Multi-mode coupling core shift fiber Bragg grating sensor and manufacturing method thereof

Abstract

The invention relates to a multimode coupling core-shift fiber Bragg grating sensor, which comprises a light source module used for generating a light source with a wavelength in a fixed range and providing exciting light for an evanescent field sensing area; the evanescent field sensing module is used for realizing evanescent field excitation by utilizing a core shift structure of a Bragg grating and a multimode optical fiber so as to sense refractive index information in the evanescent field and is used for detecting the refractive index of liquid to be detected and a molecular binding process related to the refractive index; the signal detection module is used for collecting a spectral signal which is transmitted by the multimode optical fiber and carries detection information, and carrying out real-time spectral recording; and the micro-flow cell is used for placing the evanescent field sensing area and liquid to be detected. The core shift welding technology is adopted to excite the Bragg cladding mode, the manufacturing process is simplified, damage of traditional machining to the Bragg fiber grating structure is avoided, the consistency and mechanical strength of products are remarkably improved, the long-term stability of the Bragg fiber grating sensor is enhanced, and the sensor is suitable for large-scale application.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors and relates to a multimode eccentric coupling fiber Bragg grating sensor. Background Art

[0002] With the rapid development of fiber optic sensing technology, fiber Bragg grating (FBG) evanescent field sensors have shown great potential in the field of refractive index detection due to their advantages such as high sensitivity, electromagnetic interference resistance, and miniaturization. These sensors achieve highly sensitive detection of environmental refractive index changes through the interaction of the evanescent field with the external medium and have important value in biological detection, chemical analysis, environmental monitoring, and other fields. However, the existing fiber optic evanescent field sensing technology still has the following key problems:

[0003] 1. Limited evanescent field excitation efficiency: Traditional fiber optic FBG evanescent field sensors usually rely on cladding removal, side polishing, or photonic crystal structures to excite the evanescent field. However, these methods not only reduce the mechanical strength of the optical fiber and affect its long-term stability.

[0004] 2. Poor manufacturing consistency: In the manufacturing process of current fiber optic FBG evanescent field sensors, steps such as cladding removal and polishing have high technical requirements, making it difficult to ensure that the structures of products in different batches are exactly the same, resulting in fluctuations in sensor performance and affecting its reliability in practical applications.

[0005] 3. High manufacturing cost: Since the existing fiber optic FBG evanescent field sensors rely on high-precision processing technologies, their production costs are relatively high, which limits their large-scale application.

[0006] Therefore, the core challenges faced by the existing technology are to improve the evanescent field excitation efficiency of fiber optic FBGs, enhance manufacturing consistency, increase the signal-to-noise ratio, and reduce production costs. Summary of the Invention

[0007] To solve the above problems, the technical solution adopted by the present invention is: A multimode coupled eccentric fiber Bragg grating sensor, comprising: a light source module, an evanescent field sensing module, and a signal detection module;

[0008] The light source module includes a light source and a single-mode fiber connector;

[0009] The evanescent field sensing module includes a single-mode fiber, a multimode fiber, an evanescent field sensing region, and a micro flow cell;

[0010] The signal detection module includes a spectrometer and a multimode fiber connector.

[0011] The light source is used to generate a light source with a wavelength within a fixed range and provide excitation light for the evanescent field sensing region;

[0012] The single-mode fiber optic connector is used to connect a light source and a single-mode optical fiber;

[0013] The single-mode optical fiber: is used to transmit the excitation light source without detection information transmitted by the light source, and a Bragg grating is provided at the other end, and this end is connected to one end of a multi-mode optical fiber to form an evanescent field sensing region;

[0014] The multi-mode optical fiber: is used to be eccentrically connected to the single-mode optical fiber to excite the cladding mode and form an evanescent field sensing region;

[0015] The evanescent field sensing region: is used to excite an evanescent field, thereby sensing the refractive index information in the evanescent field, and is used to detect the refractive index of the liquid to be measured and the molecular binding process related to the refractive index; the sensing light carrying the detection information is connected to a spectrometer through a multi-mode fiber optic connector;

[0016] The micro flow cell: is used to place the evanescent field sensing region and the liquid to be measured;

[0017] The multi-mode fiber optic connector: is used to connect the multi-mode optical fiber and the spectrometer;

[0018] The spectrometer: is used to collect the spectral signals carrying detection information transmitted by the multi-mode optical fiber and perform real-time spectral recording.

