CN117367512B - Sensitivity measuring method of temperature and pressure optical fiber sensor - Google Patents
Sensitivity measuring method of temperature and pressure optical fiber sensor Download PDFInfo
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Abstract
The invention discloses a novel temperature and pressure optical fiber sensor based on MZ interference and F-P interference, a preparation method thereof and a sensitivity measurement method, belonging to the technical field of optical fiber sensors, comprising the following steps: an interconnected MZ interference structure for measuring temperature and an F-P interference structure for measuring pressure; the MZ interference structure comprises a tapering peanut mixed optical fiber structure, and the tapering peanut mixed optical fiber structure comprises a peanut optical fiber structure and a tapering optical fiber structure which are mutually welded together; the F-P interference structure comprises an optical fiber Bragg grating structure, the optical fiber Bragg grating structure is welded at the hollow joint end of the peanut optical fiber structure in the tapering peanut mixed optical fiber structure, the sensor does not interfere with the measurement of temperature and pressure, and the high-precision measurement of the temperature and the pressure is creatively realized at the same time.
Description
Technical Field
The invention relates to a sensitivity measuring method of a temperature and pressure optical fiber sensor, in particular to a temperature and pressure optical fiber sensor based on MZ interference and F-P interference, a preparation method thereof and a sensitivity measuring method thereof, and belongs to the technical field of optical fiber sensors.
Background
Optical fiber technology has received increasing attention over the past decades due to its unique operating mechanisms and wide range of applications, which reduce transmission losses and are immune to electromagnetic interference, which makes their applicability broader. The optical fiber is light, sensitive, resistant to strong electromagnetic interference, resistant to high temperature, small in signal attenuation and the like, and is widely applied to the sensing field. The optical fiber is used for sensing, can be networked, is easy to realize intellectualization, integrates information transmission and sensing, and can effectively solve the measurement problem that the conventional detection technology is difficult to fully competence.
The basic principle of the optical fiber sensing system is that optical wave parameters such as light intensity, frequency, wavelength, phase and polarization state in the optical fiber change along with the change of external measured parameters, and the purpose of detecting external measured physical quantity is achieved by detecting the change of the optical wave parameters in the optical fiber.
Temperature and pressure are two very important physical parameters for materials, and are widely applied to material health monitoring, medical detection, industrial production and normal operation of large-scale flight devices, and more researches on temperature and pressure sensors are also carried out. The traditional sensor only measures a single parameter, however, the change of the single parameter can not be controlled in the actual environment like a laboratory, and the development of the sensor for simultaneously measuring the temperature and the pressure is particularly important to adapt to the complex parameter change condition in the actual environment.
Disclosure of Invention
The invention provides a temperature-pressure optical fiber sensor based on MZ interference and F-P interference, a preparation method thereof and a sensitivity measuring method, wherein a hybrid structure combining MZ interference and F-P interference is formed by combining a cone pulling structure, a peanut structure and an optical fiber Bragg grating, the temperature and pressure applied by the outside are changed by utilizing the principle that the cone pulling structure and the peanut structure are sensitive to the temperature and the Bragg grating is sensitive to the outside, so that displacement of interference spectral lines is caused, the displacement is respectively used for measuring the temperature and the pressure, and the high-precision measurement of the temperature and the pressure is creatively realized by the hybrid structure interferometer obtained by the method.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme.
In a first aspect, the present invention provides a temperature and pressure fiber optic sensor based on MZ interference and F-P interference, comprising: an interconnected MZ interference structure for measuring temperature and an F-P interference structure for measuring pressure;
The MZ interference structure comprises a tapering peanut mixed optical fiber structure, and the tapering peanut mixed optical fiber structure comprises a peanut optical fiber structure and a tapering optical fiber structure which are mutually welded together;
the F-P interference structure comprises an optical fiber Bragg grating structure, and the optical fiber Bragg grating structure is welded at the hollow connection end of the peanut optical fiber structure in the tapering peanut mixed optical fiber structure.
