A fiber pressure sensor based on fiber FPI and a preparation method thereof

Abstract

The application discloses a kind of optical fiber pressure sensors based on optical fiber FPI, including sequentially connected fixed first optical fiber, quartz capillary and second optical fiber along the axial direction, there is first fixed point between the first optical fiber and quartz capillary, there is second fixed point between the second optical fiber and quartz capillary;The local pipe body between the first fixed point and second fixed point of the quartz capillary is the strain part that can respond to external pressure and deform inward;The diameter of the second optical fiber is smaller than the inner diameter of the quartz capillary, and the end of the second optical fiber towards the first optical fiber is inserted into the quartz capillary to form the support part corresponding to the strain part, and keep a certain optical fiber gap between the first optical fiber;There is a limit gap between the support part and the strain part, to deform inwardly, when the external pressure reaches or exceeds the maximum measuring pressure of sensor, the strain part can be in contact with the support part and no longer continue to deform inwardly.This optical fiber pressure sensor has the advantages of high pressure sensitivity, environmental high pressure resistance and anti-broken.The application also discloses a preparation method of the above-mentioned optical fiber pressure sensor.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensors, and more particularly to a fiber optic pressure sensor and its fabrication method. Background Technology

[0002] Fiber optic pressure sensors are a new type of sensor that measures external pressure based on fiber Bragg gratings or fiber optic fiber polarization (FPI). Due to their all-optical structure, small size, and resistance to electromagnetic interference, fiber optic pressure sensors have significant application prospects in fields such as petrochemicals, nuclear power engineering, and underwater pressure shock, especially in pressure measurement in liquid environments.

[0003] like Figure 1 As shown, the fiber optic FPI consists of a quartz capillary 2' and two optical fibers 1' and 3' connected to the two ends of the quartz capillary 2'. The local tube between the two optical fibers 1' and 3' of the quartz capillary 2' is a strain section 20' that can deform inward in response to external pressure, and it is also the interference cavity of the fiber optic FPI. The larger the axial length of the strain section 20', the larger its pressure sensing area and the smaller its Young's modulus. Under the same pressure, it can produce a larger deformation, and the higher the sensitivity of the interferometer. However, if the cavity length of the interference cavity is too large, it will bring a series of problems such as a smaller free spectral range and measurement dynamic range, and a decrease in interference spectral contrast. It is difficult to satisfy both at the same time.

[0004] In addition, the deformation of the quartz capillary is limited. When the external pressure is too great and exceeds the maximum measurement pressure of the sensor, the excessive deformation will cause the quartz capillary 2 to break, thereby damaging the sensor. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides an optical fiber pressure sensor based on optical fiber FPI and its fabrication method, which has the advantages of high pressure sensitivity, resistance to high environmental pressure, and rupture resistance.

[0006] The technical problem to be solved by the present invention is achieved through the following technical solution: A fiber optic pressure sensor based on fiber optic FPI includes a first optical fiber, a quartz capillary tube, and a second optical fiber connected and fixed in sequence along the axial direction. There is a first fixing point between the first optical fiber and the quartz capillary tube, and a second fixing point between the second optical fiber and the quartz capillary tube. The local tube body of the quartz capillary tube located between the first fixing point and the second fixing point is a strain section that can deform inward in response to external pressure. The diameter of the second optical fiber is smaller than the inner diameter of the quartz capillary, and the end of the second optical fiber facing the first optical fiber is inserted into the quartz capillary to form a support portion corresponding to the strain portion, and a certain optical fiber gap is maintained between the support portion and the strain portion; there is a limiting gap between the support portion and the strain portion to allow the strain portion to deform inward. When the external pressure reaches or exceeds the maximum measurement pressure of the sensor, the strain portion can abut against the support portion and no longer deform inward.

[0007] Furthermore, the interference cavity length of the fiber optic FPI is smaller than the axial length of the strain section.

