Integrated optical fiber sensor for measuring temperature and strain under extremely high temperature, and preparation method therefor

Abstract

An integrated optical fiber sensor for measuring a temperature and strain under an extremely high temperature. The integrated optical fiber sensor comprises: a crystal optical fiber (10), which comprises a first optical fiber segment (11), a second optical fiber segment (12) and a third optical fiber segment (13) that are connected in sequence; a first optical fiber grating (20), which is formed in the first optical fiber segment (11) of the crystal optical fiber (10); and a second optical fiber grating (30), which is formed in the second optical fiber segment (12) of the crystal optical fiber (10), wherein the diameter of the first optical fiber segment (11) is the same as that of the third optical fiber segment (13), and the diameter of the second optical fiber segment (12) is different from that of the first optical fiber segment (11) and the third optical fiber segment (13). The integrated optical fiber sensor can simultaneously measure a temperature and strain in an extremely high-temperature environment. Further disclosed is a preparation method for the integrated optical fiber sensor.

Description

An integrated fiber optic sensor for measuring temperature strain at extreme high temperatures and its fabrication method. Technical Field

[0001] This invention relates to grating sensing technology, and more particularly to an integrated fiber optic sensor for measuring temperature strain at extreme high temperatures and its fabrication method. Background Technology

[0002] With the continuous development of modern industrial technology, the demand for temperature strain measurement under high-temperature environments is increasing. In high-end manufacturing fields such as aerospace, nuclear energy, and petrochemicals, especially in large and critical equipment such as the skin, control surfaces, and aero engines of hypersonic vehicles, which often operate at extreme temperatures, the structural safety and performance stability of these components directly affect the reliability and safety of the entire system. Therefore, sensing technologies capable of accurately monitoring strain changes under high-temperature environments are crucial for applications in these fields.

[0003] Fiber optic sensors, with their advantages of high temperature resistance, electromagnetic interference resistance, and small size, have great potential in the field of high-temperature strain measurement. Chinese patent application number CN201210351483.0 discloses a method for simultaneously measuring temperature and stress by obtaining fiber gratings of different diameters through etching. This method uses hydrofluoric acid to partially etch a single-mode fiber, resulting in etched and unetched portions of the fiber with different diameters. Fiber gratings are then written into both the etched and unetched portions of the single-mode fiber. By utilizing the characteristic that fiber gratings of different diameters respond differently to strain but have the same response to temperature, temperature and strain are decoupled, enabling simultaneous measurement of temperature and strain.

[0004] However, single-mode fiber is made of silica fiber, which is limited by the low softening temperature of silica. It can only measure temperature and strain simultaneously at a maximum of 800 ℃. In extreme environments with higher temperatures, it cannot measure temperature and strain simultaneously. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides an integrated fiber optic sensor capable of simultaneously measuring temperature and strain under extreme high-temperature environments.

[0006] The present invention also provides a method for fabricating the above-mentioned integrated fiber optic sensor.

[0007] The technical problem to be solved by the present invention is achieved through the following technical solution:

[0008] An integrated fiber optic sensor for measuring temperature strain at extreme high temperatures, comprising:

[0009] Crystal optical fiber, comprising a first fiber segment, a second fiber segment, and a third fiber segment connected in sequence;

[0010] A first fiber grating is formed in a first fiber segment of the crystal fiber;

[0011] A second fiber grating is formed in the second fiber segment of the crystal fiber;

[0012] Wherein, the first optical fiber segment and the third optical fiber segment have the same diameter, and the second optical fiber segment has a different diameter from the first optical fiber segment and the second optical fiber segment.

[0013] The fabrication method of the aforementioned integrated fiber optic sensor includes the following steps:

[0014] Step 100: Design the length and diameter of the first fiber segment, the second fiber segment, and the third fiber segment;

[0015] Step 200: Etch the crystal fiber with an acidic solution to form the first fiber segment, the second fiber segment, and the third fiber segment, respectively.

