CN113790821A - High-temperature optical fiber Bragg grating temperature sensor and manufacturing method - Google Patents
High-temperature optical fiber Bragg grating temperature sensor and manufacturing method Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/3206—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres at discrete locations in the fibre, e.g. using Bragg scattering
-
- 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
- G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
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Abstract
The invention belongs to the technical field of high-temperature detection equipment, and discloses a high-temperature fiber Bragg grating temperature sensor and a manufacturing method thereof, wherein the high-temperature fiber Bragg grating temperature sensor comprises a threaded cylinder, a metal steel pipe, a regenerated fiber bragg grating, silica fume, a corundum ceramic cake, a single-mode fiber and a threaded cap; the corundum ceramic cake is a circular cylinder with a cavity inside, the threaded cylinder is fixedly arranged on the circumferential wall of the corundum ceramic cake, threads are arranged at two ends of the metal steel pipe, one end of the metal steel pipe is sealed, the other end of the metal steel pipe is open, one end of the seal is in threaded connection with the threaded cylinder, and one end of the opening penetrates out of the center of the corundum ceramic cake and is in threaded connection with the threaded cap; one end of the single-mode optical fiber is fixedly connected with the inner end face of the sealing end of the metal steel pipe, and the other end of the single-mode optical fiber extends out of the through hole of the threaded cap; and an ash injection hole is formed above the corundum ceramic cake. The fiber grating of the invention can still have good spectral characteristics without fading under the condition of 1000 ℃, thereby carrying out accurate temperature monitoring.
Description
Technical Field
The invention belongs to the technical field of high-temperature detection equipment, and particularly relates to a high-temperature fiber Bragg grating temperature sensor and a manufacturing method thereof.
Background
The fiber Bragg grating sensor belongs to one of fiber optic sensors, the sensing process based on the fiber Bragg grating obtains sensing information by modulating the wavelength of fiber Bragg grating (Bragg) by external physical parameters, and the fiber Bragg grating sensor is a wavelength modulation type fiber optic sensor, has the advantages of strong electromagnetic interference resistance, good electrical insulation, corrosion resistance, small transmission loss, large transmission capacity, wide measurement range and the like, and is widely applied to long-term monitoring in numerous fields.
Due to the existence of the heat fading effect of the fiber bragg grating, the degradation and even disappearance of the fiber bragg grating in a high-temperature environment cause that the measurement activity is difficult to carry out, the widely applied solution at present comprises a regenerated fiber bragg grating prepared by high-temperature annealing and a IIA type fiber bragg grating written by femtosecond laser, the IIA type fiber bragg grating shows high stability at the temperature of 1000 ℃, however, due to a damage mechanism, the spectral response is difficult to customize, and the obvious out-of-band loss is shown; the regenerated fiber grating has controllable spectral response characteristics, and is an ideal choice for the fiber grating temperature sensor under high temperature conditions.
The regenerated fiber grating is manufactured by annealing I-type initial fiber grating at high temperature under specific conditions, wherein the initial fiber grating is completely erased in the annealing process, new refractive index modulation is created in an ultraviolet exposure area, and the regenerated fiber grating retains spectral information from the initial grating. Due to this characteristic, a complex fiber grating that is more stable at high temperatures can be created for making a fiber grating temperature sensor with more excellent performance.
Disclosure of Invention
Aiming at the problems of insufficient high temperature resistance and too fragile optical fiber body of the existing optical fiber grating temperature sensor, the invention provides the optical fiber Bragg grating temperature sensor which can be used in the high temperature range of 800 plus 1100 ℃ and the manufacturing method thereof, and the regenerated optical fiber grating still has good spectral characteristics without attenuation under the condition of 1100 ℃, thereby carrying out accurate temperature monitoring.
