Internal micro-flow refractive index sensor based on double-core single-hole optical fiber and preparation method of internal micro-flow refractive index sensor

Abstract

The invention discloses an internal microflow refractive index sensor based on a double-core single-hole optical fiber and a preparation method, and belongs to the technical field of optical fiber sensing. The optical fiber sensor sequentially comprises a first single-mode optical fiber, a first multi-mode optical fiber, a double-core single-hole optical fiber, a second multi-mode optical fiber and a second single-mode optical fiber; the first single-mode fiber and the first multimode fiber, the first multimode fiber and the double-core single-hole fiber, the double-core single-hole fiber and the second multimode fiber, and the second multimode fiber and the second single-mode fiber are subjected to fusion welding treatment by using a fiber fusion splicer to form a single-mode-multimode-double-core single-hole-multimode-single-mode structure; and forming a micro-flow inlet and a micro-flow outlet by using femtosecond laser drilling to obtain the optical fiber sensor, and then packaging the optical fiber sensor. The internal air hole microflow can be used for anti-interference and long-distance chemical substance concentration sensing and biological detection by virtue of a closed microenvironment.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing, and in particular relates to an internal microflow refractive index sensor based on a dual-core single-hole optical fiber and a preparation method thereof. Background Art

[0002] In recent years, fiber optic sensors have shown significant potential for application in fields such as biomedical testing, environmental monitoring, and food safety due to their high sensitivity, resistance to electromagnetic interference, miniaturization, and real-time monitoring capabilities. Traditional fiber optic sensors are typically based on technologies such as fiber Bragg gratings (FBGs), surface plasmon resonance (SPR), or microstructured fibers (MOFs), and their performance relies on the precise processing of the fiber's surface or internal structure.

[0003] Traditional fiber optic sensors (such as FBGs and SPRs) rely on precision surface or internal machining, which can lead to low machining accuracy, significant thermal damage, and difficulty in achieving complex structures. This limits the sensitivity and reliability of trace detection. While femtosecond laser processing can achieve submicron-scale micro- and nanostructures (such as microcavities and microchannels), open microfluidic channels are susceptible to environmental interference, and long-distance microfluidic integration remains challenging. Summary of the Invention

[0004] To address the significant environmental interference associated with open microfluidic channels and the insufficient machining precision of closed microfluidic structures, the present invention provides an internal microfluidic refractive index sensor based on a dual-core single-hole optical fiber and its fabrication method. This refractive index sensor utilizes an internal air hole microfluidic channel in a closed microenvironment, enabling interference-resistant, long-distance chemical concentration sensing and single-cell manipulation.

[0005] The technical solutions adopted by the present invention for an internal microflow refractive index sensor based on a dual-core single-hole optical fiber and its preparation method are as follows:

[0006] An internal microflow refractive index sensor based on a dual-core single-hole optical fiber comprises a single-mode optical fiber 1, a multimode optical fiber 1, a dual-core single-hole optical fiber, a multimode optical fiber 2, and a single-mode optical fiber 2, which are coaxially fused in sequence. A microflow inlet and a microflow outlet are provided on the surface of the dual-core single-hole optical fiber, which are formed by drilling holes on the surface of the dual-core single-hole optical fiber using a femtosecond laser. Two fiber cores and an air hole are provided inside the dual-core single-hole optical fiber, and a refractive index liquid is injected into the air hole through the microflow inlet.

[0007] A further improvement of the technical solution of the present invention is that the microflow inlet and the microflow outlet are rectangular grooves formed by femtosecond laser drilling, and the rectangular grooves are 100 μm long, 25 μm wide and 40 μm high.

[0008] A further improvement of the technical solution of the present invention is that the microflow inlet is 40 μm away from the nearest fusion point on the left end, and the microflow outlet is 40 μm away from the nearest fusion point on the right end.

[0009] A further improvement of the technical solution of the present invention is that the flow rate of the refractive index liquid injected into the micro-flow inlet is 5 μl / min.

[0010] A further improvement of the technical solution of the present invention is that the parameters of the dual-core single-hole optical fiber include: an outer diameter of 120.37 μm, a diameter of each fiber core of 9.29 μm, a spacing between the two fiber cores of 28.73 μm, and an air hole diameter of 38.02 μm.

[0011] A further improvement of the technical solution of the present invention is that the length of the multimode optical fiber 1 and the multimode optical fiber 2 are both 1 mm, the core diameters of the multimode optical fiber 1 and the multimode optical fiber 2 are both 105 μm; and the length of the dual-core single-hole optical fiber is 12 cm.

