High-sensitivity high-temperature high-pressure sensor based on high-birefringence grating and preparation method thereof

Abstract

The application discloses a high-sensitivity high-temperature high-pressure sensor based on a high-birefringence grating, which comprises a microstructure optical fiber, the microstructure optical fiber comprises a fiber core and a cladding layer, the fiber core is located at the center of the cladding layer, the microstructure optical fiber has a first polarization direction and a second polarization direction on a radial plane, the first polarization direction is perpendicular to the second polarization direction, symmetrical air hole channels are arranged in the cladding layer on both sides of the fiber core along the first polarization direction, and the air hole channels are parallel to the fiber core; and a high-birefringence grating is formed in the fiber core or the cladding layer of the microstructure optical fiber through periodic refractive index modulation. The high-sensitivity high-temperature high-pressure sensor can directly form two separated Bragg resonance peaks, does not need to use any polarization device for demodulation, and can simultaneously measure temperature and pressure, has high sensitivity to pressure, and can work in a high-temperature environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing, in particular to a high-sensitivity high-temperature high-pressure sensor based on high-birefringence grating and a preparation method thereof. BACKGROUND

[0002] Optical fiber sensor is a new generation of optical sensor, which has the unique advantages of high sensitivity, small size, light weight, corrosion resistance, anti-electromagnetic interference, and easy networking, and is expected to solve the problem of high-temperature high-pressure measurement in extreme environment. The reported optical fiber pressure sensors include fiber Fabry-Perot interferometer (FPI) pressure sensor and fiber Bragg grating (FBG) pressure sensor. The fiber Bragg grating (FBG) pressure sensor has the ability of large-scale multiplexing and can realize distributed / quasi-distributed pressure sensing. However, the Bragg grating prepared in a single-mode optical fiber has low pressure sensitivity and basically does not respond to external pressure.

[0003] A distributed pressure sensing system is disclosed in Chinese patent No. CN201610129747.6, which comprises a tunable laser, a wavelength / time signal demodulator, a computer, a polarization maintaining transmission optical fiber, a 45° polarizer, a polarizer, and a polarization maintaining fiber coupler. The polarization maintaining fiber coupler is connected with a high-birefringence fiber grating array, which is composed of Bragg gratings engraved on a high-birefringence fiber. The high-birefringence fiber includes a core and a cladding. The core is located at the center of the fiber, and symmetric stress zones are arranged in the cladding on both sides of the core. Symmetric air hole channels are arranged in the cladding on the other two sides of the core which are 90° away from the stress zones. The patent sets up air hole channels and stress zones in the polarization maintaining fiber to form a polarization maintaining fiber structure, so that the fiber has the characteristics of single-mode transmission and general high-birefringence fiber, as well as high birefringence and high sensitivity to external pressure. The grating reflection peak of the birefringence fiber grating array has double Bragg reflection peaks, and the interval of the double Bragg reflection peaks is sensitive to external pressure, bending, and twisting. The change of the interval of the double Bragg reflection peaks is used to measure the external pressure, bending, and twisting.

[0004] The above patent relies on the birefringence effect of the polarization maintaining double-hole fiber to form a birefringence fiber grating from the Bragg grating. However, the birefringence effect of the conventional Bragg grating is low, and the birefringence effect of the polarization maintaining double-hole fiber is also low, resulting in a small interval of the double Bragg reflection peaks. Therefore, polarizing devices such as polarizers and analyzers are needed to separate the double Bragg reflection peaks during demodulation, which results in a large number of devices in the demodulation device, high cost, and complex structure. At the same time, the sensitivity of the polarization maintaining fiber to pressure is insufficient, which cannot meet the measurement of small pressure. SUMMARY

[0005] In order to solve the above-mentioned problems of the prior art, the application provides a high-sensitivity high-temperature high-pressure sensor based on a high-birefringence grating, which can directly form two separated Bragg resonance peaks, does not need to use any polarization device for demodulation, and can simultaneously measure temperature and pressure, has high sensitivity to pressure, and can work in a high-temperature environment.

[0006] The application further provides a preparation method of the high-sensitivity high-temperature high-pressure sensor based on a high-birefringence grating.

[0007] The technical problem to be solved by the application is solved by the following technical scheme.

[0008] The high-sensitivity high-temperature high-pressure sensor based on a high-birefringence grating comprises a microstructured optical fiber, the microstructured optical fiber comprises a core and a cladding, the core is located at the center of the cladding, the microstructured optical fiber has a first polarization direction and a second polarization direction in a radial plane, the first polarization direction is perpendicular to the second polarization direction, symmetrical air hole channels are arranged in the cladding on both sides of the core along the first polarization direction, and the air hole channels are parallel to the core; and a high-birefringence grating is formed in the core or the cladding of the microstructured optical fiber through periodic refractive index modulation.

[0009] Further, the high-birefringence grating is formed in the core of the microstructured optical fiber and comprises a plurality of grating planes periodically distributed along the axial direction of the microstructured optical fiber, the grating planes are perpendicular to the axial direction of the microstructured optical fiber, the grating planes have a width along the first polarization direction and a height along the second polarization direction, and the height of the grating plane is greater than the width of the grating plane.

[0010] Further, the grating plane comprises a plurality of grating fringes, the fringe direction of each grating fringe is parallel to the first polarization direction, and each grating fringe in the same grating plane is arranged in sequence along the second polarization direction.

[0011] Further, the high-birefringence grating is formed in the cladding on one side or both sides of the core along the second polarization direction and comprises a plurality of stress columns periodically distributed along the axial direction of the microstructured optical fiber.

