CN212483825U - Optical fiber magnetic field and temperature sensing probe based on double F-P structure - Google Patents
Optical fiber magnetic field and temperature sensing probe based on double F-P structure Download PDFInfo
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- CN212483825U CN212483825U CN202021031887.8U CN202021031887U CN212483825U CN 212483825 U CN212483825 U CN 212483825U CN 202021031887 U CN202021031887 U CN 202021031887U CN 212483825 U CN212483825 U CN 212483825U
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Abstract
The invention relates to an optical fiber magnetic field and temperature sensing probe based on a double F-P structure. The optical fiber ring resonator comprises a laser light source (1), an optical fiber circulator (2), a sensing probe (3) and a signal processing module (4), wherein the sensing probe (3) comprises a cladding (3-1), a first fiber core (3-2), a second fiber core (3-3), a first notch groove (3-4), a second notch groove (3-5) and a reflecting membrane (3-6), the first notch groove (3-4) is filled with a magnetic fluid, the second notch groove (3-5) is filled with glycerol, and the reflecting membrane and the end faces of the two notch grooves form a double Fabry-Perot resonant cavity. By utilizing the magnetic field sensitivity characteristic of the magnetic fluid and the temperature sensitivity characteristic of the glycerin, the refractive indexes of the magnetic fluid and the glycerin are changed due to the change of the magnetic field and the temperature, so that the equivalent cavity length of the F-P cavity is changed, the phase difference between two coherent lights is finally changed, and the double-parameter measurement of the temperature and the magnetic field can be realized by detecting the change of interference signals.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to an optical fiber magnetic field and temperature sensing probe based on a double F-P structure.
Background
Magnetic fields or information related to magnetic fields exist in nature, human social life and other places, magnetic sensors are devices capable of converting various magnetic fields and variable quantities thereof into electric signals to be output, and therefore, the magnetic sensors are widely used for tasks of detecting, collecting, storing, converting and monitoring various magnetic fields and various information carried in the magnetic fields, and in recent years, with the rapid development of informatization, industrialization, transportation, electronic technology and the like, the magnetic sensors are more developed and applied. With the lower price and more varieties of optical fiber devices, the optical fiber communication technology is more and more mature, and the development of the optical fiber communication technology at the end of the seventies of the twentieth century is different from the traditional sensor technology, namely the optical fiber sensing technology. The novel sensor is formed by combining a magnetic field sensing technology and an optical fiber sensing technology, namely, the optical fiber magnetic field sensor inherits the advantages of the magnetic field sensing technology and the optical fiber magnetic field sensor, has the outstanding advantages of small size, corrosion resistance, strong anti-electromagnetic interference capability, convenience for distributed multipoint detection, all-optical transmission and the like, and becomes a research hotspot in the field of magnetic field sensing. There are many types of magnetic field sensors based on optical fibers, such as a magnetic field sensor based on a fiber grating structure, a magnetic field sensor based on an F-P interference structure, a magnetic field sensor based on an evanescent wave mechanism, and a magnetic field sensor based on surface plasmon resonance, and the like, and can be applied to different magnetic occasions according to different sensing performances.
The fiber Fabry-Perot sensor is designed based on an F-P interferometer. Since the optical fiber F-P sensor is not sensitive to external factors such as magnetic field, temperature and the like, the measurement of the parameter to be measured is realized by filling sensitive materials, packaging by using the sensitive materials or indirectly utilizing a mechanical mechanism, thereby realizing the corresponding sensor. The sensing principle of the fiber F-P sensor can be realized by two ways: firstly, the refractive index of a medium in a fixed cavity is unchanged, the length of a geometric cavity is changed, such as strain, temperature and the like, so that the length of the F-P resonant cavity is increased or decreased, the period of an output reflection spectrum is changed, the purpose of detecting a measured object can be achieved by demodulating the period variation of an output interference spectrum, and the output spectrum of the measured object is detected by using the change of the length of the geometric cavity; secondly, the length of the geometric cavity is fixed and the refractive index of the medium in the cavity is changed, if the liquid sensitive material with controllable refractive index is filled in the resonant cavity of the optical fiber F-P, the change of the equivalent cavity length of the F-P cavity is brought by the change of the refractive index of the liquid when the external measured variables such as temperature, magnetic field and the like are sensed, so that the output interference spectrum of the optical fiber F-P sensor generates corresponding wavelength drift, and the purpose of measurement is achieved by detecting the spectrum drift.
In the production application and life of the prior art, most optical sensors adopt a single-core standard optical fiber, the optical fiber sensor manufactured by using the optical fiber sensor as a basic element can only measure a single variable generally, and a cross sensitivity problem exists in the measurement of double parameters, so that the performance of the optical fiber sensor is greatly limited in application. The double-core optical fiber is light containing two fiber cores in the same cladding, each fiber core is an optical waveguide, namely two single-core optical fibers are integrated in one double-core optical fiber, and the precision of the sensor is greatly improved.