[0012] A method for preparing an internal microflow refractive index sensor based on a dual-core single-hole optical fiber, for preparing the above-mentioned refractive index sensor, comprises the following steps:

[0013] S1. Using a CCD camera for real-time monitoring, first use a fiber cleaver to accurately and smoothly cut the right end face of single-mode optical fiber 1, then connect it to the left end face of another section of multi-mode optical fiber 1 that has been ensured to be flat. Then, use a fiber fusion splicer to fuse the butted end faces of the single-mode optical fiber 1 and the multi-mode optical fiber 1 to form a single-mode-multimode structure.

[0014] S2. Use a fiber cleaver to precisely cut a 1 mm section of the multimode fiber 1, and connect it to the left end face of another section of the dual-core single-hole optical fiber that has been ensured to be flat. Then use a fiber fusion splicer to fuse the butted end faces of the multimode fiber 1 and the dual-core single-hole optical fiber to form a single-mode-multimode-dual-core single-hole structure.

[0015] S3. Use a fiber cleaver to accurately cut 12 cm of the dual-core single-hole optical fiber and connect it to the left end face of another section of multimode optical fiber 2 that has been ensured to be flat. Then use a fiber fusion splicer to fuse the butted end faces of the dual-core single-hole optical fiber and the multimode optical fiber 2 to form a single-mode-multimode-dual-core single-hole-multimode structure.

[0016] S4. Use a fiber cleaver to precisely cut a 1 mm section of the multimode optical fiber 2, and connect it to the left end face of another section of the single-mode optical fiber 2 that has been ensured to be flat. Then, use a fiber fusion splicer to fuse the butted end faces of the multimode optical fiber 2 and the single-mode optical fiber 2, finally obtaining a fiber optic sensor with a single-mode-multimode-dual-core single-hole-multimode-single-mode structure.

[0017] S5. Place the fiber optic sensor on a micromachining platform and use a 40x microscope to observe the CCD in real time. Drop a small amount of water on the dual-core single-hole part of the fiber optic sensor to machine a rectangular groove with a liquid-assisted method. The rectangular groove is 100 μm long, 25 μm wide, and 40 μm high.

[0018] S6. Place the two ends of the punched fiber optic sensor in two T-shaped glass tubes, with the microflow inlet and outlet facing the upper ends of the T-shaped glass tubes. Seal the left and right sides of the two T-shaped glass tubes with UV glue, and finally fix them on a glass slide.

[0019] S7. Inject ethanol into the liquid injection port to clean the processing debris in the cavity and dry it.

[0020] Due to the adoption of the above technical solution, the technical advancements achieved by the present invention include:

[0021] The present invention proposes an internal microfluidic refractive index sensor based on a dual-core single-hole optical fiber and a preparation method. First, the ultrashort pulse and high energy density of a femtosecond laser are utilized to focus the laser beam into the interior of the optical fiber through a focusing lens. Nonlinear effects such as multiphoton absorption are generated in the irradiated area, forming a modified or plasma region. Subsequently, by precisely controlling the laser parameters and scanning path, the material is removed layer by layer until the desired micropore or micro-nanostructure is obtained. Liquid-assisted micropore processing is the introduction of a liquid field during the laser processing process, such as changing the water layer thickness, the type of liquid, or using a water jet. It can be superimposed with electric fields, magnetic fields, etc. to form a composite field to further improve the aperture quality. When water is used as an auxiliary medium, its refractive index (≈1.3325) is similar to that of the optical fiber material, which can significantly reduce laser refraction and scattering losses, and improve processing accuracy and efficiency. In addition, the refractive index of water changes slightly with temperature, its chemical properties are stable, and it does not react with the optical fiber, ensuring the stability and reliability of the processing. This process is suitable for the manufacture of high-quality optical fiber sensors and communication components. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a structural diagram of an internal microflow refractive index sensor based on a dual-core single-hole optical fiber according to the present invention;

[0023] Figure 2 This is a structural diagram of an internal microflow refractive index sensor based on a dual-core single-hole optical fiber after packaging;

[0024] Figure 3 1 is a schematic cross-sectional view of a dual-core single-hole optical fiber of the present invention, which is a micro-flow refractive index sensor based on the dual-core single-hole optical fiber;

[0025] Figure 4 This is a schematic diagram of the rectangular slot measurement dimensions of an internal microflow refractive index sensor based on a dual-core single-hole optical fiber according to the present invention;

[0026] Figure 5 is the wavelength shift intensity of the interference spectrum corresponding to different refractive index liquids;

[0027] Figure 6It is the spectral shift of the optical fiber sensor to liquids with different refractive indices and the corresponding linear fitting results.