Optionally, the tapering optical fiber structure includes a section of single mode fiber with a middle end fused into a biconic, the peanut optical fiber structure includes two sections of single mode fiber with a microsphere structure at a single end, and the microsphere structures of the two sections of single mode fiber are fused together.
Optionally, the fiber bragg grating structure comprises a length of grating fiber having a laser interference fringe written into its core for producing a periodic variation in refractive index in its core along its core axis.
Optionally, the bragg equation of the F-P interference structure is: lambda B＝2neff Λ, wherein lambda B is the center wavelength, lambda B＝1550nm,neff represents the refractive index of the core mode, and lambda represents the grid period;
The calculation formulas of the interference intensity I and the phase difference phi m of the MZ interference structure are as follows:
Wherein I 1 and I 2 are the light intensities of the core mode and the cladding mode in the MZ interference structure, respectively, phi m is the phase difference of the core mode and the cladding mode, Is the effective refractive index RI difference between the core mode and the mth cladding mode, G is the interference length of the MZ interference structure, and λ is the input wavelength;
the free spectral range FSR of the MZ interference structure has the following calculation formula:
When the phase difference Φ m is equal to (2m+1) pi, m=1, 2,3 …, the transmittance reaches the valley at this wavelength, and the calculation formula of the center wavelength λ m of the mth-order interference valley is:
in a second aspect, the invention provides a method for preparing a temperature and pressure optical fiber sensor based on MZ interference and F-P interference, comprising the following steps:
Preparing a tapered optical fiber structure, a peanut optical fiber structure and an optical fiber Bragg grating respectively;
welding the single-mode fiber SMF part of the tapered fiber structure and the single-mode fiber SMF part of the peanut fiber structure together to obtain the MZ interference structure;
and welding the SMF part of the peanut optical fiber structure empty joint end of the MZ interference structure with the SMF part of the fiber Bragg grating to obtain the sensor.
Optionally, the preparing the tapered optical fiber structure includes: and (3) putting a section of the SMF with the coating removed into a fusion splicer, and discharging the SMF for a plurality of times by adopting an arc with the power of 80bit and the discharge time of 2000ms to obtain the tapered optical fiber structure.
Optionally, the preparing the peanut fiber structure includes:
Putting a section of SMF into a fusion splicer, and adopting an electric arc with power of +80bit, discharge time of 2000ms and 25 mu m deviated from the end face of the SMF to discharge the end face to form a microsphere cavity, so as to obtain a single-mode optical fiber with a microsphere structure;
and carrying out discharge welding on the microspheres of the two sections of single-mode optical fibers with the microsphere structures by adopting an electric arc with standard discharge power and discharge time of 1000ms to obtain the peanut optical fiber structure.
Optionally, the preparing a fiber bragg grating includes:
and placing a section of photosensitive optical fiber close to a section of grating mask capable of inhibiting zero-order diffraction and maximizing first-order diffraction, and orthographically injecting ultraviolet light into the photosensitive optical fiber through the grating mask, wherein interference fringes generated by near-field diffraction of a phase grating mask are utilized to form a periodically disturbed refractive index in the optical fiber, so as to obtain the fiber Bragg grating.
In a third aspect, the present invention provides a method for measuring sensitivity of a temperature and pressure optical fiber sensor based on MZ interference and F-P interference, including:
Constructing a test environment for simultaneously measuring pressure and temperature by using the sensor by utilizing a broadband light source BBS and a spectrum analyzer OSA;
Under the condition of simultaneously controlling two variables of pressure and temperature, an optical signal emitted by the broadband light source BBS is injected into an empty terminal of the F-P interference structure of the sensor, and the optical signal is transmitted by the F-P interference structure and the MZ interference structure to obtain a reflected light wave and a transmitted light wave;
transmitting the reflected light wave and the transmitted light wave to the spectrum analyzer OSA to obtain an F-P reflection spectrum and an MZ transmission spectrum;
And obtaining the pressure sensitivity and the temperature sensitivity of the sensor based on the change conditions of the F-P reflection spectrum characteristic and the MZ transmission spectrum characteristic along with the pressure and temperature changes.
