Micro-nano FBG (Fiber Bragg Grating) string, preparation method thereof and gas concentration detection system

Abstract

The invention relates to a micro-nano FBG string, a preparation method thereof and a gas concentration detection system. The micro-nano FBG string comprises a plurality of single-mode FBGs which are connected in series and are different in reflection center wavelength, the single-mode FBGs are used for achieving conversion from physical quantity to optical signals, and each single-mode FBG comprises a fiber core and a wrapping layer surrounding the fiber core; the etched FBG is formed on the single-mode FBG, and the etched FBG comprises a fiber core; the surface of the etched FBG is coated with the gas sensitive material, and the gas sensitive material is used for sensing specific gas molecules and changing the reflection wavelength of the etched FBG under the condition that the gas sensitive material interacts with the specific gas molecules; the pipe sleeve is arranged outside the single-mode FBG in a sleeving mode, an air groove is formed in the surface of one side in the axial direction of the pipe sleeve, the air groove right faces the etching FBG and is used for achieving gas exchange between the etching FBG and the external environment, and the two ends of the etching FBG are fixed to the pipe sleeve through ultraviolet glue. By adopting the micro-nano FBG string, the concentration of specific gas can be accurately obtained.

Description

Technical Field

[0001] The present application relates to the field of optical fiber sensing technology, and in particular to a micro-nano FBG string and a preparation method thereof, and a gas concentration detection system. Background Art

[0002] The micro-nano FBG string is a composite structure composed of multiple fiber Bragg gratings (FBGs). The uniqueness of this structure is that by connecting multiple FBG gratings in series, each grating has a different reflection center wavelength, which enables simultaneous monitoring of multiple gas parameters, thus providing an efficient solution for gas sensing in complex environments.

[0003] However, in practical applications, sensors often face complex environmental conditions, such as changes in temperature and humidity. These environmental factors may affect the performance of the micro-nano FBG string and cause errors in the measured gas concentration. Summary of the invention

[0004] Based on this, it is necessary to provide a micro-nano FBG string and its preparation method, and a gas concentration detection system that can accurately obtain the concentration of specific gases in order to address the above technical problems.

[0005] In a first aspect, the present application provides a micro-nano FBG string, comprising:

[0006] Multiple single-mode FBGs with different reflection center wavelengths connected in series are used to realize the conversion of physical quantities into optical signals. The single-mode FBG includes a core and a cladding surrounding the core.

[0007] An etched FBG formed on the single-mode FBG, the etched FBG comprising a core;

[0008] A gas-sensitive material coated on the surface of the etched FBG, the gas-sensitive material is used to sense specific gas molecules and change the reflection wavelength of the etched FBG when interacting with the specific gas molecules;

[0009] The sleeve is sleeved outside the single-mode FBG, and an air groove is provided on one side surface of the sleeve along the axial direction. The air groove is opposite to the etched FBG and is used to realize gas exchange between the etched FBG and the external environment. Both ends of the etched FBG are fixed to the sleeve by ultraviolet glue.

[0010] In one of the embodiments, the cross-sectional diameter of the micro-nano FBG string is in the range of 9-13 microns, and the length of the micro-nano FBG string is in the range of 5-20 millimeters; the reflection center wavelength of the single-mode FBG is in the range of 1540 nanometers to 1590 nanometers, and the reflection bandwidth of the single-mode FBG is in the range of 0.2-1 nanometers.

[0011] In one embodiment, the gas-sensitive materials corresponding to the etched FBGs are different, and are respectively used to realize the detection of the corresponding specific gases by the etched FBGs, so as to realize the detection of multiple specific gases by the micro-nano FBG string.

[0012] In a second aspect, the present application also provides a gas concentration detection system, including a micro-nano FBG string, a light source module and a data processing module;

[0013] The light source module includes an optical fiber circulator and a photodetector. The optical fiber circulator is connected to one end of the micro-nano FBG string. The light source module is used to transmit the light source to the micro-nano FBG string through the optical fiber circulator and receive the reflected light generated by the micro-nano FBG string according to the light source.

