Air microbubble high-sensitivity strain sensor based on vernier effect

Abstract

The invention belongs to the technical field of optical fiber sensing application, and particularly relates to an air microbubble high-sensitivity strain sensor based on a vernier effect and a manufacturing method. The sensor is composed of a micro-bubble sensing cavity Fabry-Perot interferometer and an air reference cavity Fabry-Perot interferometer which are parallel to each other. The microbubble sensing cavity Fabry-Perot interferometer is formed by welding two single-mode optical fibers, and an ellipsoidal microbubble is embedded in the center of a conical area of the microbubble sensing cavity Fabry-Perot interferometer; the air reference cavity Fabry-Perot interferometer is formed by welding two single-mode optical fibers through a hollow capillary tube, and the two single-mode optical fibers in the hollow capillary tube form an air cavity. When the microbubble sensing cavity and the air reference cavity are connected in parallel, signals of the microbubble sensing cavity and the air reference cavity are overlapped, so that an envelope modulation effect is generated. Compared with the single use of the microbubble sensing cavity, the sensitivity can be obviously amplified, the sensing performance of the sensor is improved, and high-sensitivity air microbubble strain sensing is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensing applications, and in particular relates to an air microbubble high-sensitivity strain sensor based on a vernier effect and a manufacturing method thereof. Background Art

[0002] Strain is an important parameter in medical monitoring, civil engineering, aerospace, structural engineering, automotive industry and military fields. Fiber optic sensors have been widely studied due to their unique advantages such as small size, remote monitoring, high flexibility, low propagation loss, low manufacturing cost and immunity to electromagnetic interference. Fiber optic sensors based on different principles have been demonstrated and studied, including fiber Bragg gratings (FBGs), Sagnac interferometers, Mach-Zehnder interferometers (MZIs) and Fabry-Perot interferometers (FPIs). Compared with other sensor structures, fiber optic sensors based on the Fabry-Perot interferometer principle have the advantages of high sensitivity, linear response, low temperature cross sensitivity and miniature size.

[0003] In strain measurement, optical fiber sensors based on the Fabry-Perot interferometer principle have the advantages of high sensitivity, linear response, low temperature cross-sensitivity, and small size compared with other sensor structures. Among them, bubble strain sensors have higher sensitivity than traditional strain sensors. In addition, since the thermal expansion effect of air is very small and does not contain hygroscopic materials, when the Fabry-Perot interferometer composed of bubbles works in an atmospheric environment, the influence of ambient temperature and humidity on the sensor strain measurement can be ignored, so the bubble strain sensor has little cross-sensitivity to temperature and humidity. Summary of the invention

[0004] Based on the prior art in the background technology, in order to obtain a high-sensitivity stress measurement sensor, the present invention provides an air microbubble high-sensitivity strain sensor based on the vernier effect and a manufacturing method thereof. The strain sensor can significantly improve the sensitivity of stress measurement and is low in cost.

[0005] The technical solution adopted by the present invention is: an air microbubble high-sensitivity strain sensor based on the vernier effect, the strain sensor is composed of a parallel microbubble sensing cavity Fabry-Perot interferometer and an air reference cavity Fabry-Perot interferometer.

[0006] The microbubble sensing cavity Fabry-Perot interferometer is made by fusing two single-mode optical fibers, and an ellipsoidal microbubble is embedded in the center of the conical area of ​​the microbubble sensing cavity Fabry-Perot interferometer; the air reference cavity Fabry-Perot interferometer is made by fusing two single-mode optical fibers through a hollow capillary, and two sections of single-mode optical fibers in the hollow capillary form an air cavity.

[0007] Furthermore, the axial diameter of the ellipsoidal microbubble is 51.15 μm-53.15 μm, the longitudinal diameter thereof is 65.15 μm-67.15 μm; and the length of the air cavity is 62.32 μm-64.32 μm.

[0008] Furthermore, the axial diameter of the ellipsoidal microbubble is 51.15 μm, the longitudinal diameter thereof is 65.15 μm, and the length of the air cavity is 62.32 μm.

