Preparation method of miniature optical fiber sensor based on conical fiber bragg grating
By using staggered fusion splicing and integrated tapered fiber grating, a highly sensitive miniature fiber optic sensor was fabricated, solving the problem of simultaneously monitoring multiple parameter changes in a closed environment in existing technologies, and realizing accurate measurement of refractive index, temperature and humidity.
Patent Information
- Application Number
- CN202511190918.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-25
- Publication Date
- 2025-12-05
AI Technical Summary
Existing fiber optic sensors struggle to simultaneously and accurately monitor changes in multiple parameters, such as temperature and humidity, in enclosed environments.
A miniature fiber optic sensor based on a tapered fiber grating is used. A misaligned Fabry-Perot interferometer is formed by misaligned fusion splicing and integrated with the tapered fiber grating. The thermo-optic coefficient of the UV adhesive and hydrofluoric acid etching are used to form a highly sensitive multi-parameter sensor.
It achieves highly sensitive simultaneous measurement of refractive index, temperature, and humidity, and features miniaturization and simple structure, enabling it to respond quickly to environmental changes.
Smart Images
Figure CN121069561A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of optical fiber sensing, and particularly relates to a preparation method of a micro optical fiber sensor based on a tapered fiber grating. BACKGROUND
[0002] Silica-based optical fiber sensors have excellent performance and wide application prospects. In terms of performance, they have high sensitivity, anti-electromagnetic interference, light weight, and compatibility with digital communication systems. In terms of application, they can be widely used to detect environmental temperature, relative humidity, refractive index, strain and ultrasonic waves.
[0003] Current optical fiber sensors are mostly used in single environmental factor measurement scenarios, such as measuring only the temperature or humidity in the environment. However, in industrial production and life, such as the storage of large quantities of grain in a closed environment, environmental temperature and humidity and other parameters change simultaneously. Single-parameter optical fiber sensors are difficult to accurately monitor environmental changes. Simultaneous monitoring and real-time demodulation of multiple environmental parameters become crucial. SUMMARY
[0004] The purpose of the present application is to solve the problem of weak response characteristics of micro-nano optical fiber devices to refractive index, temperature and relative humidity in the prior art, and to provide a preparation method of a micro optical fiber sensor based on a tapered fiber grating, which realizes high-sensitivity simultaneous measurement of refractive index, temperature and relative humidity.
[0005] In order to achieve the above purpose, the application adopts the following technical scheme: The preparation method of the micro optical fiber sensor based on the tapered fiber grating comprises the following steps: Step 1: twice misalignment fusion of a single-mode optical fiber to form a misalignment section; Step 2: transferring UV glue droplets to the misalignment section of the optical fiber, and obtaining a misalignment type Fabry-Perot interferometer after UV curing; Step 3: immersing any section of the fiber Bragg grating in a hydrofluoric acid droplet, etching and cutting to form a tapered fiber grating; Step 4: fusing the misalignment type Fabry-Perot interferometer and the tapered fiber grating to obtain an integrated micro optical fiber sensor; Step 5: performing refractive index sensing test, temperature sensing test and humidity sensing test on the micro optical fiber sensor respectively.
[0006] As a further preferred solution, in step one, the single-mode optical fiber is cut to form fiber segment A and fiber segment B, the end face of fiber segment A and the end face of fiber segment B are misaligned and fused, then fiber segment B is cut to form fiber segment B and fiber segment C, the end face of fiber segment B and the end face of fiber segment C are misaligned and fused, thereby forming a continuous optical fiber structure of fiber segment A, fiber segment B and fiber segment C, wherein fiber segment A and fiber segment C are coaxial, and fiber segment B is a misaligned segment.
[0007] As a further preferred solution, the misaligned distance of fiber segment A and fiber segment B is less than or equal to 20 µm, and the length of fiber segment B is 50-200 µm.
[0008] As a further preferred solution, in step two, the UV glue droplet is transferred to the misaligned segment of the optical fiber.
