Capillary inner diameter optical fiber measurement device and method based on FP interference principle

Abstract

The present invention belongs to the field of optical fiber sensing technology and discloses an optical fiber measurement device and method for the inner diameter of a capillary tube based on the F-P interference principle. The device comprises a broadband light source, an optical fiber circulator, an optical spectrum analyzer, and a transmission optical fiber. One end of the transmission optical fiber is an optical fiber connection end, and the other end is an optical fiber sensing end. The broadband light source is optically connected to the light incident port of the optical fiber circulator, the optical spectrum analyzer is optically connected to the light reflection port of the optical fiber circulator, and the optical fiber connection end is optically connected to the light output port of the optical fiber circulator. The optical fiber sensing end comprises a bare fiber body with a protective layer and a coating layer stripped off, the bare fiber body consisting of a fiber core and a cladding, and the end of the bare fiber body is a 45-degree obliquely polished end face. The device has the characteristics of simple structure, strong robustness, flexible measurement, etc., and is particularly suitable for measurement in narrow and difficult-to-reach spatial environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing, and in particular relates to an optical fiber measuring device and method for measuring the inner diameter of a capillary tube based on the FP interference principle. Background Art

[0002] Measuring internal dimensions in tight and hard-to-reach places is a challenge for many measurement devices. In many cases, narrow air inlets can prevent relatively large sensors from entering holes, tubes, cylinders, or other confined spaces for measurement.

[0003] Electronic sensors are commonly used for internal dimension measurement. In 2009, Chang Ting-Yen et al. proposed a three-dimensional micropore measurement system based on the capacitive sensing principle. However, due to the large size of the sensor device, the measurable micropore size is limited. In 2015, Liu Bo et al. proposed a non-contact measurement system for the internal dimensions of tubular parts, which can significantly improve the measurement resolution. However, electronic sensors have inherent problems and are easily affected by electromagnetic interference and are not suitable for use in chemical environments. The problems of electronic sensors can be overcome by using optical measurement methods. In 2018, Jin Lianhua et al. used light generated by a disk beam detector to illuminate a cylindrical opening, measured the cylindrical opening, and could determine the diameter based on the cross-sectional image of the object. In 2019, Zhang Xiaoyun et al. proposed a confocal X-ray scattering method based on X-ray capillary optics to achieve non-destructive measurement of the inner and outer diameters of capillaries. In 2021, Guo Jiang et al. proposed a method for measuring the wall thickness of thin-walled shell parts using a sub-micron resolution coordinate measuring machine. The established measurement reference conformity model can obtain thickness information in a spatial coordinate system. However, the aforementioned optical sensors are complex and expensive, or are implemented indirectly.

[0004] A Chinese patent document, publication number CN108613926A, discloses a capillary interferometry experimental device. This device can be used to measure the fringe distribution when a laser beam is incident on a capillary tube at a vertical or oblique angle. Based on the observed interference fringe data, the inner and outer diameters of the capillary tube, the refractive index of the tube wall, and the refractive index of the liquid inside the capillary tube are calculated. Using the principle of light interference to perform high-precision micro-size measurements has obvious advantages.

[0005] In recent years, fiber optic sensors have developed rapidly and found widespread application. They offer advantages such as compact sensor heads, immunity to electromagnetic interference, safety in hazardous environments, real-time parameter monitoring, remote sensing capabilities, and high operational flexibility. Therefore, using interferometry-based fiber optic sensors to measure capillary inner diameters is an effective and feasible approach. Summary of the Invention

[0006] The present invention aims to solve the problems existing in the prior art and proposes a device and method for measuring the inner diameter of a capillary tube using an optical fiber based on the FP interferometer principle. The technical solution adopted to achieve the above-mentioned purpose is as follows:

[0007] The optical fiber measuring device for the inner diameter of a capillary tube based on the FP interference principle includes a broadband light source, an optical fiber circulator, an optical spectrum analyzer, and a transmission optical fiber. One end of the transmission optical fiber is an optical fiber connection end, and the other end is an optical fiber sensing end. The broadband light source is optically connected to the light incident port of the optical fiber circulator, the optical spectrum analyzer is optically connected to the light reflection port of the optical fiber circulator, and the optical fiber connection end is optically connected to the light output port of the optical fiber circulator. The optical fiber sensing end includes a bare fiber body with the protective layer and coating layer stripped off. The bare fiber body consists of a fiber core and a cladding, and the end of the bare fiber body is a 45-degree oblique polished end face.