[0016] Step 300: Use a femtosecond laser to write the first fiber segment and the second fiber segment to form the first fiber grating and the second fiber grating in the first fiber segment and the second fiber segment, respectively.

[0017] The present invention has the following beneficial effects:

[0018] The integrated fiber optic sensor of this invention uses the crystal fiber for optical signal transmission. The crystal fiber is fabricated into first, second, and third fiber segments with different diameters. First and second fiber gratings are then formed in the first and second fiber segments, respectively. By utilizing the characteristic that the first and second fiber gratings, with their different diameters, respond differently to strain but have the same temperature response, temperature and strain are decoupled to achieve simultaneous temperature and strain measurement. Due to the unique crystal structure of the crystal fiber, it possesses a high melting point (approximately 2045°C) and excellent mechanical properties. Using the crystal fiber as the substrate, the first and second fiber gratings can simultaneously measure temperature and strain in extreme high-temperature environments (e.g., 1600°C). It has numerous advantages such as high-temperature resistance, compact structure, and low crosstalk, and has significant application value in aerospace, nuclear reactors, metallurgy, and other fields.

[0019] The integrated fiber optic sensor of the present invention designs the second fiber segment with a larger diameter in the middle to be relatively short, while the first and third fiber segments with smaller diameters at both ends are designed to be relatively long. This allows the first and third fiber segments with smaller diameters at both ends to occupy most of the length of the crystal fiber, which can disperse the stress acting on the crystal fiber in the first and third fiber segments, thereby improving the strain range and making the strain measurement range closer to the tensile strength value of the crystal fiber itself.

[0020] The integrated fiber optic sensor of the present invention has a relatively short second fiber segment with a smaller diameter in the middle, while the first and third fiber segments with larger diameters at both ends are designed to be relatively long. This allows the first and third fiber segments with larger diameters at both ends to occupy most of the length of the crystal fiber, which can concentrate the stress acting on the crystal fiber on the second fiber segment, thereby improving strain sensitivity and making it suitable for high-sensitivity static and dynamic strain sensing.

[0021] The integrated fiber optic sensor of the present invention reduces the high coupling loss caused by the change in fiber diameter when the optical signal enters the second fiber segment and the third fiber segment from the first fiber segment and the second fiber segment, respectively, by setting a first fiber tapered segment and a second fiber tapered segment with gradually changing diameter between the first fiber segment and the second fiber segment and between the second fiber segment and the third fiber segment, thereby improving the spectral signal-to-noise ratio of the small-diameter fiber grating. Attached Figure Description

[0022] Figure 1 is a schematic diagram of the integrated fiber optic sensor provided by the present invention.

[0023] Figure 2 is a length chart of each part of the integrated fiber optic sensor shown in Figure 1.

[0024] Figure 3 is a schematic diagram of another integrated fiber optic sensor provided by the present invention.

[0025] Figure 4 shows the length markings of each part of the integrated fiber optic sensor shown in Figure 3.

[0026] Figure 5 is a flowchart of the fabrication method of the integrated optical fiber sensor provided by the present invention.

[0027] Figure 6 is a flowchart of step 200 in the fabrication method of the integrated optical fiber sensor provided by the present invention.

[0028] Figure 7 is a schematic diagram of the corrosion process in step 200 of the fabrication method of the integrated optical fiber sensor provided by the present invention. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and embodiments, examples of which are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0030] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0031] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this invention, "multiple" means two or more, unless otherwise explicitly specified.

[0032] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," and "setting," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. Example 1

[0033] As shown in Figures 1 and 3, an integrated fiber optic sensor for measuring temperature strain at extreme high temperatures includes:

[0034] The crystal optical fiber 10 includes a first optical fiber segment 11, a second optical fiber segment 12 and a third optical fiber segment 13 connected in sequence.

[0035] The first fiber grating 20 is formed in the first fiber segment 11 of the crystal fiber 10;

[0036] The second fiber grating 30 is formed in the second fiber segment 12 of the crystal fiber 10;

[0037] Wherein, the first optical fiber segment 11 and the third optical fiber segment 13 have the same diameter, and the second optical fiber segment 12 has a different diameter from the first optical fiber segment 11 and the second optical fiber segment 12.