[0019] Further, the single-mode fiber optic connector and the multi-mode fiber optic connector adopt FC / PC connectors.

[0020] Further: The light source module is used to emit a light source with a wavelength range of 1525 - 1610 nm.

[0021] Further: The distance d between the center point of the core of the multi-mode optical fiber and the center point of the core of the single-mode optical fiber ranges from: 10 μm ≥ d ≥ 5 μm.

[0022] Further: An FBG grating region is provided at one end where the single-mode optical fiber is connected to the multi-mode optical fiber.

[0023] Further: The signal detection module adopts a spectrometer with a detection range of 600 - 1700 nm.

[0024] Further: The liquid to be detected includes a sample solution containing protein, polypeptide, nucleic acid or polysaccharide molecules.

[0025] Further, a manufacturing method of a multi-mode coupled eccentric fiber Bragg grating sensor includes the following steps:

[0026] S1: Select single-mode fiber and multi-mode fiber, remove the coating layer of the single-mode fiber containing the FBG grating region, strip the protective layer near the grating region at 0 mm, and expose the cladding part for subsequent welding process. Also remove the coating layer of the multi-mode fiber to ensure the cleanliness of the coupling surface. Finally, use a high-precision fiber cutter to cut the fiber end face.

[0027] Fix the fiber to be welded with a high-precision fiber fixture to ensure the stability of the fiber during the welding process.

[0028] S2: Use a fusion splicer to perform eccentric welding on the FBG grating region and the multi-mode fiber.

[0029] Through the six-axis precision motion platform of the fusion splicer, accurately adjust the position of the fiber in the X-axis, Y-axis, and Z-axis directions respectively, and set the initial eccentricity according to the range of the core offset of the single-mode fiber and the multi-mode fiber.

[0030] S3: Optimize the fusion splicing parameters of the fusion splicer; set the low-power pre-fusion splicing mode to perform the welding of the single-mode fiber and the multi-mode fiber.

[0031] S4: Connect the spectrometer through the non-welded end of the multi-mode fiber.

[0032] A multi-mode coupled eccentric fiber Bragg grating sensor provided by the present invention is a novel fiber FBG evanescent field sensor based on eccentric welding technology. By introducing a single-mode-multi-mode fiber eccentric structure in the fiber sensing area, accurately controlling the eccentric parameters of the fiber, that is, the core center distance between the single-mode fiber and the multi-mode fiber, efficient evanescent field excitation is achieved, overcoming the limitations of traditional technologies. This method not only avoids the problem of mechanical strength decline caused by cladding removal or polishing, but also improves the batch manufacturing consistency of the sensor, optimizes the signal-to-noise ratio, and reduces the production cost, providing a more stable and efficient solution for high-precision refractive index sensing.

[0033] The present invention optimizes the structure of the fiber evanescent field sensor through eccentric welding technology and achieves the following remarkable technical effects:

[0034] 1. Improve sensitivity

[0035] By precisely controlling the eccentric welding process and optimizing the evanescent field distribution, the response ability of the optical field to the change of the external refractive index is improved. Compared with the traditional structure, the present invention enhances the interaction between the fiber and the surrounding medium, significantly improves the detection sensitivity, and can more accurately sense the tiny refractive index change.

[0036] 2. Improve manufacturing consistency and enhance structural stability;

[0037] The present invention adopts an eccentric welding technology, which simplifies the manufacturing process, avoids the damage to the fiber optic structure caused by traditional machining, significantly improves the product consistency and mechanical strength, and enhances the long-term stability of the sensor. Therefore, the product has higher production consistency, can maintain excellent performance during long-term use, and is suitable for large-scale applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0039] Figure 1 It is a schematic diagram of the overall structure of the sensor;

[0040] Figure 2 It is the spectrogram of the multimode-coupled eccentric fiber Bragg grating sensor.