[0014] The micro-nano FBG string is used to detect specific gases. When the gas-sensitive material in the micro-nano FBG string interacts with the specific gas, the wavelength of the reflected light generated by the light source is adjusted.

[0015] The data processing module is connected to the photodetector and is used to obtain the reflected light of the micro-nano FBG string through the photodetector and determine the corresponding specific gas concentration according to the wavelength of the reflected light.

[0016] In one of the embodiments, the light source module further includes a narrow linewidth laser and a fiber coupler;

[0017] The number of narrow linewidth lasers is the same as the number of single-mode FBGs in the micro-nano FBG string, and each narrow linewidth laser is used to generate a light source with a wavelength corresponding to the linear interval of the corresponding single-mode FBG reflection spectrum;

[0018] The optical fiber coupler is connected to the narrow linewidth laser and the optical fiber circulator respectively, and is used to couple the light sources generated by all the narrow linewidth lasers into one path, and transmit the coupled light sources to the micro-nano FBG string through the optical fiber circulator.

[0019] In one embodiment, the optical fiber circulator includes three ports, namely port 1, port 2 and port 3;

[0020] The light source coupled by the fiber coupler enters through port 1 and exits through port 2 into the micro-nano FBG string;

[0021] Each single-mode FBG generates corresponding reflected light according to the light source. The reflected light enters through port 2 and is emitted through port 3 to the photodetector.

[0022] In a third aspect, the present application also provides a method for preparing a micro-nano FBG string, comprising:

[0023] Functionalizing multiple single-mode optical fibers respectively by molecular lasers to obtain corresponding multiple single-mode FBGs; the functionalizing treatment includes ultraviolet exposure treatment and grating writing treatment;

[0024] For each single-mode FBG, immerse the single-mode FBG in hydrofluoric acid of a first concentration to form an etched FBG, and apply a corresponding gas-sensitive material on the surface of the etched FBG according to the gas detection requirements; the hydrofluoric acid is used to corrode the cladding of the single-mode FBG; the gas-sensitive material is used to sense specific gas molecules corresponding to the gas detection requirements;

[0025] A lateral air slot is cut along the axial direction of the sleeve, the single-mode FBG is placed in the sleeve through the air slot, and the two ends of the etched FBG are fixed to the sleeve by ultraviolet glue.

[0026] In one embodiment, the gas detection requirement is to detect hydrogen sulfide gas; according to the gas detection requirement, the step of coating the corresponding gas sensitive material on the surface of the etched FBG includes:

[0027] According to the first number, a first immersion process of etching FBG is performed; the first immersion process includes sequentially immersing the etched FBG in the PDDA solution and the PSS solution for a first time period;

[0028] When the first immersion process is completed, a second immersion process of etching the FBG is performed according to the second number; the second immersion process includes sequentially immersing the etched FBG in the cupric chloride dispersion and the graphene oxide solution for a second time period;

[0029] When the second immersion process is completed, the etched FBG is placed in a drying oven and dried at the first temperature for a third period of time.

[0030] In one embodiment, the gas detection requirement is to detect sulfur dioxide gas; according to the gas detection requirement, the step of coating the corresponding gas sensitive material on the surface of the etched FBG includes:

[0031] Put the copper foil plate lined with PMMA and graphene into ferric chloride solution for etching for a fourth time, and transfer the etched composite layer material to the surface of the etched FBG;

[0032] The composite layer and the etched FBG are immersed in the acetone solution for a fifth period of time, and the etched FBG and diethylenetriamine are evaporated at the second temperature.

[0033] In one embodiment, the gas detection requirement is to detect carbon monoxide gas; according to the gas detection requirement, the step of coating the corresponding gas sensitive material on the surface of the etched FBG includes:

[0034] Place the etched FBG liner on the glass sheet and fix it;

[0035] According to the third number, the etched FBG was cleaned by deionized water and ethanol in turn;

[0036] When the cleaning is completed, the titration process of the etched FBG is performed for a fourth number of times; the titration process includes dropping a preset milliliter of palladium potassium sulfite solution on the etched FBG fixed by the glass sheet, and drying it in a vacuum environment for a sixth time period.