In order to achieve the purpose, the invention provides the following technical scheme:
a high-temperature optical fiber Bragg grating temperature sensor comprises a threaded cylinder (1), a metal steel pipe (2), a regenerated optical fiber grating (3), silica fume (4), a corundum ceramic cake (5), a single-mode optical fiber (6) and a threaded cap (8); the corundum ceramic cake (5) is a cylinder with a cavity inside, the threaded cylinder (1) is fixedly arranged on the circumferential wall of the corundum ceramic cake (5), threads are arranged at two ends of the metal steel pipe (2), one end of the metal steel pipe is sealed, the other end of the metal steel pipe is open, one end of the seal is in threaded connection with the threaded cylinder (1), and one end of the seal penetrates out of the center of the corundum ceramic cake (5) and is in threaded connection with the threaded cap (8); a through hole is arranged at the center of the roof fall of the threaded cap (8); one end of the single-mode fiber (6) is fixedly connected with the inner end face of the sealing end of the metal steel pipe (2), the other end of the single-mode fiber extends out of the through hole of the threaded cap (8), and the middle section of the single-mode fiber (6) in the metal steel pipe (2) is provided with a regenerated fiber grating (3); an ash injection hole is formed above the corundum ceramic cake (5), and the ash injection hole is used for injecting silica fume (4) into the inner cavity of the corundum ceramic cake (5).
Furthermore, a V-shaped structural groove is formed in the center of the metal steel pipe (2), the regenerated fiber grating (3) and the single-mode fiber (6) are arranged in the V-shaped structural groove, and the opposite side distance of the V-shaped groove is 225 micrometers; the metal steel pipe (2) with the V-shaped groove structure clamps the single-mode optical fiber (6).
Furthermore, the single-mode optical fiber (6) extending from the threaded cap (8) is left with a pigtail (9).
Furthermore, the threaded cylinder (1) is hermetically connected with the metal steel pipe (2), the metal steel pipe (2) is hermetically connected with the threaded cap (8), and the metal steel pipe (2) is hermetically connected with the corundum ceramic cake (5).
Furthermore, the threaded cylinder (1) is made of tungsten steel materials, threads are arranged in the cylinder, one end of the threaded cylinder is sealed, the other end of the threaded cylinder is opened, the open end of the threaded cylinder is connected with the metal steel pipe (2), the threaded cylinder (1) is welded on the circumferential wall of the corundum ceramic cake (5), therefore, the cylinder bottom of the threaded cylinder (1) seals the outer circumferential surface of the corundum ceramic cake (5), the inner diameter of the threaded cylinder (1) is 2-4cm, and the thickness of the threaded cylinder (1) is 1-2 cm.
Furthermore, the metal steel pipe (2) is internally packaged in a vacuum mode and is made of tungsten steel materials; the outer diameter of the steel pipe (2) is 2-4cm, and the length is 8-14 cm. The whole packaging process of the metal steel pipe (2) is carried out in a vacuum glove box, and the inside of the packaged metal steel pipe (2) is kept in a vacuum state.
Further, the appearance of the silica fume (4) is gray or grey white powder, and refractoriness>The density reaches (1.5-1.6) g/cm at 1400 DEG C3The silica fume (4) has a fineness less than 1 μm accounting for more than 85% and an average particle size of 0.1-0.3 μm.
Further, the corundum ceramic cake (5) has an outer diameter of 10-14cm, a wall thickness of 1-3cm, preferably a wall thickness of 2cm, a height of 5-8cm, and AL2O3The content is more than 98 percent.
Furthermore, the used screw cap (8) is made of tungsten steel material, the inner diameter is 2-4cm, the thickness is 1-2cm, the single-mode optical fiber (6) extends out of a through hole in the end of the screw cap (8) and then is sealed by high-temperature glue, and the aperture of the through hole is 225 microns.
A manufacturing method of a high-temperature fiber Bragg grating temperature sensor is characterized in that a coating layer of a single-mode fiber (6) is completely stripped, the single-mode fiber (6) is clamped by a metal steel pipe (2) with a V-shaped groove structure in a vacuum state, and one end of the single-mode fiber (6) is fixed on an inner end face of a sealing end of the metal steel pipe (2) through high-temperature glue; the sealing end of the metal steel pipe (2) is screwed into a threaded cylinder (1) welded on the circumferential wall of the corundum ceramic cake (5), the other end is an open end, the corundum ceramic cake (5) extends out of the open end, and the sealing end is tightly clamped by a threaded cap (8) with a through hole; and the other end of the single-mode optical fiber (6) extends out of the through hole of the threaded cap (8), the through hole is sealed by high-temperature glue, the corundum ceramic cake (5) and the outer surface of a contact region of the metal steel pipe (2) are sealed by a sealing ring (7) and the high-temperature glue, silica fume (4) is injected into a fume injection hole formed above the corundum ceramic cake (5), and after the cavity of the corundum ceramic cake (5) is filled with the silica fume (4), an iron sheet and the high-temperature glue are used for sealing to obtain the temperature sensor.