[0009] Furthermore, the axial diameter of the ellipsoidal microbubble is 52.15 μm, the longitudinal diameter thereof is 66.15 μm, and the length of the air cavity is 63.32 μm.

[0010] Furthermore, the axial diameter of the ellipsoidal microbubble is 53.15 μm, the longitudinal diameter thereof is 67.15 μm, and the length of the air cavity is 64.32 μm.

[0011] Furthermore, the preparation method of the microbubble sensing cavity Fabry-Perot interferometer comprises the following steps: Step 1: Wipe the single-mode optical fiber with the coating stripped off with alcohol, and use a fiber optic cutter to smoothly cut the single-mode optical fiber; then put the single-mode optical fiber into the fiber optic fusion splicer (Fujikura 80 s), and accurately control the left and right motors of the fiber optic fusion splicer so that the single-mode optical fiber is placed near the discharge electrode.

[0012] Step 2: Adjust the discharge time and discharge power parameters of the fiber fusion splicer to trim the flat end face of the single-mode optical fiber into a smooth spherical surface through multiple discharges; manually take out the two sections of single-mode optical fiber in the fiber fusion splicer, and dip a small amount of refractive index matching liquid (Nd: 1.47) on the surface of the smooth spherical surface of the two single-mode optical fibers.

[0013] Step 3. Put the single-mode optical fiber processed in step 2 back into the optical fiber fusion splicer. Align the cores of the two sections of single-mode optical fiber by adjusting the driving motor on the optical fiber fusion splicer, that is, align the centers of the two cores (align the centers of the two cores on the X plane and the Y plane). After alignment, the two sections of single-mode optical fiber are in a slightly squeezed state to be fused. By accurately controlling the discharge time and discharge power of the optical fiber fusion splicer, microbubbles are formed in the middle of the two smooth spherical surfaces.

[0014] Step 4: discharge the microbubbles generated in step 3 several times, apply axial tension to the single-mode optical fiber by precisely controlling the motor of the optical fiber fusion splicer, and use arc discharge technology to precisely control and adjust the discharge time and discharge power; form thin-walled ellipsoidal microbubbles through arc discharge technology, and the obtained optical fiber with ellipsoidal microbubbles is a microbubble sensing cavity Fabry-Perot interferometer.

[0015] Furthermore, the preparation method of the air reference cavity Fabry-Perot interferometer comprises the following steps: Step 1. Insert the flattened end of the single-mode optical fiber into the hollow capillary tube, and then put the hollow capillary tube with the inserted single-mode optical fiber into the optical fiber fusion splicer. Use the optical fiber fusion splicer to discharge the end of the hollow capillary tube with a discharge power of +5 and a discharge time of 600ms to fuse the hollow capillary tube and the single-mode optical fiber together.

[0016] Step 2, take another single-mode optical fiber, insert the end of the single-mode optical fiber with a flattened end face into the hollow capillary, and adjust the distance between the end faces of the two single-mode optical fibers in the hollow capillary by the driving motor of the optical fiber fusion splicer until the distance between the two end faces is close to the cavity length of the ellipsoidal microbubble; then use the optical fiber fusion splicer to discharge the end of the hollow capillary, the discharge power is +5, the discharge time is 600ms, the hollow capillary and another single-mode optical fiber are fused together, and the two single-mode optical fibers butt-jointed with the hollow capillary form an air cavity in the hollow capillary; the prepared optical fiber with an air cavity is an air reference cavity Fabry-Perot interferometer.

[0017] Furthermore, applying the optical simulation of the vernier effect to fiber interferometers is an effective means to improve the sensitivity and resolution of optical sensors. The vernier effect is achieved by obtaining two slightly detuned interference signals and overlapping them to produce a vernier envelope, which shows amplified sensitivity relative to the single interferometer that constitutes the structure. Structurally, a parallel structure fiber Fabry-Perot interferometer is made using the optical vernier effect. The elliptical microbubble formed by two single-mode optical fibers prepared by arc discharge of a fusion splicer is made into a microbubble sensing cavity, and the air reference cavity is composed of two end-cut flat single-mode optical fibers inserted into a quartz capillary.