[0008] Furthermore, the fiber optic pressure sensor also includes at least one of a first reflective film and a second reflective film. The first reflective film is disposed on the end face of the first optical fiber facing the second optical fiber; The second reflective film is disposed on the end face of the second optical fiber facing the first optical fiber.

[0009] Furthermore, an axial cavity communicating with the fiber gap is formed on one end face of the second optical fiber facing the first optical fiber. The fiber gap and the axial cavity together constitute the interference cavity of the optical fiber FPI.

[0010] Furthermore, the fiber optic pressure sensor also includes at least one of a first reflective film and a second reflective film. The first reflective film is disposed on the end face of the first optical fiber facing the second optical fiber; The second reflective film is disposed on the bottom of the axial cavity of the second optical fiber.

[0011] Furthermore, the other end face of the first optical fiber facing away from the second optical fiber is roughened to form an uneven diffuse reflection structure.

[0012] Furthermore, a temperature-measuring fiber grating is fabricated outside the quartz capillary and near the quartz capillary in the second optical fiber.

[0013] The above-mentioned method for fabricating the fiber optic pressure sensor includes the following steps: Step 1: First, cut one end face of the first optical fiber flat, then align the central axes of the first optical fiber and the quartz capillary with each other, and then connect and fix the flattened end of the first optical fiber to one end of the quartz capillary to form the first fixing point. Step 2: Cut the quartz capillary according to the required axial length of the strain section; Step 3: First, cut one end face of the second optical fiber flat. Then, align the central axes of the second optical fiber and the quartz capillary tube. Next, insert the flattened end of the second optical fiber into the other end of the quartz capillary tube. Adjust the insertion depth of the second optical fiber according to the required axial length of the optical fiber gap. Finally, connect and fix the flattened end of the second optical fiber to the other end of the quartz capillary tube to form the second fixing point.

[0014] Furthermore, the preparation method further includes at least one of the following steps: In step 1, before aligning with the quartz capillary, the first reflective film is made on the flat end face of the first optical fiber. In step 3, before aligning with the quartz capillary, the second reflective film is made on the flat-cut end of the second optical fiber, or the axial cavity is first made on the flat-cut end of the second optical fiber, and then the second reflective film is made on the bottom of the axial cavity. In step 3, after being connected and fixed to the quartz capillary, the other end face of the first optical fiber facing away from the second optical fiber is roughened to form an uneven diffuse reflection structure.

[0015] Furthermore, the preparation method further includes the following steps: Step 4: Use a femtosecond laser to fabricate a temperature-measuring fiber optic grating at a position where the second optical fiber is located outside and close to the quartz capillary.

[0016] The present invention has the following beneficial effects: The fiber optic pressure sensor of the present invention connects and fixes one end of the quartz capillary to a second optical fiber with a smaller diameter, and inserts the end of the second optical fiber facing the first optical fiber into the quartz capillary to form the support portion. This allows the strain portion to resist the support portion and stop deforming inward when the external pressure reaches or exceeds the sensor's maximum measurement pressure, thus avoiding the problem of tube rupture due to excessive deformation of the strain portion, thereby achieving the purpose of resisting high environmental pressure and preventing rupture. In addition, since the axial length of the strain portion is equal to the sum of the axial lengths of the optical fiber gap and the support portion, which is greater than the axial length of the optical fiber gap, the strain portion has a larger pressure sensing area and a smaller Young's modulus compared to the prior art, enabling higher pressure sensitivity. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the existing fiber optic FPI structure.

[0018] Figure 2 This is a schematic diagram of the structure of the fiber optic pressure sensor provided by the present invention.

[0019] Figure 3 This is a schematic diagram of the structure of the fiber optic pressure sensor provided by the present invention, showing the strain section abutting against the support section.

[0020] Figure 4 This is a schematic diagram of another fiber optic pressure sensor provided by the present invention.