Further, the iron piece is preferably a circular iron piece.
Further, the preparation method of the regenerated fiber grating (3) comprises the following steps:
at room temperature, putting a common single-mode optical fiber (6) into a pressure tank, and downloading hydrogen under the pressure of 10-14bar for 4-7 days to improve the photosensitivity of the optical fiber;
using 248nm or 193nm excimer laser to write I-type fiber grating (seed grating) on the single-mode fiber (6) which is processed by hydrogen loading by phase mask method; the repetition frequency of the laser is 20-40Hz, the single pulse energy is 10-20mJ, the total pulse is 8000-12000 times, the length of the grating region of the written seed fiber grating is 10-15mm, the central wavelength is 1545-1553nm, the 3dB bandwidth is 0.2-0.4nm, and the reflectivity is 80-99%;
placing the I-type fiber grating (seed grating) into a high-temperature tube furnace filled with argon, raising the temperature from room temperature to 600-800 ℃ at the rate of 10-30 ℃/min for pre-annealing, and naturally cooling to room temperature in the tube furnace to obtain the seed grating subjected to the first high-temperature annealing;
and (3) putting the seed grating subjected to the first high-temperature annealing into a high-temperature tube furnace filled with argon, heating from room temperature to 900 ℃ at the heating rate of 40-60 ℃/min, heating from 900 ℃ to 1000 ℃ at the heating rate of 3-7 ℃/min, preserving the temperature at 1000 ℃ for 80-120 minutes, taking out the seed grating from the tube furnace after the heat preservation is finished, and putting the seed grating into ice water for rapid cooling to obtain the regenerated fiber grating.
Further, the corundum ceramic cake (5) is made by passing Al-SIO2The preparation method comprises the following steps: mixing Al metal and SiO2After the powder is uniformly mixed, reacting under the condition of argon at the temperature of 1500 ℃ for 2-4 h to prepare alumina ceramic, forming by a mechanical press method to obtain a corundum ceramic cake (5), and finally arranging an ash injection hole with the diameter of 1cm above the corundum ceramic cake (5).
Further, the single-mode optical fiber (6) is a G.652 optical fiber, the length of the single-mode optical fiber is 12-18cm, a coating layer is stripped, and a 50-micrometer thin gold film is plated by using a chemical vapor deposition method after a grid is carved; the single-mode fiber (6) is lightly clamped in the V-shaped groove, the stress of the grid region is relieved, the single-mode fiber (6) can keep alignment by the V-shaped groove structure, and a tail fiber (9) is reserved on the single-mode fiber (6) extending out of the threaded cap (8).
Furthermore, the sealing ring (7) is directly pressed and molded in a metal mold by using a flexible graphite material, has the inner diameter of 2-4cm and the thickness of 0.5-1mm in a relaxed state, and completely expands at 1000 ℃.
Furthermore, the high-temperature adhesive is a semi-fluid HBC-1096 high-temperature sealing adhesive which does not contain silicon element. Can be stably used for a long time at-85 ℃ to 1250 ℃.
Compared with the prior art, the invention provides a high-temperature fiber Bragg grating temperature sensor which has the following beneficial effects:
(1) the temperature sensor adopts a three-layer protection structure, and the corundum ceramic cake is filled with silica fume, so that the effects of uniform heating and heat insulation are achieved, the damage to the fiber grating temperature sensor caused by overhigh local temperature is avoided, and the stability and the accuracy are higher.
(2) The metal steel pipe adopts a V-shaped groove structure and is packaged in vacuum, the optical fiber is lightly clamped in the metal steel pipe, the high-temperature glue is only used for fixing one end of the optical fiber, the optical fiber keeps collimation, and the grid region stress is relieved; the regenerated fiber grating is only affected by temperature, and the measuring result is more accurate and stable.
(3) The pre-annealing and the formal annealing of the fiber grating are carried out in argon, and the fiber grating is rapidly cooled after the heat preservation; the fiber grating regenerated in the mode has higher regeneration rate and mechanical strength through tests.
(4) The fiber grating temperature sensor of the invention mainly adopts corundum ceramics and tungsten steel materials, and has very high physical strength.
(5) The whole sensor adopts a movable packaging mode, and is easy to disassemble and assemble during later maintenance and inspection.
