A multimode side-coupled fiber Bragg grating sensor and a manufacturing method thereof

Abstract

The application discloses a multimode coupling eccentric core fiber Bragg grating sensor, which comprises the following modules: an optical source module, which is used for generating an optical source with a fixed wavelength range to provide excitation light for an evanescent field sensing area; an evanescent field sensing module, which is used for sensing the refractive index information in the evanescent field by utilizing the eccentric core structure of the Bragg grating and the multimode fiber to excite the evanescent field, so as to detect the refractive index of a to-be-detected liquid and a molecular combination process related to the refractive index; a signal detection module, which is used for collecting spectral signals carrying detection information transmitted by the multimode fiber and performing real-time spectral recording; and a micro flow cell, which is used for placing the evanescent field sensing area and the to-be-detected liquid. The application excites a Bragg cladding mode by using an eccentric core welding technology, simplifies a manufacturing process, avoids the damage of a traditional mechanical processing to a Bragg fiber grating structure, significantly improves the consistency and mechanical strength of a product, enhances the long-term stability of the Bragg fiber grating sensor, and is suitable for large-scale application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sensors, and relates to a multimode eccentric core coupling fiber Bragg grating sensor. BACKGROUND

[0002] With the rapid development of optical fiber sensing technology, optical fiber Bragg grating (FBG) evanescent field sensors have shown wide application potential in refractive index detection due to their high sensitivity, electromagnetic interference resistance, miniaturization and other advantages. Such sensors interact with the outside medium through evanescent field to achieve high-sensitivity sensing of environmental refractive index changes, and have important value in biological detection, chemical analysis, environmental monitoring and other fields. However, the existing optical fiber evanescent field sensing technology still has the following key problems:

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

[0004] 2. Poor manufacturing consistency: In the manufacturing process of the current optical fiber FBG evanescent field sensor, there are high technical requirements for the cladding removal and polishing steps, which is difficult to ensure that the structures of different batches of products are completely consistent, resulting in fluctuations in sensor performance and affecting its reliability in actual application.

[0005] 3. High manufacturing cost: Since the existing optical fiber FBG evanescent field sensor relies on high-precision processing technology, its production cost is high, which limits its large-scale application.

[0006] Therefore, the core challenge of the existing technology is to improve the evanescent field excitation efficiency of the optical fiber FBG, improve the manufacturing consistency, enhance the signal-to-noise ratio and reduce the production cost. SUMMARY

[0007] To solve the above problems, the technical scheme adopted by the application is: a multimode coupling eccentric core fiber Bragg grating sensor, comprising: a light source module, an evanescent field sensing module and a signal detection module.

[0008] The light source module comprises a light source and a single-mode optical fiber joint.

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

[0010] The signal detection module comprises a spectrometer and a multimode optical fiber joint.

[0011] The light source is used to generate a light source with a fixed range of wavelengths to provide excitation light for the evanescent field sensing region.

[0012] The single-mode fiber joint is used for connecting the light source and the single-mode fiber.

[0013] The single-mode fiber is used for transmitting the excitation light source without carrying detection information, and the other end is provided with a Bragg grating, which is connected with one end of the multi-mode fiber to form an evanescent field sensing area.

[0014] The multi-mode fiber is used for connecting with the single-mode fiber with a core offset, exciting a cladding mode, and forming an evanescent field sensing area.

[0015] The evanescent field sensing area is used for exciting an evanescent field to perceive the refractive index information in the evanescent field, detecting the refractive index of the liquid to be measured and the molecular binding process related to the refractive index, and transmitting the sensing light carrying detection information through the multi-mode fiber joint to the optical spectrum analyzer.

[0016] The micro flow cell is used for placing the evanescent field sensing area and the liquid to be measured.

[0017] The multi-mode fiber joint is used for connecting the multi-mode fiber and the optical spectrum analyzer.

[0018] The optical spectrum analyzer is used for collecting the spectral signal carrying detection information transmitted by the multi-mode fiber and recording the spectrum in real time.

[0019] Further, the single-mode fiber joint and the multi-mode fiber joint adopt FC / PC joints.

[0020] Further, the light source module is used for emitting light source with a wavelength range of 1525-1610nm.