[0021] Figure 5 This is a schematic diagram of another fiber optic pressure sensor provided by the present invention.

[0022] Figure 6 This is a schematic diagram of another fiber optic pressure sensor provided by the present invention.

[0023] Figure 7 This is a schematic diagram of another fiber optic pressure sensor provided by the present invention.

[0024] Figure 8 A flowchart illustrating the steps of the fabrication method of the fiber optic pressure sensor provided by the present invention. Detailed Implementation

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] Example 1 like Figure 2 As shown, an optical fiber pressure sensor based on fiber optic FPI includes a first optical fiber 1, a quartz capillary tube 2, and a second optical fiber 3 connected and fixed along the axial direction. There is a first fixing point 10 between the first optical fiber 1 and the quartz capillary tube 2, and a second fixing point 30 between the second optical fiber 3 and the quartz capillary tube 2. The local tube body of the quartz capillary tube 2 located between the first fixing point 10 and the second fixing point 30 is a strain section 20 that can deform inward in response to external pressure. The diameter of the second optical fiber 3 is smaller than the inner diameter of the quartz capillary tube 2, and the end of the second optical fiber 3 facing the first optical fiber 1 is inserted into the quartz capillary tube 2 to form a support portion 31 corresponding to the strain section 20, and maintains a certain optical fiber gap 21 between it and the first optical fiber 1; a limiting gap 22 is provided between the support portion 31 and the strain section 20 to allow the strain section 20 to deform inward, such as Figure 3 As shown, when the external pressure reaches or exceeds the maximum measurement pressure of the sensor, the strain section 20 can abut against the support section 31 and stop deforming inward.

[0030] The fiber optic pressure sensor of the present invention connects and fixes one end of the quartz capillary tube 2 to a second optical fiber 3 with a smaller diameter, and inserts the end of the second optical fiber 3 facing the first optical fiber 1 into the quartz capillary tube 2 to form the support part 31. This allows the strain section 20 to abut against the support part 31 and stop deforming inward when the external pressure reaches or exceeds the sensor's maximum measurement pressure, thus avoiding the problem of tube rupture due to excessive deformation of the strain section 20. This achieves the purpose of withstanding high environmental pressure and preventing rupture. In addition, since the axial length of the strain section 20 is equal to the sum of the axial lengths of the optical fiber gap 21 and the support part 31, and is greater than the axial length of the optical fiber gap 21, the strain section 20 has a larger pressure sensing area and a smaller Young's modulus compared to the prior art, enabling higher pressure sensitivity.

[0031] The end face of the first optical fiber 1 facing the second optical fiber 3, the end face of the second optical fiber 3 facing the first optical fiber 1, and the fiber gap 21 between these two end faces together constitute a fiber optic FPI (Fabry-Perot interferometer). During measurement, an optical signal is input into the fiber optic FPI from the end face of the second optical fiber 3 facing away from the first optical fiber 1. The optical signal is reflected when passing through both the end face of the first optical fiber 1 facing the second optical fiber 3 and the end face of the second optical fiber 3 facing the first optical fiber 1. The interference light formed by the coherent mixing of the two reflected beams has an interference peak. The peak wavelength of the interference peak is related to the cavity length of the fiber optic FPI. Since the fiber gap 21 between the first optical fiber 1 and the second optical fiber 3 constitutes part or all of the interference cavity, changes in the fiber gap 21 can induce... The interference peak causes wavelength shift. When the external pressure acts on the strain section 20 of the quartz capillary 2, the strain section 20 deforms inward, causing a change in its axial length. This change in axial length can be transmitted to the first optical fiber 1 and the second optical fiber 3 through the first fixed point 10 and the second fixed point 30, respectively, thereby causing a change in the axial length of the optical fiber gap 21. Ultimately, this changes the interference cavity length of the optical fiber FPI, resulting in a wavelength shift in the interference peak. Therefore, the magnitude of the pressure on the strain section 20 can be calculated by reverse derivation of the wavelength shift of the interference peak.