[0012] Further, the stress column has a width along the first polarization direction and a height along the second polarization direction, and the height of the stress column is greater than the width of the stress column.

[0013] The preparation method of the high-sensitivity high-temperature high-pressure sensor comprises the following steps:

[0014] Step 100: providing a micro-structured optical fiber, the micro-structured optical fiber comprising a core and a cladding, the core being located in the center of the cladding, the micro-structured optical fiber having a first polarization direction and a second polarization direction in a radial plane, the first polarization direction being perpendicular to the second polarization direction, symmetric air-hole channels being provided in the cladding on both sides of the core along the first polarization direction, the air-hole channels being parallel to the core;

[0015] Step 200: using a femtosecond laser beam to perform refractive index modulation on the core or the cladding of the micro-structured optical fiber to form a high-birefringence grating in the core or the cladding;

[0016] Step 300: testing and calibrating the high-birefringence grating to obtain a relationship between the wavelength interval of two Bragg resonance peaks of the high-birefringence grating and an external pressure, and a relationship between a center wavelength of the high-birefringence grating and an external temperature.

[0017] Further, in step 100, further comprising: etching the air-hole channels of the micro-structured optical fiber to expand the aperture of the air-hole channels.

[0018] Further, in step 100, etching the air-hole channels of the micro-structured optical fiber to expand the aperture of the air-hole channels is as follows:

[0019] Step 110: connecting one end of the micro-structured optical fiber to a micro-flow pump through a syringe, the needle of the syringe being inserted into one end of the air-hole channels, and placing the other end of the micro-structured optical fiber in an etching solution so that the other end of the air-hole channels is completely immersed in the etching solution;

[0020] Step 120: starting the micro-flow pump to draw the etching solution into the air-hole channels of the micro-structured optical fiber through the syringe until the air-hole channels are etched to a predetermined aperture;

[0021] Step 130: repeating steps 110 and 120 until all the air-hole channels of the micro-structured optical fiber are etched to a predetermined aperture.

[0022] Further, the high-birefringence grating is formed in the core of the micro-structured optical fiber, comprising a plurality of grating planes periodically distributed along the axial direction of the micro-structured optical fiber, the grating planes being perpendicular to the axial direction of the micro-structured optical fiber; the grating planes having a width along the first polarization direction and a height along the second polarization direction, the height of the grating planes being greater than the width of the grating planes; in step 200, the core of the micro-structured optical fiber is refractive index modulated to write the high-birefringence grating in the core is as follows:

[0023] Step 210: emitting a femtosecond laser beam, and adjusting the position of the microstructured fiber so that the femtosecond laser beam is focused in the core of the microstructured fiber, and the incident direction of the femtosecond laser beam is perpendicular to the first polarization direction;

[0024] Step 220: adjusting the polarization state of the femtosecond laser beam so that the polarization direction of the femtosecond laser beam is perpendicular to the first polarization direction;

[0025] Step 230: adjusting the output power of the femtosecond laser beam so that the femtosecond laser beam induces plasma wave in the core at the laser focus, and the femtosecond laser beam is coherent with the plasma wave to form an interference spot in the core, thereby writing the grating plane in the core;

[0026] Step 240: moving the microstructured fiber along its axial direction and controlling the on-off of the femtosecond laser beam, thereby writing a plurality of grating planes periodically distributed along the axial direction in the core, to form the high-birefringence grating.

[0027] Further, the high-birefringence grating is formed in the cladding on one side or both sides of the core along the second polarization direction, and includes a plurality of stress columns periodically distributed along the axial direction of the microstructured fiber; in step 200, the refractive index of the cladding of the microstructured fiber is modulated to write the high-birefringence grating in the cladding as follows:

[0028] Step 210: emitting a femtosecond laser beam, and adjusting the position of the microstructured fiber so that the femtosecond laser beam is focused in the cladding of the microstructured fiber, and the incident direction of the femtosecond laser beam is parallel to the second polarization direction;

[0029] Step 220: adjusting the output power of the femtosecond laser beam so that the femtosecond laser beam induces expansion of the cladding at the laser focus, and the expanded cladding extrudes the cladding at the periphery of the focus to form the stress column;

[0030] Step 230: moving the microstructured fiber along its axial direction and controlling the on-off of the femtosecond laser beam, thereby writing a plurality of stress columns periodically distributed along the axial direction in the cladding, to form the high-birefringence grating.

[0031] The application has the following beneficial effects: the high-birefringence grating is prepared in the core or cladding of the microstructure optical fiber, the high-birefringence grating itself has a high birefringence effect, the reflection spectrum does not need to be demodulated by any polarization device, and two separated Bragg resonance peaks can be directly formed, the number of devices of the demodulation device and the structural complexity can be reduced, temperature and pressure can be measured at the same time, the aperture of the microstructure optical fiber is increased by etching, the sensitivity of pressure is improved, and the micro pressure can be measured; and the high-birefringence grating is prepared by femtosecond laser, and can work in a high-temperature environment. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The axial plane structure schematic diagram of the high-sensitivity high-temperature high-pressure sensor provided by the application.

[0033] Figure 2 The radial plane structure schematic diagram of the high-sensitivity high-temperature high-pressure sensor provided by the application.

[0034] Figure 3 The grating plane structure schematic diagram of the high-sensitivity high-temperature high-pressure sensor provided by the application.

[0035] Figure 4 The axial plane structure schematic diagram of another high-sensitivity high-temperature high-pressure sensor provided by the application.

[0036] Figure 5 The radial plane structure schematic diagram of another high-sensitivity high-temperature high-pressure sensor provided by the application.