[0038] The integrated fiber optic sensor of this invention uses the crystal fiber 10 for optical signal transmission. The crystal fiber 10 is fabricated into a first fiber segment 11, a second fiber segment 12, and a third fiber segment 13 with different diameters. Then, a first fiber grating 20 and a second fiber grating 30 are formed in the first fiber segment 11 and the second fiber segment 12, respectively. By utilizing the characteristic that the first fiber grating 20 and the second fiber grating 30 with different diameters respond differently to strain but have the same response to temperature, temperature and strain are decoupled to achieve simultaneous measurement of temperature and strain. Due to the unique crystal structure of the crystal fiber 10, it has a high melting point (approximately 2045°C) and excellent mechanical properties. The first fiber grating 20 and the second fiber grating 30 use the crystal fiber 10 as a substrate, enabling simultaneous measurement of temperature and strain in extreme high-temperature environments (such as 1600°C). It has many advantages such as high temperature resistance, compact structure, and low crosstalk, and has important application value in aerospace, nuclear reactors, metallurgy, and other fields.

[0039] The first fiber grating 20 and the second fiber grating 30 have different center wavelengths. During measurement, the optical signal is coupled into the crystal fiber 10, and the optical signal emitted after passing through the first fiber grating 20 and the second fiber grating 30 in sequence is received, thereby obtaining the resonant spectrum of the integrated fiber optic sensor. The resonant spectrum has a first resonant peak corresponding to the center wavelength of the first fiber grating 20 and a second resonant peak corresponding to the center wavelength of the second fiber grating 30.

[0040] When the temperature changes, the first fiber grating 20 and the second fiber grating 30 expand and contract along the fiber axis due to thermal expansion and contraction, causing a shift in their center wavelengths. Since the degree of thermal expansion and contraction mainly depends on the coefficient of thermal expansion of the material and is less affected by the material diameter, the difference in the center wavelength shift caused by the first fiber grating 20 and the second fiber grating 30 under the same temperature change is small (only on the order of millimeters) and can be ignored. Therefore, even if the first fiber grating 20 and the second fiber grating 30 have different diameters, they respond to temperature changes in the same way.

[0041] When the strain changes, the first fiber grating 20 and the second fiber grating 30 are stretched along the fiber axis under the strain, which causes the center wavelength of both to drift. Since the degree of strain stretching depends not only on the elastic coefficient of the material but also on the material diameter, the center wavelength drift caused by the first fiber grating 20 and the second fiber grating 30 under the same strain change is quite different. Therefore, the first fiber grating 20 and the second fiber grating 30 respond differently to strain changes due to their different diameters.

[0042] Assume that the temperature sensitivity and strain sensitivity of the first fiber grating 20 are respectively and The temperature sensitivity and strain sensitivity of the second fiber grating 30 are respectively and The measured temperature change and dependent variables Satisfy the following formula:

[0043] ,

[0044] in, and These are the wavelength shifts of the first fiber grating 20 and the second fiber grating 30, respectively.

[0045] The crystal optical fiber 10 may be, but is not limited to, sapphire optical fiber, zirconium oxide optical fiber, lutetium oxide optical fiber, or YAG optical fiber.

[0046] The first fiber grating 20 and the second fiber grating 30 may be, but are not limited to, Bragg fiber gratings, chirped fiber gratings, or phase-shifted fiber gratings. Example 2

[0047] As an optimized solution of Embodiment 1, in this embodiment, as shown in Figures 1 and 2, the diameters of the first optical fiber segment 11 and the third optical fiber segment 13 are the first diameter, the diameter of the second optical fiber segment 12 is the second diameter, the total length of the first optical fiber segment 11 and the third optical fiber segment 13 is the first length L1+L3, and the length of the second optical fiber segment 12 is the second length L2; the first diameter is smaller than the second diameter, and the first length L1+L3 is greater than the second length L2.