[0009] As a further preferred solution, in step three, the region of the fiber Bragg grating at the hydrofluoric acid droplet is etched from the middle to both sides along the grating length direction, the fiber Bragg grating forms a beam waist structure gradually thickening from the middle to both sides, and the thinnest part of the beam waist structure is cut to form a tapered fiber grating.
[0010] As a further preferred solution, during etching, the hydrofluoric acid droplet is replaced once an hour, and the microfiber diameter is monitored in real time using an optical microscope; the thinnest part of the beam waist structure of the fiber Bragg grating has a beam waist diameter of 4.9 µm.
[0011] As a further preferred solution, in step four, the end face of the tapered fiber grating is coaxially positioned and fused with the misaligned Fabry-Perot interferometer.
[0012] As a further preferred solution, in step five, the refractive index sensing test, the integrated microfiber sensor is immersed in a salt solution adjusted between 1.33 and 1.36, and the ambient temperature is maintained at 25 ℃.
[0013] As a further preferred solution, in step five, the temperature sensing test, the integrated microfiber sensor is placed in an oven with a temperature accuracy of 0.1 ℃, an ambient refractive index of about 1, and a humidity of about 50 %RH.
[0014] As a further preferred solution, in step five, the humidity sensing test, the integrated microfiber sensor is placed in a humidity control box with a humidity accuracy of 1 %RH, an ambient refractive index of about 1, and a temperature of about 25 ℃.
[0015] Beneficial effects: The microfiber sensor of the tapered fiber grating integrated Fabry-Perot interferometer has the characteristics of miniaturization, simple structure, high sensitivity and multi-parameter measurement, and has potential application prospects in refractive index, temperature and humidity sensing applications. Specifically, the application also has the following advantages: 1. The tapered fiber grating is integrated with the Fabry-Perot interferometer, the ultra-small diameter fiber grating taper can quickly respond to the disturbance around, the misalignment structure of the Fabry-Perot interferometer enhances the interaction between the multimode interference and the propagation mode and the environment medium, and the fiber device can realize the fast response to the environmental refractive index, temperature and humidity.
[0016] 2. The ultraviolet glue is coated on the Fabry-Perot interferometer, the high thermal-optical coefficient of the ultraviolet glue can improve the temperature sensitivity of the device. Meanwhile, based on the characteristics of the rapid absorption and excretion of water molecules of the ultraviolet glue, the fiber device can also realize the fast response to the environmental humidity.
[0017] 3. The integration of the tapered fiber grating and the Fabry-Perot interferometer is researched, the performance of the hybrid fiber sensor can be further explored, and finally the miniature fiber sensor with high sensitivity for multi-parameter measurement can be realized. BRIEF DESCRIPTION OF DRAWINGS
[0018] Figure 1 Fig. 1 is a structural schematic diagram of the miniature fiber sensor based on the tapered fiber grating of the application; Figure 2 Fig. 2 is an experimental sample diagram of the application: (a) a manufacturing process diagram of the application; (b) a process diagram of transferring the ultraviolet glue droplet to the misalignment section of the fiber; (c) an experimental diagram of etching the fiber grating by hydrofluoric acid; (d) an experimental diagram of the Fabry-Perot interferometer after the ultraviolet glue is cured; (e) an experimental diagram of the tapered fiber grating; Figure 3 Fig. 3 is an experimental diagram of etching a certain part of the fiber Bragg grating by hydrofluoric acid in the application: (a) a curve of the waist diameter of the miniature fiber grating changing with the etching time of hydrofluoric acid; (b) typical photos of the miniature fiber grating under different etching time conditions of hydrofluoric acid; Figure 4 Fig. 4 is an experimental principle schematic diagram of the embodiment: (a) an experimental system schematic diagram of the fiber sensor of the tapered fiber grating integrated with the Fabry-Perot interferometer for measuring the refractive index, temperature and relative humidity in turn; (b) a comparison of the reflection spectra of four structures; Figure 5 Fig. 5 is a refractive index sensing test diagram of the embodiment: (a) and (b) show the change trend of the reflection spectrum when the environmental refractive index increases and decreases respectively; (c) a graph of the wavelength shift of the reflection spectrum and the environmental refractive index; Figure 6 Fig. 6 is a temperature sensing test diagram of the embodiment: (a) and (b) show the change trend of the reflection spectrum when the temperature increases and decreases respectively; (c) a graph of the wavelength shift of the reflection spectrum and the temperature; Figure 7Figures (a) and (b) show the change trend of the reflection spectrum when the humidity increases and decreases, respectively; and (c) shows the relationship between the wavelength shift of the reflection spectrum and the humidity. DETAILED DESCRIPTION
[0019] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application.
