CN111257285B - Optical fiber sensor and preparation method thereof - Google Patents
Optical fiber sensor and preparation method thereof Download PDFInfo
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- CN111257285B CN111257285B CN202010167885.XA CN202010167885A CN111257285B CN 111257285 B CN111257285 B CN 111257285B CN 202010167885 A CN202010167885 A CN 202010167885A CN 111257285 B CN111257285 B CN 111257285B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/255—Splicing of light guides, e.g. by fusion or bonding
- G02B6/2552—Splicing of light guides, e.g. by fusion or bonding reshaping or reforming of light guides for coupling using thermal heating, e.g. tapering, forming of a lens on light guide ends
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
- G01N2021/458—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods using interferential sensor, e.g. sensor fibre, possibly on optical waveguide
Abstract
The invention discloses an optical fiber sensor and a preparation method thereof, wherein a Bragg grating is processed by adopting a fusion tapering method to form a tapered transition region and a waist region with the diameter in a micro-nano scale; and coating graphene on the waist region by using graphene dispersion liquid through vacuum suction filtration, forming a graphene film on the waist region, and separating filter paper to obtain the optical fiber sensor. According to the invention, by utilizing the structural characteristics and the stronger adsorption capacity of graphene, the sensitivity and the response characteristics of the sensor are improved, the selective identification and detection of harmful gas molecules by the optical fiber sensor are improved, the measurement stability under the room temperature condition is realized, and reliable monitoring data are obtained. The preparation method is simple, the sensor is novel in structure, high in sensitivity and convenient to carry, and compared with a dripping method process, the graphene and optical fiber sensor composite structure prepared by vacuum suction filtration is more compact, the self-assembly structure is optimized, the sensor is convenient to expose, the gas detection sensitivity is high, the optical fiber mechanical property is better, and the like.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensors, and particularly relates to an optical fiber sensor and a preparation method thereof.
Background
With the continuous progress of modern science and technology and the continuous improvement and improvement of optical fiber manufacturing process, various optical fibers with special structures and functions are rapidly developed. The optical fiber gas sensor has the advantages of quick response, high precision, good selectivity, corrosion resistance, easiness in networking and the like, and is widely applied to the field of toxic and harmful gas detection in recent years. The optical fiber sensor can realize non-light source detection under severe conditions, and the realization of underground gas detection becomes a hot spot of current research.
The existing interference type optical fiber sensor has relatively high sensitivity, but has poor stability, and far does not reach industrial use standard under extreme environment, if special functional type optical fibers are adopted, the cost is high, and in order to further improve the response characteristic of the common interference type optical fiber sensor, a large amount of research work shows that the optical fiber is pulled to form a transition waist region with the diameter of a few micrometers or even the nanometer level, so that the sensing sensitivity of the optical fibers can be greatly improved. However, a new problem arises in that this very thin waist region is very prone to fracture and therefore can only stay in the qualitative or quantitative detection phase of the laboratory and still cannot be used in a specific outdoor environment.
Disclosure of Invention
In order to solve the problems existing in the prior art, the invention aims to provide the optical fiber sensor and the preparation method thereof, and the optical fiber sensor solves the problems that the waist area of the existing interference type optical fiber sensor is easy to break and the whole sensor cannot be used in a detection environment, and simultaneously can improve the response characteristic and the sensitivity of the interference type optical fiber sensor.
The technical scheme adopted by the invention is as follows:
the utility model provides an optical fiber sensor, includes that the fiber bragg grating adopts the sensor body structure that the processing of melting tapering method formed, and the diameter of sensor body structure's waist district is at micro-nano scale, and the cladding of waist district surface has the graphite alkene film, and the graphite alkene film has extension along the radial of waist district.
Preferably, the graphene film adopts a graphene film doped with metal nano particles.
Preferably, the metal nanoparticles are silver nanoparticles.
Preferably, the graphene film has a thickness of 20nm to 1.5 μm.
The preparation method of the optical fiber sensor comprises the following steps:
processing the Bragg grating by adopting a fusion tapering method to form a tapered transition region and a waist region with the diameter in a micro-nano scale;
and coating graphene on the waist region by using graphene dispersion liquid through vacuum suction filtration, forming a graphene film on the waist region, and separating filter paper to obtain the optical fiber sensor.
Preferably, the vacuum filtration process comprises the following steps:
s1.1, spreading filter paper between a filter cup and a filter flask, soaking the filter paper in water, and fixing and clamping the filter paper;
s1.2, placing and fixing the waist region of the Bragg grating processed by adopting a fusion tapering method on filter paper;
s1.3, adding graphene dispersion liquid into a filter bowl, starting suction filtration, and depositing a layer of graphene film on filter paper;
s1.4, separating the graphene film from the filter paper to obtain the optical fiber sensor.