Optionally, the changes of the F-P reflection spectrum characteristic and the MZ transmission spectrum characteristic with the pressure and the temperature include:
When the temperature is constant, the relation between the central wavelength drift quantity delta lambda B of the reflected wave of the F-P interference structure and the axial strain quantity epsilon 1 of the fiber Bragg grating is as follows:
ΔλB＝λB(1-Pε)ε1＝Kεε1，
Wherein, P ε is the effective elasto-optical coefficient of the fiber Bragg grating, K ε is the strain coefficient pm/mu epsilon of the fiber Bragg grating, K ε＝1.18pm/με,λB is the central wavelength, lambda B =1550 nm;
When the pressure is constant, the relation between the displacement delta lambda m of the trough of the transmission wave of the MZ interference structure and the applied temperature change epsilon 2 is as follows:
wherein lambda m is the center wavelength of the m-th order interference trough, Is the effective refractive index RI difference between the fiber core mode and the m cladding mode, T represents the temperature, deltaT represents the temperature variation, epsilon 2 is the variation rate of the effective refractive index RI difference between the fiber core and the m cladding mode along with the temperature T, epsilon 2＝dL2/L2,L2 represents the interaction length between the two tapered lumbar vertebrae.
Compared with the prior art, the invention has the beneficial effects that: the invention utilizes a Bragg grating structure, a cone pulling structure and a peanut structure to manufacture an MZ and F-P interference mixed structure, and can simultaneously realize high-precision measurement of temperature and pressure; in the field of temperature measurement, a cone pulling and peanut structure is commonly used for manufacturing a high-precision temperature sensor by utilizing a Mach-Zehnder interference principle, and the sensitivity reaches an extremely high level; in the field of pressure measurement, an F-P interference structure is formed by the fiber Bragg grating and is used for manufacturing a high-precision pressure sensor, the sensitivity reaches an extremely high level, and the fiber tapering structure can be obtained by discharging a single-mode fiber by using a commercial fusion splicer, so that the manufacturing is simple and easy; the peanut structure is formed by respectively manufacturing spherical structures on two single-mode fibers, and the balls are welded together, so that the peanut structure is simple and easy to manufacture; the fiber Bragg grating structure can be manufactured by a phase mask method, a photosensitive fiber is attached to the phase grating mask, and interference fringes generated by near field diffraction of the phase grating mask are utilized to form a periodically disturbed refractive index in the fiber, so that a fiber grating is formed, and the manufacturing process is very simple; the combination of the three can be realized by using single-mode fiber fusion, which is very simple and is beneficial to production and manufacture.
Drawings
FIG. 1 is a schematic illustration of a tapered structure according to an embodiment of the present invention;
FIG. 2 is a schematic drawing showing a tapering structure according to an embodiment of the present invention;
FIG. 3 is a schematic illustration of a single mode fiber with microsphere structures according to one embodiment of the present invention;
FIG. 4 is a schematic diagram of a single mode optical fiber with microsphere structures according to one embodiment of the present invention;
FIG. 5 is a schematic representation of the preparation of a peanut structure in accordance with one embodiment of the present invention;
FIG. 6 is a schematic view of a peanut structure according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of the fabrication of an MZ interference structure in accordance with one embodiment of the present invention;
FIG. 8 is a schematic diagram of an MZ interference structure in accordance with one embodiment of the present invention;
FIG. 9 is a schematic diagram of the preparation of a fiber Bragg grating in accordance with one embodiment of the present invention;
FIG. 10 is a schematic diagram of a fiber Bragg grating structure according to an embodiment of the present invention;
FIG. 11 is a schematic illustration of the preparation of a hybrid interference structure in an embodiment of the present invention;
FIG. 12 is a schematic diagram of a hybrid interference architecture in accordance with one embodiment of the present invention;
FIG. 13 is a schematic diagram of the propagation modes of light in a hybrid interference structure in accordance with an embodiment of the present invention;
FIG. 14 is a schematic view of an environmental setup for measuring temperature sensitivity in an embodiment of the invention;
figure 15 is a schematic view of an environmental setup for measuring pressure sensitivity in one embodiment of the invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.