[0048] The stress generated by the first optical fiber segment 1, the second optical fiber segment 12, and the third optical fiber segment 13 is inversely proportional to their cross-sectional area, while the cross-sectional area of ​​the first optical fiber segment 11, the second optical fiber segment 12, and the third optical fiber segment 13 is directly proportional to the square of their diameter.

[0049] The integrated fiber optic sensor of the present invention designs the second fiber segment 12 with a larger diameter in the middle to be relatively short, while the first fiber segment 11 and the third fiber segment 13 with smaller diameters at both ends are designed to be relatively long. This allows the first fiber segment 11 and the third fiber segment 13 with smaller diameters at both ends to occupy most of the length of the crystal fiber 10. This enables the stress acting on the crystal fiber 10 to be distributed in the first fiber segment 11 and the third fiber segment 13, thereby improving the strain range and making the strain measurement range closer to the tensile strength value of the crystal fiber 10 itself. Example 3

[0050] As another optimized solution of Embodiment 1, in this embodiment, as shown in Figures 3 and 4, the diameter of the first optical fiber segment 11 and the third optical fiber segment 13 is a first diameter, the diameter of the second optical fiber segment 12 is a second diameter, the total length of the first optical fiber segment 11 and the third optical fiber segment 13 is a first length L1+L3, and the length of the second optical fiber segment 12 is a second length L2; the first diameter is greater than the second diameter, and the first length L1+L3 is greater than the second length L2.

[0051] The stress generated by the first optical fiber segment 1, the second optical fiber segment 12, and the third optical fiber segment 13 is inversely proportional to their cross-sectional area, while the cross-sectional area of ​​the first optical fiber segment 11, the second optical fiber segment 12, and the third optical fiber segment 13 is directly proportional to the square of their diameter.

[0052] The integrated fiber optic sensor of the present invention has a relatively short second fiber segment 12 with a smaller diameter in the middle, while the first fiber segment 11 and the third fiber segment 13 with larger diameters at both ends are designed to be relatively long. This makes the first fiber segment 11 and the third fiber segment 13 with larger diameters at both ends occupy most of the length of the crystal fiber 10, which can concentrate the stress acting on the crystal fiber 10 on the second fiber segment 12, thereby improving the strain sensitivity and making it suitable for high-sensitivity static and dynamic strain sensing. Example 4

[0053] Single-mode optical fiber consists of a core and a cladding. The optical signal is transmitted only in the core. It has a small numerical aperture and only has a fundamental mode for transmission. Therefore, existing technologies can partially etch the cladding of the single-mode optical fiber to form optical fibers with different diameters without affecting the transmission of the optical signal in the core.

[0054] However, the crystal fiber 10 has a cladding-free structure, and the optical signal is transmitted throughout the entire interior of the crystal fiber 10. It has a large numerical aperture and transmits both the fundamental mode and higher-order modes. Therefore, by partially etching the crystal fiber 10 to form fibers with different diameters, this invention will affect the transmission of the optical signal in the crystal fiber 10. This will cause high coupling loss due to mode field mismatch when the optical signal is transmitted in the crystal fiber 10, thereby deteriorating the spectral signal-to-noise ratio of the smaller diameter fiber grating.

[0055] To address the aforementioned technical problems, as a further optimization of Embodiment 1, Embodiment 2, or Embodiment 3, in this embodiment, as shown in Figures 1 and 3, the crystal optical fiber 10 further includes a first graded fiber section 14 and a second graded fiber section 15. The first graded fiber section 14 is connected between the first optical fiber section 11 and the second optical fiber section 12, and the second graded fiber section 15 is connected between the second optical fiber section 12 and the third optical fiber section 13; the diameters of the first graded fiber section 14 and the second graded fiber section 15 gradually change.

[0056] The integrated fiber optic sensor of the present invention provides a first fiber tapered section 14 and a second fiber tapered section 15 with gradually changing diameters between the first fiber segment 11 and the second fiber segment 12, and between the second fiber segment 12 and the third fiber segment 13, respectively. This reduces the high coupling loss caused by the change in fiber diameter when the optical signal enters the second fiber segment 12 from the first fiber segment 11 and the third fiber segment 13 from the second fiber segment 12, thereby improving the spectral signal-to-noise ratio of the small-diameter fiber grating.