[0020] The present application discloses a preparation method of a micro optical fiber sensor based on a tapered fiber grating. (1) A plurality of single-mode optical fibers are misaligned and fused to form a misaligned region with a misaligned distance of 11.9 µm and a length of 132.8 µm; (2) The UV glue droplet is transferred to the misaligned region of the optical fiber, and a Fabry-Perot interferometer is obtained after UV curing; (3) The optical fiber Bragg grating is immersed in a hydrofluoric acid droplet, and the silica material is gradually etched to obtain a tapered fiber grating with a waist diameter of 4.9 µm; (4) The misaligned Fabry-Perot interferometer and the tapered fiber grating are fused to obtain an integrated micro optical fiber sensor.
[0021] The sensing mechanism is as follows: when the input laser passes through the misaligned region, scattering occurs, forming scattered light transmitted in different directions, i.e. various high-order modes. The beams are reflected at the end faces on both sides of the misaligned region, and then interact in the single-mode optical fiber to form a multi-mode interference, obtaining a reflection spectrum. Changes in temperature and humidity in the environment will cause thermal expansion and contraction and changes in the refractive index of the UV glue in the misaligned region, thereby causing changes in the optical path of the reflected light. The reflection spectrum shifts accordingly, i.e. the corresponding sensing function is realized. In addition, the light beams continue to transmit forward along the optical fiber into the tapered fiber grating. Among them, the light beams that meet the Bragg wavelength will be reflected, combined with the reflected light of the Fabry-Perot interferometer, and finally form a composite reflection spectrum. Due to the extremely fine diameter of the tapered fiber grating, it can sensitively sense the refractive index changes in the environment, realizing refractive index sensing.
[0022] The misaligned and fused Fabry-Perot interferometer of the plurality of single-mode optical fibers can generate many high-order propagation modes, enhance the intensity of the multi-mode interference, and directly interact with the environment medium, further improving the sensitivity of the sensor.
[0023] Tapered fiber Bragg grating can be obtained by etching fiber Bragg grating with hydrofluoric acid liquid or alkaline solution. The structure can quickly respond to changes in environmental refractive index and temperature. Integrating the tapered fiber grating with another microstructure fiber sensor is a potential way to achieve high sensitivity and simultaneous detection of multiple parameters.
[0024] As shown in Figures 1-3 , the present application misaligns the multi-section single-mode fiber to form a fiber misalignment region with a misalignment distance of 11.9 μm and a length of 132.8 μm, and obtains a Fabry-Perot interferometer. Then, the misalignment region is coated with a drop of UV glue liquid for enhancing the sensitivity of the fiber sensor. The single-mode fiber-based fiber Bragg grating is immersed in a drop of hydrofluoric acid liquid to gradually etch the silica material. During the etching process, the hydrofluoric acid drop is replaced every hour to maintain a stable etching speed, and the microfiber diameter is monitored in real time using an optical microscope. Finally, a tapered fiber grating with a waist diameter of 4.9 μm is obtained. The prepared misalignment type Fabry-Perot interferometer is fused with the tapered fiber grating to obtain an integrated micro-fiber sensor. The experimental device is shown in Figure 4 , (a) is a schematic diagram of the experimental system for measuring refractive index, temperature and relative humidity in sequence using the fiber sensor of the tapered fiber grating integrated Fabry-Perot interferometer; (b) is a comparison of the reflection spectra of four structures, wherein the reflection spectra of the misalignment type Fabry-Perot interferometer without UV glue coating (black curve), the Fabry-Perot interferometer with UV glue coating (green curve), the tapered fiber grating alone (blue curve), and the micro-fiber sensor of the tapered fiber grating integrated Fabry-Perot interferometer (red curve) are compared.