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

[0022] Further, an FBG grating area is arranged on the end of the single-mode fiber connected with the multi-mode fiber.

[0023] Further, the signal detection module adopts an optical spectrum analyzer with a detection range of 600-1700nm.

[0024] Further, the detection liquid includes a sample solution of protein, polypeptide, nucleic acid or polysaccharide molecules.

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

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

[0027] Use a high-precision optical fiber clamp to fix the optical fiber to be welded, and ensure that the optical fiber remains stable during the welding process;

[0028] S2: Use a fusion machine to offset core weld FBG grating area and multi-mode optical fiber;

[0029] Through the six-axis precision motion platform of the fusion machine, the position of the optical fiber is accurately adjusted in the X-axis, Y-axis and Z-axis directions, and the initial core offset is set according to the core offset range of the single-mode optical fiber and the multi-mode optical fiber;

[0030] S3: Optimize the fusion parameters of the fusion machine; set a low-power pre-fusion mode to weld the single-mode optical fiber and the multi-mode optical fiber;

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

[0032] The multi-mode coupling offset core fiber Bragg grating sensor provided by the application is a novel fiber FBG evanescent field sensor based on offset core welding technology. By introducing a single-mode-multimode optical fiber offset core structure in the optical fiber sensing area, the offset core parameters of the optical fiber, i.e. the center distance of the cores of the single-mode optical fiber and the multi-mode optical fiber, are accurately controlled, efficient evanescent field excitation is realized, and the limitations of traditional technology are overcome. This method not only avoids the mechanical strength reduction problem 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 application optimizes the structure of the optical fiber evanescent field sensor through offset core welding technology, and achieves the following technical effects:

[0034] 1. Improve sensitivity

[0035] By precisely controlling the offset core welding process, optimizing the evanescent field distribution, and improving the response ability of the optical field to external refractive index changes, the application enhances the interaction between the optical fiber and the surrounding medium, significantly improves the detection sensitivity, and can more accurately perceive small changes in refractive index.

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

[0037] The application adopts the eccentric core welding technology, simplifies the manufacturing process, avoids the damage to the optical fiber structure caused by the traditional mechanical processing, significantly improves the consistency and mechanical strength of the product, and enhances the long-term stability of the sensor. Therefore, the product has higher production consistency and can maintain excellent performance in long-term use, and is suitable for large-scale application. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

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

[0040] Figure 2 is a spectrum diagram of the multimode coupling eccentric core optical fiber Bragg grating sensor.

[0041] The drawings show that: 1 is a signal detection module, 2 is a spectrometer, 3 is a multimode optical fiber joint, 4 is a potential field sensing module, 5 is a multimode optical fiber, 6 is a micro flow cell, 7 is a single mode optical fiber, 8 is an inlet, 9 is an outlet, 10 is a welding point, 11 is an FBG, 12 is a single mode optical fiber joint, 13 is a light source, and 14 is a light source module. DETAILED DESCRIPTION

[0042] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict, and the present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0043] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

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

[0045] A multi-mode coupling eccentric fiber Bragg grating sensor, comprising: a signal detection module 1, a spectrometer 2, a multi-mode fiber joint 3, an evanescent field sensing module 4, a multi-mode 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 joint 12, a light source 13, and a light source module 14;

[0046] The light source module 14 comprises the light source 13 and the single-mode fiber joint 12, and the single-mode fiber joint 12 is connected to the light source 13 at one end;

[0047] The evanescent field sensing module 4 comprises the single-mode fiber 7, the multi-mode fiber 5, the welding point 10, an evanescent field sensing area, and the micro flow cell 6;

[0048] The single-mode fiber joint 12 is connected to the single-mode fiber 7 at the other end,

[0049] The other end of the single-mode fiber is connected to one end of the multi-mode fiber 5, forming an evanescent field sensing area;

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

[0051] The signal detection module 1 comprises the spectrometer 2 and the multi-mode fiber joint 3, one end of the multi-mode fiber joint 3 is connected to the multi-mode fiber 5, and the other end of the multi-mode fiber joint 3 is connected to the spectrometer 2;

[0052] The light source module 14 is used to generate the light source 13 with a fixed range of wavelengths, providing excitation light for the evanescent field sensing area;

[0053] The single-mode fiber 7 is used to transmit the light carrying no detection information transmitted by the light source module 14, and transmit the excitation light from the light source 13 to the evanescent field sensing area;

[0054] The multi-mode fiber 5 is used to be connected to the single-mode fiber 7 eccentrically, excite the cladding mode, form the evanescent field sensing area, and excite the evanescent field to perceive the refractive index information in the evanescent field, so as to 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 area and the liquid to be measured;

[0056] The signal detection module 1 is used to collect the spectral signal carrying the detection information transmitted by the multi-mode fiber 5, and record the spectrum in real time.

