of the U-shaped humidity-sensitive optical fiber sensor, in the step C5, the sol obtained in the steps C3 and C4 is mixed with silicon dioxide according to the mass ratio of (95-98): (5-2): 0.5-10.
According to the preferable scheme of the manufacturing method of the U-shaped humidity-sensitive optical fiber sensor, in the step C1, the mass ratio of the N-methylpyrrolidone, the 4, 4' -diaminodiphenyl ether powder and the pyromellitic dianhydride is (40-45): 1-2.
The U-shaped humidity-sensitive optical fiber sensor is prepared by the manufacturing method of the U-shaped humidity-sensitive optical fiber sensor.
The U-shaped humidity-sensitive optical fiber sensor with the humidity-sensitive film and the sensitization film has the advantages that the refraction index of the sensitization film is larger than that of the optical fiber core, and light scattered by a low-order mode transmitted inside the optical fiber and the surface of the optical fiber core can be coupled into the sensitization film so as to improve the light intensity transmitted inside the sensitization film; the light radiated on the surface of the sensitivity enhancing film is coupled into the humidity sensitive film, after the humidity sensitive film absorbs water molecules, the refractive index changes, the more water molecules are absorbed, the larger the refractive index variation is, the stronger the light attenuation in the humidity sensitive film is, and finally, the smaller the light intensity output from the optical fiber is, so that the humidity measurement is realized by detecting the light intensity change at the output end of the optical fiber; the invention has the characteristics of high response sensitivity to the relative humidity change in the environment and simple method, and can be widely applied to the fields of energy, chemical engineering, biochemical detection and the like.
Drawings
FIG. 1 is a schematic structural diagram of a U-shaped moisture-sensitive optical fiber sensor according to the present invention.
FIG. 2 is a response curve of the U-shaped moisture-sensitive optical fiber sensor obtained in example 3 with respect to humidity.
Detailed Description
Example 1, referring to fig. 1, a method for manufacturing a U-shaped moisture-sensitive optical fiber sensor, the method comprising the steps of:
step A, fiber grating pretreatment: taking a section of optical fiber, wherein the optical fiber is provided with an optical fiber core 3, an optical fiber cladding 2 and a protective layer 1; firstly, removing the protective layer at the middle section of the optical fiber, and then grinding the middle section of the optical fiber to 200-91500 mu m by using optical fiber grinding paper with the particle size of 3-5 mu m to obtain a fiber core with a rough surface; and bending the ground optical fiber into a U shape, putting the optical fiber into an oil bath pan with the temperature of 110-.
Step B, preparing the U-shaped optical fiber with the sensitization film:
step B1, firstly, dissolving the light guide material polysulfone in dimethyl sulfoxide solution, wherein the mass ratio of the polysulfone to the dimethyl sulfoxide solution is 1:2, then adding germanium dioxide with the diameter of 50-1000nm into the solution, wherein the germanium dioxide plays a role in light scattering and refractive index modulation, and stirring uniformly to obtain polysulfone GeO2Sol; GeO2The mass accounts for 0.5-5% of the total mass of the sol.
And step B2, dissolving the tackifier Canadian resin in xylene, wherein the mass ratio of the Canadian resin to the xylene is 1:3, and obtaining the Canadian resin sol.
Step B3, polysulfone GeO2The sol and the Canadian resin sol are mixed according to the mass ratio of 9:1 to obtain the sensitization sol.
Step B4, coating the sensitization sol on the surface of the U-shaped area of the plastic optical fiber, drying for 10-20h at 50-90 ℃ in a vacuum drying oven, and drying the sensitization sol to form a sensitization membrane 5 to obtain the U-shaped optical fiber with the sensitization membrane with the thickness of 2-2000 μm, wherein the sensitization membrane is made of polysulfone, Canadian resin and GeO2Mixing to form; the refractive index of the U-shaped optical fiber of the sensitization film is larger than that of the fiber core of the optical fiber, so that the light coupling of a low-order mode transmitted inside the optical fiber and the light scattered on the surface of the fiber core of the optical fiber can enter the sensitization film, and the light intensity transmitted inside the sensitization film is improved; with GeO2The light will be scattered and the intensity of the radiation on the surface of the sensitization film will be increased to further provide the sensitivity of the sensor.
Step C, preparation of humidity-sensitive optical fiber sensor
Step C1, adding a certain mass of N-methylpyrrolidone solution into a container, continuously stirring for 30-60min at the rotating speed of 60-100rpm/min under the protection of nitrogen, then adding 4,4 '-diaminodiphenyl ether powder, adding pyromellitic dianhydride particles after the 4, 4' -diaminodiphenyl ether powder is completely dissolved, and reacting for 6-8h to obtain a transparent light yellow polyamic acid PAA solution; the mass ratio of the N-methylpyrrolidone to the 4, 4' -diaminodiphenyl ether powder to the pyromellitic dianhydride is (40-45) to (1-2), and specifically 40:1:1 can be selected.