[0032] The first optical fiber 1 and the quartz capillary tube 2 can be fixed by fusion splicing, adhesive bonding or solder welding, and the first fixing point 10 is a fusion splice point, adhesive bonding point or solder welding point. For example, when the diameter of the first optical fiber 1 is greater than the inner diameter of the quartz capillary tube 2, first align the central axes of the first optical fiber 1 and the quartz capillary tube 2, then tightly attach and fuse one end face of the first optical fiber 1 to one end face of the quartz capillary tube 2; when the diameter of the first optical fiber 1 is equal to the inner diameter of the quartz capillary tube 2, first align the central axes of the first optical fiber 1 and the quartz capillary tube 2, then insert one end of the first optical fiber 1 into one end opening of the quartz capillary tube 2 and fuse it; when the diameter of the first optical fiber 1 is also smaller than the inner diameter of the quartz capillary tube 2, first align the central axes of the first optical fiber 1 and the quartz capillary tube 2, then insert one end of the first optical fiber 1 into one end opening of the quartz capillary tube 2, and then use glue or solder to fix them at the edge of the gap.

[0033] The second optical fiber 3 and the quartz capillary tube 2 can be fixed together by adhesive bonding or soldering, and the second fixing point 30 is the bonding point or soldering point. For example, after aligning the central axes of the second optical fiber 3 and the quartz capillary tube 2, one end of the second optical fiber 3 is inserted into the other end of the quartz capillary tube 2, and the two are fixed together by adhesive bonding or soldering at the edge of the gap.

[0034] Preferably, the interference cavity length of the fiber optic FPI is less than the axial length of the strain section 20, so that by adjusting the insertion depth of the second fiber 3 in the quartz capillary 2, the axial length of the strain section 20 can be increased while ensuring that the interference cavity length of the fiber optic FPI is within a reasonable range.

[0035] like Figure 1 As shown, when no microcavity structure is fabricated on the end face of the first optical fiber 1 facing the second optical fiber 3, the interference cavity of the optical fiber FPI is formed only by the optical fiber gap 21 between the first optical fiber 1 and the second optical fiber 3. In this case, the cavity length of the interference cavity is equal to the axial length of the optical fiber gap 21. Figure 7 As shown, when an axial cavity 32 communicating with the fiber gap 21 is formed on the end face of the first optical fiber 1 facing the second optical fiber 3, the interference cavity of the optical fiber FPI is jointly formed by the fiber gap 21 between the first optical fiber 1 and the second optical fiber 3, and the axial cavity 32 in the first optical fiber 1. At this time, the cavity length of the interference cavity is equal to the sum of the axial lengths of the fiber gap 21 and the axial cavity 32.

[0036] The axial cavity 32 can increase the insertion depth of the second optical fiber 3 in the quartz capillary 3 without changing the interference cavity length of the optical fiber FPI, thereby increasing the axial length of the support part 31 and improving the support capability of the support part 31 for the strain part 20.

[0037] The axial cavity 32 is prepared by a combination of femtosecond laser etching and hydrofluoric acid etching. Specifically, hydrofluoric acid is first used to create the approximate size and outline of the axial cavity 32 on one end face of the second optical fiber 3. Then, the femtosecond laser is used to perform fine etching on the axial cavity 32 to remove the cavity wall on the axial cavity 32 that has been damaged by the hydrofluoric acid in terms of molecular network structure.

[0038] like Figure 4 As shown, in one example, a first reflective film 4 is disposed on the end face of the first optical fiber 1 facing the second optical fiber 3, such as... Figure 5 As shown, in another example, a second reflective film 5 is disposed on the end face of the second optical fiber 3 facing the first optical fiber 1, such as... Figure 6As shown, in another example, a first reflective film 4 and a second reflective film 5 are respectively provided on the end face of the first optical fiber 1 facing the second optical fiber 3 and on the end face of the second optical fiber 3 facing the first optical fiber 1.