[0028] In the accompanying drawings: 1. Single-mode optical fiber 1; 2. Multi-mode optical fiber 1; 3. Dual-core single-hole optical fiber; 4. Multi-mode optical fiber 2; 5. Single-mode optical fiber 2; 6. Microflow inlet; 7. Microflow outlet. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. In the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concept of the present invention.

[0030] The present invention prepares an optical fiber sensor with a structure of single-mode fiber-multimode fiber-dual-core single-hole fiber-multimode fiber-single-mode fiber through manual fusion splicing. Compared with the automatic fusion splicing of a fusion splicer, manual splicing has strong operability and is convenient for flexible adjustment of fusion parameters and alignment methods to achieve the best fusion effect. It also avoids unnecessary cleaning discharge and reduces the degree of air hole collapse. The discharge intensity is 120 and the arc duration is 140ms as the fusion parameters.

[0031] like Figure 1 As shown, the present invention discloses an internal microflow refractive index sensor based on a dual-core single-hole optical fiber, comprising a single-mode optical fiber 1, a multimode optical fiber 2, a dual-core single-hole optical fiber 3, a multimode optical fiber 2 4 and a single-mode optical fiber 2 5 coaxially fused in sequence, and the dual-core single-hole optical fiber 3 comprises a microflow inlet 6 and a microflow outlet 7 located on the surface of the dual-core single-hole optical fiber 3.

[0032] The sensor is based on a Mach-Zehnder interferometer (MZI) constructed from a dual-core single-hole optical fiber, which includes a sensing fiber core and a reference fiber core: the sensing fiber core is adjacent to the microfluidic channel, and its effective refractive index is affected by the liquid environment; the reference fiber core is embedded inside the cladding. After the light is coupled to the dual cores through a multimode optical fiber, it is transmitted in separate paths and interferes. The change in the refractive index of the liquid is reflected as a wavelength drift of the interference spectrum through the change in the phase difference of the sensing fiber core, achieving high-sensitivity detection.

[0033] In the refractive index sensor of the present invention, the outer diameters of the single-mode optical fiber 1, the multimode optical fiber 2, the dual-core single-hole optical fiber 3, the multimode optical fiber 24, and the single-mode optical fiber 25 are all 125 μm, the core diameters of the single-mode optical fiber 1 and the single-mode optical fiber 25 are both 9 μm, and the core diameters of the multimode optical fiber 2 and the multimode optical fiber 24 are both 105 μm.

[0034] At the same time, the outer diameter of the dual-core single-hole optical fiber 3 in the refractive index sensor of the present invention is 120.37 μm, and two cores and an air hole are provided therein. The distance between the two cores is 28.73 μm, and the diameter of each core is 9.29 μm. The central core is located at the center of the dual-core single-hole optical fiber, and the diameter of the air hole is 38.02 μm. The two cores and the air hole are distributed on the same straight line. Figure 3 shown.

[0035] In the refractive index sensor of the present invention, the lengths of the multimode optical fiber 1 2 and the multimode optical fiber 2 4 are 1 mm, and the length of the dual-core single-hole optical fiber 3 is 12 cm.

[0036] In the refractive index sensor of the present invention, the distance between the microflow inlet 6 and the nearest fusion point on the left end is about 40 μm, while the distance between the microflow outlet 7 and the nearest fusion point on the right end is about 40 μm.

[0037] The microflow inlet 6 and the microflow outlet 7 in the refractive index sensor of the present invention are rectangular grooves formed by punching with a femtosecond laser. The rectangular grooves are 100 μm long, 25 μm wide, and 40 μm high.

[0038] The present invention also provides a method for preparing an internal microflow refractive index sensor based on a dual-core single-hole optical fiber, comprising the following steps:

[0039] S1. Using a CCD camera for real-time monitoring, first use a fiber cleaver to accurately and smoothly cut the right end face of the single-mode optical fiber 1, and then connect it to the left end face of another section of multi-mode optical fiber 2 that has been ensured to be flat. Then use a fiber fusion splicer to fuse the butt end faces of the single-mode optical fiber 1 and the multi-mode optical fiber 2 to form a single-mode-multimode structure.

[0040] S2. Use a fiber optic cutter to accurately cut 1 mm of the multimode optical fiber 2, and connect it to the left end face of another section of dual-core single-hole optical fiber 3 that has been ensured to be flat. Then use a fiber fusion splicer to fuse the butt end faces of the multimode optical fiber 2 and the dual-core single-hole optical fiber 3 to form a single-mode-multimode-dual-core single-hole structure.