[0008] Preferably, a coating layer for enhancing light reflection in the bare fiber body is provided on the oblique polished end face at an angle of 45 degrees.

[0009] Preferably, the transmission optical fiber is a single-mode optical fiber.

[0010] Preferably, a detection platform is further included, on which a fiber optic clamping seat, a three-dimensional mobile platform and an electron microscope are assembled. The capillary to be tested is fixed on the three-dimensional mobile platform, and the fiber optic sensing end is fixed on the fiber optic clamping seat and horizontally points toward the direction inside the capillary hole to be tested. The electron microscope is used to obtain real-time image information when the fiber optic sensing end is docked with the capillary hole.

[0011] Preferably, the optical fiber clamping seat includes a base, on which a hollow chuck is rotatably connected, and the optical fiber sensing end is coaxially fixed in the hollow chuck, and when the hollow chuck rotates, the optical fiber sensing end is driven to rotate coaxially.

[0012] A method for measuring the inner diameter of a capillary tube using the optical fiber measuring device as described above comprises the following steps:

[0013] Step A: Fix the capillary to be tested on a three-dimensional moving platform, pre-fix the optical fiber sensing end on the optical fiber clamping seat and point it parallel to the inner direction of the capillary hole to be tested. Then, connect a red light test pen to the optical fiber connection end. When the test red light is transmitted along the fiber core to the 45-degree oblique polished end face, it is reflected and emitted in the radial direction of the bare fiber body. Rotate the optical fiber sensing end so that the emitted test red light is in the vertical or horizontal direction. Finally, fix the optical fiber sensing end firmly.

[0014] Step B: Turn on the electron microscope and adjust it so that the optical fiber sensing end is within its field of view. Then, move the three-dimensional mobile platform to move the capillary to the test red light. Let the test red light shine vertically on the capillary. Then, continue to fine-tune the three-dimensional mobile platform under the electron microscope field of view until the test red light passes through the center of the capillary.

[0015] Step C: The three-dimensional mobile platform then moves, causing the capillary to retreat axially, and then moves in the opposite direction of the test red light to align the optical fiber sensing end with the capillary hole. The three-dimensional mobile platform then drives the capillary to move so that the optical fiber sensing end is located inside the capillary.

[0016] Step D: Remove the red light test pen, connect the fiber connector to the light output port of the fiber circulator, turn on the broadband light source and optical spectrum analyzer, and then use the three-dimensional mobile platform to move the capillary under test along the direction of the test red light until the bare fiber body is in close contact with the inner wall of the capillary under test. Then, the inner diameter of the capillary under test can be calculated based on the reflection spectrum obtained on the optical spectrum analyzer.

[0017] Preferably, the method further includes step E: the three-dimensional moving platform drives the capillary to be tested to move in the opposite direction of the test red light until the bare fiber body is close to the inner wall of the capillary to be tested, and then the wall thickness of the capillary to be tested can be calculated based on the reflection spectrum obtained on the optical spectrum analyzer.

[0018] A method for measuring the inner diameter of a capillary tube using the optical fiber measuring device as described above comprises the following steps:

[0019] Step A: Fix the capillary to be tested on a three-dimensional moving platform, and pre-fix the optical fiber sensing end on the optical fiber clamping seat and point it parallel to the inner direction of the capillary hole to be tested;

[0020] Step B: Turn on the electron microscope and adjust it so that the optical fiber sensing end is within its field of view. Fine-tune the three-dimensional moving platform under the electron microscope field of view so that the optical fiber sensing end is within the capillary to be measured.

[0021] Step C: Connect the optical fiber connector to the light output port of the optical fiber circulator, turn on the broadband light source and optical spectrum analyzer, and set four measurement points on the optical fiber sensing end: the measurement point at the original position of the hollow chuck, the measurement point when the hollow chuck is rotated 90 degrees, the measurement point when the hollow chuck is rotated 180 degrees, and the measurement point when the hollow chuck is rotated 270 degrees. The optical spectrum analyzer obtains a reflection spectrum of each measurement point, and then calculates the distance between the cladding and the inner wall of the capillary to be measured at each measurement point. Finally, the inner diameter of the capillary to be measured is calculated based on these four distance values.