[0039] The first reflective film 4 and the second reflective film 5 can increase the end face reflectivity of the fiber optic FPI, thereby improving the precision and contrast of the sensor interference spectrum. When an axial cavity 32 communicating with the fiber gap 21 is formed on the end face of the second fiber 3 facing the first fiber 1, the second reflective film 5 is disposed on the bottom of the axial cavity 32.

[0040] The first reflective film 4 and the second reflective film 5 are preferably metal thin films, such as nano-gold thin films or nano-silver thin films, which are respectively covered on the end face of the first optical fiber 1 facing the second optical fiber 3 and the end face of the second optical fiber 3 facing the first optical fiber 1 (or the bottom of the axial cavity 32) by magnetron sputtering, vacuum evaporation or chemical vapor deposition.

[0041] like Figure 7 As shown, the second optical fiber 3 includes an optical fiber cladding 33 and an optical fiber core 34. The optical fiber cladding 33 surrounds the outer peripheral sidewall of the optical fiber core 34. The axial cavity 32 is formed on the end face of the optical fiber core 34 facing the first optical fiber 1.

[0042] Preferably, a temperature-measuring fiber grating 35 is formed on the outside of the quartz capillary 2 and near the quartz capillary 2 in the second optical fiber 3.

[0043] The temperature-sensing fiber optic grating 35 can measure the external temperature independently, and during signal demodulation, it can perform temperature compensation on the pressure measurement results of the fiber optic FPI based on the external temperature measured by the temperature-sensing fiber optic grating 35.

[0044] In this embodiment, the first optical fiber 1 is a single-mode optical fiber, and the second optical fiber 3 is a narrow-diameter optical fiber. Preferably, the end face of the first optical fiber 1 facing away from the second optical fiber 3 is roughened to form an uneven diffuse reflection structure 11, thereby disrupting the total internal reflection condition of the first optical fiber 1 at this end face and preventing the optical signal from forming a third reflected beam due to specular reflection when passing through this end face, thus reducing interference with the interference light.

[0045] Example 2 like Figure 8 As shown, a method for fabricating an optical fiber pressure sensor is provided for fabricating the optical fiber pressure sensor described in Example 1; the fabrication method includes the following steps: Step 1: First, cut one end face of the first optical fiber flat, then align the central axes of the first optical fiber and the quartz capillary with each other, and then connect and fix the flattened end of the first optical fiber to one end of the quartz capillary to form the first fixing point. Step 2: Cut the quartz capillary according to the required axial length of the strain section; Step 3: First, cut one end face of the second optical fiber flat. Then, align the central axes of the second optical fiber and the quartz capillary tube. Next, insert the flattened end of the second optical fiber into the other end of the quartz capillary tube. Adjust the insertion depth of the second optical fiber according to the required axial length of the optical fiber gap. Finally, connect and fix the flattened end of the second optical fiber to the other end of the quartz capillary tube to form the second fixing point. Step 4: Use a femtosecond laser to fabricate a temperature-measuring fiber optic grating at a position where the second optical fiber is located outside and close to the quartz capillary.

[0046] The preparation method further includes at least one of the following steps: In step 1, before aligning with the quartz capillary, the first reflective film is made on the flat end face of the first optical fiber. In step 3, before aligning with the quartz capillary, the second reflective film is made on the flat-cut end of the second optical fiber, or the axial cavity is first made on the flat-cut end of the second optical fiber, and then the second reflective film is made on the bottom of the axial cavity. In step 3, after being connected and fixed to the quartz capillary, the other end face of the first optical fiber facing away from the second optical fiber is roughened to form an uneven diffuse reflection structure.