In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first", "a second", etc. may explicitly or implicitly include one or more such feature. In the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art in a specific case.
Example 1
The embodiment provides a temperature and pressure optical fiber sensor based on MZ interference and F-P interference, which comprises: an interconnected MZ interference structure for measuring temperature and an F-P interference structure for measuring pressure; the MZ interference structure comprises a tapering peanut mixed optical fiber structure, and the tapering peanut mixed optical fiber structure comprises a peanut optical fiber structure and a tapering optical fiber structure which are mutually welded together; the F-P interference structure comprises an optical fiber Bragg grating structure, the optical fiber Bragg grating structure is welded at the hollow joint end of the peanut optical fiber structure in the tapering peanut mixed optical fiber structure, as shown in fig. 12, the left end is the optical fiber Bragg grating structure, the middle is the peanut structure, the right end is the tapering structure, and the MZ/F-P mixed interference is formed.
The principle that the cone pulling and peanut structures are sensitive to temperature is utilized, so that the displacement of an interference spectrum line is caused, the temperature can be measured, the laser can reflect when passing through the Bragg grating, the reflected light can interfere with the incident light by F-P, when the pressure is applied to the outside, the reflected light wavelength of the grating can change slightly, and accordingly certain influence is generated on the relevant interference characteristics, the Bragg grating has higher sensitivity to the outside pressure, the pressure can be measured through the principle, and the mixed interference structure is formed by combining the Bragg grating structure, the cone pulling structure and the peanut structure, so that the high-precision measurement of the temperature and the pressure is creatively realized.
Example 2
On the basis of embodiment 1, this embodiment also makes the following design.
As shown in fig. 13, when light passes through the fiber bragg grating from left to right, two beams of coherent light reflected by the grating interfere, and at the same time, two beams of coherent light are energy-coupled to form a reflected light wave with a specific wavelength, and a bragg equation of the F-P interference structure is obtained by a wavelength matching condition δβ=0, where: lambda B＝2neff Λ, where lambda B is the center wavelength, lambda B＝1550nm,neff represents the refractive index of the core mode,Delta is the phase difference of the forward propagating LP mode and the backward propagating LP mode, beta is the mode propagation constant,/>Λ is a constant representing the grid period.
The transmission light of the grating continues to propagate, the first excitation occurs at the peanut structure, part of the light of the core mode is excited to the cladding mode, the rest of the light continues to propagate along the fiber core, then the cladding mode and the light of the core mode are coupled at the tapering structure to form MZ interference, the MZ interference propagates to the spectrum analyzer OSA to obtain an MZ transmission spectrum and an F-P reflection spectrum, the arc arrow in FIG. 13 represents the working condition of the F-P mode, the straight arrow represents the working condition of the MZ mode, the temperature is measured through the transmission spectrum, and the formula of the related parameters of the transmission spectrum is as follows.
The calculation formulas of the interference intensity I and the phase difference phi m of the MZ interference structure are as follows:
Wherein I 1 and I 2 are the light intensities of the core mode and the cladding mode in the MZ interference structure, respectively, phi m is the phase difference of the core mode and the cladding mode, Is the effective refractive index RI difference between the core mode and the mth cladding mode, G is the interference length of the MZ interference structure, and λ is the input wavelength.
The free spectral range FSR of the MZ interference structure has the following calculation formula:
FSR increases with decreasing interference length G, and when the phase difference Φ m is equal to (2m+1) pi, m=1, 2,3, …, the transmittance reaches the valley at this wavelength, and the calculation formula of the center wavelength λ m of the mth-order interference trough is:
Example 3
The embodiment provides a preparation method of a temperature and pressure optical fiber sensor based on MZ interference and F-P interference, which comprises the following steps.
The materials are prepared by single mode fiber (SMF-28, corning) and multimode fiber (MMF, nineteen-core four-mode is used herein), and the equipment is prepared by a fiber fusion splicer (80S, fujikura), a spectrum analyzer (AQ 6370D, yokogawa, optical Spectrum Analyzer, OSA), a broadband light source (Benchtop Broadband Source, BBS), a fiber cutter (CKFC-1, commking), a micro-displacement platform, a fiber clamp and a microscope.