[0022] The beneficial effects of this device are as follows: (1) by designing the oblique polished end face at a 45-degree angle at the end of the bare fiber body, a 90-degree change in the transmission direction of the light beam in the single-mode optical fiber is achieved, so that the light beam is incident vertically on each medium surface. This incident angle is convenient for calculating the optical path difference on the one hand, and on the other hand, the light beam returns along the original path after being reflected by the medium surface, which is more conducive to the formation of Fabry-Perot interference;

[0023] (2) By utilizing the vertical emission characteristic of the reflected light beam and combining the positional relationship between the core, cladding, gap, and inner wall media, a cascade FPI cavity is formed, thereby achieving rapid and high-precision measurement of the inner diameter and wall thickness of the capillary;

[0024] (3) When measuring the inner diameter by rotating the optical fiber sensing end, it is only necessary to place the optical fiber sensing end in the capillary to be measured and then rotate it four positions. There is no need to adjust the coaxiality between the optical fiber sensing end and the capillary to be measured. There is also no need to adjust the measuring position of the oblique polished end face and the inclined position of the oblique surface during measurement, which further increases the measurement flexibility and convenience.

[0025] (4) The present invention as a whole has the characteristics of simple structure, strong robustness, and flexible measurement, and is particularly suitable for measurement in narrow and difficult-to-reach space environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the present invention;

[0027] Figure 2 for Figure 1 A magnified schematic diagram of the structure of the middle K part;

[0028] Figure 3 This is a magnified schematic diagram of the microscope at the optical fiber sensing end;

[0029] Figure 4 Schematic diagram of the working principle when measuring inner diameter;

[0030] Figure 5 This is a magnified diagram of the microscope when measuring the inner diameter;

[0031] Figure 6 Schematic diagram of the working principle when measuring wall thickness;

[0032] Figure 7 Schematic diagram of microscope magnification when measuring wall thickness;

[0033] Figure 8 Schematic diagram of the working principle of measuring the inner diameter by rotating the optical fiber sensing end. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to the accompanying drawings.

[0035] like Figure 1 As shown, the optical fiber measuring device for the inner diameter of a capillary tube based on the FP interferometer principle includes a broadband light source 1, an optical fiber circulator 3, an optical spectrum analyzer 2, and a transmission optical fiber 5. One end of the transmission optical fiber 5 is an optical fiber connection end 4, and the other end is an optical fiber sensing end 6. The broadband light source 1 is optically connected to the light incident port of the optical fiber circulator 4, the optical spectrum analyzer 2 is optically connected to the light reflection port of the optical fiber circulator 3, and the optical fiber connection end 4 is optically connected to the light output port of the optical fiber circulator 3; as shown in FIG. Figure 2 and Figure 3 As shown, the optical fiber sensing end 6 includes a bare fiber body with the protective layer and the coating layer stripped off. The bare fiber body consists of a fiber core 62 and a cladding 61 . The end of the bare fiber body is a 45-degree oblique polished end face 64 .

[0036] Among them, the transmission optical fiber 5 adopts a single-mode optical fiber, so that the light beam in the fiber core 62 is transmitted approximately axially, and when it is transmitted to the 45-degree oblique polished end face 64, it is reflected and emitted along the radial direction of the bare fiber body; at the same time, a coating layer is provided on the 45-degree oblique polished end face 64 to enhance the light reflection in the bare fiber body, thereby further increasing the reflected light intensity and improving the measurement effect.

[0037] This embodiment may also include a detection platform, on which are assembled a fiber optic clamping seat, a three-dimensional movable platform and an electron microscope. The capillary tube 7 to be tested is fixed on the three-dimensional movable platform. The three-dimensional movable platform adopts a high-precision three-dimensional movable control mechanism. The fiber optic sensing end 6 is fixed on the fiber optic clamping seat and horizontally points toward the direction inside the capillary tube hole 7 to be tested. The electron microscope is used to obtain real-time image information when the fiber optic sensing end 6 is docked with the capillary tube 7 to be tested.