[0057] When the diameter of the second fiber segment 12 is greater than the diameters of the first fiber segment 11 and the third fiber segment 13, the diameter of the first fiber tapered segment 14 gradually increases, and the diameter of the end connected to the first fiber segment 11 is the smallest (the same as the first diameter of the first fiber segment 11), while the diameter of the end connected to the second fiber segment 12 is the largest; the diameter of the second fiber tapered segment 15 gradually decreases, and the diameter of the end connected to the second fiber segment 12 is the largest, while the diameter of the end connected to the third fiber segment 13 is the smallest.

[0058] When the diameter of the second fiber segment 12 is smaller than the diameters of the first fiber segment 11 and the third fiber segment 13, the diameter of the first fiber tapered segment 14 gradually decreases, with the end connected to the first fiber segment 11 having the largest diameter and the end connected to the second fiber segment 12 having the smallest diameter; the diameter of the second fiber tapered segment 15 gradually increases, with the end connected to the second fiber segment 12 having the smallest diameter and the end connected to the third fiber segment 13 having the largest diameter.

[0059] Preferably, in order to avoid exciting higher-order leakage modes and causing significant optical loss, the cone angles of the first graded section 14 and the second graded section 15 of the optical fiber should be reduced as much as possible to improve the signal-to-noise ratio of the resonance peak of the resonance spectrum. The diameter change rate of the first graded section 14 and the second graded section 15 of the optical fiber satisfies the following formula:

[0060] ,

[0061] in, The local propagation constant of the fundamental mode of the crystal fiber 10 is given by [the term "propagation constant"]. The local propagation constant of the higher-order modes of the crystal fiber 10 is... For the first fiber graded section 14 and the second fiber graded section 15 per unit length The change in diameter within. Example 5

[0062] As shown in Figure 5, a method for fabricating an integrated fiber optic sensor is provided for fabricating the integrated fiber optic sensor described in Example 1, Example 2, Example 3, or Example 4; the fabrication method includes the following steps:

[0063] Step 100: Design the length and diameter of the first fiber segment 11, the second fiber segment 12 and the third fiber segment 13.

[0064] In step 100, the relationship between the stress and diameter on the crystal fiber 10 is as follows:

[0065] ,

[0066] in, It is the Young's modulus of the crystal fiber 10. It is the axial tensile force acting on the crystal optical fiber 10. It is the cross-sectional area of ​​the crystal optical fiber 10. It is the change in length of the crystal optical fiber 10. It is the original length of the crystal fiber 10. It is the stress generated by the crystal optical fiber 10. It is the axial strain of the crystal optical fiber 10.

[0067] As can be seen from the above formula, the stress generated by the crystal optical fiber 10 The cross-sectional area of ​​the crystal fiber 10 It is inversely proportional, while the cross-sectional area of ​​the crystal fiber 10 is... It is also proportional to the square of the diameter, so the difference in strain sensitivity between the first fiber grating 20 and the second fiber grating 30 can be adjusted by designing the diameter ratio of the first fiber segment 11 and the second fiber segment 12.

[0068] The strain sensitivity of the first fiber grating 20 and the second fiber grating 30 satisfies the following formula:

[0069] ,

[0070] in, and These are the strain sensitivities of the first fiber grating 20 and the second fiber grating 30, respectively. and These are the diameters of the first optical fiber segment 11 and the second optical fiber segment 12, respectively.

[0071] The diameters of the first optical fiber segment 11 and the third optical fiber segment 13 are the first diameters, the diameter of the second optical fiber segment 12 is the second diameter, the total length of the first optical fiber segment 11 and the third optical fiber segment 13 is the first length L1+L3, and the length of the second optical fiber segment 12 is the second length L2.