1. Manufacturing of tapered structure
As shown in fig. 1 and 2, in an optical fiber, the tapered structure can efficiently excite light in the core into the cladding. As shown in fig. 1, the manufacturing process of the structure is as follows: the first step, a section of SMF with the coating removed is fixed in an optical fiber fusion splicer; in a second step, in order to ensure that the middle end of the SMF melts to form the desired taper, the stripped SMF is discharged multiple times with an arc power of 80 bits and an arc discharge time of 2000ms to form a tapered structure.
2. Production of peanut structure
As shown in fig. 3 and 4, firstly, a section of single-mode fiber is put into an optical fiber fusion splicer, an arc with an arc power of +80bit and a discharge time of 2000ms is adopted to discharge the end face of the single-mode fiber, so as to form a microsphere cavity, in order to ensure that the end face of the fiber is fused into silicon microspheres, the arc deviates from the end face of the fiber by 25 μm, and the end face of the fiber can be accurately adjusted to the position of an electrode in a manual mode because the discharge position is positioned at the center of a display screen of the fusion splicer. The diameter of the amplified optical fiber is measured by a ruler, the diameter is measured to be 25 mu m by a proportional relation, and the optical fiber is vertically placed (vertically placed fusion splicer) in the discharging process, so that the center of the microsphere is ensured to be positioned on the axis of the optical fiber. As shown in fig. 3.
As shown in fig. 5 and 6, the above steps are repeated 2 times to obtain two sections of single-mode optical fibers with microsphere structures, and then the single-mode optical fibers are welded two by two. When the two microspheres are welded, a peanut structure can be obtained by adopting 1000ms discharge time and standard discharge power as shown in fig. 4.
3. MZ interference structure fabrication
After the peanut structure is manufactured, the SMF part of the tapering structure and the SMF part of the peanut structure are directly welded together by an optical fiber welding machine, and discharge is carried out to finish welding, as shown in fig. 7, so that a complete MZ interference structure is formed, as shown in fig. 8.
4. Manufacture of fiber Bragg grating structure
The main manufacturing method of the Bragg grating is a phase mask method, namely, the interference fringes generated by near field diffraction of the phase grating mask are utilized to form a periodically disturbed refractive index in the optical fiber. The key component phase mask plate of the manufacturing method is a phase diffraction element which is precisely etched under the control of a computer, as shown in fig. 9, zero-order fringes are restrained (3%) after normal incident ultraviolet light is diffracted by the mask plate, + -1-order fringes reach the maximum (35%) respectively, and interacted incoming interference fringes expose a doped fiber core which is clung to the back of the mask plate to form FBG (fiber Bragg grating) with the phase grating period being 1/2 of the phase template period, so that an F-P interference structure is formed, as shown in fig. 10, the phase template and the optical fiber are placed at a certain angle, and FBG with different periods and Bragg wavelengths can be manufactured.
5. Fabrication of hybrid interference structures
After the fiber bragg grating is manufactured, as shown in fig. 11 and 12, the SMF part of the fiber bragg grating and the SMF part of the peanut structure are automatically fused together by an optical fiber fusion splicer in the same manner as before, and then discharged to finish fusion.
Example 4
The embodiment provides a sensitivity measuring method of a temperature and pressure optical fiber sensor based on MZ interference and F-P interference, which respectively comprises the measurement of temperature sensitivity and the measurement of pressure sensitivity.
The device for measuring temperature is shown in fig. 14 below, light is emitted from the light source BBS and enters an adjustable temperature box in which a prepared hybrid interference structure is placed, the temperature in the box is from 20 ℃ to 100 ℃, and the transmission lines in the spectrum analyzer OSA are measured every 10 ℃ for about 10min, so that the temperature sensitivity of the hybrid interference structure is obtained.