[0057] An FBG 11 grating area is arranged at the end of the single-mode fiber 7 connected to the multi-mode fiber 5;

[0058] The light source module 14 is connected with one end of the single-mode optical fiber 7 through the single-mode optical fiber joint 12;

[0059] The other end of the single-mode optical fiber 7 is connected with one end of the multi-mode optical fiber 5 through the welding point 10, the core of the single-mode optical fiber 7 is away from the core of the multi-mode optical fiber 5 by a distance d, 10 μm ≥ d ≥ 5 μm;

[0060] The micro flow cell 6 comprises 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 detected, so as to ensure the stable flow of the detection liquid in the sensitive area of the optical fiber and realize the high-efficiency refractive index detection.

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

[0063] The spectrometer 2 is used for real-time monitoring of the coupled optical fiber signal and analyzing the spectral change.

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

[0065] The multi-mode optical fiber joint 3 and the single-mode optical fiber joint 12 adopt FC joints or PC jumpers;

[0066] A manufacturing method of a multi-mode coupling eccentric fiber Bragg grating sensor, characterized in that the method comprises the following steps:

[0067] S1: fiber preparation and fixing; selecting a single-mode optical fiber 7 and a multi-mode optical fiber 5, removing the coating layer of the single-mode optical fiber 7 containing the FBG 11 grating area, stripping the protective layer close to the grating area 0 mm, and exposing the cladding part, so as to provide conditions for the subsequent welding of the optical fiber;

[0068] The coating layer of the multi-mode optical fiber 5 is removed, and the cladding part is also exposed, so as to ensure the cleanliness of the coupling surface of the optical fiber. A high-precision optical fiber cutting knife is used for end face cutting;

[0069] A high-precision optical fiber clamp is used to fix the optical fiber to be welded, so as to ensure the stability of the optical fiber during the welding process.

[0070] Two FC joints are connected with the multi-mode optical fiber 5 and the single-mode optical fiber 7 respectively, and the FC joint connected with the multi-mode optical fiber 5 is connected with the spectrometer 2, and the FC joint of the single-mode optical fiber 7 is connected with the light source 13;

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

[0072] Core misalignment alignment and precision control;

[0073] An optical detection system is used to monitor the relative position of the optical fiber.

[0074] The position of the optical fiber is accurately adjusted in the X-axis, Y-axis and Z-axis directions by the six-axis precision motion platform of the fusion machine, and the initial core misalignment is set according to the core misalignment range of the single-mode optical fiber 7 and the multi-mode optical fiber 5.

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

[0076] A low-power pre-fusion mode is set to avoid excessive melting of the optical fiber end face, which can cause core misalignment failure.

[0077] S4: Connect the multi-mode optical fiber joint 3 through the un-fused end of the multi-mode optical fiber 5.

[0078] S5: Welding quality detection and optimization;

[0079] The structural integrity of the fusion point is detected by an optical microscope or a scanning electron microscope.

[0080] A method for using a multi-mode coupling core misalignment optical fiber Bragg grating sensor, comprising the following steps:

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

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

[0083] Step three: Pass the drug to be tested into the micro flow cell 6, and record the spectrum change;

[0084] After the sample is added, the spectrum data is collected; the spectrum change is recorded in real time by the spectrum demodulator.

[0085] Step four: Data analysis and detection results

[0086] Through the above steps, the sensor can monitor the spectral changes in the sensing area in real time, and then analyze the small changes of the external refractive index. The cladding mode of the excitation fiber forms a comb spectrum structure. When the liquid with different refractive indexes flows through the sensing area, the resonance wavelength of the comb spectrum will be shifted. By detecting the spectral shift, the concentration of the target substance can be accurately determined, realizing high-sensitivity refractive index sensing, and thus realizing high-precision detection of the measured substance.