[0072] When the first diameter is smaller than the second diameter, and the first length L1+L3 is greater than the second length L2, the first fiber segment 11 and the third fiber segment 13, which have smaller diameters at both ends, occupy most of the length of the crystal fiber 10. This allows the stress acting on the crystal fiber 10 to be dispersed in the first fiber segment 11 and the third fiber segment 13, thereby increasing the strain range and making the strain measurement range closer to the tensile strength value of the crystal fiber 10 itself. When the first diameter is greater than the second diameter, and the first length L1+L3 is greater than the second length L2, the first fiber segment 11 and the third fiber segment 13, which have larger diameters at both ends, occupy most of the length of the crystal fiber 10. This allows the stress acting on the crystal fiber 10 to be concentrated on the second fiber segment 12, thereby increasing the strain sensitivity.

[0073] Therefore, by designing the length ratio between the second fiber segment 12 and the total length of the first fiber segment 11 and the third fiber segment 13, the strain sensitivity, strain resolution, and strain range of the first fiber grating 20 and the second fiber grating 30 can be adjusted.

[0074] Step 200: Etch the crystal fiber 10 with an acidic solution to form the first fiber segment 11, the second fiber segment 12 and the third fiber segment 13 respectively.

[0075] As shown in Figure 6, in step 200, the etching of the crystal optical fiber 10 using an acidic solution is as follows:

[0076] Step 210: Place the glass protective tube over the non-corroded portion of the crystal optical fiber 10.

[0077] In step 210, the crystal fiber 10 includes a non-corroded portion 11' and a corroded portion 12', wherein the non-corroded portion 11' corresponds to the fiber segment with a larger diameter, and the corroded portion 12' corresponds to the fiber segment with a smaller diameter. That is, if the diameter of the second fiber segment 12 is greater than the diameters of the first fiber segment 11 and the third fiber segment 13, then the non-corroded portion 11' corresponds to the second fiber segment 12, and the corroded portion 12' corresponds to the first fiber segment 11 and the third fiber segment 13. If the diameter of the second fiber segment 12 is smaller than the diameters of the first fiber segment 11 and the third fiber segment 13, then the non-corroded portion 11' corresponds to the first fiber segment 11 and the third fiber segment 13, and the corroded portion 12' corresponds to the second fiber segment 12.

[0078] If the crystal fiber 10 needs to be etched into a structure with a large diameter in the middle and a small diameter at both ends, then there is only one glass protective tube 40, which is sleeved on the non-etched part 11' in the middle of the crystal fiber 10; if the crystal fiber 10 needs to be etched into a structure with a small diameter in the middle and a large diameter at both ends, then there are two glass protective tubes 40, which are respectively sleeved on the non-etched parts 11' at both ends of the crystal fiber 10.

[0079] Step 220: Immerse the etched portion 12' of the crystal fiber 10 in a first acidic solution to etch it to the desired diameter.

[0080] In step 220, due to their different materials, the crystal optical fiber 10 and the glass protective tube 40 can be corroded by different acidic solutions. The first acidic solution can only corrode the crystal optical fiber 10, but cannot corrode the glass protective tube 40.

[0081] If the diameter of the second optical fiber segment 12 is greater than the diameters of the first optical fiber segment 11 and the third optical fiber segment 13, then the etched portion 12' forms the first optical fiber segment 11 and the third optical fiber segment 13 after etching. If the diameter of the second optical fiber segment 12 is smaller than the diameters of the first optical fiber segment 11 and the third optical fiber segment 13, then the etched portion 12' forms the second optical fiber segment 12 after etching.

[0082] In this embodiment, the first acidic solution is a mixture of sulfuric acid and phosphoric acid.

[0083] Preferably, in step 220, the end of the glass protective tube 40 near the corroded portion 12' is also immersed in the first acidic solution, so that the first acidic solution corrodes the end of the non-corroded portion 11' near the corroded portion 12' into a graded fiber segment.