Drawings
FIG. 1 is a schematic structural diagram of a fiber grating temperature sensor according to the present invention;
FIG. 2 is a schematic top view of a cross-sectional structure of a fiber grating temperature sensor according to the present invention;
FIG. 3 is a schematic structural diagram of a V-shaped groove on the metal steel pipe 2;
fig. 4 is a schematic structural diagram of the regenerated fiber grating 3 in a V-groove of the metal steel pipe 2;
FIG. 5 is a schematic cross-sectional view of the threaded cap 8 of FIG. 1;
FIG. 6 is a mechanical property test chart of the regenerated fiber grating 3;
FIG. 7 is a temperature sensitivity test chart of the regenerated fiber grating 3;
FIG. 8 is a regenerated fiber grating reflection spectrum.
The reference numerals in the figures have the meaning: 1. a threaded barrel; 2. a metal steel pipe; 3. regenerating the fiber grating; 4. Silica fume; 5. corundum ceramic cakes; 6. an optical fiber; 7. a seal ring; 8. a threaded cap; 9. and (4) tail fibers.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1 to 5, the temperature sensor of the present invention includes a threaded cylinder 1, a metal steel pipe 2, a regenerated fiber grating 3, silica fume 4, a corundum ceramic cake 5, a single-mode fiber 6, and a threaded cap 8; the corundum ceramic cake 5 is a cylinder with a cavity inside, the threaded cylinder 1 is fixedly arranged on the circumferential wall of the corundum ceramic cake 5, threads are arranged at two ends of the metal steel pipe 2, one end of the metal steel pipe is sealed, the other end of the metal steel pipe is open, one end of the seal is in threaded connection with the threaded cylinder 1, and one end of the opening penetrates out of the center of the corundum ceramic cake 5 and is in threaded connection with the threaded cap 8; a through hole is arranged in the center of the roof fall of the threaded cap 8; one end of the single mode fiber 6 is fixedly connected with the inner end face of the sealing end of the metal steel pipe 2, the other end of the single mode fiber extends out of the through hole of the threaded cap 8, and the middle section of the single mode fiber 6 in the metal steel pipe 2 is provided with the regenerated fiber bragg grating 3; an ash injection hole is arranged above the corundum ceramic cake 5 and used for injecting silica fume 4 into the inner cavity of the corundum ceramic cake 5.
As shown in fig. 2 and fig. 3, in a specific embodiment of this embodiment, a V-shaped structural groove is disposed at the center of the metal steel pipe 2, the regenerated fiber grating 3 and the single-mode fiber 6 are disposed in the V-shaped structural groove, and the V-shaped groove has a side-to-side distance of 225 μm; the single-mode optical fiber 6 is clamped by the metal steel pipe 2 with the V-shaped groove structure.
In one embodiment of this embodiment, the single mode optical fiber 6 extends from the threaded cap 8 leaving a pigtail 9.
In a specific embodiment of this embodiment, the threaded cylinder 1 and the metal steel pipe 2, the metal steel pipe 2 and the threaded cap 8, and the metal steel pipe 2 and the corundum ceramic cake 5 are all connected in a sealing manner.
In a specific embodiment of this embodiment, the threaded cylinder 1 is made of tungsten steel, the thread is arranged in the cylinder, one end of the threaded cylinder is sealed, the other end of the threaded cylinder is open, the open end of the threaded cylinder is connected with the metal steel pipe 2, the threaded cylinder 1 is welded on the circumferential wall of the corundum ceramic cake 5, thus, the cylinder bottom of the threaded cylinder 1 seals the end surface of the corundum ceramic cake 5, and the threaded cylinder 1 has an inner diameter of 2-4cm and a thickness of 1-2 cm.
In a specific implementation manner of this embodiment, the metal steel tube 2 is vacuum-sealed and made of tungsten steel; the outer diameter of the steel pipe 2 is 2-4cm, and the length is 8-14 cm. The whole packaging process of the metal steel pipe 2 is carried out in a vacuum glove box, and the inside of the packaged metal steel pipe 2 is kept in a vacuum state.
In one embodiment of this example, the silica fume 4 is a gray or off-white powder in appearance, with a degree of refractoriness>The density reaches (1.5-1.6) g/cm at 1400 DEG C3The silica fume 4 has a fineness less than 1 μm accounting for more than 85% and an average particle size of 0.1-0.3 μm.