[0041] S3. Use a fiber optic cutter to accurately cut 12 cm of the dual-core single-hole optical fiber 3, and connect it to the left end face of another section of multimode optical fiber 2 4 that has been ensured to be flat. Then use a fiber fusion splicer to fuse the butt end faces of the dual-core single-hole optical fiber 3 and the multimode optical fiber 2 4 to form a single-mode-multimode-dual-core single-hole-multimode structure.

[0042] S4. Use a fiber optic cutter to accurately cut 1 mm of the multimode optical fiber 24, and connect it to the left end face of another section of single-mode optical fiber 25 that has been ensured to be flat. Then use a fiber optic fusion splicer to fuse the butt end faces of the multimode optical fiber 24 and the single-mode optical fiber 25, and finally obtain a fiber optic sensor with a single-mode-multimode-dual-core single-hole-multimode-single-mode structure.

[0043] S5. Place the fiber optic sensor on the micromachining platform and use a 40x microscope to observe it in real time through the CCD. Drop a small amount of water on the dual-core single-hole part of the fiber optic sensor to machine a rectangular groove with liquid assistance. The rectangular groove is 100 μm long, 25 μm wide, and 40 μm high.

[0044] S6, such as Figure 2 As shown, the two ends of the punched optical fiber sensor are placed in two T-shaped glass tubes, so that the microflow inlet 6 and the microflow outlet 7 are respectively opposite to the upper ends of the T-shaped glass tubes, and then the left and right sides of the two T-shaped glass tubes are sealed with ultraviolet glue, and finally fixed on a glass slide.

[0045] S7, introducing ethanol into the micro-flow inlet 6 to clean the processing debris in the cavity and dry it.

[0046] The present invention also provides a method for detecting a substance (dimethyl sulfoxide), comprising the following steps:

[0047] Step 1: diluting high-concentration dimethyl sulfoxide with water to form solutions with different refractive indices;

[0048] Step 2: Connect the other end of single-mode fiber 1 to the light source, and the other end of single-mode fiber 2 to the spectrometer, and turn on the light source;

[0049] Step 3: Use a syringe to draw in a certain volume of dimethyl sulfoxide solution, connect it to the microflow inlet 6, and slowly inject the solution into the air hole of the dual-core single-hole optical fiber 3 through the microflow inlet 6 until a small amount of solution is discharged from the microflow outlet 7;

[0050] Step 4: Wait for the spectrum to stabilize and record the transmission spectrum at that time;

[0051] Step 5: Clean the residual liquid in the cavity by using dimethyl sulfoxide solution of different concentrations and repeat the above steps.

[0052] like Figure 4 and 5 Shown are the results of the sensing experiment.

[0053] In the above-mentioned embodiments, the present invention provides an internal microfluidic refractive index sensor based on a dual-core single-hole optical fiber and its fabrication method. First, utilizing the ultrashort pulses and high energy density of a femtosecond laser, the laser beam is focused into the optical fiber through a focusing lens. Nonlinear effects such as multiphoton absorption are generated in the irradiated area, forming a modified or plasma region. Subsequently, by precisely controlling the laser parameters and scanning path, material is removed layer by layer until the desired micropore or micro-nanostructure is obtained. Liquid-assisted micropore processing involves introducing a liquid field during laser processing, such as by varying the water layer thickness or liquid type or using a water jet. This field can be superimposed with electric and magnetic fields to form a composite field to further improve aperture quality. When water is used as the auxiliary medium, its refractive index (≈1.3325) is similar to that of the optical fiber material, significantly reducing laser refraction and scattering losses and improving processing accuracy and efficiency. Furthermore, water's refractive index varies minimally with temperature, its chemical properties are stable, and it does not react with the optical fiber, ensuring processing stability and reliability. This process is suitable for the manufacture of high-quality optical fiber sensors and communication components.

[0054] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the concept and scope of the present invention. Any modifications and improvements made to the technical solution of the present invention by a person of ordinary skill in the art without departing from the design concept of the present invention shall fall within the scope of protection of the present invention. The technical content for which protection is sought in the present invention is fully set forth in the claims.

Claims

1. An internal microflow refractive index sensor based on a dual-core single-hole optical fiber, characterized by: The invention comprises a single-mode optical fiber (1), a multimode optical fiber (2), a dual-core single-hole optical fiber (3), a multimode optical fiber (4), and a single-mode optical fiber (5) which are coaxially fused in sequence; a micro-flow inlet (6) and a micro-flow outlet (7) are provided on the surface of the dual-core single-hole optical fiber (3); the micro-flow inlet (6) and the micro-flow outlet (7) are formed by punching holes on the surface of the dual-core single-hole optical fiber (3) by a femtosecond laser; two fiber cores and an air hole are provided inside the dual-core single-hole optical fiber (3); a refractive index liquid is injected into the air hole through the micro-flow inlet (6).