[0037] Figure 6 The structure schematic diagram of the demodulation device provided by the application.

[0038] Figure 7 The structure schematic diagram of the demodulation instrument provided by the application.

[0039] Figure 8 The step block diagram of the preparation method of the high-sensitivity high-temperature high-pressure sensor provided by the application.

[0040] Figure 9 The structure schematic diagram of the femtosecond laser writing system provided by the application.

[0041] Figure 10 The sub-step block diagram of step 100 in the preparation method of the high-sensitivity high-temperature high-pressure sensor provided by the application.

[0042] Figure 11 The structure schematic diagram of the test calibration device provided by the application.

[0043] Figure 12The substep block diagram of step 200 in the preparation method of the high-sensitivity high-temperature high-pressure sensor provided by the application.

[0044] Figure 13 The substep block diagram of another step 200 in the preparation method of the high-sensitivity high-temperature high-pressure sensor provided by the application. DETAILED DESCRIPTION

[0045] The application will be described in detail below with reference to the drawings and embodiments, examples of which are shown in the drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the drawings are exemplary and are intended to explain the application, and cannot be understood as a limitation of the application.

[0046] In the description of the application, it should be understood that the terms "length", "width", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the application.

[0047] In addition, the terms "first", "second", "third" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second", "third" can explicitly or implicitly include one or more of the features. In the description of the application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified and limited.

[0048] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing", "setting" and the like should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0049] Example 1

[0050] As Figures 1-3Or 4-5, a high sensitivity high temperature and high pressure sensor 100 based on high birefringence grating 120, including a microstructured optical fiber 110, the microstructured optical fiber 110 includes a core 111 and a cladding 112, the core 111 is located in the center of the cladding 112, the microstructured optical fiber 110 has a first polarization direction y and a second polarization direction z in the radial plane, the first polarization direction y is perpendicular to the second polarization direction z, a symmetrical air hole channel 113 is arranged in the cladding 112 on both sides of the core 111 along the first polarization direction y, the air hole channel 113 is parallel to the core 111; The core 111 or the cladding 112 of the microstructured optical fiber 110 is periodically modulated by refractive index to form a high birefringence grating 120.

[0051] The present patent prepares the high birefringence grating 120 in the core 111 or the cladding 112 of the microstructured optical fiber 110, which itself has a higher birefringence effect, and its reflection spectrum does not need any polarization device demodulation, but can directly form two separated Bragg resonance peaks, which can reduce the number of devices and the complexity of structure of the demodulation device 200 or the demodulation instrument 210, and can measure temperature and pressure at the same time.

[0052] As shown in Figure 6 The demodulation device 200 includes a broadband light source 201, a spectrometer 203, a fiber ring 202 and a computer 204, the fiber ring 202 has an incident end, a reflection end and a transmission end, the incident end of the fiber ring 202 is connected with the broadband light source 201, the reflection end of the fiber ring 202 is connected with the spectrometer 203, and the transmission end of the fiber ring 202 is connected with the high sensitivity high temperature and high pressure sensor 100; The computer 204 is connected with the spectrometer 203. The broadband light beam emitted by the broadband light source 201 enters the high sensitivity high temperature and high pressure sensor 100 after coupling through the fiber ring 202, and part of the broadband light beam in the high sensitivity high temperature and high pressure sensor 100 is reflected back when passing through the high birefringence grating 120. The reflected light beam reflected by the high birefringence grating 120 enters the spectrometer 203 after coupling through the fiber ring 202, the spectrometer 203 demodulates the light beam signal of the reflected light beam, obtains the center wavelength of the high birefringence grating 120 and the wavelength interval of the two Bragg resonance peaks; The computer 204 stores the relationship between the center wavelength of the high birefringence grating 120 and the external temperature, and the relationship between the wavelength interval of the two Bragg resonance peaks and the external pressure, and can calculate the external temperature and the external pressure according to the center wavelength of the high birefringence grating 120 and the wavelength interval of the two Bragg resonance peaks obtained by the spectrometer 203.

[0053] Or asFigure 7 As shown, the high-sensitivity high-temperature high-pressure sensor 100 is directly connected with the demodulator 210.

[0054] In pressure detection, due to the high birefringence effect, the high birefringence grating 120 forms different Bragg resonance peaks in the first polarization direction y and the second polarization direction z; when external pressure acts on the microstructure optical fiber 110, the external pressure is conducted to the two-sided air hole channels 113, causing the two-sided air hole channels 113 to deform, and the two-sided air hole channels 113 convert the external pressure into internal stress to extrude the high birefringence grating 120; since the microstructure optical fiber 110 is only distributed with the air hole channels 113 on the two sides of the first polarization direction y, and is not distributed with any air hole channels 113 on the two sides of the second polarization direction z, the extrusion force of the high birefringence grating 120 in the first polarization direction y is greater than that in the second polarization direction z, causing the wavelength drift amounts of the two Bragg resonance peaks to be different, so that the wavelength spacing of the two Bragg resonance peaks changes; the greater the external pressure, the greater the stress difference between the first polarization direction y and the second polarization direction z, and the greater the change of the wavelength spacing of the two Bragg resonance peaks, and the change of the external pressure can be demodulated and calculated by using the change amount of the wavelength spacing of the two Bragg resonance peaks.

[0055] In temperature detection, external temperature acts on the microstructure optical fiber 110, and the high birefringence grating 120 changes the effective refractive index and grating period due to the thermo-optic effect and thermal expansion effect of the microstructure optical fiber 110, causing the center wavelength to drift; the greater the external temperature, the greater the center wavelength drift of the high birefringence grating 120, and the change of the external temperature can be demodulated and calculated by using the center wavelength drift amount of the high birefringence grating 120.