In a particular embodiment of this example, the corundum ceramic cake 5 has an outer diameter of 10-14cm, a wall thickness of 1-3cm, preferably a wall thickness of 2cm, a height of 5-8cm, AL2O3The content is more than 98 percent.
As shown in FIG. 5, in a specific embodiment of this embodiment, the screw cap 8 is made of tungsten steel, the inner diameter is 2-4cm, the thickness is 1-2cm, the single-mode optical fiber 6 extends out of the through hole at the end of the screw cap 8 and is sealed by high-temperature glue, and the aperture of the through hole is 225 μm.
The manufacturing method of the temperature sensor comprises the following steps: the coating layer of the single mode optical fiber 6 is completely stripped, the single mode optical fiber 6 is clamped by the metal steel pipe 2 with the V-shaped groove structure in a vacuum state, and one end of the single mode optical fiber 6 is fixed on the inner end face of the sealing end of the metal steel pipe 2 through high-temperature glue; the sealing end of the metal steel pipe 2 is screwed into a threaded cylinder 1 welded on the circumferential wall of a corundum ceramic cake 5, the other end is an opening end, the opening end extends out of the corundum ceramic cake 5, and the corundum ceramic cake is tightly clamped by a threaded cap 8 with a through hole; and the other end of the single-mode optical fiber 6 extends out of the through hole of the threaded cap 8, the through hole is sealed by high-temperature glue, the outer surface of a contact area between the corundum ceramic cake 5 and the metal steel pipe 2 is sealed by a sealing ring 7 and the high-temperature glue, finally, silica fume 4 is injected into a fume injection hole formed above the corundum ceramic cake 5, and after the cavity of the corundum ceramic cake 5 is filled with the silica fume 4, an iron sheet and the high-temperature glue are used for sealing to obtain the temperature sensor.
Example 1
The regenerated fiber grating 3 is prepared by three basic steps of high-hydrogen ballast, phase mask method writing and high-temperature annealing regeneration:
step one, at room temperature, placing a G.652 optical fiber with the length of 15cm (in order to obtain accurate data for comparison, the length of the single-mode optical fiber in the step one of the invention is 15cm, in fact, the length of the single-mode optical fiber is matched with the whole structure of the temperature sensor of the invention, and the length is not limited.) into a pressure tank, and downloading hydrogen under the hydrogen pressure of 12bar for 7 days to improve the photosensitivity of the optical fiber;
and step two, writing an I-type seed fiber grating on the optical fiber by using a 248 or 193nm excimer laser phase mask method (the parameter setting is that the repetition frequency is 30Hz, the single pulse energy is 10mJ, the total pulse is 8000 times, and the grid region length is 12 mm). The central wavelength of the seed grating for writing is 1548nm, the 3dB bandwidth is 0.3nm, and the reflectivity is up to 88%.
And step three, putting the inscribed seed grating into a high-temperature tube furnace filled with argon, heating the seed grating from room temperature to 700 ℃ at the heating rate of 20 ℃/min for pre-annealing, and naturally cooling the seed grating in the tube furnace after the pre-annealing is finished.
Step four, putting the seed grating into a high-temperature tube furnace, heating the seed grating from room temperature to 900 ℃ at a heating rate of 50 ℃/min, heating the seed grating from 900 ℃ to 1000 ℃ at a heating rate of 5 ℃/min, and keeping the temperature at 1000 ℃ for 100 minutes, wherein the regenerated fiber grating appears and is stable (as shown in fig. 6 to 8, the central wavelength of the regenerated fiber grating is 1548.9nm, the 3dB bandwidth is 0.24nm, the temperature sensitivity is 13.57 pm/DEG C, and the reflectivity can reach 70%); and after the heat preservation is finished, immediately taking out the fiber grating from the tubular furnace, putting the fiber grating into ice water for rapid cooling, and then testing the mechanical property of the regenerated fiber grating by using a high-temperature fiber tensile tester, wherein the median value of the breaking strength of the regenerated fiber grating is 95dN and the mechanical property is good when the environment temperature of the regenerated fiber grating is 25 ℃ and the tensile speed is 3 mm/min.