When the pressure is constant and temperature change is applied to the Mach-Zehnder sensing part, the modal index and the length of the optical fiber are changed, so that the spectral trough is displaced, and the relation between the displacement delta lambda m of the trough of the transmission wave of the MZ interference structure and the applied temperature change rate epsilon 2 is as follows:
wherein lambda m is the center wavelength of the m-th order interference trough, Is the effective refractive index RI difference between the fiber core mode and the m cladding mode, T represents the temperature, deltaT represents the temperature variation, epsilon 2 is the variation rate of the effective refractive index RI difference between the fiber core and the m cladding mode along with the temperature T, epsilon 2＝dL2/L2,L2 represents the interaction length between the two tapered lumbar vertebrae.
As shown in fig. 15, for the purpose of measuring the pressure, the prepared mixed interference structure is pressed between two glass slides, a single mode fiber is placed in parallel beside the sensor as a reference substance, the sensor is ensured to be uniformly stressed, light is emitted from the light source BBS, one end of the light passes through the circulator and is connected into the mixed interference structure, the other end of the light passes through the spectrum analyzer OSA, weights are added on the glass slides by taking 50g as a step length, the movement condition of the spectral line on the spectrum analyzer is recorded, and the pressure sensitivity of the mixed interference structure is obtained.
When the temperature is constant and only the axial strain epsilon of the grating is considered, the relation between the central wavelength drift delta lambda B of the reflected wave of the F-P interference structure and the axial strain epsilon 1 of the fiber Bragg grating is as follows:
ΔλB＝λB(1-Pε)ε1＝Kεε1，
Wherein, P ε is the effective elasto-optical coefficient of the fiber bragg grating, K ε is the strain coefficient pm/με of the fiber bragg grating, K ε＝1.18pm/με,λB is the center wavelength, λ B =1550 nm.
The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above-described embodiments, which are merely illustrative and not restrictive, and many forms may be made by those having ordinary skill in the art without departing from the spirit of the present invention and the scope of the claims, which are all within the protection of the present invention.
Claims (8)
1. A sensitivity measuring method of a temperature and pressure optical fiber sensor is characterized in that,
The sensor comprises an MZ interference structure and an F-P interference structure which are connected with each other, wherein the MZ interference structure is used for measuring temperature, and the F-P interference structure is used for measuring pressure;
The sensitivity measurement method comprises the following steps:
Constructing a test environment for simultaneously measuring pressure and temperature by using the sensor by utilizing a broadband light source BBS and a spectrum analyzer OSA;
Under the condition of simultaneously controlling two variables of pressure and temperature, an optical signal emitted by the broadband light source BBS is injected into an empty terminal of the F-P interference structure of the sensor, and the optical signal is transmitted by the F-P interference structure and the MZ interference structure to obtain a reflected light wave and a transmitted light wave;
transmitting the reflected light wave and the transmitted light wave to the spectrum analyzer OSA to obtain an F-P reflection spectrum and an MZ transmission spectrum;
obtaining pressure sensitivity and temperature sensitivity of the sensor based on the change conditions of the F-P reflection spectrum characteristic and the MZ transmission spectrum characteristic along with the pressure and temperature changes;
The changes of the F-P reflection spectrum characteristic and the MZ transmission spectrum characteristic along with the pressure and temperature change comprise:
When the temperature is constant, the relation between the central wavelength drift quantity delta lambda B of the reflected wave of the F-P interference structure and the axial strain quantity epsilon 1 of the fiber Bragg grating is as follows:
ΔλB＝λB(1-Pε)ε1＝Kεε1，
Wherein, P ε is the effective elasto-optical coefficient of the fiber Bragg grating, K ε is the strain coefficient pm/mu epsilon of the fiber Bragg grating, K ε＝1.18pm/με,λB is the central wavelength, lambda B =1550 nm;
When the pressure is constant, the relation between the displacement delta lambda m of the trough of the transmission wave of the MZ interference structure and the applied temperature change rate epsilon 2 is as follows:
wherein lambda m is the center wavelength of the m-th order interference trough, Is the effective refractive index RI difference between the fiber core mode and the m cladding mode, T represents temperature, deltaT represents temperature variation, epsilon 2 is the variation rate of the effective refractive index RI difference between the fiber core and the m cladding mode along with the temperature T, epsilon 2＝dL2/L2,L2 represents the interaction length between the lumbar vertebrae of the two tapering structures;
The MZ interference structure comprises a tapering peanut mixed optical fiber structure, wherein the tapering peanut mixed optical fiber structure comprises a peanut optical fiber structure and a tapering optical fiber structure which are mutually welded together;
the F-P interference structure comprises an optical fiber Bragg grating structure, and the optical fiber Bragg grating structure is welded at the hollow connection end of the peanut optical fiber structure in the tapering peanut mixed optical fiber structure.