[0056] Preferably, the high birefringence grating 120 is written by a femtosecond laser beam.

[0057] The conventional high birefringence grating 120 is written by a phase mask method based on ultraviolet continuous laser, which needs to perform sensitization treatment on the microstructure optical fiber 110 before writing, and the obtained high birefringence grating 120 is usually a type I grating, which gradually decouples and recovers at high temperature, so it cannot work stably for a long time in a high-temperature environment.

[0058] The high birefringence grating 120 written by the femtosecond laser beam in the present patent is a type II grating, which can withstand high temperature, and the change of the external temperature can be demodulated and calculated by using the center wavelength drift amount, so that the pressure and temperature can be detected simultaneously in a high-temperature environment.

[0059] The number of air pore channels 113 on each side can be one or more, but the number of air pore channels 113 on both sides should be the same, and the arrangement of air pore channels 113 on both sides should also be the same, so that the air pore channels 113 on both sides form a point-symmetric structure with the center of the fiber core 111 as the symmetry point, and form an axis-symmetric structure with the diameter of the fiber core 111 as the axis of symmetry.

[0060] Specifically, the microstructured optical fiber 110 may be, but is not limited to, a double-hole optical fiber 110 or a photonic crystal optical fiber 110.

[0061] Example 2

[0062] As an optimization of Embodiment 1, in this embodiment, such as Figures 1-3 As shown, the high birefringence grating 120 is fabricated within the core 111 of the microstructured optical fiber 110, and includes a plurality of grating planes 121 periodically distributed along the axial direction x of the microstructured optical fiber 110. The grating planes 121 are perpendicular to the axial direction x of the microstructured optical fiber 110. The grating planes 121 have a width along the first polarization direction y and a height along the second polarization direction z. The height of the grating planes 121 is greater than the width of the grating planes 121.

[0063] The high birefringence grating 120 in this embodiment is composed of multiple grating planes 121 within the fiber core 111. Since each grating plane 121 is periodically distributed along the axial direction x of the microstructure fiber 110, it has the periodic modulation characteristics of a Bragg grating and can form a Bragg resonance peak. Furthermore, since the height of the grating plane 121 along the second polarization direction z is greater than its width along the first polarization direction y, it has anisotropic uniformity, resulting in a large refractive index difference between the first polarization direction y and the second polarization direction z of the high birefringence grating 120, i.e., it has a high birefringence effect.

[0064] The grating plane 121 includes a plurality of grating stripes 122, the stripe direction of each grating stripe 122 is parallel to the first polarization direction y, and the grating stripes 122 in the same grating plane 121 are arranged sequentially along the second polarization direction z.

[0065] The grating plane 121 is composed of multiple grating stripes 122. The medium density and refractive index of the grating stripes 122 are different from those of other positions in the fiber core 111. At the same time, the stripe direction of the grating stripes 122 is parallel to the first polarization direction y, and the grating stripes 122 in the same grating plane 121 are arranged sequentially along the second polarization direction z. This grating plane 121 with non-uniformly distributed grating stripes 122 can further improve the birefringence effect of the high birefringence grating 120.

[0066] Preferably, the extension length of each grating stripe 122 within the same grating plane 121 gradually increases and then gradually decreases along the second polarization direction z to form a grating plane 121 that resembles a rhombus or ellipse.

[0067] Example 3

[0068] As another optimization of Embodiment 1, in this embodiment, such as Figures 4-5 As shown, the high birefringence grating 120 is formed in the cladding 112 on one or both sides of the fiber core 111 along the second polarization direction z, and includes a plurality of stress pillars 123 periodically distributed along the axial direction x of the microstructure fiber 110.

[0069] The high birefringence grating 120 in this embodiment is composed of a plurality of stress pillars 123 within the cladding 112. Since each stress pillar 123 is periodically distributed along the axial direction x of the microstructure optical fiber 110, it has the periodic modulation characteristics of a Bragg grating and can form a Bragg resonance peak. At the same time, the stress pillars 123 are only disposed in the cladding 112 on one or both sides of the fiber core 111 along the second polarization direction z. The fiber core 111 is only subjected to the stress (compression force) of the stress pillars 123 in the second polarization direction z, thereby increasing the refractive index difference in the first polarization direction y and the second polarization direction z, that is, it has a high birefringence effect.

[0070] Preferably, the stress column 123 has a width along the first polarization direction y and a height along the second polarization direction z, wherein the height of the stress column 123 is greater than its width. Because the stress column 123 has a larger height along the second polarization direction z and a smaller width along the first polarization direction y, the stress asymmetry experienced by the fiber core 111 in the first polarization direction y and the second polarization direction z can be further improved, thereby further enhancing the birefringence effect.

[0071] The stress column 123 includes a central region and a peripheral region. The central region is located at the center of the peripheral region. The dielectric density of the central region is less than the dielectric density of other unmodulated locations of the cladding 112, and the dielectric density of the peripheral region is greater than the dielectric density of other unmodulated locations of the cladding 112.

[0072] On the axial x-plane of the microstructured optical fiber 110, the stress column 123 can be a vertical stress column 123 perpendicular to the fiber core 111 (e.g., Figure 4 Or a diagonal stress column 123 that is inclined to the fiber core 111.

[0073] Example 4

[0074] A preparation method of a high-sensitivity high-temperature high-pressure sensor, for preparing the high-sensitivity high-temperature high-pressure sensor 100 described in embodiment one.