In a specific embodiment of this embodiment, a thin gold film with a thickness of 50 μm is plated on the surface of the g.652 single-mode fiber 6 by using a chemical vapor deposition method, all the package assemblies are placed in a vacuum glove box, and the V-shaped groove schematic diagram of fig. 2 is combined, the single-mode fiber 6 is lightly clamped inside the metal steel tube 2 with a V-shaped groove with an outer diameter of 3cm, a length of 12cm and an inner distance of 225 μm, and one end of the single-mode fiber 6 is fixed at one sealed end of the metal steel tube 2 by using a high temperature adhesive.
In a specific embodiment of the embodiment, a threaded cylinder 1 with an inner diameter of 3.1cm, a length of 3cm and a thickness of 1cm is welded on the circumferential wall of a corundum ceramic cake 5 with a diameter of 10cm, a height of 7cm and a thickness of 1 cm; the two ends of the metal steel pipe 2 are provided with threads, and the sealing end is screwed into a threaded cylinder on the circumferential wall of the corundum ceramic cake 5.
In a specific implementation mode of the embodiment, the open end of the metal steel pipe 2 extends out of a hole which is opposite to the internal thread cylinder 1 of the corundum ceramic cake 5 and has the diameter of 3.1cm, and is screwed into a threaded cap 8 with the inner diameter of 3.1cm and the thickness of 1 cm; the end of the screw cap 8 is provided with a small hole with the diameter of 225 mu m, and the optical fiber is sealed by high-temperature glue after extending out of the small hole.
In a specific implementation manner of this embodiment, the junction between the corundum ceramic cake 5 and the metal steel pipe 2 is sealed by a flexible graphite sealing ring 7 with an inner diameter of 3cm and a thickness of 1mm and a high temperature glue.
In a specific implementation manner of this embodiment, a circular hole with a diameter of 1cm is formed above the corundum ceramic cake 5 as an ash injection hole, silica ash is injected into the corundum ceramic cake 5, and after the corundum ceramic cake is filled with silica ash, a circular iron sheet with a diameter of 2cm and high-temperature glue are used for sealing.
In a specific embodiment of this embodiment, in consideration of convenience in actual use, the protruding optical fiber 6 is left with an FC interface pigtail and can be directly connected to another optical fiber in actual use.
Example 2
In this example, the parameters in the step of preparing the regenerated fiber grating 3 were adjusted as compared with example 1, and the preparation steps were as follows:
step one, placing a G.652 optical fiber with the length of 15cm into a pressure tank at room temperature, and carrying out hydrogen loading under the hydrogen pressure of 10bar for 4 days to improve the photosensitivity of the optical fiber;
and step two, writing an I-type seed fiber grating on the optical fiber by using a 248 or 193nm excimer laser phase mask method (the parameter setting is that the repetition frequency is 20Hz, the single pulse energy is 10mJ, the total pulse is 8000 times, and the grid region length is 10 mm). The central wavelength of the seed grating for writing is 1548.1nm, the 3dB bandwidth is 0.31nm, and the reflectivity is up to 82%.
And step three, putting the inscribed seed grating into a high-temperature tube furnace filled with argon, heating from room temperature to 800 ℃ at the heating rate of 10 ℃/min for pre-annealing, and naturally cooling in the tube furnace after the pre-annealing is finished.
Step four, putting the seed grating into a high-temperature tube furnace, heating the seed grating from room temperature to 900 ℃ at the heating rate of 40 ℃/min, heating the seed grating from 900 ℃ to 1000 ℃ at the heating rate of 3 ℃/min, preserving the temperature at 1000 ℃ for 80 minutes, taking the regenerated fiber grating out of the tube furnace immediately after the heat preservation is finished, putting the regenerated fiber grating into ice water for rapid cooling, wherein the central wavelength of the cooled regenerated fiber grating is 1549nm, the 3dB bandwidth is 0.26nm, the temperature sensitivity is 14.05 pm/DEG C, and the reflectivity can reach 64%; and then testing the mechanical property of the regenerated fiber grating by a high-temperature fiber tensile tester, wherein the median value of the breaking strength of the regenerated fiber grating is 97dN and the mechanical property is good when the environment temperature of the regenerated fiber grating is 25 ℃ and the tensile speed is 3 mm/min.