[0018] Furthermore, the parallel micro-bubble sensing cavity Fabry-Perot interferometer and the air reference cavity Fabry-Perot interferometer are connected via a two-to-two coupler.

[0019] Furthermore, the elliptical microbubble and the air cavity of the high-sensitivity strain sensor are used as the sensing cavity and the reference cavity respectively, and the parallel sensing cavity and the reference cavity are strain sensors with high sensitivity.

[0020] The beneficial effects of the present invention are as follows: a high-sensitivity air microbubble strain sensor based on the vernier effect and a preparation method thereof are provided. The strain sensor with a parallel structure can significantly improve the sensitivity of stress measurement, and can reach an ultra-high strain sensitivity of -42.04 pm / με. Compared with the existing single microbubble sensing cavity, the lateral strain sensitivity is increased by 4.76 times. In the temperature range of 30-60°C, the temperature sensitivity and lateral temperature sensitivity of the sensor are 3.64 pm / °C and 0.087 µε / °C, respectively, thereby reducing the measurement error caused by temperature changes, making the strain measurement in a complex environment less affected by temperature and the data more accurate. The manufacturing process is simple and the manufacturing cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of the air microbubble high-sensitivity strain sensor based on the vernier effect in Example 1; Figure 2 is a schematic structural diagram of a microbubble sensing cavity Fabry-Perot interferometer in Embodiment 1; Figure 3 is a schematic structural diagram of the air reference cavity Fabry-Perot interferometer in Example 1; Figure 4 is a schematic diagram of step 1 of the method for manufacturing a high-sensitivity strain sensor in Example 5; Figure 5 It is a schematic diagram of step 2 of the method for manufacturing an air microbubble high-sensitivity strain sensor based on the vernier effect in Example 5; Figure 6 It is a schematic diagram of step 3 of the method for manufacturing an air microbubble high-sensitivity strain sensor based on the vernier effect in Example 5; Figure 7 It is a schematic diagram of step 4 of the method for manufacturing an air microbubble high-sensitivity strain sensor based on the vernier effect in Example 5; Figure 8 is a schematic diagram of step 1 of the method for manufacturing an air microbubble high-sensitivity strain sensor based on the vernier effect in Example 6; Fig. 9 It is a schematic diagram of step 2 of the method for manufacturing an air microbubble high-sensitivity strain sensor based on the vernier effect in Example 6; Fig.10 This is the interference curve spectrum of the air microbubble high-sensitivity strain sensor based on the vernier effect after applying axial stress of 0-1000 με to the sensor with a step size of 200 με; Fig.11 This is the interference curve spectrum of the air microbubble high-sensitivity strain sensor based on the vernier effect when the temperature is increased from 30°C to 60°C in steps of 5°C.

[0022] Figure numerals: 1. microbubble sensing cavity Fabry-Perot interferometer; 2. air reference cavity Fabry-Perot interferometer; 3. ellipsoidal microbubble; 4. hollow capillary; 5. air cavity; 6. optical fiber fusion splicer; 7. smooth spherical surface; 8. refractive index matching liquid; 9. fiber core; 10. microbubble. DETAILED DESCRIPTION Example

[0023] like Figure 1 As shown, the air microbubble high-sensitivity strain sensor based on the vernier effect is composed of a parallel microbubble sensing cavity Fabry-Perot interferometer 1 and an air reference cavity Fabry-Perot interferometer 2.