[0041] Reference numerals: 1, signal detection module; 2, spectrometer; 3, multimode fiber connector; 4, evanescent field sensing module; 5, multimode fiber; 6, micro flow cell; 7, single-mode fiber; 8, inlet; 9, outlet; 10, welding point; 11, FBG; 12, single-mode fiber connector; 13, light source; 14, light source module. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine the embodiments to detail the present invention.

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. The description of at least one exemplary embodiment is actually only illustrative and in no way restrictive of the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0044] Figure 1 It is a schematic diagram of the overall structure of the sensor;

[0045] A multimode-coupled eccentric fiber Bragg grating sensor, comprising: a signal detection module 1, a spectrometer 2, a multimode fiber connector 3, an evanescent field sensing module 4, a multimode fiber 5, a micro flow cell 6, a single-mode fiber 7, an inlet 8, an outlet 9, a welding point 10, an FBG 11, a single-mode fiber connector 12, a light source 13, and a light source module 14;

[0046] The light source module 14 includes a light source 13 and a single-mode fiber connector 12, and one end of the single-mode fiber connector 12 is connected to the light source 13;

[0047] The evanescent field sensing module 4 includes a single-mode fiber 7, a multimode fiber 5, a welding point 10, an evanescent field sensing region, and a micro flow cell 6;

[0048] The other end of the single-mode fiber is connected to one end of the multimode fiber 5 through the single-mode fiber connector 12,

[0049] The other end of the single-mode fiber is connected to one end of the multimode fiber 5 to form an evanescent field sensing region;

[0050] The micro flow cell 6 is used to place the evanescent field sensing region and the liquid to be measured;

[0051] The signal detection module 1 includes a spectrometer 2 and a multimode fiber connector 3. One end of the multimode fiber connector 3 is connected to the other end of the multimode fiber 5; the other end of the multimode fiber connector is connected to the spectrometer 2;

[0052] The light source module 14 is used to generate a light source 13 with a wavelength within a fixed range to provide excitation light for the evanescent field sensing region;

[0053] The single-mode fiber 7 is used to transmit the light that does not carry detection information transmitted by the light source module 14 and transmit the excitation light from the light source 13 to the evanescent field sensing region;

[0054] The multimode fiber 5 is used to be eccentrically connected to the single-mode fiber 7 to excite the cladding mode to form an evanescent field sensing region. The evanescent field sensing region is used to excite an evanescent field to sense the refractive index information in the evanescent field and detect the refractive index of the liquid to be measured and the molecular binding process related to the refractive index;

[0055] The micro flow cell 6 is used to place the evanescent field sensing region and the liquid to be measured;

[0056] The signal detection module 1 is used to collect the spectral signals carrying detection information transmitted by the multimode fiber 5 and perform real-time spectral recording.

[0057] An FBG 11 grating region is provided at the end where the single-mode fiber 7 is connected to the multimode fiber 5;

[0058] The light source module 14 is connected to one end of the single-mode optical fiber 7 through a single-mode fiber optic connector 12;

[0059] The other end of the single-mode optical fiber 7 is eccentrically connected to one end of the multi-mode optical fiber 5 through a welding point 10, and the distance d between the cores of the single-mode optical fiber 7 and the multi-mode optical fiber 5 satisfies 10μm ≥ d ≥ 5μm;

[0060] The micro flow cell 6 has a structure including an inlet 8 and an outlet 9;

[0061] The inlet 8 and the outlet 9 are respectively used for the inflow and outflow of the liquid to be measured; to ensure that the detection liquid forms a stable flow within the fiber optic sensitive area and achieve efficient refractive index detection.

[0062] The signal detection module 1 uses a spectrometer 2 with a detection range of 600 - 1700nm, and the spectrometer 2 is connected to the multi-mode optical fiber 5 through a multi-mode fiber optic connector 12;

[0063] The spectrometer 2 is used to monitor the coupled fiber optic signal in real time and analyze the spectral changes.

[0064] The single-mode optical fiber 7 uses a commercial single-mode optical fiber 7 combined with a commercial FBG 11 sensing element; the multi-mode optical fiber 5 is a commercial multi-mode optical fiber 5 to ensure the system stability and sensitivity.