Example 3
In this example, the parameters in the step of preparing the recycled fiber grating 3 were adjusted again as compared with example 2, and the preparation steps were as follows:
step one, placing a G.652 optical fiber with the length of 15cm into a pressure tank at room temperature, and carrying out hydrogen loading for 7 days under the hydrogen pressure of 14bar to improve the photosensitivity of the optical fiber;
and step two, writing I-type seed fiber gratings on the optical fiber by using a 248 or 193nm excimer laser phase mask method (parameter setting: repetition frequency 30Hz, single pulse energy 15mJ, total pulse 10000 times, and grating region length 15 mm). The central wavelength of the seed grating for writing is 1547.8nm, the 3dB bandwidth is 0.26nm, and the reflectivity is up to 90%.
And step three, putting the inscribed seed grating into a high-temperature tube furnace filled with argon, raising the temperature from room temperature to 600 ℃ at the temperature rise rate of 30 ℃/min for pre-annealing, and naturally cooling in the tube furnace after the pre-annealing is finished.
Step four, putting the seed grating into a high-temperature tube furnace, heating the seed grating from room temperature to 900 ℃ at a heating rate of 60 ℃/min, heating the seed grating from 900 ℃ to 1000 ℃ at a heating rate of 7 ℃/min, preserving the temperature at 1000 ℃ for 120 minutes, taking the regenerated fiber grating out of the tube furnace immediately after the heat preservation is finished, putting the regenerated fiber grating into ice water for rapid cooling, and measuring the central wavelength of the regenerated fiber grating to be 1548.8nm, the 3dB bandwidth to be 0.23nm, the temperature sensitivity to be 13.44 pm/DEG C and the reflectivity to be 72%; and then testing the mechanical property of the regenerated fiber grating by a high-temperature fiber tensile tester, wherein the median value of the breaking strength of the regenerated fiber grating is 87dN and the mechanical property is good when the environment temperature of the regenerated fiber grating is 25 ℃ and the tensile speed is 3 mm/min.
The working principle and the process of the invention are as follows: when the temperature sensor is placed at a temperature measuring position, the tail fiber 9 is connected to the transmission fiber, and when the temperature sensor is used, the light source emits light waves, and preferably a wide-spectrum light source with enough power is selected to ensure that a reflected signal has a good signal-to-noise ratio; the light wave enters the regenerated fiber grating 3 and then reflects back to the optical signal with the specific central wavelength, when the environmental temperature changes, the period and the refractive index of the regenerated fiber grating 3 change, so that the central wavelength of the reflected optical signal correspondingly changes, the reflected optical signal is transmitted to a wavelength discriminator or a wavelength analyzer through a 3dB optical fiber directional coupler, then photoelectric conversion is carried out through an optical detector, and finally, after analysis is carried out through a connected computer, the environmental temperature information around the fiber grating temperature sensor can be obtained.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (10)
1. A high temperature fiber bragg grating temperature sensor, characterized by: the device comprises a threaded cylinder (1), a metal steel pipe (2), a regenerated fiber grating (3), silica fume (4), a corundum ceramic cake (5), a single-mode fiber (6) and a threaded cap (8); the corundum ceramic cake (5) is a cylinder with a cavity inside, the threaded cylinder (1) is fixedly arranged on the circumferential wall of the corundum ceramic cake (5), threads are arranged at two ends of the metal steel pipe (2), one end of the metal steel pipe is sealed, the other end of the metal steel pipe is open, one end of the seal is in threaded connection with the threaded cylinder (1), and one end of the seal penetrates out of the center of the corundum ceramic cake (5) and is in threaded connection with the threaded cap (8); the roof of the screw cap (8) is provided with a through hole; one end of the single-mode fiber (6) is fixedly connected with the inner end face of the sealing end of the metal steel pipe (2), the other end of the single-mode fiber extends out of the through hole of the threaded cap (8), and the middle section of the single-mode fiber (6) in the metal steel pipe (2) is provided with a regenerated fiber grating (3); an ash injection hole is formed above the corundum ceramic cake (5), and the ash injection hole is used for injecting silica fume (4) into the inner cavity of the corundum ceramic cake (5).
2. A high temperature fiber bragg grating temperature sensor according to claim 1, wherein: the center of the metal steel pipe (2) is provided with a V-shaped structural groove, and the regenerated fiber bragg grating (3) and the single-mode fiber (6) are located in the V-shaped structural groove.
3. A high temperature fiber bragg grating temperature sensor according to claim 1, wherein: the single-mode optical fiber (6) extending from the threaded cap (8) is provided with a tail fiber (9).