[0087] According to the spectral peak shift, the concentration or other related information of the target substance can be further calculated.

[0088] First, qualitative test is carried out, the standard is used to calibrate the sensing system, and the sensitivity parameter is obtained. When detecting the measured substance, the spectral shift is collected, and the sensitivity and the resonance wavelength shift of the comb spectrum are used to calculate the concentration.

[0089] Figure 2 is a spectral diagram of a multimode coupling 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 application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part 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 application.

Claims

1. A multi-mode coupled off-centre fibre Bragg grating sensor, characterised in that: The application relates to a kind of evanescent field sensor module, including: light source module, evanescent field sensing module and signal detection module. The light source module includes a light source and a single-mode fiber joint. The evanescent field sensing module includes a single-mode fiber, a multi-mode fiber, an evanescent field sensing area and a micro flow cell. The signal detection module includes a spectrometer and a multi-mode fiber joint. The light source generates a light source with a fixed range of wavelengths, providing excitation light for the evanescent field sensing area. The single-mode fiber joint connects the light source and the single-mode fiber. The single-mode fiber transmits the excitation light source without carrying detection information from the light source, and the other end is provided with a Bragg grating, which is connected to one end of the multi-mode fiber to form an evanescent field sensing area. The multi-mode fiber is connected to the single-mode fiber with a core offset to excite the cladding mode and form an evanescent field sensing area. The evanescent field sensing area excites an evanescent field to sense the refractive index information in the evanescent field, detects 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 the multi-mode fiber joint. The micro flow cell is used to place the evanescent field sensing area and the liquid to be measured. The multi-mode fiber joint connects the multi-mode fiber to the spectrometer. The spectrometer collects the spectral signal carrying detection information transmitted by the multi-mode fiber and records the spectrum in real time. The light source module emits a light source with a wavelength range of 1525-1610 nm.

2. A multi-mode core-offset fiber Bragg grating sensor according to claim 1, wherein: The distance d between the core center point of the multi-mode fiber and the core center point of the single-mode fiber is in the range of 10 um >= d >= 5 um.

3. The multi-mode side polished fiber Bragg grating sensor according to claim 1, wherein: A Bragg grating area is provided on the end of the single-mode fiber connected to the multi-mode fiber.

4. The multi-mode side polished fiber Bragg grating sensor according to claim 1, wherein: The signal detection module uses a spectrometer with a detection range of 600-1700 nm.

5. The multi-mode side polished fiber Bragg grating sensor according to claim 1, wherein: The detection liquid includes a sample solution of protein, polypeptide, nucleic acid or polysaccharide molecules.

6. The multi-mode side polished fiber Bragg grating sensor according to claim 1, wherein: The single-mode fiber joint and the multi-mode fiber joint use FC / PC joints.

7. The multi-mode side polished fiber Bragg grating sensor according to claim 1, wherein: The application includes the following steps:

8. The method of claim 1-7, wherein the method further comprises: S1: Select a single-mode fiber and a multi-mode fiber, remove the coating layer of the single-mode fiber containing the Bragg grating area, strip the protective layer at 0 mm near the grating area, and expose the cladding layer for subsequent welding process. ​ Remove the coating layer of the multi-mode fiber to ensure that the exposed cladding surface is clean and smooth for subsequent sample detection of the liquid to be detected. Finally, use a high-precision fiber cutting knife to cut the fiber end face, and the single-mode fiber cutting position is 0 mm away from the grating area. Use a high-precision fiber clamp to fix the fiber to be welded to ensure that the fiber remains stable during welding. S2: Use a fusion machine to offset weld the FBG grating area of the single-mode fiber and the multi-mode fiber. Use the six-axis precision motion platform of the fusion machine to accurately adjust the position of the fiber in the X, Y and Z directions, and set the initial core offset according to the core offset range of the single-mode fiber and the multi-mode fiber. S3: Optimize the fusion parameters of the fusion machine; set a low-power pre-fusion mode to weld 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 through the FC / PC joint respectively.

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