[0075] As shown in Figure 8 , the preparation method comprises the following steps:

[0076] Step 100: providing a micro-structured optical fiber 110, the micro-structured optical fiber 110 comprising a fiber core 111 and a cladding 112, the fiber core 111 being located at the center of the cladding 112, the micro-structured optical fiber 110 having a first polarization direction y and a second polarization direction z in a radial plane, the first polarization direction y being perpendicular to the second polarization direction z, symmetrical air hole channels 113 being provided in the cladding 112 on both sides of the fiber core 111 along the first polarization direction y, the air hole channels 113 being parallel to the fiber core 111.

[0077] In this step 100, since the wavelength interval change of the two Bragg resonance peaks is caused by the deformation of the high-birefringence grating 120 under the pressure of the air hole channels 113 on both sides, the sensitivity of the high-birefringence grating 120 to external pressure is related to the aperture of the air hole channels 113 on both sides, the larger the aperture of the air hole channels 113 on both sides, the higher the sensitivity of the high-birefringence grating 120 to external pressure, therefore, in this step 100, it further comprises: etching the air hole channels 113 of the micro-structured optical fiber 110 to expand the aperture of the air hole channels 113.

[0078] Preferably, wet etching can be used to etch the air hole channels 113 of the micro-structured optical fiber 110, as shown in Figure 10 , the specific steps are as follows:

[0079] Step 110: connecting one end of the micro-structured optical fiber 110 to a micro-flow pump through a syringe, inserting the needle of the syringe into one end of the air hole channels 113, and placing the other end of the micro-structured optical fiber 110 in an etching solution so that the other end of the air hole channels 113 is completely immersed in the etching solution.

[0080] In this step 110, the needle of the syringe and the air hole channels 113 of the micro-structured optical fiber 110 are sealed and fixed by sealing glue, and the push-pull rod of the syringe is connected to the micro-flow pump. The sealing glue is preferably but not limited to ultraviolet curing glue.

[0081] Step 120: starting the micro-flow pump, so that the micro-flow pump draws the etching solution into the air hole channels 113 of the micro-structured optical fiber 110 through the syringe, until the air hole channels 113 are etched to a predetermined aperture.

[0082] In step 120, when the microfluidic pump pulls the syringe push rod out of the syringe barrel, the syringe barrel draws air from the vent channel 113 through the needle tip, and the etching liquid flows into the vent channel 113 under the negative pressure of the vent channel 113 to etch the inner wall of the vent channel 113.

[0083] The microfluidic pump should pull the push-pull rod slowly and evenly to ensure that the etching solution flows slowly and evenly within the pore channel 113, guaranteeing the uniformity of etching the inner wall of the pore channel 113. Simultaneously, the syringe has a certain capacity to store used etching solution, preventing excessively short single pull-pull times. Furthermore, by repeatedly pushing and pulling the push-pull rod, used etching solution can be pushed out of the pore channel 113, and unused etching solution can be drawn into the pore channel 113, ensuring the concentration of etching solution within the pore channel 113.

[0084] Step 130: Repeat steps 110 and 120 until all the air channels 113 of the microstructured optical fiber 110 are etched to the predetermined aperture.

[0085] Step 200: Modulate the refractive index of the core 111 or cladding 112 of the microstructure fiber 110 to write a high birefringence grating 120 in the core 111 or cladding 112.

[0086] In step 200, such as Figure 9 As shown, a femtosecond laser beam writing system 300 is preferably used to modulate the refractive index of the core 111 or cladding 112 of the microstructure fiber 110. The femtosecond laser beam writing system 300 includes a femtosecond laser 301, a power attenuator 302, a polarization controller 303, a mechanical shutter 304, a dichroic mirror 305, a focusing objective 306, a CCD camera 307, a three-dimensional displacement platform 308, and a rotating fixture 309. The femtosecond laser 301, power attenuator 302, polarization controller 303, mechanical shutter 304, dichroic mirror 305, and focusing objective 306 are arranged sequentially along the propagation path of the femtosecond laser beam. The CCD camera 307 is located on the side of the dichroic mirror 305 facing away from the focusing objective 306. The three-dimensional displacement platform 308 is located on the side of the focusing objective 306 facing away from the dichroic mirror 305. The rotating fixture 309 is disposed on the three-dimensional displacement platform 308.

[0087] The femtosecond laser 301 is used to emit the femtosecond laser beam, the optical power attenuator 302 is used to adjust the power of the femtosecond laser beam, the polarization controller 303 is used to adjust the polarization state of the femtosecond laser beam, the mechanical shutter 304 is used to control the on-off of the femtosecond laser beam, the dichroic mirror divides the femtosecond laser beam into two beams, one of which is provided to the focusing objective 306 for grating writing, and the other of which is provided to the CCD camera 307 for grating imaging, the rotary clamp 309 is used to clamp and fix the microstructure fiber 110 and drive the microstructure fiber 110 to rotate around the axis x, and the three-dimensional displacement platform 308 is used to drive the microstructure fiber 110 to move along three directions x, y and z.

[0088] Step 300: Test calibration is performed on the high-birefringence grating 120 to obtain a relationship between the wavelength interval of the two Bragg resonance peaks of the high-birefringence grating 120 and the external pressure, and a relationship between the center wavelength of the high-birefringence grating 120 and the external temperature.