Disclosure of Invention
Aiming at the problems, the invention provides a design scheme of an optical fiber magnetic field and a temperature sensing probe based on a double F-P structure, the double parameter measurement of the temperature magnetic field is realized by fixing the geometric cavity length of an F-P resonant cavity to be constant and changing the refractive index of a sensitive medium in the cavity, because the magnetic field and the temperature can change the refractive index of a magnetic fluid, glycerol liquid is only modulated by the temperature, and the change of the external magnetic field hardly influences the refractive index of the glycerol, the sensing probe can realize the simultaneous measurement of the double parameters of the magnetic field and the temperature, has the temperature compensation capability and improves the precision of the magnetic field measurement.
In order to achieve the purpose, the invention adopts the following technical scheme:
as shown in fig. 1, a fiber magnetic field and temperature sensing probe based on a double F-P structure comprises a laser light source (1), a fiber circulator (2), a sensing probe (3), and a signal processing module (4), wherein the sensing probe (3) comprises a cladding (3-1), a first fiber core (3-2), a second fiber core (3-3), a first notch (3-4), a second notch (3-5), and a reflective membrane (3-6), and is characterized in that: the sensing probe (3) adopts an axisymmetric non-coaxial double-core optical fiber, the diameter of a cladding (3-1) of the sensing probe is 125 mu m, the diameter of a first fiber core (3-2) is 8 mu m, the diameter of a second fiber core (3-3) is 8 mu m, and the distance between the two fiber cores is 62.5 mu m; the first notch groove (3-3) and the second notch groove (3-4) are identical in size and are obtained by etching the end face of the double-core optical fiber through femtosecond laser, the length of the first notch groove (3-4) is 30 micrometers, the width of the first notch groove (3-3) is 30 micrometers, the depth of the second notch groove (3-5) is 20 micrometers, the first notch groove (3-4) is filled with magnetic fluid, the second notch groove (3-5) is filled with glycerol, the filling mode adopts a syringe pressurization method, the reflection diaphragm (3-6) is formed by plating aluminum on a polypropylene film through a vacuum evaporation method, the thickness of the diaphragm is 3 micrometers, the reflection diaphragm and the end face of the first notch groove (3-4) form a first F-P cavity for measuring a magnetic field, and the reflection diaphragm and the end face of the second notch groove (3-5) form a second F-P cavity for measuring temperature and compensating the magnetic field measurement.
The magnetic fluid filled in the first notch groove (3-4) is a water-based magnetic fluid and is made of Fe3O4The nano particles are magnetic particles, and linoleic acid is used as a surfactant.
As shown in fig. 2, the sensing probe is based on an axisymmetric non-coaxial dual-core optical fiber, the diameters of two fiber cores are the same, two identical grooves are etched on the right end face of the dual-core optical fiber through femtosecond laser, magnetofluid and glycerol are respectively filled in a first notch groove and a second notch groove through an injector pressurization method, then, a reflection diaphragm is used for packaging, the reflection diaphragm and the two notch groove end faces form a double fabry-perot resonant cavity, an F-P cavity filled with the magnetofluid can realize measurement of a magnetic field by using the adjustable refractive index characteristic of the magnetofluid, an F-P cavity filled with the glycerol can realize measurement of temperature by using the temperature sensitive characteristic of the glycerol, and temperature compensation is carried out on the measurement of the magnetic.
The sensing probe is based on the interference characteristic of an F-P structure, and when interference occurs, the phase difference of adjacent coherent light is
Comprises the following steps:
in the formula, lambda is the wavelength of incident light, n is the refractive index of a medium between two reflecting surfaces, d is the length of an F-P cavity, and delta is the optical path difference of adjacent light beams.
When the cavity length d and the incident light wavelength lambda are constant, the refractive index n and the phase difference of the medium between the two reflecting surfaces
There is a relationship:
when the cavity length d and the incident light wavelength lambda are fixed, k is a constant, when the refractive index of the medium is changed, the phase difference can be changed, so that the interference spectrum drift is caused, and the measured change is calculated by detecting the change of the spectrum.
When the temperature and the magnetic field act together, the interference spectrum generated by the first fiber core responds to the external magnetic field change and the temperature change. The change of the magnetic field causes the change of the refractive index of the magnetic fluid, thereby bringing about the change of the phase difference and causing the drift of the interference spectrum. Meanwhile, the change of the temperature can also influence the change of the refractive index of the magnetic fluid, and the interference spectrum drift can also be caused. However, the interference peak generated in the second fiber core does not respond to the external magnetic field change and only responds to the temperature change. The temperature change causes the refractive index of the glycerol to change, further causes the phase difference between the second reflected light and the second incident light to change, and finally causes the interference spectrum generated by the second reflected light and the second incident light to shift. Therefore, the temperature change can be calculated by detecting the drift of the interference spectrum generated in the second optical fiber, and the temperature compensation is further carried out on the interference spectrum generated by the first optical fiber, so that the influence of the temperature on the magnetic field measurement is reduced.