[0038] like Figure 2 As shown, the inherent FPI cavity in the optical fiber sensing end 6 is:

[0039] When the incident light 63 passes through the fiber core 62 and reaches the obliquely polished end face 64, it is reflected by the obliquely polished end face 64 and emitted along the radial direction A of the bare fiber body. The reflected light 67 enters the core-cladding interface and the cladding-air interface vertically, thereby generating a first partially reflected light 65 at the core-cladding interface and a second partially reflected light 66 at the cladding-air interface. The first partially reflected light 65 and the second partially reflected light 66 return to the fiber core 62 along the original path and superimpose to form Fabry-Perot interference (FPI). Since the two reflection surfaces of the FPI cavity are the core-cladding interface and the cladding-air interface, the optical path difference (OPD) of the FPI cavity is:

[0040] OPD 芯-包 =2n 包 r 包

[0041] Among them, n 包 is the cladding refractive index, r 包 is the cladding thickness. For standard single-mode optical fiber (SMF-28e), the core diameter is 8.2 microns, the cladding refractive index is 1.4679, and the cladding thickness is 58.4 microns, that is:

[0042] OPD 芯-包 =2n 包 r 包 =2×1.4679×58.4=171.45 microns

[0043] Then, the OPD is calculated based on the reflection spectrum of the FPI cavity obtained by the optical spectrum analyzer 2. 芯-包 It is 180.10 microns, which is close to the calculated value of 171.45 microns.

[0044] like Figure 4 As shown, when the optical fiber sensing end 6 measures the inner diameter of the capillary hole 7 to be measured, the cascade FPI cavity formed is:

[0045] exist Figure 2 On the basis of the above, when the optical fiber sensing end 6 is extended into the measuring capillary hole 7 and the top surface corresponding to the opposite direction of the reflected light 67 is close to the inner wall of the capillary hole 7 to be measured, the reflected light 67 continues to propagate along the radial direction A. After passing through the cladding-air interface, it continues to transmit and encounters the air-inner wall interface, generating a third local reflected light 68 at the air-inner wall interface.

[0046] At this point, there are three reflection interfaces: the core-cladding interface, the cladding-air interface, and the air-inner wall interface. Thus, three FPI cavities are formed by the core-cladding interface and the cladding-air interface, the cladding-air interface and the air-inner wall interface, and the core-cladding interface and the air-inner wall interface to form a cascaded FPI cavity. The optical path differences (OPDs) of the other two FPI cavities are:

[0047] OPD 包-壁 =2n 气 r 气

[0048] OPD 芯-壁 =OPD 芯-包 +OPD 包-壁 =2(n 包 r 包 +n 气 r 气 )

[0049] Among them, n 包 is the cladding refractive index, r 包 is the cladding thickness, n 气 is the refractive index of air, r 气It is the distance between the bottom of the cladding 61 and the inner wall of the capillary hole 7 to be measured.

[0050] Then, the OPD is calculated based on the reflection spectra of the three FPI cavities obtained by the optical spectrum analyzer 2. 芯-壁 、OPD 芯-包 or OPD 包-壁 , and thus calculate r 气 Finally, the inner diameter D of the capillary hole 7 to be measured is calculated 管 :

[0051] D 管 =r 气 +D 纤

[0052] Among them, D 纤 is the diameter of the bare fiber body, that is, D 纤 =125 microns.

[0053] like Figure 6 As shown, when the optical fiber sensing end 6 measures the wall thickness of the capillary hole 7 to be measured, the cascade FPI cavity formed is:

[0054] correspond Figure 4 In the embodiment, when the optical fiber sensing end 6 is extended into the measuring capillary hole 7 and the bottom surface corresponding to the positive direction of the reflected light 67 is close to the inner wall of the capillary hole 7 to be measured, the reflected light 67 continues to propagate along the radial direction A. After passing through the cladding-inner wall interface, it continues to transmit and encounters the inner wall-outer space interface, generating a fourth local reflected light 69 at the inner wall-outer space interface.

[0055] As mentioned above Figure 4 The working principle of the intermediate cascade FPI cavity is explained in the same way. Figure 6 Middle r 壁 Position equivalent to Figure 4 Middle r 气 Position, that is, calculate the optical path difference of each FPI cavity according to the reflection spectrum diagram of the three FPI cavities obtained by the optical spectrum analyzer 2, and thus calculate r 壁 . Specific embodiment 2:

[0057] The difference from the specific embodiment 1 lies in the clamping method of the optical fiber sensing end 6 and whether rotation is required during measurement, thereby further improving the optical fiber clamping seat.

[0058] The optical fiber sensing end 6 is designed to rotate when measuring the inner diameter of the capillary hole 7 to achieve completely non-contact inner diameter measurement, while also avoiding the need to measure the 45-degree angled polished end face 64, further increasing measurement flexibility and convenience. The optical fiber clamping base includes a base to which a hollow chuck is rotatably connected. The optical fiber sensing end 6 is coaxially fixed within the hollow chuck. Rotation of the hollow chuck drives the optical fiber sensing end 6 to coaxially rotate. The hollow chuck can adopt a variety of structural forms, as long as it can achieve coaxial rotation of the optical fiber sensing end 6.