[0047] 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. A fiber optic pressure sensor based on fiber optic FPI, comprising a first optical fiber, a quartz capillary tube, and a second optical fiber sequentially and fixedly connected along the axial direction, wherein a first fixing point is located between the first optical fiber and the quartz capillary tube, and a second fixing point is located between the second optical fiber and the quartz capillary tube; the local tube portion of the quartz capillary tube located between the first and second fixing points is a strain section capable of inward deformation in response to external pressure; characterized in that... The diameter of the second optical fiber is smaller than the inner diameter of the quartz capillary, and the end of the second optical fiber facing the first optical fiber is inserted into the quartz capillary to form a support portion corresponding to the strain portion, and a certain optical fiber gap is maintained between the support portion and the strain portion; there is a limiting gap between the support portion and the strain portion to allow the strain portion to deform inward. When the external pressure reaches or exceeds the maximum measurement pressure of the sensor, the strain portion can abut against the support portion and no longer deform inward.

2. The fiber optic pressure sensor according to claim 1, characterized in that, The interference cavity length of the fiber optic FPI is less than the axial length of the strain section.

3. The fiber optic pressure sensor according to claim 1, characterized in that, The fiber optic pressure sensor also includes at least one of a first reflective film and a second reflective film. The first reflective film is disposed on the end face of the first optical fiber facing the second optical fiber; The second reflective film is disposed on the end face of the second optical fiber facing the first optical fiber.

4. The fiber optic pressure sensor according to claim 1, characterized in that, An axial cavity communicating with the fiber gap is formed on one end face of the second optical fiber facing the first optical fiber. The fiber gap and the axial cavity together constitute the interference cavity of the optical fiber FPI.

5. The fiber optic pressure sensor according to claim 4, characterized in that, The fiber optic pressure sensor also includes at least one of a first reflective film and a second reflective film. The first reflective film is disposed on the end face of the first optical fiber facing the second optical fiber; The second reflective film is disposed on the bottom of the axial cavity of the second optical fiber.

6. The fiber optic pressure sensor according to claim 1, characterized in that, The end face of the first optical fiber facing away from the second optical fiber is roughened to form an uneven diffuse reflection structure.

7. The fiber optic pressure sensor according to claim 1, characterized in that, The second optical fiber is located outside the quartz capillary and a temperature-measuring fiber grating is fabricated near the quartz capillary.

8. The method for preparing the fiber optic pressure sensor according to claim 1, characterized in that, Includes the following steps: Step 1: First, cut one end face of the first optical fiber flat, then align the central axes of the first optical fiber and the quartz capillary with each other, and then connect and fix the flattened end of the first optical fiber to one end of the quartz capillary to form the first fixing point. Step 2: Cut the quartz capillary according to the required axial length of the strain section; Step 3: First, cut one end face of the second optical fiber flat. Then, align the central axes of the second optical fiber and the quartz capillary tube. Next, insert the flattened end of the second optical fiber into the other end of the quartz capillary tube. Adjust the insertion depth of the second optical fiber according to the required axial length of the optical fiber gap. Finally, connect and fix the flattened end of the second optical fiber to the other end of the quartz capillary tube to form the second fixing point.

9. The preparation method according to claim 8, characterized in that, The preparation method further includes at least one of the following steps: In step 1, before aligning with the quartz capillary, the first reflective film is made on the flat end face of the first optical fiber. In step 3, before aligning with the quartz capillary, the second reflective film is made on the flat-cut end of the second optical fiber, or the axial cavity is first made on the flat-cut end of the second optical fiber, and then the second reflective film is made on the bottom of the axial cavity. In step 3, after being connected and fixed to the quartz capillary, the other end face of the first optical fiber facing away from the second optical fiber is roughened to form an uneven diffuse reflection structure.

10. The preparation method according to claim 8, characterized in that, The preparation method further includes the following steps: Step 4: Use a femtosecond laser to fabricate a temperature-measuring fiber optic grating at a position where the second optical fiber is located outside and close to the quartz capillary.

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