[0037] The above-mentioned micro-nano FBG string and its preparation method, and gas concentration detection system, by connecting multiple single-mode FBGs with different reflection center wavelengths in series, can detect specific gases from multiple angles when used for gas detection. By etching the surface of the FBG and accurately coating the gas-sensitive material for sensing specific gas molecules, the gas-sensitive material can directly interact with the specific gas molecules, enhancing the selectivity and sensitivity of the FBG to the specific gas, so that the specific gas concentration can be accurately obtained. In addition, since an air groove is provided on the axial side surface of the sleeve, and the air groove is directly opposite to the etched FBG, the gas exchange between the etched FBG and the external environment can be accurately controlled to ensure that the specific gas can effectively reach the gas-sensitive material on the surface of the etched FBG, so that the gas-sensitive material can sense the specific gas molecules in time. On the other hand, it can avoid excessive interference factors in the external environment from affecting the accuracy of detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments of the present application or related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0039] FIG1 is a block diagram of a gas concentration detection system in one embodiment;

[0040] FIG2 is a schematic diagram of the structure of a micro-nano FBG string in one embodiment;

[0041] FIG3 is a schematic flow chart of a method for preparing a micro-nano FBG string in one embodiment;

[0042] FIG4 is a reflection spectrum diagram of a micro-nano FBG string in one embodiment;

[0043] FIG5 is a graph showing the response of the central wavelength of a micro-nano FBG string to gas concentration in one embodiment;

[0044] FIG6 is a graph showing the response of the central wavelength of a micro-nano FBG string to gas concentration in another embodiment;

[0045] FIG. 7 is a graph showing the response of the central wavelength of a micro-nano FBG string to gas concentration in another embodiment.

[0046] Description of reference numerals:

[0047] 100: micro-nano FBG string, 200: light source module, 300: data processing module;

[0048] 110: single-mode FBG, 120: etched FBG, 130: gas-sensitive material, 140: sleeve;

[0049] 210: fiber circulator, 220: photodetector, 230: narrow linewidth laser, 240: fiber coupler. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0051] In an exemplary embodiment, as shown in FIG. 1 , a gas concentration detection system is provided, including: a micro-nano FBG string 100 , a light source module 200 and a data processing module 300 .

[0052] Among them, the micro-nano FBG string 100 is used to detect specific gases. When the gas-sensitive material in the micro-nano FBG string 100 interacts with the specific gas, the wavelength of the reflected light generated by the light source is adjusted. The light source module 200 includes an optical fiber circulator 210 and a photodetector 220. The optical fiber circulator 210 is connected to one end of the micro-nano FBG string 100. The light source module 200 is used to transmit the light source to the micro-nano FBG string 100 through the optical fiber circulator 210, and receive the reflected light generated by the micro-nano FBG string 100 according to the light source. The data processing module 300 is connected to the photodetector 220, and is used to obtain the reflected light of the micro-nano FBG string 100 through the photodetector 220, and determine the corresponding specific gas concentration according to the wavelength of the reflected light.

[0053] In this embodiment, the light source can be accurately transmitted to the micro-nano FBG string through the optical fiber circulator, and the reflected light of the micro-nano FBG string can be obtained in real time through the photoelectric detector. When the gas-sensitive material interacts with the specific gas, the wavelength of the reflected light will change, and the photoelectric detector can instantly detect this change, so that the data processing module can accurately calculate the concentration of the specific gas according to the pre-established wavelength-concentration relationship, thereby realizing the automated detection of the specific gas concentration.

[0054] In an exemplary embodiment, still as shown in FIG. 1 , the light source module 200 further includes a narrow linewidth laser 230 and a fiber coupler 240 .