2. The method of claim 1, wherein the tapered fiber structure comprises a single-mode fiber with a middle end fused into a biconic, the peanut fiber structure comprises two single-mode fibers with microsphere structures at a single end, and the microsphere structures of the two single-mode fibers are fused together.
3. A method of measuring sensitivity of a temperature and pressure fiber optic sensor according to claim 1, wherein the fiber bragg grating structure comprises a length of grating fiber having laser interference fringes written therein for producing a periodic variation in refractive index in its core along its core axis.
4. The method for measuring sensitivity of a temperature and pressure optical fiber sensor according to claim 1, wherein the bragg equation of the F-P interference structure is: lambda B＝2neff Λ, wherein lambda B is the center wavelength, lambda B＝1550nm,neff represents the refractive index of the core mode, and lambda represents the grid period;
The calculation formulas of the interference intensity I and the phase difference phi m of the MZ interference structure are as follows:
Wherein I 1 and I 2 are the light intensities of the core mode and the cladding mode in the MZ interference structure, respectively, phi m is the phase difference of the core mode and the cladding mode, Is the effective refractive index RI difference between the core mode and the mth cladding mode, G is the interference length of the MZ interference structure, and λ is the input wavelength;
the free spectral range FSR of the MZ interference structure has the following calculation formula:
When the phase difference Φ m is equal to (2m+1) pi, m=1, 2,3 …, the transmittance reaches the valley at this wavelength, and the calculation formula of the center wavelength λ m of the mth-order interference valley is:
5. the method for measuring sensitivity of a temperature-pressure optical fiber sensor according to any one of claims 1 to 4, wherein the method for manufacturing the sensor comprises:
Preparing a tapered optical fiber structure, a peanut optical fiber structure and an optical fiber Bragg grating respectively;
welding the single-mode fiber SMF part of the tapered fiber structure and the single-mode fiber SMF part of the peanut fiber structure together to obtain the MZ interference structure;
and welding the SMF part of the peanut optical fiber structure empty joint end of the MZ interference structure with the SMF part of the fiber Bragg grating to obtain the sensor.
6. The method for measuring the sensitivity of a temperature and pressure optical fiber sensor according to claim 5, wherein the preparing the tapered optical fiber structure comprises: and (3) putting a section of the SMF with the coating removed into a fusion splicer, and discharging the SMF for a plurality of times by adopting an arc with the power of 80bit and the discharge time of 2000ms to obtain the tapered optical fiber structure.
7. The method for measuring the sensitivity of a temperature and pressure optical fiber sensor according to claim 5, wherein the preparing the peanut optical fiber structure comprises:
Putting a section of SMF into a fusion splicer, and adopting an electric arc with power of +80bit, discharge time of 2000ms and 25 mu m deviated from the end face of the SMF to discharge the end face to form a microsphere cavity, so as to obtain a single-mode optical fiber with a microsphere structure;
and carrying out discharge welding on the microspheres of the two sections of single-mode optical fibers with the microsphere structures by adopting an electric arc with standard discharge power and discharge time of 1000ms to obtain the peanut optical fiber structure.
8. The method for measuring sensitivity of a temperature and pressure fiber sensor according to claim 5, wherein the preparing a fiber bragg grating comprises:
and placing a section of photosensitive optical fiber close to a section of grating mask capable of inhibiting zero-order diffraction and maximizing first-order diffraction, and orthographically injecting ultraviolet light into the photosensitive optical fiber through the grating mask, wherein interference fringes generated by near-field diffraction of a phase grating mask are utilized to form a periodically disturbed refractive index in the optical fiber, so as to obtain the fiber Bragg grating.
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