[0024] like Figure 2 and Figure 3 As shown, the microbubble sensing cavity Fabry-Perot interferometer 1 is made by fusing two single-mode optical fibers, and an ellipsoidal microbubble 3 is embedded in the center of the conical region of the microbubble sensing cavity Fabry-Perot interferometer 1; the air reference cavity Fabry-Perot interferometer 2 is made by fusing two single-mode optical fibers through a hollow capillary 4, and two sections of single-mode optical fibers in the hollow capillary 4 form an air cavity 5. The axial diameter of the ellipsoidal microbubble 3 is 51.15 μm, and its longitudinal diameter is 65.15 μm; the length of the air cavity 5 is 62.32 μm. Example

[0025] On the basis of the technical solution of the first embodiment, the parameters of the microbubbles and the air cavity are changed, the axial diameter of the ellipsoidal microbubbles 3 is 52.15 μm, and the longitudinal diameter thereof is 66.15 μm; the length of the air cavity 5 is 63.32 μm. Example

[0026] On the basis of the technical solution of the first embodiment, the parameters of the microbubbles and the air cavity are changed, the axial diameter of the ellipsoidal microbubbles 3 is 53.15 μm, and the longitudinal diameter thereof is 67.15 μm; the length of the air cavity 5 is 64.32 μm. Example

[0027] The air microbubble high-sensitivity strain sensor based on the vernier effect in the above three embodiments is applied to the field of strain measurement technology. Example

[0028] like Figure 4-Figure 7 As shown, the preparation method of the microbubble sensing cavity Fabry-Perot interferometer includes the following steps: Step 1: Wipe the single-mode optical fiber with the coating stripped off with alcohol, and use a fiber optic cutter to smoothly cut the single-mode optical fiber; then put the single-mode optical fiber into the fiber optic fusion splicer 6, and accurately control the left and right motors of the fiber optic fusion splicer so that the single-mode optical fiber is placed near the discharge electrode.

[0029] Step 2: Adjust the discharge time and discharge power parameters of the optical fiber fusion splicer 6, and repair the flat end face of the single-mode optical fiber into a smooth spherical surface 7 through multiple discharges; manually take out the two sections of single-mode optical fiber in the optical fiber fusion splicer 6, and dip a small amount of refractive index matching liquid 8 on the surface of the smooth spherical surface 7 of the two single-mode optical fibers.

[0030] Step three, put the single-mode optical fiber processed in step two back into the optical fiber fusion splicer 6, and align the cores 9 of the two sections of single-mode optical fiber by adjusting the driving motor on the optical fiber fusion splicer 6, that is, align the centers of the two cores. After alignment, the two sections of single-mode optical fiber are in a slightly squeezed state to be fused; by accurately controlling the discharge time and discharge power of the optical fiber fusion splicer 6, microbubbles 10 are formed in the middle of the two smooth spherical surfaces 7.

[0031] Step 4: discharge the microbubbles 10 generated in step 3 several times, apply axial tension to the single-mode optical fiber by precisely controlling the motor of the optical fiber fusion splicer 6, and use arc discharge technology to precisely control and adjust the discharge time and discharge power; form thin-walled ellipsoidal microbubbles 3 through arc discharge technology, and the obtained optical fiber with ellipsoidal microbubbles 3 is a microbubble sensing cavity Fabry-Perot interferometer. Example

[0032] like Figure 8 and Fig. 9 As shown, the preparation method of the air reference cavity Fabry-Perot interferometer comprises the following steps: Step 1, insert the flattened end of the single-mode optical fiber into the hollow capillary 4, then put the hollow capillary 4 with the inserted single-mode optical fiber into the optical fiber fusion splicer 6, use the optical fiber fusion splicer to discharge the end of the hollow capillary 4, the discharge power is +5, the discharge time is 600ms, and the hollow capillary 4 and the single-mode optical fiber are fused together.

[0033] Step 2, take another single-mode optical fiber, insert the end of the single-mode optical fiber with a flattened end face into the hollow capillary 4, and adjust the distance between the end faces of the two single-mode optical fibers in the hollow capillary 4 by the driving motor of the optical fiber fusion splicer 6 until the distance between the two end faces is close to the cavity length of the ellipsoidal microbubble 3; then use the optical fiber fusion splicer 6 to discharge the end of the hollow capillary 4, the discharge power is +5, the discharge time is 600ms, the hollow capillary 4 and another single-mode optical fiber are fused together, and the two single-mode optical fibers docked with the hollow capillary 4 form an air cavity 5 in the hollow capillary 4; the prepared optical fiber with the air cavity 5 is an air reference cavity Fabry-Perot interferometer.