[0025] Figure 5 The figure shows the refractive index sensing test of the embodiment. In the experiment, the integrated micro-fiber sensor is immersed in a salt solution for refractive index response measurement. The refractive index of the salt solution can be adjusted between 1.33 and 1.36. The environmental temperature is maintained at about 25 ℃. In order to ensure that the sensor is in a stable state, the fiber sensor is placed in each refractive index salt solution for 10 minutes to obtain the reflection spectrum. Due to the evanescent field effect of the core mode and the Bragg wavelength modulation mechanism, when the environmental refractive index changes, the Bragg peak of the tapered fiber grating will change significantly. For the Fabry-Perot interferometer, the 15 μm thick UV glue around the misalignment region effectively blocks the disturbance of the external refractive index on the propagation mode, so the reflection spectrum does not shift. The results are shown in Figure 5 . Figure 5 (a) and 5(b) respectively show the change trend of the reflection spectrum with the increase and decrease of the refractive index, and the inset is an enlarged display of the spectral shift of the micro-fiber sensor. Figure 5(c) describes the corresponding wavelength shift and the relationship with the environmental refractive index, and the refractive index sensitivity is about 28.4 nm / RIU. As can be seen from the figure, there is a good linear relationship between the two, and the repeatability of the sensor is good. This shows that in the case of increasing refractive index and decreasing refractive index, the sensing performance of the tapered fiber grating is almost the same, indicating that the proposed fiber sensor has stable performance.
[0026] Figure 6 The temperature sensing test diagram for the embodiment. In the experiment, the integrated micro fiber sensor is placed in an oven with a temperature accuracy of 0.1℃. When the temperature gradually increases, the reflection spectrum moves accordingly. The relative refractive index of the environment is about 1, and the relative humidity is about 50%RH. The test results are shown in Figure 6 . Figure 6 (a) and 6(b) respectively show the change trend of the reflection spectrum when the temperature increases and decreases, and the insert is the spectral shift of the micro fiber sensor shown in an enlarged view. Figure 6 (c) shows the relationship between the shift of the reflection spectrum and the temperature. As can be seen from the figure, there is a good linear relationship between the shift of the reflection spectrum and the ambient temperature, and the repeatability of the sensor is good. The temperature sensitivities of the tapered fiber grating and the Fabry-Perot interferometer are 9.7 pm / ℃ and -270 pm / ℃, respectively.
[0027] Figure 7 The humidity sensing test diagram for the embodiment. In the experiment, the integrated micro fiber sensor is placed in a humidity control box with a humidity accuracy of 1%RH. The environmental refractive index is about 1, and the temperature is about 25℃. When the relative humidity around changes, the ultraviolet glue droplet will absorb or seep water molecules, causing the refractive index of the ultraviolet glue to change. In turn, it affects the propagation of the light beam in the interferometer misregistration area, and finally causes the reflection spectrum to drift. For the tapered fiber grating, the change of the environmental refractive index caused by the change of the humidity is very weak. Therefore, the Bragg peak almost does not drift. The test results are shown in Figure 7 . Figure 7 (a) and 7(b) respectively show the change trend of the reflection spectrum when the humidity increases and decreases, and the insert is the spectral shift of the micro fiber sensor shown in an enlarged view. Figure 7 (c) shows the relationship between the shift of the reflection spectrum and the relative humidity. As can be seen from the figure, the sensing performance of the fiber sensor has good linear characteristics and repeatability. The relative humidity sensitivity of the Fabry-Perot interferometer is -14.9 pm / %RH, and the relative humidity sensitivity of the tapered fiber grating is 0 pm / %RH.
[0028] In the present application, the integrated micro fiber sensor has excellent performance, small size, high sensitivity, etc., and can simultaneously measure any two of the three parameters of environmental refractive index, temperature and humidity.