[0055] The number of narrow linewidth lasers 230 is the same as the number of single-mode FBGs in the micro-nano FBG string 100, and each narrow linewidth laser 230 is used to generate a light source with a wavelength corresponding to the linear interval of the corresponding single-mode FBG reflection spectrum. The optical fiber coupler 240 is connected to the narrow linewidth laser 230 and the optical fiber circulator 210, respectively, and is used to couple the light sources generated by all narrow linewidth lasers 230 into one path, and transmit the coupled light sources to the micro-nano FBG string 100 through the optical fiber circulator 210.

[0056] In this embodiment, since the number of narrow linewidth lasers is the same as the number of single-mode FBGs, and each narrow linewidth laser can generate a light source with a wavelength corresponding to the linear interval of the corresponding single-mode FBG reflection spectrum, it can be ensured that each single-mode FBG can receive the light source wavelength that best suits its characteristics, thereby improving the sensitivity and accuracy of specific gas detection. In addition, by coupling the light sources generated by all narrow linewidth lasers into one path through an optical fiber coupler, the energy of the light source can be effectively integrated, and the coupled light source can transmit energy to the micro-nano FBG string more concentratedly, thereby improving the stability and reliability of specific gas detection.

[0057] In an exemplary embodiment, the fiber circulator 240 includes three ports, namely port 1, port 2, and port 3. The light source coupled by the fiber coupler 240 is injected through port 1 and emitted through port 2 to the micro-nano FBG string 100. Each single-mode FBG generates corresponding reflected light according to the light source, and the reflected light is injected through port 2 and emitted through port 3 to the photodetector 220.

[0058] In an exemplary embodiment, as shown in FIG. 2 , a micro-nano FBG string 100 is provided, including: a single-mode FBG 110 , an etched FBG 120 , a gas-sensitive material 130 , and a sleeve 140 .

[0059] Among them, multiple single-mode FBGs 110 with different reflection center wavelengths are connected in series to form a micro-nano FBG string 100. The single-mode FBG 110 is used to realize the conversion of physical quantities into optical signals, including a core and a cladding surrounding the core. The etched FBG 120 is formed on the single-mode FBG 110, including a core. The gas-sensitive material 130 is coated on the surface of the etched FBG 120. The gas-sensitive material 130 is used to sense specific gas molecules and change the reflection wavelength of the etched FBG 120 when interacting with the specific gas molecules. The sleeve 140 is sleeved on the outside of the single-mode FBG 110, and an air groove is provided on one side surface along the axial direction of the sleeve 140. The air groove is opposite to the etched FBG 120 and is used to realize gas exchange between the etched FBG 120 and the external environment. The two ends of the etched FBG 120 are fixed to the sleeve 140 by ultraviolet glue.

[0060] In this embodiment, by connecting multiple single-mode FBGs with different reflection center wavelengths in series, when used for gas detection, specific gases can be detected from multiple angles. By etching the surface of the FBG and accurately coating the gas-sensitive material for sensing specific gas molecules, the gas-sensitive material can directly interact with the specific gas molecules, thereby enhancing the selectivity and sensitivity of the FBG to the specific gas, thereby accurately obtaining the specific gas concentration. In addition, since an air groove is provided on the axial side surface of the sleeve, and the air groove is directly opposite to the etched FBG, the gas exchange between the etched FBG and the external environment can be accurately controlled to ensure that the specific gas can effectively reach the gas-sensitive material on the surface of the etched FBG, so that the gas-sensitive material can sense the specific gas molecules in a timely manner. On the other hand, it can avoid excessive interference factors in the external environment from affecting the accuracy of detection.

[0061] In an exemplary embodiment, the cross-sectional diameter of the micro-nano FBG string 100 is in the range of 9-13 microns, and the length of the micro-nano FBG string 100 is in the range of 5-20 millimeters; the reflection center wavelength of the single-mode FBG 110 is in the range of 1540 nanometers to 1590 nanometers, and the reflection bandwidth of the single-mode FBG 110 is in the range of 0.2-1 nanometers.