[0034] The microbubble sensing cavity Fabry-Perot interferometer is used as the sensing cavity, and the air reference cavity Fabry-Perot interferometer is used as the reference cavity. Since the cavity lengths of the sensing cavity and the reference cavity are close, the interference frequencies generated by the two interferometers are slightly offset. When the microbubble sensing cavity is connected in parallel with the air reference cavity, the signals of the two overlap, resulting in an envelope modulation effect. Compared with the use of the microbubble sensing cavity alone, this structure can significantly amplify the sensitivity and improve the sensing performance of the sensor. Therefore, the use of parallel configuration of the sensing cavity and the reference cavity, based on the design of the vernier effect, can achieve high-sensitivity air microbubble strain sensing. The sensor combines the optical vernier effect. The sensing cavity of the optical fiber sensor is composed of ellipsoidal microbubbles formed by arc discharge of a single-mode optical fiber through a fusion splicer, and the reference cavity is composed of two single-mode optical fibers with flat end faces inserted into a hollow capillary.

[0035] like Fig.10 As shown in the figure, the change of interference spectrum after applying axial stress of 0-1000 με to the air microbubble high-sensitivity strain sensor based on the vernier effect with a step size of 200 με. Through the linear relationship between different stress levels and wavelengths and the fitting based on wavelength drift and stress, the strain sensitivity of the sensor is obtained to be -42.04 pm / με.

[0036] like Fig.11 As shown in the figure, the temperature is increased from 30°C to 60°C in steps of 5°C, and the interference spectrum at each temperature is collected. The temperature sensitivity of the air microbubble high-sensitivity strain sensor based on the vernier effect is 3.64 pm / °C, and the temperature cross sensitivity is 0.087με / °C. It has a low temperature sensitivity, thereby reducing the measurement error caused by temperature changes, making the strain measurement in a complex environment less affected by temperature and the data more accurate.

[0037] The air microbubble high-sensitivity strain sensor based on the vernier effect combined with the optical vernier effect can significantly improve the sensitivity of stress measurement. Compared with the existing technology, the sensor only needs a single-mode optical fiber, a hollow capillary and a commercial fusion splicer to produce a high-sensitivity strain sensor, which is simple to make, easy to operate and low in cost.

Claims

1. An air microbubble high-sensitivity strain sensor based on the vernier effect, characterized in that: The strain sensor is composed of a parallel micro-bubble sensing cavity Fabry-Perot interferometer (1) and an air reference cavity Fabry-Perot interferometer (2); The microbubble sensing cavity Fabry-Perot interferometer (1) is made by fusing two single-mode optical fibers, and an ellipsoidal microbubble (3) is embedded in the center of the conical region of the microbubble sensing cavity Fabry-Perot interferometer (1); the air reference cavity Fabry-Perot interferometer (2) is made by fusing two single-mode optical fibers through a hollow capillary (4), and two sections of single-mode optical fibers in the hollow capillary (4) form an air cavity (5).

2. The air microbubble high-sensitivity strain sensor based on the vernier effect according to claim 1 is characterized in that: The axial diameter of the ellipsoidal microbubble (3) is 51.15 μm-53.15 μm, and the longitudinal diameter is 65.15 μm-67.15 μm; the length of the air cavity (5) is 62.32 μm-64.32 μm.

3. The air microbubble high-sensitivity strain sensor based on the vernier effect according to claim 2 is characterized in that: The axial diameter of the ellipsoidal microbubble (3) is 51.15 μm, and the longitudinal diameter is 65.15 μm; the length of the air cavity (5) is 62.32 μm.

4. The air microbubble high-sensitivity strain sensor based on the vernier effect according to claim 2 is characterized in that: The axial diameter of the ellipsoidal microbubble (3) is 52.15 μm, and the longitudinal diameter is 66.15 μm; the length of the air cavity (5) is 63.32 μm.