[0029] The above merely provides the preferred embodiment of the present application, and the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical scheme and the inventive concept of the present application, can make equivalent substitutions or changes within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.
Claims
1. A method for fabricating a miniature fiber optic sensor based on a tapered fiber grating, characterized in that, Includes the following steps: Step 1: Perform two staggered fusion splices on the single-mode fiber to form a staggered segment; Step 2: Transfer the UV adhesive droplets to the misaligned section of the optical fiber, and obtain the misaligned Fabry-Perot interferometer after UV curing; Step 3: Immerse any section of the fiber Bragg grating in a drop of hydrofluoric acid, etch it, and then cut it to form a tapered fiber Bragg grating; Step 4: Fusion the misaligned Fabry-Perot interferometer with the tapered fiber grating to obtain an integrated miniature fiber optic sensor; Step 5: Testing of the miniature fiber optic sensor; The miniature fiber optic sensor will be tested for refractive index sensing, temperature sensing, and humidity sensing respectively.
2. The method for fabricating a miniature fiber optic sensor based on a tapered fiber grating according to claim 1, characterized in that: In step one, the single-mode fiber is cut to form fiber segment A and fiber segment B. The end faces of fiber segment A and fiber segment B are fused together with a staggered arrangement. Then, fiber segment B is cut to form fiber segment B and fiber segment C. The end faces of fiber segment B and fiber segment C are fused together with a staggered arrangement, forming a fiber structure in which fiber segments A, B, and C are continuously arranged. Fiber segments A and C are coaxial, and fiber segment B is a staggered segment.
3. The method for fabricating a miniature fiber optic sensor based on a tapered fiber grating according to claim 2, characterized in that: The misalignment distance between fiber segment A and fiber segment B is less than or equal to 20 µm, and the length of fiber segment B is between 50 and 200 µm.
4. The method for fabricating a miniature fiber optic sensor based on a tapered fiber grating according to claim 1, characterized in that: In step two, the UV adhesive droplets are transferred to the misaligned section of the optical fiber.
5. The method for fabricating a miniature fiber optic sensor based on a tapered fiber grating according to claim 1, characterized in that: In step three, the fiber Bragg grating is etched in the region of the hydrofluoric acid droplet from the center of the droplet outwards along the length of the grating, forming a waist structure that gradually thickens from the center to the sides. The grating is then cut at the thinnest point of the waist structure to form a tapered fiber grating.
6. The method for fabricating a miniature fiber optic sensor based on a tapered fiber grating according to claim 1, characterized in that: In step three, during the etching process, the hydrofluoric acid droplets are replaced every hour, and the diameter of the microfiber is monitored in real time using an optical microscope; the smallest waist diameter of the fiber Bragg grating is 4.9 µm.
7. The method for fabricating a miniature fiber optic sensor based on a tapered fiber grating according to claim 1, characterized in that: In step four, the end face of the tapered fiber grating is coaxially positioned with the misaligned Fabry-Perot interferometer and then fused together.
8. The method for fabricating a miniature fiber optic sensor based on a tapered fiber grating according to claim 1, characterized in that: In step five, the refractive index sensing test involves immersing the integrated miniature fiber optic sensor in a salt solution with the refractive index adjusted between 1.33 and 1.36, while maintaining the ambient temperature at 25°C.
9. The method for fabricating a miniature fiber optic sensor based on a tapered fiber grating according to claim 1, characterized in that: In step five, the temperature sensing test involves placing the integrated miniature fiber optic sensor in an oven with a temperature accuracy of 0.1 °C, an ambient refractive index of approximately 1, and a humidity of 50%RH.
10. The method for fabricating a miniature fiber optic sensor based on a tapered fiber grating according to claim 1, characterized in that: In step five, the humidity sensing test involves placing the integrated miniature fiber optic sensor in a humidity control box with a humidity accuracy of 1%RH, an ambient refractive index of approximately 1, and a temperature of 25°C.