[0062] In an exemplary embodiment, the gas-sensitive materials 130 corresponding to each etched FBG 120 are different, and are respectively used to realize the detection of corresponding specific gases by the etched FBG 120, so as to realize the detection of multiple specific gases by the micro-nano FBG string 100.

[0063] In an exemplary embodiment, as shown in FIG3 , a method for preparing a micro-nano FBG string is provided, and the method is applied to the micro-nano FBG string 100 in FIG2 as an example for description, including the following steps 302 to 306. Among them:

[0064] S302: performing functionalization processing on multiple single-mode optical fibers respectively by molecular laser to obtain corresponding multiple single-mode FBGs; the functionalization processing includes ultraviolet exposure processing and grating writing processing.

[0065] Optionally, during the UV exposure process, the core and cladding materials in the single-mode optical fiber will respond to the UV light, and the energy of the UV light can change the refractive index distribution inside the optical fiber. For the core part of the optical fiber, the UV light irradiation causes the refractive index of the core to change periodically according to a certain rule, and this periodic refractive index change is the basis for the formation of FBG. At the same time, the UV light is written into the optical fiber according to a certain pattern through a specific optical device, and the periodic change of the core refractive index is further accurately controlled, thereby forming a single-mode FBG with a specific reflection wavelength. For example, a 248nm KrF excimer laser is used to perform UV exposure and grating writing on the optical fiber to prepare FBG.

[0066] S304: For each single-mode FBG, immerse the single-mode FBG in hydrofluoric acid of a first concentration to form an etched FBG, and apply a corresponding gas-sensitive material on the surface of the etched FBG according to gas detection requirements; hydrofluoric acid is used to corrode the cladding of the single-mode FBG; the gas-sensitive material is used to sense specific gas molecules corresponding to the gas detection requirements.

[0067] Optionally, the single-mode FBG is immersed in hydrofluoric acid of a first concentration. Since hydrofluoric acid can corrode the cladding of the single-mode FBG, after the cladding is corroded, the structure of the optical fiber changes, and the core is relatively more exposed, which affects the propagation characteristics of light in the optical fiber, especially the reflection characteristics of the FBG. The etched FBG (etched FBG) has special optical properties, for example, its sensitivity to the surrounding environment may be improved. Exemplarily, the core diameter of the single-mode optical fiber is 9μm, and the FBG is immersed in hydrofluoric acid with a concentration of 20%, and the cladding of the FBG is etched away. The diameter of the optical fiber after corrosion is 12-13μm.

[0068] Furthermore, by combining a gas-sensitive material with a specific sensing function with an etched FBG, a composite microstructure with a specific gas detection function can be obtained. Since different gas-sensitive materials have the ability to selectively adsorb or react to different specific gas molecules, when specific gas molecules approach the gas-sensitive material, physical adsorption, chemical adsorption or chemical reaction will occur between the gas-sensitive material and the gas molecules. This interaction will cause certain physical properties of the gas-sensitive material (such as refractive index, volume, etc.) to change, thereby affecting the optical properties of the etched FBG (such as reflection wavelength).

[0069] For example, as shown in FIG4 , FIG4 is a transmission spectrum of an etched FBG modified with a gas-sensitive material. After the single-mode FBG is etched, its cladding is corroded, which changes the optical structure of the optical fiber, disturbs the original light propagation mode of the optical fiber, and changes the constraints of the light in the optical fiber. This structural change leads to the appearance of secondary peaks in addition to the main peak. When the etched FBG is used for gas detection, the secondary peak can provide an additional detection dimension, and the change of the secondary peak can reflect the interaction between the gas and the gas-sensitive material from different optical mode angles. For example, different specific gases may have different effects on high-order modes. By observing the changes in the secondary peak, the accuracy of gas type and concentration detection can be increased.

[0070] S306: cutting a lateral air slot along the axial direction of the tube sleeve, placing the single-mode FBG in the tube sleeve through the air slot, and fixing both ends of the etched FBG to the tube sleeve by ultraviolet glue.