[0089] In this step 300, as Figure 11As shown, first, the high-birefringence grating 120 of the high-sensitivity high-temperature high-pressure sensor 100 is inserted into the high-temperature resistant pressure tube 400 from one end, and the high-sensitivity high-temperature high-pressure sensor 100 is sealed and fixed with the high-temperature resistant pressure tube 400 by high-temperature glue, then the other end of the high-temperature resistant pressure tube 400 is communicated with the gas cylinder 600, so that the inert gas is introduced into the closed space of the high-temperature resistant pressure tube 400 through the gas cylinder 600, to provide a high-pressure test environment for the high-sensitivity high-temperature high-pressure sensor 100; then the high-temperature resistant pressure tube 400 is put into the heating device 500, and the heating device 500 is used to heat the high-temperature resistant pressure tube 400, to provide a high-temperature test environment for the high-sensitivity high-temperature high-pressure sensor 100, then the other end of the high-sensitivity high-temperature high-pressure sensor 100 is connected with the demodulation device 200 or the demodulation instrument 210, and the reflection spectrum of the high-birefringence grating 120 is demodulated by the demodulation device 200 or the demodulation instrument 210; by fixing the test temperature, changing the test pressure, and according to the spectrum demodulation of the demodulation device 200 or the demodulation instrument 210, the corresponding data of the external pressure and the wavelength interval of the two Bragg resonance peaks of the high-birefringence grating 120 is obtained, and the data is fitted to obtain the relationship between the external pressure and the wavelength interval of the two Bragg resonance peaks of the high-birefringence grating 120; then by fixing the test pressure, changing the test temperature, and according to the spectrum demodulation of the demodulation device 200 or the demodulation instrument 210, the corresponding data of the external temperature and the center wavelength of the high-birefringence grating 120 is obtained, and the data is fitted to obtain the relationship between the external temperature and the center wavelength of the high-birefringence grating 120, to complete the calibration of the high-birefringence grating 120, and finally the two relationship formulas are input into the demodulation module, and in the subsequent pressure and temperature detection, the pressure change and temperature change of the external environment can be calculated by obtaining the spectrum information of the high-birefringence grating 120 and combining the two relationship formulas.

[0090] Embodiment five

[0091] As an optimization scheme of embodiment four, in the present embodiment, the high-birefringence grating 120 is formed in the core 111 of the micro-structured optical fiber 110, and includes a plurality of grating planes 121 periodically distributed along the axial direction x of the micro-structured optical fiber 110, and the grating planes 121 are perpendicular to the axial direction x of the micro-structured optical fiber 110; the grating plane 121 has a width along the first polarization direction y and a height along the second polarization direction z, and the height of the grating plane 121 is greater than the width of the grating plane 121; as shown in Figure 12 As shown, in step 200, the core 111 of the micro-structured optical fiber 110 is refractive index modulated to write the high-birefringence grating 120 in the core 111, and the steps are as follows:

[0092] Step 210: a femtosecond laser beam is emitted, and the position of the microstructured fiber 110 is adjusted so that the femtosecond laser beam is focused in the core 111 of the microstructured fiber 110, and the incident direction of the femtosecond laser beam is perpendicular to the first polarization direction y.

[0093] In this step 210, the microstructured fiber 110 is moved in the x, y and z directions by the three-dimensional displacement platform 308 so that the femtosecond laser beam is focused in the core 111 of the microstructured fiber 110, and the microstructured fiber 110 is rotated around the x axis by the rotating clamp 309 so that the incident direction of the femtosecond laser beam is perpendicular to the first polarization direction y.

[0094] Step 220: the polarization state of the femtosecond laser beam is adjusted so that the polarization direction of the femtosecond laser beam is perpendicular to the first polarization direction y.

[0095] In this step 220, the polarization state of the femtosecond laser beam is adjusted by the polarization controller 303 so that the polarization direction of the femtosecond laser beam is perpendicular to the first polarization direction y.

[0096] Step 230: the output power of the femtosecond laser beam is adjusted so that the femtosecond laser beam induces a plasma wave in the core 111 at the laser focus, and the femtosecond laser beam and the plasma wave are coherent to form an interference spot in the core 111, thereby writing the grating plane 121 in the core 111.

[0097] In this step 230, the output power of the femtosecond laser beam is adjusted by the power attenuator 302 so that the femtosecond laser beam induces a plasma wave in the core 111 at the laser focus. The interference plane of the interference spot is perpendicular to the x axis of the microstructured fiber 110, and the height of the interference plane along the second polarization direction z is greater than the width of the interference plane along the first polarization direction y, corresponding to the height and width of the grating plane 121, respectively.

[0098] The interference spot includes a plurality of interference fringes, each interference fringe has a fringe direction parallel to the first polarization direction y, and each interference fringe is arranged along the second polarization direction z in sequence; one interference fringe corresponds to one grating fringe 122.

[0099] Step 240: the microstructured fiber 110 is moved along the x axis and the on-off of the femtosecond laser beam is controlled, so as to write a plurality of grating planes 121 periodically distributed along the x axis in the core 111, thereby forming the high-birefringence grating 120.

[0100] In step 240, the microstructured optical fiber 110 is moved along the x-axis by the three-dimensional displacement platform 308 so that the focal point of the femtosecond laser beam is positioned at each writing point. During the movement of the microstructured optical fiber 110, the mechanical shutter 304 controls the on / off state of the femtosecond laser beam so that the femtosecond laser beam is only turned on when it reaches each writing point to modulate the fiber core 111, and is turned off at other positions to not modulate the fiber core 111.

[0101] When preparing the high birefringence grating 120, the real-time spectral pattern of the high birefringence grating 120 during the writing process can also be obtained by the demodulation device 200 or demodulator 210. By adjusting parameters such as the energy, focusing position, and grating length of the femtosecond laser beam, the high birefringence grating 120 with the required spectral pattern can be finally written.