2. The internal microflow refractive index sensor based on a dual-core single-hole optical fiber according to claim 1, characterized in that: The microflow inlet (6) and the microflow outlet (7) are rectangular grooves formed by punching with a femtosecond laser, and the rectangular grooves are 100 μm long, 25 μm wide, and 40 μm high.

3. The internal microflow refractive index sensor based on a dual-core single-hole optical fiber according to claim 1, characterized in that: The microflow inlet (6) is 40 μm away from the nearest fusion point on the left end, and the microflow outlet (7) is 40 μm away from the nearest fusion point on the right end.

4. The internal microflow refractive index sensor based on a dual-core single-hole optical fiber according to claim 1, characterized in that: The refractive index liquid is injected into the microfluidic inlet (6) at a flow rate of 5 μl / min.

5. The internal microflow refractive index sensor based on a dual-core single-hole optical fiber according to claim 1, characterized in that: The parameters of the dual-core single-hole optical fiber (3) include: an outer diameter of 120.37 μm, a diameter of each fiber core of 9.29 μm, a distance between two fiber cores of 28.73 μm, and an air hole diameter of 38.02 μm.

6. The internal microflow refractive index sensor based on a dual-core single-hole optical fiber according to claim 1, characterized in that: The lengths of the multimode optical fiber 1 (2) and the multimode optical fiber 2 (4) are both 1 mm, and the core diameters of the multimode optical fiber 1 (2) and the multimode optical fiber 2 (4) are both 105 μm; the length of the dual-core single-hole optical fiber (3) is 12 cm.

7. A method for preparing an internal microflow refractive index sensor based on a dual-core single-hole optical fiber, characterized by: The method for preparing the refractive index sensor according to any one of claims 1 to 6 comprises the following steps: S1. Using a CCD camera for real-time monitoring, first use a fiber optic cutter to accurately and smoothly cut the right end face of the single-mode optical fiber (1), and then connect it to the left end face of another multi-mode optical fiber (2) that has been ensured to be flat. Then use a fiber optic fusion splicer to fuse the butt end faces of the single-mode optical fiber (1) and the multi-mode optical fiber (2) to form a single-mode-multi-mode structure. S2. Use an optical fiber cutter to accurately cut 1 mm of the multimode optical fiber 1 (2), and connect it to the left end face of another section of the double-core single-hole optical fiber (3) that has been ensured to be flat. Then use an optical fiber fusion splicer to fuse the butt end faces of the multimode optical fiber 1 (2) and the double-core single-hole optical fiber (3) to form a single-mode-multimode-double-core single-hole structure; S3, using an optical fiber cutter to accurately cut 12 cm of the dual-core single-hole optical fiber (3), and connect it to the left end face of another section of multimode optical fiber 2 (4) that has been ensured to be flat, and then using an optical fiber fusion splicer to fuse the butt end faces of the dual-core single-hole optical fiber (3) and the multimode optical fiber 2 (4) to form a single-mode-multimode-dual-core single-hole-multimode structure; S4. Use an optical fiber cutter to accurately cut 1 mm of the multimode optical fiber 2 (4), and connect it to the left end face of another section of single-mode optical fiber 2 (5) that has been ensured to be flat. Then use an optical fiber fusion splicer to fuse the butt end faces of the multimode optical fiber 2 (4) and the single-mode optical fiber 2 (5), and finally obtain a single-mode-multimode-dual-core single-hole-multimode-single-mode structure optical fiber sensor; S5. Place the fiber optic sensor on a micromachining platform and use a 40x microscope to observe the CCD in real time. Drop a small amount of water on the dual-core single-hole part of the fiber optic sensor to machine a rectangular groove with a liquid-assisted method. The rectangular groove is 100 μm long, 25 μm wide, and 40 μm high. S6. Place the two ends of the punched optical fiber sensor in two T-shaped glass tubes, respectively, so that the microflow inlet (6) and the microflow outlet (7) are respectively aligned with the upper ends of the T-shaped glass tubes, and then seal the left and right sides of the two T-shaped glass tubes with UV glue, and finally fix them on a glass slide; S7. Inject ethanol into the liquid injection port to clean the processing debris in the cavity and dry it.

Images