[0071] Optionally, a lateral air groove is cut along the axial direction of the tube sleeve and a single-mode FBG is placed in the tube sleeve. This design is mainly to achieve gas exchange between the FBG and the external environment while protecting the FBG. The air groove provides a gas inlet and outlet channel so that the external specific gas can reach the gas-sensitive material on the surface of the etched FBG. The two ends of the etched FBG are fixed to the tube sleeve by ultraviolet glue. The ultraviolet glue will undergo a curing reaction under ultraviolet light, thereby firmly fixing the etched FBG in the tube sleeve. This fixing method can ensure the stability of the position of the FBG in the tube sleeve, and ensure that the relative position between the FBG, the tube sleeve and the gas-sensitive material remains unchanged during the gas detection process, thereby ensuring the accuracy and stability of gas detection.

[0072] In the preparation method of the above-mentioned micro-nano FBG string, functionalization is carried out through ultraviolet exposure and grating writing processing, so that the reflection wavelength of the single-mode FBG can be accurately controlled. After the etched FBG cladding is corroded by hydrofluoric acid, it is more sensitive to the surrounding environment. At the same time, the detection of specific gases can be achieved through the coating of gas-sensitive materials. The interaction between specific gas molecules and gas-sensitive materials can more significantly change the reflection wavelength of the etched FBG, thereby improving the sensitivity of gas detection. Different gas-sensitive materials can be selected for different specific gases, thereby realizing selective detection of specific gases.

[0073] In an exemplary embodiment, the gas detection requirement is to detect hydrogen sulfide gas; according to the gas detection requirement, the step of coating the corresponding gas sensitive material on the surface of the etched FBG includes: according to the first number, performing the first immersion process of etching the FBG; the first immersion process includes sequentially immersing the etched FBG in the PDDA solution and the PSS solution for a first time; when the first immersion process is completed, according to the second number, performing the second immersion process of etching the FBG; the second immersion process includes sequentially immersing the etched FBG in the cupric chloride dispersion and the graphene oxide solution for a second time; when the second immersion process is completed, placing the etched FBG in a drying oven at the first temperature for a third time.

[0074] For example, when preparing a specific composite structure for detecting hydrogen sulfide (H2S) gas, a layer-by-layer self-assembly method was used to soak FBG in polydienyl dimethyl ammonium chloride (PDDA) and polystyrene sulfonate (PSS) solutions twice, soaking for 10 minutes each time and washing with water to enhance the fit between FBG and the material, wherein the concentrations of PDDA and PSS solutions were 1.5wt% and 0.3wt%, respectively. Afterwards, FBG was soaked in copper oxide (CuO) dispersion and graphene oxide solution (GO) five times, soaking for 15 minutes each time and washing with water, and the concentrations of both solutions were 0.5mg / mL. Finally, FBG was placed in a drying oven at 50°C and dried overnight.

[0075] Exemplarily, as shown in FIG5 , FIG5 is a response diagram of the central wavelength of the micro-nano FBG string to the gas concentration. The specific composite structure prepared in this way is more sensitive to the detection of H2S molecules.

[0076] In an exemplary embodiment, the gas detection requirement is to detect sulfur dioxide gas; according to the gas detection requirement, the step of coating the corresponding gas sensitive material on the surface of the etched FBG includes: placing a copper foil board lined with PMMA and graphene in ferric chloride solution for etching for a fourth time, and transferring the etched composite layer material to the surface of the etched FBG; immersing the composite layer and the etched FBG in an acetone solution for a fifth time, and evaporating the etched FBG and diethylenetriamine at a second temperature.

[0077] Exemplarily, when preparing a specific composite structure for detecting sulfur dioxide (SO2) gas, a chemical deposition method is used to transfer the prepared graphene to a micro-nano fiber grating by wet transfer technology. Specifically, a copper foil plate lined with polymethyl methacrylate (PMMA) and graphene is placed in a ferric chloride solution for etching, and after complete etching, it is transferred to the FBG surface. Then, the FBG is immersed in an acetone solution to remove the PMMA layer, and finally a graphene sample transferred on the FBG is obtained. Then, the gas phase molecular doping of graphene is achieved by thermal evaporation of diethylenetriamine, and the evaporation temperature is controlled at 70°C, and finally a composite microstructure with a specific sensing function for SO2 is obtained.