[0065] The multi-mode fiber optic connector 3 and the single-mode fiber optic connector 12 use FC connectors or PC jumpers;

[0066] A manufacturing method of a multi-mode coupled eccentric fiber Bragg grating sensor, characterized by comprising the following steps:

[0067] S1: Optical fiber preparation and fixation; Select the single-mode optical fiber 7 and the multi-mode optical fiber 5, remove the coating layer of the single-mode optical fiber 7 containing the FBG 11 grating area, peel off the protective layer near the grating area at 0mm, expose the cladding part, and provide conditions for subsequent optical fiber welding;

[0068] Remove the coating layer of the multi-mode optical fiber 5, also expose the cladding part, and ensure the cleanliness of the fiber optic coupling surface. And use a high-precision fiber optic cutter for end face cutting;

[0069] Use a high-precision fiber optic fixture to fix the optical fibers to be welded to ensure the stability of the optical fibers during the welding process.

[0070] Connect two FC connectors to the multi-mode optical fiber 5 and the single-mode optical fiber 7 respectively, connect the FC connector connecting the multi-mode optical fiber 5 to the spectrometer 2, and connect the FC connector of the single-mode optical fiber 7 to the light source 13;

[0071] S2: Use a fusion splicer to perform eccentric welding on the FBG 11 grating area and the multi-mode optical fiber 5;

[0072] Eccentric alignment and precise control;

[0073] Use an optical detection system to monitor the relative position of the optical fiber.

[0074] Through the six-axis precision motion platform of the fusion splicer, accurately adjust the position of the optical fiber in the X-axis, Y-axis, and Z-axis directions respectively, and set the initial eccentricity according to the offset range of the cores of the single-mode fiber 7 and the multi-mode fiber 5;

[0075] S3: Optimize the fusion splicing parameters of the fusion splicer; the fusion splicing parameters include fusion splicing time, fusion splicing loss, fusion splicing loss, fusion splicing temperature range, centering holding accuracy, moving position accuracy, and centering degree, etc.;

[0076] Set the low-power pre-fusion splicing mode to avoid the failure of eccentricity caused by excessive melting of the optical fiber end face.

[0077] S4: Connect the multi-mode fiber joint 3 through the unwelded end of the multi-mode fiber 5;

[0078] S5: Welding quality inspection and optimization;

[0079] Detect the structural integrity of the fusion splicing point through an optical microscope or a scanning electron microscope.

[0080] A method for using a multi-mode coupled eccentric fiber Bragg grating sensor, comprising the following steps:

[0081] Step 1: Start the light source module 14 and the signal detection module 1 to ensure that the device is in a stable working state. The light source 13 used should have a stable optical power output;

[0082] Step 2: Connect the single-mode fiber 7 to the light source 13 through the single-mode fiber joint 12, and connect the multi-mode fiber 5 to the spectrometer 2 through the multi-mode fiber joint 3. At this time, an initial spectrogram will be obtained and recorded;

[0083] Step 3: Pass the drug to be tested into the microfluidic cell 6 and record the spectral changes;

[0084] After the sample is dropped, perform spectral data acquisition; record the spectral changes in real time through the spectral demodulator.

[0085] Step 4: Data analysis and test results

[0086] Through the above steps, the sensor can monitor the spectral changes in the sensing area in real time, and then analyze the minute changes in the external refractive index. By exciting the cladding mode of the optical fiber to form a comb-like spectral structure, when liquids with different refractive indices flow through the sensing area, the resonance wavelength of this comb-like spectrum will shift. By detecting the spectral shift amount, the concentration of the target substance can be accurately measured, achieving high-sensitivity refractive index sensing, and thus realizing high-precision detection of the substance to be measured.

[0087] The concentration of the target substance or other relevant information can be further calculated based on the spectral peak drift.

[0088] First, a qualitative test is carried out. The sensing system is calibrated using standard samples to obtain the sensitivity parameters. When detecting the substance to be measured, the spectral drift is collected, and the concentration is calculated using the sensitivity and the resonance wavelength shift amount of the comb-like spectrum.

[0089] Figure 2 It is the spectrogram of the multimode-coupled eccentric fiber Bragg grating sensor.