[0059] The present application also discloses a method for measuring the inner diameter of a capillary tube using the optical fiber measuring device in specific embodiment 1, which comprises the following steps:

[0060] Step A: Fix the capillary tube 7 to be tested on a three-dimensional movable platform, pre-fix the optical fiber sensing end 6 on the optical fiber clamping seat and point it parallel to the inner direction of the capillary tube 7 to be tested, then connect a red light test pen to the optical fiber connection end 4. When the test red light is transmitted along the fiber core 62 to the 45-degree oblique polished end face, it is reflected and emitted along the radial direction A of the bare fiber body. Rotate the optical fiber sensing end 6 so that the emitted test red light is in the vertical or horizontal direction, and finally fix the optical fiber sensing end 6 firmly.

[0061] Step B: Turn on the electron microscope and adjust the microscope so that the optical fiber sensing end 6 is within its observation field. Then, the three-dimensional movable platform moves, driving the capillary tube 7 to move to the test red light. The test red light is irradiated vertically on the capillary tube 7. Then, under the electron microscope field of view, the three-dimensional movable platform is further fine-tuned until the test red light passes through the center of the capillary tube 7.

[0062] Step C: The three-dimensional mobile platform then moves to move the capillary tube 7 axially backward, and then moves in the opposite direction of the test red light to align the optical fiber sensing end 6 with the hole of the capillary tube 7 . The three-dimensional mobile platform then drives the capillary tube 7 to move so that the optical fiber sensing end 6 is located inside the capillary tube 7 .

[0063] Step D: Remove the red light test pen, connect the optical fiber connector 4 to the light output port of the optical fiber circulator 3, turn on the broadband light source 1 and the optical spectrum analyzer 2, and then use the three-dimensional mobile platform to move the capillary tube 7 to be tested in the direction of the test red light until the bare fiber body is in close contact with the inner wall of the capillary tube 7 to be tested. Then, the inner diameter of the capillary tube 7 to be tested can be calculated based on the reflection spectrum obtained on the optical spectrum analyzer 2.

[0064] The method further includes step E: the three-dimensional moving platform drives the capillary tube 7 to move in the opposite direction of the test red light until the bare fiber body is close to the inner wall of the capillary tube 7 to be tested, and then the wall thickness of the capillary tube 7 to be tested can be calculated based on the reflection spectrum obtained on the optical spectrum analyzer 2.

[0065] The present application also discloses a method for measuring the inner diameter of a capillary tube using the optical fiber measuring device in specific embodiment 2, which comprises the following steps:

[0066] Step A: Fix the capillary tube 7 to be tested on a three-dimensional moving platform, and pre-fix the optical fiber sensing end 6 on the optical fiber clamping seat and point it parallel to the direction inside the hole of the capillary tube 7 to be tested;

[0067] Step B: Turn on the electron microscope and adjust the electron microscope so that the optical fiber sensing end 6 is located within its observation field. Fine-tune the three-dimensional moving platform under the electron microscope field of view so that the optical fiber sensing end 6 is located within the capillary 7 to be measured.

[0068] Step C: Connect the optical fiber connection end 4 to the light output port of the optical fiber circulator 3, turn on the broadband light source 1 and the optical spectrum analyzer 2, as shown in FIG. Figure 8 As shown, the optical fiber sensing end 6 has four measurement points, namely the measurement point of the hollow chuck original position, the measurement point of the hollow chuck rotated 90 degrees, the measurement point of the rotation 180 degrees, and the measurement point of the rotation 270 degrees. The optical spectrum analyzer 2 obtains the reflection spectrum of each measurement point, and then calculates the distance between the cladding 61 and the inner wall of the capillary hole 7 to be measured at each measurement point, that is, the corresponding distance value is: r1 气 , r2 气 , r3 气 , r4 气 Then, the inner diameter D of the capillary hole 7 to be measured is calculated based on the four distance values. 管 , the calculation process is as follows:

[0069] Figure 8 In the equation, GN = r1 气 +d 纤 , GQ=r2 气 +d 纤 ,GM=r3 气 +d 纤 , GP=r4 气 +d 纤 ; Among them, d 纤 =0.5D 纤 Since the inner chords MN and PQ intersect perpendicularly, the inner diameter of the capillary tube 7 to be measured can be calculated using the lengths of GN, GQ, GM, and GP.