[0078] Exemplarily, as shown in FIG6 , FIG6 is a response diagram of the central wavelength of the micro-nano FBG string to the gas concentration. The specific composite structure prepared in this way is more sensitive to the detection of SO2 molecules.

[0079] In an exemplary embodiment, the gas detection requirement is to detect carbon monoxide gas; according to the gas detection requirement, the step of coating the corresponding gas sensitive material on the surface of the etched FBG includes: lining the etched FBG on a glass sheet and fixing it; cleaning the etched FBG with deionized water and ethanol in turn for a third time; when the cleaning is completed, performing a titration process of the etched FBG for a fourth time; the titration process includes dropping a preset milliliter of potassium palladium sulfite solution on the etched FBG fixed by a glass sheet, and drying it under a vacuum environment for a sixth time.

[0080] For example, when preparing a specific composite structure for detecting carbon monoxide (CO) gas, 80 mg of potassium palladium sulfite solution (K2Pd(SO3)2) was dissolved in 10 mL of hot deionized water to prepare a specific gas-sensitive material. The FBG was lined on a glass slide and fixed, and washed with deionized water and ethanol three times to remove impurity interference. After that, 30 μL of K2Pd(SO3)2 solution was dropped on the FBG fixed by the glass slide, vacuum dried for 1 hour, and the titration was repeated 4 times to obtain better CO sensing performance.

[0081] Exemplarily, as shown in FIG. 7 , FIG. 7 is a response diagram of the central wavelength of the micro-nano FBG string to the gas concentration. The specific composite structure prepared in this way is more sensitive to the detection of CO molecules.

[0082] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0083] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0084] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A micro-nano FBG string, characterized in that: include: A plurality of single-mode FBGs with different reflection center wavelengths connected in series are used to realize the conversion of physical quantity into optical signal, wherein the single-mode FBG comprises a core and a cladding surrounding the core; an etched FBG formed on the single-mode FBG, wherein the etched FBG includes the core; A gas-sensitive material coated on the surface of the etched FBG, wherein the gas-sensitive material is used to sense specific gas molecules and change the reflection wavelength of the etched FBG when interacting with the specific gas molecules; A sleeve is sleeved outside the single-mode FBG, and an air groove is provided on one side surface of the sleeve along the axial direction. The air groove is directly opposite to the etched FBG and is used to achieve gas exchange between the etched FBG and the external environment. Both ends of the etched FBG are fixed to the sleeve by ultraviolet glue.

2. The micro-nano FBG string according to claim 1, characterized in that: The cross-sectional diameter of the micro-nano FBG string is in the range of 9-13 microns, and the length of the micro-nano FBG string is in the range of 5-20 millimeters; the reflection center wavelength of the single-mode FBG is in the range of 1540 nanometers to 1590 nanometers, and the reflection bandwidth of the single-mode FBG is in the range of 0.2-1 nanometer.

3. The micro-nano FBG string according to claim 1, characterized in that: The gas-sensitive materials corresponding to the etched FBGs are different, and are respectively used to realize the detection of corresponding specific gases by the etched FBGs, so as to realize the detection of multiple specific gases by the micro-nano FBG string.

4. A gas concentration detection system, characterized in that: Comprising the micro-nano FBG string, light source module and data processing module as described in any one of claims 1 to 3; The light source module includes an optical fiber circulator and a photodetector, the optical fiber circulator is connected to one end of the micro-nano FBG string, and the light source module is used to transmit the light source to the micro-nano FBG string through the optical fiber circulator, and receive the reflected light generated by the micro-nano FBG string according to the light source; The micro-nano FBG string is used to detect specific gases, and when the gas-sensitive material in the micro-nano FBG string interacts with the specific gas, the wavelength of the reflected light generated by the light source is adjusted; The data processing module is connected to the photoelectric detector and is used to obtain the reflected light of the micro-nano FBG string through the photoelectric detector, and determine the corresponding specific gas concentration according to the wavelength of the reflected light.