[0084] As shown in Figure 7, during corrosion, as the first acidic solution corrodes the corroded portion 12' of the crystal optical fiber 10, the diameter of the corroded portion 12' gradually decreases. Meanwhile, the end side 13' of the non-corroded portion 11', which is enclosed by the glass protective tube 40, near the corroded portion 12', gradually becomes exposed. The exposed end side 13' is corroded again after contacting the first acidic solution, so that the first acidic solution not only has a corrosive effect on the corroded portion 12' along the diameter direction, but also has a corrosive effect on the non-corroded portion 11' along the optical fiber axis. Moreover, the closer the non-corroded portion 11' is to the corroded portion 12', the greater the degree of corrosion and the smaller the diameter, ultimately forming a gradually changing optical fiber segment with a gradually changing diameter.

[0085] The fiber gradient segment consists of two segments: a first fiber gradient segment 14 connected between the first fiber segment 11 and the second fiber segment 12, and a second fiber gradient segment 15 connected between the second fiber segment 12 and the third fiber segment 13.

[0086] Step 230: Use a second acidic solution to etch and remove the glass protective tube 40 outside the crystal optical fiber 10.

[0087] In step 230, the second acidic solution can only corrode the glass protective tube 40, but not the crystal optical fiber 10.

[0088] In this embodiment, the second acidic solution is a hydrofluoric acid solution.

[0089] Step 300: Use a femtosecond laser to write the first fiber segment 11 and the second fiber segment 12 to form the first fiber grating 20 and the second fiber grating 30 in the first fiber segment 11 and the second fiber segment 12, respectively.

[0090] In step 300, a femtosecond laser processing system is constructed using a high-repetition-rate femtosecond laser, a high-precision electrically controlled three-dimensional displacement platform, and a high-magnification objective lens, so as to etch the first fiber grating 20 and the second fiber grating 30 in the first fiber segment 11 and the second fiber segment 12 of the crystal fiber 10, respectively.

[0091] Based on the different diameters of the first fiber segment 11 and the second fiber segment 12, the femtosecond laser beam is focused at different depths of the first fiber segment 11 and the second fiber segment 12 respectively, and parameters such as writing cycle, writing speed, and writing length are set.

[0092] Since the first fiber grating 20 and the second fiber grating 30 use wavelength demodulation, it is necessary to properly set their respective grating periods to ensure that their resonance peaks do not overlap in the resonance spectrum.

[0093] When wavelength bandwidth is limited, fiber gratings with larger periods can be inscribed in fiber segments with smaller diameters, and fiber gratings with smaller periods can be inscribed in fiber segments with larger diameters. In fiber segments with smaller diameters, fiber gratings can be inscribed point-by-point or line-by-line, while in fiber segments with larger diameters, multi-layer line-by-line or surface-by-surface fiber gratings can be inscribed to increase the refractive index modulation region area of ​​the fiber grating and improve its reflectivity. This can, to some extent, offset the light leakage caused by the optical signal passing through the first graded section 14 and the second graded section 15 of the fiber, thereby improving the signal-to-noise ratio.

[0094] Finally, one end of the crystal fiber 10 of the integrated fiber optic sensor is fused to the multimode quartz fiber. The dual-grating signal of the integrated fiber optic sensor is tested and demodulated through the multimode quartz fiber using a broadband light source, fiber optic spectrometer, 3dB multimode fiber coupler, mode scrambler, flange, etc.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and not to limit them. Although the embodiments of the present invention have been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the embodiments of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An integrated fiber optic sensor for measuring temperature strain at extreme high temperatures, characterized in that, include: Crystal optical fiber, comprising a first fiber segment, a second fiber segment, and a third fiber segment connected in sequence; A first fiber grating is formed in a first fiber segment of the crystal fiber; A second fiber grating is formed in the second fiber segment of the crystal fiber; Wherein, the first optical fiber segment and the third optical fiber segment have the same diameter, and the second optical fiber segment has a different diameter from the first optical fiber segment and the second optical fiber segment.