5. The air microbubble high-sensitivity strain sensor based on the vernier effect according to claim 2 is characterized in that: The axial diameter of the ellipsoidal microbubble (3) is 53.15 μm, and the longitudinal diameter is 67.15 μm; the length of the air cavity (5) is 64.32 μm.

6. The air microbubble high-sensitivity strain sensor based on the vernier effect as claimed in claim 1 is used in strain measurement.

7. A method for preparing a microbubble sensing cavity Fabry-Perot interferometer, characterized in that: The preparation method comprises the following steps: Step 1: wipe the single-mode optical fiber with the coating stripped off with alcohol, and use a fiber optic cutter to smoothly cut the single-mode optical fiber; then put the single-mode optical fiber into the optical fiber fusion splicer (6), and control the left and right motors of the optical fiber fusion splicer so that the single-mode optical fiber is placed near the discharge electrode; Step 2: adjusting the discharge time and discharge power parameters of the optical fiber fusion splicer (6) to trim the flat end face of the single-mode optical fiber into a smooth spherical surface (7) by multiple discharges; manually taking out two sections of single-mode optical fiber from the optical fiber fusion splicer (6), and dipping the surface of the smooth spherical surface (7) of the two single-mode optical fibers into a refractive index matching liquid (8); Step 3: Place the single-mode optical fiber processed in step 2 back into the optical fiber fusion splicer (6), and align the cores (9) of the two sections of single-mode optical fiber by adjusting the driving motor on the optical fiber fusion splicer (6). After alignment, the two sections of single-mode optical fiber are in a state to be fusion spliced; and form microbubbles (10) in the middle of the two smooth spherical surfaces (7) by precisely controlling the discharge time and discharge power of the optical fiber fusion splicer (6). Step 4: discharge the microbubbles (10) generated in step 3 several times, apply axial tension to the single-mode optical fiber by precisely controlling the motor of the optical fiber fusion splicer (6), and use arc discharge technology to precisely control and adjust the discharge time and discharge power; form thin-walled ellipsoidal microbubbles (3) through arc discharge technology, and the obtained optical fiber with ellipsoidal microbubbles (3) is a microbubble sensing cavity Fabry-Perot interferometer (1).

8. A method for preparing an air reference cavity Fabry-Perot interferometer, characterized in that: The preparation method comprises the following steps: Step 1, inserting the flattened end of the single-mode optical fiber into the hollow capillary (4), then placing the hollow capillary (4) with the inserted single-mode optical fiber into an optical fiber fusion splicer (6), using the optical fiber fusion splicer (6) to discharge the end of the hollow capillary (4), and fusing the hollow capillary (4) and the single-mode optical fiber together; Step 2, take another single-mode optical fiber, insert the end of the single-mode optical fiber with a flattened end face into the hollow capillary (4), and adjust the distance between the end faces of the two single-mode optical fibers in the hollow capillary (4) by the driving motor of the optical fiber fusion splicer (6) until the distance between the two end faces is close to the cavity length of the ellipsoidal microbubble (3); then use the optical fiber fusion splicer (6) to discharge the end of the hollow capillary (4), fuse the hollow capillary (4) and another single-mode optical fiber together, and the two single-mode optical fibers connected to the hollow capillary (4) form an air cavity (5) in the hollow capillary (4); the optical fiber with the air cavity (5) obtained is an air reference cavity Fabry-Perot interferometer.

9. The method for preparing the air reference cavity Fabry-Perot interferometer according to claim 8, characterized in that: In step 1, a fiber fusion splicer (6) is used to discharge the end of the hollow capillary (4), wherein the discharge power is +5 and the discharge time is 600 ms.

10. The method for preparing the air reference cavity Fabry-Perot interferometer according to claim 8, characterized in that: In step 2, a fiber fusion splicer (6) is used to discharge the end of the hollow capillary (4), with a discharge power of +5 and a discharge time of 600 ms.

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