5. The gas concentration detection system according to claim 4, characterized in that: The light source module also includes a narrow line width laser and a fiber coupler; The number of the narrow linewidth lasers is the same as the number of single-mode FBGs in the micro-nano FBG string, and each of the narrow linewidth lasers is used to generate a light source with a wavelength corresponding to the linear interval of the corresponding single-mode FBG reflection spectrum; The optical fiber coupler is connected to the narrow linewidth laser and the optical fiber circulator respectively, and is used to couple the light sources generated by all narrow linewidth lasers into one path, and transmit the coupled light sources to the micro-nano FBG string through the optical fiber circulator.

6. The gas concentration detection system according to claim 5, characterized in that: The optical fiber circulator comprises three ports, namely port 1, port 2 and port 3; The light source coupled by the optical fiber coupler is injected through the port 1, and emitted through the port 2 to the micro-nano FBG string; Each of the single-mode FBGs generates corresponding reflected light according to the light source, and the reflected light is injected through the port No. 2 and emitted to the photodetector through the port No.

3.

7. A method for preparing a micro-nano FBG string, characterized in that: Applicable to the micro-nano FBG string according to any one of claims 1 to 3; the method comprises: Performing functionalization treatment on multiple single-mode optical fibers respectively by molecular laser to obtain corresponding multiple single-mode FBGs; the functionalization treatment includes ultraviolet exposure treatment and grating writing treatment; For each single-mode FBG, immerse the single-mode FBG in hydrofluoric acid of a first concentration to form an etched FBG, and apply a corresponding gas-sensitive material on the surface of the etched FBG according to gas detection requirements; the hydrofluoric acid is used to corrode the cladding of the single-mode FBG; the gas-sensitive material is used to sense specific gas molecules corresponding to the gas detection requirements; A lateral air slot is cut along the axial direction of the sleeve, the single-mode FBG is placed in the sleeve through the air slot, and both ends of the etched FBG are fixed to the sleeve by ultraviolet glue.

8. The method according to claim 7, characterized in that The gas detection requirement is to detect hydrogen sulfide gas; and according to the gas detection requirement, coating the surface of the etched FBG with a corresponding gas-sensitive material includes: According to the first number, performing a first immersion process of the etched FBG; the first immersion process comprises sequentially immersing the etched FBG in a PDDA solution and a PSS solution for a first time period; When the first immersion process is completed, performing a second immersion process of the etched FBG according to the second number; the second immersion process comprises sequentially immersing the etched FBG in a cupric chloride dispersion and a graphene oxide solution for a second time period; When the second immersion process is completed, the etched FBG is placed in a drying oven and dried at the first temperature for a third period of time.

9. The method according to claim 7, characterized in that: The gas detection requirement is to detect sulfur dioxide gas; and according to the gas detection requirement, coating the surface of the etched FBG with a corresponding gas-sensitive material includes: Put the copper foil plate lined with PMMA and graphene into ferric chloride solution for etching for a fourth time, and transfer the etched composite layer material to the surface of the etched FBG; The composite layer and the etched FBG are immersed in an acetone solution for a fifth period of time, and the etched FBG and diethylenetriamine are evaporated at a second temperature.

10. The method according to claim 7, characterized in that The gas detection requirement is to detect carbon monoxide gas; and according to the gas detection requirement, coating the surface of the etched FBG with a corresponding gas-sensitive material includes: The etched FBG substrate is placed on a glass sheet and fixed; According to the third number, the etched FBG is cleaned by deionized water and ethanol in turn; When the cleaning is completed, the titration process of the etched FBG is performed for a fourth number of times; the titration process includes dropping a preset milliliter of palladium potassium sulfite solution on the etched FBG fixed by the glass sheet, and drying it in a vacuum environment for a sixth period of time.

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