[0102] Example 6

[0103] As an optimization of Embodiment 3, in this embodiment, such as Figure 13 As shown, the high birefringence grating 120 is formed in the cladding 112 on one or both sides of the fiber core 111 along the second polarization direction z, and includes a plurality of stress pillars 123 periodically distributed along the axial direction x of the microstructure fiber 110; in step 200, the refractive index of the cladding 112 of the microstructure fiber 110 is modulated to write the high birefringence grating 120 in the cladding 112 as follows:

[0104] Step 210: Emit a femtosecond laser beam and adjust the position of the microstructure fiber 110 so that the femtosecond laser beam is focused within the cladding 112 of the microstructure fiber 110, while simultaneously ensuring that the incident direction of the femtosecond laser beam is parallel to the second polarization direction z.

[0105] In step 210, the microstructured optical fiber 110 is moved in the x, y and z directions by the three-dimensional displacement platform 308 so that the femtosecond laser beam is focused in the core 111 of the microstructured optical fiber 110. At the same time, the microstructured optical fiber 110 is rotated around the x-axis by the rotating clamp 309 so that the incident direction of the femtosecond laser beam is parallel to the second polarization direction z.

[0106] Step 220: Adjust the output power of the femtosecond laser beam so that the femtosecond laser beam induces the cladding 112 located at the laser focus to expand, and the expanded cladding 112 compresses the cladding 112 outside the focus to form the stress column 123.

[0107] In the step 220, the output power of the femtosecond laser beam is adjusted by the power attenuator 302, so that the femtosecond laser beam induces the cladding 112 at the laser focus to expand. The cladding 112 at the laser focus expands, so that the medium density of the cladding 112 at the laser focus is less than the medium density of the cladding 112 at other positions, thereby forming the central region of the stress column 123. The cladding 112 at the periphery of the laser focus is extruded, so that the medium density of the cladding 112 at the periphery of the laser focus is greater than the medium density of the cladding 112 at other positions, thereby forming the peripheral region of the stress column 123. Since the incident direction of the femtosecond laser beam is parallel to the second polarization direction z, the writing range of the stress column 123 in the second polarization direction z is large, so that the height of the stress column 123 is greater than the width of the stress column 123.

[0108] In the step 230, the microstructured fiber 110 is moved along the axial direction x, and the on-off of the femtosecond laser beam is controlled, so that a plurality of stress columns 123 periodically distributed along the axial direction x are written in the cladding 112, thereby forming the high-birefringence grating 120.

[0109] In the step 230, the microstructured fiber 110 is moved along the axial direction x by the three-dimensional displacement platform 308, so that the focal point of the femtosecond laser beam is positioned at each writing point. During the movement of the microstructured fiber 110, the on-off of the femtosecond laser beam is controlled by the mechanical shutter 304, so that the femtosecond laser beam is turned on only when it reaches each writing point, and the cladding 112 is modulated. The cladding 112 is not modulated at other positions.

[0110] In the preparation of the high-birefringence grating 120, the real-time spectrum of the high-birefringence grating 120 during writing can also be obtained by the demodulation device 200 or the demodulation instrument 210. By adjusting the energy, focal position, grating length and other parameters of the femtosecond laser beam, the high-birefringence grating 120 with the required spectrum can be finally written.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them. Although the embodiments of the present application have been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents, and these modifications or replacements cannot make the modified technical solutions deviate from the scope of the technical solutions of the present application.

Claims

1. A high-sensitivity high-temperature high-pressure sensor based on a high-birefringence grating, comprising a microstructured optical fiber, the microstructured optical fiber comprising a core and a cladding, the core being located at the center of the cladding, the microstructured optical fiber having a first polarization direction and a second polarization direction in a radial plane, the first polarization direction being perpendicular to the second polarization direction, symmetrical air-hole channels being arranged in the cladding on both sides of the core along the first polarization direction, the air-hole channels being parallel to the core; characterized in that, The high-birefringence grating is formed in the core of the microstructured optical fiber, and includes a plurality of grating planes periodically distributed along the axial direction of the microstructured optical fiber, the grating planes being perpendicular to the axial direction of the microstructured optical fiber; the grating planes have a width along the first polarization direction and a height along the second polarization direction, the height of the grating planes being greater than the width of the grating planes; the grating planes include a plurality of grating fringes, each grating fringe having a fringe direction parallel to the first polarization direction, and each grating fringe in the same grating plane being arranged along the second polarization direction in sequence. Alternatively, the high-birefringence grating is formed in the core or the cladding on one side or both sides of the core along the second polarization direction, and includes a plurality of stress columns periodically distributed along the axial direction of the microstructured optical fiber; the stress columns have a width along the first polarization direction and a height along the second polarization direction, the height of the stress columns being greater than the width of the stress columns. The method comprises the following steps:

2. A method of manufacturing a high sensitivity high temperature high pressure sensor as claimed in claim 1, characterized in that, Step 100: providing a microstructured optical fiber, the microstructured optical fiber comprising a core and a cladding, the core being located at the center of the cladding, the microstructured optical fiber having a first polarization direction and a second polarization direction on a radial plane, the first polarization direction being perpendicular to the second polarization direction, and symmetrical air hole channels being arranged in the cladding on both sides of the core along the first polarization direction, the air hole channels being parallel to the core; Step 200: modulating the refractive index of the core or the cladding of the microstructured optical fiber by using a femtosecond laser beam to form a high-birefringence grating in the core or the cladding; Step 300: testing and calibrating the high-birefringence grating to obtain a relationship between the wavelength spacing of two Bragg resonance peaks of the high-birefringence grating and an external pressure, and a relationship between the center wavelength of the high-birefringence grating and an external temperature. In step 100, the method further comprises etching the air hole channels of the microstructured optical fiber to expand the aperture of the air hole channels, and the steps are as follows:

3. The method for preparing the high-sensitivity, high-temperature, and high-pressure sensor according to claim 2, characterized in that, Step 110: connecting one end of the microstructured optical fiber to a microflow pump through a syringe, inserting a needle of the syringe into one end of the air hole channel, and placing the other end of the microstructured optical fiber in an etching liquid so that the other end of the air hole channel is completely immersed in the etching liquid; Step 120: starting the microflow pump to draw the etching liquid into the air hole channel of the microstructured optical fiber through the syringe until the air hole channel is etched to a predetermined aperture; Step 130: repeating steps 110 and 120 until all the air hole channels of the microstructured optical fiber are etched to the predetermined aperture. ​ 4. The method for preparing the high-sensitivity, high-temperature, and high-pressure sensor according to claim 2, characterized in that, In the step 300, first, the high birefringence grating of the high-sensitivity high-temperature high-pressure sensor is inserted into the high-temperature resistant pressure tube from one end, and the high-sensitivity high-temperature high-pressure sensor is sealed and fixed with the high-temperature resistant pressure tube by high-temperature glue, then the other end of the high-temperature resistant pressure tube is communicated with the gas cylinder, so that inert gas is introduced into the closed space of the high-temperature resistant pressure tube through the gas cylinder, to provide a high-pressure test environment for the high-sensitivity high-temperature high-pressure sensor; then the high-temperature resistant pressure tube is put into the heating device, the heating device is used to heat the high-temperature resistant pressure tube, to provide a high-temperature test environment for the high-sensitivity high-temperature high-pressure sensor, and then the other end of the high-sensitivity high-temperature high-pressure sensor is connected with a demodulation device or a demodulation instrument, the reflected spectrum of the high birefringence grating is demodulated through the demodulation device or the demodulation instrument; By fixing the test temperature, changing the test pressure, and demodulating the spectrum of the demodulation device or the demodulation instrument, corresponding data of the external pressure and the wavelength interval of the two Bragg resonance peaks of the high birefringence grating are obtained, and the relationship between the external pressure and the wavelength interval of the two Bragg resonance peaks of the high birefringence grating is obtained by fitting the data; then by fixing the test pressure, changing the test temperature, and demodulating the spectrum of the demodulation device or the demodulation instrument, corresponding data of the external temperature and the central wavelength of the high birefringence grating are obtained, and the relationship between the external temperature and the central wavelength of the high birefringence grating is obtained by fitting the data, to complete the calibration of the high birefringence grating, finally, the two relationship formulas are input into the demodulation device or the demodulation instrument, in the subsequent pressure and temperature detection, the pressure change and the temperature change of the external environment can be calculated by obtaining the spectrum information of the high birefringence grating and combining the two relationship formulas.

5. The method for preparing the high-sensitivity, high-temperature, and high-pressure sensor according to claim 2, characterized in that, The high birefringence grating is formed in the core of the microstructured optical fiber, and includes a plurality of grating planes periodically distributed along the axial direction of the microstructured optical fiber, and the grating planes are perpendicular to the axial direction of the microstructured optical fiber; the grating plane has a width along the first polarization direction and a height along the second polarization direction, and the height of the grating plane is greater than the width of the grating plane; in the step 200, the refractive index of the core of the microstructured optical fiber is modulated to write the high birefringence grating in the core, and the steps are as follows: Step 210: a femtosecond laser beam is emitted, and the position of the microstructured optical fiber is adjusted so that the femtosecond laser beam is focused in the core of the microstructured optical fiber, and the incident direction of the femtosecond laser beam is perpendicular to the first polarization direction; Step 220: the polarization state of the femtosecond laser beam is adjusted so that the polarization direction of the femtosecond laser beam is perpendicular to the first polarization direction; Step 230: the output power of the femtosecond laser beam is adjusted so that the femtosecond laser beam induces plasma waves in the core at the laser focus, and the femtosecond laser beam and the plasma waves are coherent to form an interference spot in the core, so as to write the grating plane in the core; Step 240: moving the microstructured optical fiber along its axial direction and controlling the on-off of the femtosecond laser beam to write a plurality of grating planes periodically distributed along the axial direction in the core to form the high-birefringence grating.

6. The method for preparing the high-sensitivity, high-temperature, and high-pressure sensor according to claim 2, characterized in that, The high-birefringence grating is formed in the cladding on one side or both sides of the core along the second polarization direction and includes a plurality of stress columns periodically distributed along the axial direction of the microstructured optical fiber; in step 200, the refractive index of the cladding of the microstructured optical fiber is modulated to write the high-birefringence grating in the cladding as follows: Step 210: emitting a femtosecond laser beam and adjusting the position of the microstructured optical fiber so that the femtosecond laser beam is focused in the cladding of the microstructured optical fiber while the incident direction of the femtosecond laser beam is parallel to the second polarization direction; Step 220: adjusting the output power of the femtosecond laser beam so that the femtosecond laser beam induces the cladding at the laser focus to expand, and the expanded cladding extrudes the cladding around the focus to form the stress column; Step 230: moving the microstructured optical fiber along its axial direction and controlling the on-off of the femtosecond laser beam to write a plurality of stress columns periodically distributed along the axial direction in the cladding to form the high-birefringence grating.

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