Drawings
FIG. 1 is a schematic structural diagram of a fiber magnetic field and temperature sensing probe based on a double F-P structure according to the present invention;
FIG. 2 is a cross-sectional view of a fiber optic magnetic field and temperature sensing probe based on a dual F-P structure according to the present invention;
fig. 3 is a schematic diagram of a first signal detection optical path of a fiber magnetic field and temperature sensing probe based on a double F-P structure according to the present invention.
Detailed Description
The following will further describe the embodiment of the present invention with reference to fig. 1.
The invention relates to an optical fiber magnetic field and temperature sensing probe based on a double F-P structure, which can detect a magnetic field, and comprises the following specific implementation steps:
the method comprises the following steps: optical fiber end face pretreatment
Selecting a double-core optical fiber with proper length, scraping a coating layer at one end of the double-core optical fiber by using a wire stripper, then cutting the end face of the coating layer by using an optical fiber cutting machine to be flat, and then cleaning the optical fiber by using an ultrasonic cleaning machine.
Step two: grooving the upper end face of the double-core optical fiber
The end face of the fiber is observed to be flat under an electron microscope and then is fixed on an optical fiber clamp, the fact that the fiber is horizontally placed on a three-dimensional platform is guaranteed, a femtosecond laser is kept to be still, the three-dimensional platform is adjusted to enable the femtosecond laser to be focused on the center of a first fiber core on the end face of a cut-flat optical fiber through an optical lens, the position of an x-y two-dimensional micro-motion platform is adjusted step by step from the contact of a focal point to the optical fiber, the focal spot of the femtosecond laser is enabled to make relative displacement, and the width and. When the laser finishes scanning and etching one layer in the two-dimensional platform, the objective lens correspondingly descends 10 micrometers in the z-axis direction, enters a second layer for scanning, the first grooving process with the depth of 20 micrometers can be realized by scanning for 2 times totally, then the femtosecond laser is focused on the right center of a second fiber core on the end face of the optical fiber through the optical lens, and the steps are repeated to finish the second groove etching.
Step three: cleaning with hydrofluoric acid
In the laser working process, fine scraps of the optical fiber are splashed out and adhered to the cavity and the optical fiber, so that the end face of the cavity is damaged, the reflectivity is influenced, and the intensity of the interference spectrum and the accuracy of the contrast are also influenced. Most of the fine scraps adhered to the end face of the cavity and the surface of the optical fiber are removed by using an ultrasonic cleaning device, then the etching is carried out by using hydrofluoric acid with the concentration of 5%, and the etching time is controlled for 30 seconds, so that the few fine scraps remained on the surface of the cavity can be removed, and the unevenness of the groove can be modified.
Step three: filling glycerin and magnetic fluid into the first notch groove and the second notch groove respectively
The double-core optical fiber is vertically placed, and the end face of the notch groove faces upwards. Under an optical microscope, an injector is inserted into any one of the notches, magnetic fluid is poured into the injector, the magnetic fluid is injected into the injector by pressurizing the injector to obtain a first notch (3-4) after pouring, then one injector is inserted into the other notch, glycerin is poured into the injector, and the glycerin is injected into the injector by pressurizing the injector to obtain a second notch (3-5) after pouring. During the filling process, the filling process cannot be carried out too fast, and the sensing effect is prevented from being influenced by the fact that air bubbles enter due to too fast extrusion.
Step four: the grooved end face of the double-core optical fiber is packaged by a polypropylene membrane plated with metal aluminum
The film covering the F-P cavity is made of an aluminum-plated polypropylene film, a proper amount of polypropylene is stretched into a cake-shaped film with the diameter of 1mm by a precision instrument, and the surface of the film needs to be subjected to corona treatment before evaporation so as to have good adhesiveness. During vapor deposition, the film roll is placed in a vacuum chamber, the evaporation boat is heated to 1300-1400 ℃ in a vacuum state, and then high-purity aluminum wires are continuously fed onto the evaporation boat. Adjusting the unwinding speed, the winding speed, the wire feeding speed and the evaporation capacity, opening a cooling source to continuously melt and evaporate the aluminum wire on an evaporation boat, so that a metal aluminum film with the thickness of 1 mu m is formed on the surface of a moving film after cooling, vertically placing one end of an engraved groove of the double-core optical fiber upwards, coating an unetched area on the end surface of the optical fiber by using epoxy resin glue, finally placing an aluminized polypropylene film right above the double-core optical fiber, controlling the double-core optical fiber to slowly move upwards until the film is tightly pressed, and cutting the film after the glue is solidified.