4. A high temperature fiber bragg grating temperature sensor according to claim 1, wherein: the threaded cylinder (1) is hermetically connected with the metal steel pipe (2), the metal steel pipe (2) is hermetically connected with the threaded cap (8), and the metal steel pipe (2) is hermetically connected with the corundum ceramic cake (5).
5. A method for manufacturing a high-temperature optical fiber Bragg grating temperature sensor is characterized by comprising the following steps: the coating layer of the single-mode optical fiber (6) is completely stripped, the single-mode optical fiber (6) is clamped by the metal steel pipe (2) with the V-shaped groove structure in a vacuum state, and one end of the single-mode optical fiber (6) is fixed on the inner end face of the sealing end of the metal steel pipe (2) through high-temperature glue; the sealing end of the metal steel pipe (2) is screwed into a threaded cylinder (1) welded on the circumferential wall of the corundum ceramic cake (5), the other end is an open end, the corundum ceramic cake (5) extends out of the open end, and the sealing end is tightly clamped by a threaded cap (8) with a through hole; and the other end of the single-mode optical fiber (6) extends out of the through hole of the threaded cap (8), the through hole is sealed by high-temperature glue, the corundum ceramic cake (5) and the outer surface of a contact region of the metal steel pipe (2) are sealed by a sealing ring (7) and the high-temperature glue, finally, silica fume (4) is injected into a fume injection hole formed above the corundum ceramic cake (5), and after the cavity of the corundum ceramic cake (5) is filled with the silica fume (4), an iron sheet and the high-temperature glue are used for sealing to obtain the temperature sensor as claimed in any of claims 2 to 4.
6. The method of claim 5, wherein the method comprises: the preparation method of the regenerated fiber grating (3) comprises the following steps:
putting a common single-mode optical fiber (6) into a pressure tank at room temperature, and downloading hydrogen under the pressure of 10-14bar for 4-7 days;
using 248 or 193nm excimer laser to write I-type fiber grating on the single mode fiber (6) which is processed by hydrogen loading by phase mask method;
placing the I-type fiber grating which is well inscribed into a tubular furnace filled with argon, raising the temperature from room temperature to 600-800 ℃ at the temperature rise rate of 10-30 ℃/min for pre-annealing, and naturally cooling the fiber grating to room temperature in the tubular furnace after the pre-annealing is finished to obtain a seed grating which is annealed at high temperature for the first time;
and (3) putting the seed grating subjected to the first high-temperature annealing into a tubular furnace filled with argon, heating the seed grating from room temperature to 900 ℃ at the heating rate of 40-60 ℃/min, heating the seed grating from 900 ℃ to 1000 ℃ at the heating rate of 3-7 ℃/min, preserving the temperature at 1000 ℃ for 80-120 minutes, generating a stable regenerated fiber grating in the heat preservation process, taking the seed grating out of the tubular furnace after the heat preservation is finished, putting the seed grating into ice water, and quickly cooling to obtain the regenerated fiber grating.
7. The method of claim 5, wherein the method comprises: the corundum ceramic cake (5) is made to pass through AL-SIO2The preparation method comprises the following steps: mixing Al metal and SiO2After the powder is uniformly mixed, reacting under the condition of argon at the temperature of 1500 ℃ for 2-4 h to prepare alumina ceramic, forming by a mechanical press method to obtain a corundum ceramic cake (5), and finally arranging an ash injection hole with the diameter of 1cm above the corundum ceramic cake (5).
8. The method of claim 5, wherein the method comprises: the single-mode optical fiber (6) is a G.652 optical fiber with the length of 12-18cm, a coating layer is stripped, and a 50-micrometer thin gold film is plated by using a chemical vapor deposition method after grid etching; the single-mode fiber (6) is clamped in the V-shaped groove, the stress of the grid region is relieved, the single-mode fiber (6) can keep alignment by the V-shaped groove structure, and a tail fiber (9) is reserved on the single-mode fiber (6) extending out of the threaded cap (8).
9. The method of claim 5, wherein the method comprises: the sealing ring (7) is directly formed by pressing a flexible graphite material in a metal die, has an inner diameter of 2-4cm and a thickness of 0.5-1mm in a relaxed state, and fully expands at 1000 ℃.
10. The method of claim 5, wherein the method comprises: the high-temperature adhesive is a semi-fluid HBC-1096 high-temperature sealant without silicon element.
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