[0090] 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 foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multimode-coupled eccentric fiber Bragg grating sensor, characterized in that: Comprising: A light source module, an evanescent field sensing module, and a signal detection module; The light source module includes a light source and a single-mode fiber optic connector; The evanescent field sensing module includes a single-mode fiber, a multi-mode fiber, an evanescent field sensing region, and a microfluidic flow cell; The signal detection module includes a spectrometer and a multi-mode fiber optic connector; The light source is used to generate a light source with a wavelength within a fixed range to provide excitation light for the evanescent field sensing region; The single-mode fiber optic connector is used to connect the light source and the single-mode fiber; The single-mode fiber: is used to transmit the excitation light source that does not carry detection information transmitted by the light source, and a Bragg grating is provided at the other end, and this end is connected to one end of the multi-mode fiber to form an evanescent field sensing region; The multi-mode fiber: is used to be eccentrically connected to the single-mode fiber to excite the cladding mode and form an evanescent field sensing region; The evanescent field sensing region: is used to excite an evanescent field, thereby sensing the refractive index information in the evanescent field, and is used to detect the refractive index of the liquid to be measured and the molecular binding process related to the refractive index; The sensing light carrying detection information is connected to the spectrometer through a multi-mode fiber optic connector; The microfluidic flow cell: is used to place the evanescent field sensing region and the liquid to be measured; The multi-mode fiber optic connector: is used to connect the multi-mode fiber and the spectrometer; The spectrometer: is used to collect the spectral signal carrying detection information transmitted by the multi-mode fiber and perform real-time spectral recording.

2. The multimode-coupled eccentric fiber Bragg grating sensor according to claim 1, characterized in that: The light source module is used to emit a light source with a wavelength range of 1525 - 1610 nm.

3. The multimode-coupled eccentric fiber Bragg grating sensor according to claim 1, wherein: The distance d between the center point of the core of the multi-mode fiber and the center point of the core of the single-mode fiber ranges from: 10 μm ≥ d ≥ 5 μm.

4. A multimode-coupled eccentric fiber Bragg grating sensor according to claim 1, characterized in that: A Bragg grating region is provided at one end where the single-mode fiber is connected to the multi-mode fiber.

5. A multimode-coupled eccentric fiber Bragg grating sensor according to claim 1, characterized in that: The signal detection module uses a spectrometer with a detection range of 600 - 1700 nm.

6. The multimode-coupled eccentric fiber Bragg grating sensor according to claim 1, wherein: The liquid to be detected includes a sample solution containing protein, polypeptide, nucleic acid, or polysaccharide molecules.

7. A multimode-coupled eccentric fiber Bragg grating sensor according to claim 1, characterized in that: The single-mode fiber optic connector and the multi-mode fiber optic connector adopt FC / PC connectors.

8. The manufacturing method of a multimode-coupled eccentric fiber Bragg grating sensor according to any one of claims 1-7, characterized in that: Including the following steps: S1: Select a single-mode fiber and a multi-mode fiber, and remove the coating layer of the single-mode fiber containing the Bragg grating region, strip the protective layer near 0 mm from the grating region, and expose the cladding part for subsequent welding process; Similarly remove the coating layer of the multi-mode fiber to ensure that the exposed cladding surface is clean and flat for subsequent sample detection of the liquid to be detected; finally, use a high-precision fiber optic cutter to cut the fiber end face, where the cutting position of the single-mode fiber is 0 mm from the grating region. Use a high-precision fiber optic fixture to fix the fiber to be welded to ensure the stability of the fiber during the welding process; S2: Use a fusion splicer to perform eccentric welding on the FBG grating region of the single-mode fiber and the multi-mode fiber; Through the six-axis precision motion platform of the fusion splicer, precisely adjust the position of the fiber in the X-axis, Y-axis, and Z-axis directions respectively, and set the initial eccentricity according to the range where the cores of the single-mode fiber and the multi-mode fiber can be offset; S3: Optimize the fusion splicing parameters of the fusion splicer; set a low-power pre-fusion splicing mode to perform the welding of the single-mode fiber and the multi-mode fiber; S4: Connect the single-mode fiber and the multi-mode fiber to the light source and the spectrometer respectively through FC / PC connectors.

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