As shown in fig. 3, a schematic diagram of a first signal detection optical path is that light emitted by a laser light source (1) is transmitted to a first reflection surface of the F-P sensing probe (3) through an optical fiber circulator (2) to be partially reflected, another part of the light is continuously transmitted to a second reflection surface of the F-P cavity sensor to be partially reflected, two beams of reflected light interfere at the optical fiber circulator, and an output signal is received and processed by a signal processing module (4). The components required for the second signal detection path are as described above.
The basic principle of the invention is as follows: the reflecting membrane and the two grooved end faces form a double Fabry-Perot resonant cavity, and the groove depth of the grooves is the cavity length of the F-P cavity. Modulated light emitted by a laser light source enters an optical fiber through a coupler, enters a Fabry-Perot cavity, returns along the original path after being reflected by an optical fiber end face and a reflecting film in the Fabry-Perot cavity, meets the optical fiber end face and the reflecting film to generate interference, is received by a photoelectric detector, changes the refractive indexes of glycerin and the magnetic fluid by the change of magnetic field and temperature by utilizing the magnetic field sensitivity characteristic of the magnetic fluid and the temperature sensitivity characteristic of the glycerin, so that the equivalent cavity length of an F-P cavity is changed, the change of phase difference between two coherent light is finally caused, and the change of the magnetic field and the temperature can be calculated by detecting the change of interference signals.
Claims (2)
1. The utility model provides an optic fibre magnetic field and temperature sensing probe based on two F-P structures, includes laser source (1), optic fibre circulator (2), sensing probe (3), signal processing module (4), sensing probe (3) including cladding (3-1), first fibre core (3-2), second fibre core (3-3), first notch (3-4), second notch (3-5), reflective membrane piece (3-6), its characterized in that: the sensing probe (3) adopts an axisymmetric non-coaxial double-core optical fiber, the diameter of a double-core optical fiber cladding (3-1) is 125 mu m, the diameter of a first fiber core (3-2) is 8 mu m, the diameter of a second fiber core (3-3) is 8 mu m, the distance between the two fiber cores is 62.5 mu m, the first notch groove (3-4) and the second notch groove (3-5) have the same size, the sensing probe is obtained by etching the end face of the double-core optical fiber through femtosecond laser, the length is 30 mu m, the width is 30 mu m, the depth is 20 mu m, the first notch groove (3-4) is filled with magnetic fluid, the second notch groove (3-5) is filled with glycerol, the filling mode adopts an injector metal plating pressurization method, the reflecting membrane (3-6) is made of aluminum on a polypropylene film by using a vacuum evaporation method, the thickness is 3 mu m, and the reflecting membrane and the end faces of the two notch grooves form a double Fabry-Perot resonant cavity, the F-P cavity filled with the magnetic fluid can realize the measurement of a magnetic field by utilizing the adjustable refractive index characteristic of the magnetic fluid, and the F-P cavity filled with the glycerin can realize the measurement of temperature by utilizing the temperature sensitive characteristic of the glycerin and carry out temperature compensation on the measurement of the magnetic field.
2. The fiber optic magnetic field and temperature sensing probe based on the double F-P structure of claim 1, wherein: the magnetic fluid filled in the first notch grooves (3-4) is a water-based magnetic fluid and is made of Fe3O4The nano particles are magnetic particles, and linoleic acid is used as a surfactant.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114089232A (en) * | 2021-11-25 | 2022-02-25 | 西安电子科技大学 | Magnetic field sensor and magnetic field measuring method |
| CN114136486A (en) * | 2021-11-30 | 2022-03-04 | 哈尔滨理工大学 | Magnetic field and temperature sensor based on FP cascade FBG structure |
| CN114137450A (en) * | 2021-11-30 | 2022-03-04 | 哈尔滨理工大学 | Magnetofluid-filled fiber optic magnetic field and displacement sensor |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114089232A (en) * | 2021-11-25 | 2022-02-25 | 西安电子科技大学 | Magnetic field sensor and magnetic field measuring method |
| CN114089232B (en) * | 2021-11-25 | 2022-08-09 | 西安电子科技大学 | Magnetic field sensor and magnetic field measuring method |
| CN114136486A (en) * | 2021-11-30 | 2022-03-04 | 哈尔滨理工大学 | Magnetic field and temperature sensor based on FP cascade FBG structure |
| CN114137450A (en) * | 2021-11-30 | 2022-03-04 | 哈尔滨理工大学 | Magnetofluid-filled fiber optic magnetic field and displacement sensor |
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