[0070] With this measurement method, it is only necessary to place the optical fiber sensing end 6 in the capillary 7 to be measured and then rotate it four positions. There is no need to adjust the coaxiality between the optical fiber sensing end 6 and the capillary 7 to be measured. There is also no need to adjust the measurement position and the inclination position of the oblique polished end face 64 during measurement, which further increases the measurement flexibility and convenience.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for measuring the inner diameter of a capillary tube using an optical fiber measuring device, characterized in that: The invention comprises a capillary inner diameter optical fiber measuring device, which comprises a broadband light source, an optical fiber circulator, an optical spectrum analyzer, and a transmission optical fiber. One end of the transmission optical fiber is an optical fiber connection end, and the other end is an optical fiber sensing end. The broadband light source is optically connected to the light incident port of the optical fiber circulator, the optical spectrum analyzer is optically connected to the light reflection port of the optical fiber circulator, and the optical fiber connection end is optically connected to the light output port of the optical fiber circulator. The optical fiber sensing end comprises a bare fiber body with the protective layer and the coating layer stripped off, the bare fiber body consisting of a fiber core and a cladding, and the end of the bare fiber body is a 45-degree oblique polished end face. The specific steps include: Step A: Fix the capillary to be tested on a three-dimensional moving platform, pre-fix the optical fiber sensing end on the optical fiber clamping seat and point it parallel to the inner direction of the capillary hole to be tested. Then, connect a red light test pen to the optical fiber connection end. When the test red light is transmitted along the fiber core to the 45-degree oblique polished end face, it is reflected and emitted in the radial direction of the bare fiber body. Rotate the optical fiber sensing end so that the emitted test red light is in the vertical or horizontal direction. Finally, fix the optical fiber sensing end firmly. Step B: Turn on the electron microscope and adjust it so that the optical fiber sensing end is within its field of view. Then, move the three-dimensional mobile platform to move the capillary to the test red light. Let the test red light shine vertically on the capillary. Then, continue to fine-tune the three-dimensional mobile platform under the electron microscope field of view until the test red light passes through the center of the capillary. Step C: The three-dimensional mobile platform then moves, causing the capillary to retreat axially, and then moves in the opposite direction of the test red light to align the optical fiber sensing end with the capillary hole. The three-dimensional mobile platform then drives the capillary to move so that the optical fiber sensing end is located inside the capillary. Step D: Remove the red light test pen, connect the fiber connector to the light output port of the fiber circulator, turn on the broadband light source and optical spectrum analyzer, and then use the three-dimensional mobile platform to move the capillary under test along the direction of the test red light until the bare fiber body is in close contact with the inner wall of the capillary under test. Then, the inner diameter of the capillary under test can be calculated based on the reflection spectrum obtained on the optical spectrum analyzer.

2. The method for measuring the inner diameter of a capillary according to claim 1, wherein: The method further includes step E: the three-dimensional moving platform drives the capillary to be tested to move in the opposite direction of the test red light until the bare fiber body is close to the inner wall of the capillary to be tested, and then the wall thickness of the capillary to be tested can be calculated based on the reflection spectrum obtained on the optical spectrum analyzer.

3. The method for measuring the inner diameter of a capillary according to claim 1, wherein: A coating layer for enhancing light reflection in the bare fiber body is provided on the oblique polished end face at an angle of 45 degrees, and the transmission optical fiber is a single-mode optical fiber.

4. The method for measuring the inner diameter of a capillary according to claim 1, wherein: It also includes a detection platform, on which are assembled a fiber optic clamping seat, a three-dimensional movable platform and an electron microscope. The capillary to be tested is fixed on the three-dimensional movable platform, the fiber optic sensing end is fixed on the fiber optic clamping seat and points horizontally toward the inner direction of the capillary hole to be tested, and the electron microscope is used to obtain real-time image information when the fiber optic sensing end is docked with the capillary hole.

5. The method for measuring the inner diameter of a capillary according to claim 4, wherein: The optical fiber clamping seat includes a base, on which a hollow chuck is rotatably connected. The optical fiber sensing end is coaxially fixed in the hollow chuck. When the hollow chuck rotates, the optical fiber sensing end is driven to rotate coaxially.

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