And step C2, standing the prepared polyamic acid PAA solution for 30-60min, adding a pyridine solution into the polyamic acid PAA solution after bubbles in the solution disappear, wherein the mass ratio of the pyridine solution to the PAA solution is 5:42, and mutually dissolving the solutions under magnetic stirring.
And step C3, adding a propionic anhydride solution into the mixed solution obtained in the step C2, wherein the mass ratio of the propionic anhydride solution to the pyridine solution to the PAA solution is 1.5:5:42, and continuously reacting for 20-30h under the stirring condition to obtain the orange-yellow polyimide humidity sensitive sol.
And step C4, adding polyether copolyamide PEBA2533 into the n-butanol, wherein the mass ratio of the polyether copolyamide PEBA2533 to the n-butanol is 1:9, and continuously stirring for 3-5h at the temperature of 75-90 ℃ by using a magnetic stirrer at the rpm of 50-80 to obtain the polyether copolyamide and n-butanol sol.
And step C5, mixing the sol obtained in the step C3 and the step C4 with silicon dioxide with the diameter of 5nm-1000nm according to the mass ratio of (95-98) to (5-2) to (0.5-10) to obtain the humidity sensitive sol. The mass ratio of the three is 95:5: 2.
And C6, coating the moisture-sensitive sol obtained in the step C5 on the surface of the U-shaped area of the sensitization membrane U-shaped optical fiber obtained in the step B4, drying the moisture-sensitive sol in a vacuum drying oven at the temperature of 40-80 ℃ for 20-30h to form a moisture-sensitive membrane 4 with the thickness of 20nm-1000 mu m, and obtaining the U-shaped moisture-sensitive optical fiber sensor with the moisture-sensitive membrane and the sensitization membrane. At the interface of the humidity-sensitive film and the sensitivity-sensitive film, light radiated from the surface of the sensitivity-sensitive film is coupled into the humidity-sensitive film, after the humidity-sensitive film absorbs water molecules, the refractive index changes, the more water molecules are absorbed, the larger the refractive index change is, the stronger the light attenuation in the humidity-sensitive film is, finally, the smaller the light intensity output from the optical fiber is, and the measurement of the humidity is realized by detecting the change of the light intensity at the output end of the optical fiber.
Example 2. a U-shaped moisture-sensitive optical fiber sensor prepared according to the method of example 1.
Example 3, in contrast to example 1:
in step A, the middle section of the optical fiber is ground to 900 μm with a length of 5cm, and the bending radius of the U-region is 2 cm.
The thickness of the sensitization film formed in step B4 was 200 μm, and the thickness of the humidity-sensitive film F formed in step C5 was 20 μm.
The U-shaped humidity-sensitive optical fiber sensor obtained in example 3 was subjected to a humidity response test at 40 ℃ to obtain a humidity response characteristic as shown in FIG. 2, wherein in FIG. 2, the sensor output light intensity IoutAnd relative humidity (x) has a linear relationship: i isout=-0.9165x+554.05。
(R20.9817), x in the range of 10-80% RH, sensitivity up to-0.9 nW/(1% RH), 6.9 times higher than when a 10 μm moisture-sensitive film is coated on a 1500 μm optical fiber surface due to the rough optical fiber surface, the U-shaped structure of the optical fiber, the high refractive index of the sensitizing film, GeO2The light scattering and the water swelling property of polyimide cause the change of the refractive index, the polyether copolyamide PEBA2533 enhances the water absorption molecules of the humidity-sensitive film, and the silicon dioxide enhances the greater light attenuation caused by the transmission of light on the humidity-sensitive film, so the comprehensive effects enhance the light intensity and the light attenuation in the humidity-sensitive film, and further improve the sensitivity of the sensor.
Thus, the rough surface of the optical fiber increases the light scattering on the surface of the fiber core of the optical fiber, and polysulfone and GeO2The refractive index of the coating sensitization film is higher than that of the fiber core of the optical fiber, and the sensitization film with proper thickness is helpful for coupling the low-order mode transmitted in the fiber core into polysulfone and GeO2A coating layer to increase light intensity into the humidity sensitive membrane; finally, the appropriate thickness of the humidity sensitive film is beneficial to enhancing the light attenuation and improving the sensitivity of the sensor; when the diameter of the fiber core of the optical fiber is 900 μm, the thickness of the sensitization film is 200 μm, and the thickness of the humidity sensitive film is 20 μm, the sensitivity of the sensor reaches-0.9 nW/(1% RH).
Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.