2. The integrated fiber optic sensor according to claim 1, characterized in that, The temperature sensitivity and strain sensitivity of the first fiber grating are respectively and The temperature sensitivity and strain sensitivity of the second fiber grating are respectively and The measured temperature change and dependent variables Satisfy the following formula: ， in, and These are the wavelength shifts of the first fiber grating and the second fiber grating, respectively.

3. The integrated fiber optic sensor according to claim 1, characterized in that, The diameters of the first and third fiber segments are the first diameter, the diameter of the second fiber segment is the second diameter, the total length of the first and third fiber segments is the first length, and the length of the second fiber segment is the second length; the first diameter is smaller than the second diameter, and the first length is greater than the second length.

4. The integrated fiber optic sensor according to claim 1, characterized in that, The diameters of the first and third fiber segments are the first diameter, the diameter of the second fiber segment is the second diameter, the total length of the first and third fiber segments is the first length, and the length of the second fiber segment is the second length; the first diameter is greater than the second diameter, and the first length is greater than the second length.

5. The integrated fiber optic sensor according to claim 3 or 4, characterized in that, The stress generated by the first, second, and third fiber segments is inversely proportional to their cross-sectional area, while the cross-sectional area of ​​the first, second, and third fiber segments is directly proportional to the square of their diameter.

6. The integrated fiber optic sensor according to any one of claims 1-4, characterized in that, The crystal optical fiber further includes a first graded fiber section and a second graded fiber section. The first graded fiber section is connected between the first fiber section and the second fiber section, and the second graded fiber section is connected between the second fiber section and the third fiber section. The diameters of the first graded fiber section and the second graded fiber section gradually change.

7. The integrated fiber optic sensor according to claim 6, characterized in that, The diameter change rates of the first and second graded-section optical fibers satisfy the following formula: ， in, Let be the local propagation constant of the fundamental mode of the crystal fiber. The local propagation constant of the higher-order modes of the crystal fiber is denoted as . For the first and second fiber graded-change segments per unit length The change in diameter within.

8. The integrated fiber optic sensor according to claim 1, characterized in that, The crystal fiber may be, but is not limited to, sapphire fiber, zirconia fiber, lutetium oxide fiber, or YAG fiber.

9. The method for fabricating the integrated fiber optic sensor according to claim 1, characterized in that, Includes the following steps: Step 100: Design the length and diameter of the first fiber segment, the second fiber segment, and the third fiber segment; Step 200: Etch the crystal fiber with an acidic solution to form the first fiber segment, the second fiber segment, and the third fiber segment, respectively. Step 300: Use a femtosecond laser to write the first fiber segment and the second fiber segment to form the first fiber grating and the second fiber grating in the first fiber segment and the second fiber segment, respectively.

10. The preparation method according to claim 9, characterized in that, In step 100, the difference in strain sensitivity between the first fiber grating and the second fiber grating is adjusted by designing the diameter ratio of the first fiber segment and the second fiber segment.

11. The preparation method according to claim 10, characterized in that, The strain sensitivity of the first fiber grating and the second fiber grating satisfies the following formula: ， in, and These are the strain sensitivities of the first fiber grating and the second fiber grating, respectively. and These are the diameters of the first optical fiber segment and the second optical fiber segment, respectively.

12. The preparation method according to claim 9, characterized in that, In step 100, the strain sensitivity, strain resolution, and strain range of the first fiber grating and the second fiber grating are adjusted by designing the length ratio between the second fiber segment and the total length of the first fiber segment and the third fiber segment.

13. The preparation method according to claim 9, characterized in that, In step 200, the etching of the crystal optical fiber using an acidic solution is as follows: Step 210: Place the glass protective tube over the non-corroded portion of the crystal optical fiber; Step 220: Immerse the etched portion of the crystal fiber in a first acidic solution to etch it to the desired diameter; Step 230: Use a second acidic solution to etch and remove the glass protective tube outside the crystal optical fiber.

14. The preparation method according to claim 13, characterized in that, In step 220, the end of the glass protective tube near the corroded portion is also immersed in the first acidic solution, so that the first acidic solution corrodes the end of the non-corroded portion near the corroded portion into a graded fiber segment.

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