Preferably, the graphene dispersion liquid adopts a graphene dispersion liquid doped with metal nano particles.
Preferably, the metal nanoparticles in the graphene dispersion liquid doped with the metal nanoparticles are silver nanoparticles.
Preferably, the preparation of the silver nanoparticle doped graphene dispersion liquid comprises the following steps:
s2.1, carrying out ultrasonic dispersion on graphene oxide powder in deionized water to obtain uniform graphene oxide dispersion liquid;
s2.2, adding the dimethylacetamide aqueous solution into the graphene oxide dispersion liquid, and uniformly stirring to obtain a mixed liquid;
s2.3, adding the silver nitrate aqueous solution into the mixed solution obtained in the step S2.2, and uniformly stirring to obtain a precursor solution;
s2.4, fully reacting the precursor liquid;
s2.5, carrying out suction filtration and cleaning on the precursor liquid after the full reaction, filtering to obtain a precipitate, and drying the precipitate to obtain the silver-doped graphene;
s2.6, preparing silver-doped graphene dispersion liquid by using silver-doped graphene powder.
Preferably:
s2.1, wherein the concentration of graphene oxide in the obtained graphene oxide dispersion liquid is 0.05-0.5 mg/mL;
s2.2, in the aqueous solution of the dimethylacetamide, the volume ratio of the dimethylacetamide to the deionized water is 1:1; the volume ratio of the dimethylacetamide to the graphene oxide dispersion liquid is 1 (1-1.5);
s2.3, wherein the mass percentage of solute in the silver nitrate aqueous solution is 2.5-10%; the mass ratio of the silver nitrate to the graphene oxide in the mixed solution is 10:1;
s2.4, reacting the precursor solution at 160 ℃, and continuously stirring in the reaction process, wherein the reaction time is 24-36 hours;
s2.5, filtering by a 0.45 mu m microporous filter, and vacuum drying the precipitate for 48-60 hours at 60 ℃;
in S2.6, the concentration of the silver-doped graphene in the silver-doped graphene dispersion liquid is 0.05-0.5 mg/mL.
Preferably, the Bragg grating is processed by flame fusion tapering.
The invention has the following beneficial effects:
the sensor body structure of the optical fiber sensor adopts a structure that a Bragg grating is processed by adopting a fusion tapering method, the Bragg grating (FBG) is an inherent sensor distributed along the length of the optical fiber, when incident light propagates in the grating, waves with specific wavelength are reflected, the rest wave bands of the spectrum are not affected, and the reflected wave bands are Bragg wave bands lambda B Wherein lambda is B ＝2·n eff ·Λ，n eff Is the effective refractive index of the core, Λ is the grating period. The Bragg grating adopted by the invention adopts a sensor body structure processed by a fusion tapering method, and the grating period is correspondingly changed from lambda to lambda when axial stretching deformation is generated t And n is eff The external refractive index and the deformation caused by melt-pulling the phase will cause n, depending on the diameter of the fiber and the external refractive index eff The center wavelength of Bragg is shifted and the reflection wavelength is changed, denoted as lambda Bt Because the Bragg grating has a one-time instrument calibration function, the strain value and other derivative parameters can be dynamically measured. The Bragg grating has the advantages of high response speed, high reliability, no electromagnetic interference, safe operation in toxic and harmful gas environment, and the like, and has the characteristics that evanescent field propagation is easily influenced by environment refractive index change, and the refractive index change information of the external environment can be obtainedThe light is converted into wavelength change, so that the light can be applied to gas refractive index sensing measurement, and has potential application value in the fields of low-concentration, colorless odorless gas-sensitive sensing, environment monitoring and the like. According to the invention, the waist region has the characteristics of strong light field constraint and strong evanescent field, so that weak change of the external environment can be sensed, the selective recognition of gas molecules is enhanced, meanwhile, the graphene film is coated on the surface of the waist region, and the graphene film is provided with an extension part along the radial direction of the waist region, so that the contact area of the optical fiber sensor and target gas is greatly increased, and the measurement with high precision, high sensitivity and low loss is realized. Meanwhile, the graphene film is coated on the surface of the waist region, so that the graphene film has an excellent mechanical property and a reinforcing effect on the waist region, the mechanical property of the whole waist region is stronger, breakage is not easy to occur, and the optical fiber device is not easy to damage while the gas-sensitive property is ensured. In summary, the invention solves the problems that the waist region of the existing interference type optical fiber sensor is easy to break and the whole sensor cannot be used in a detection environment, and simultaneously, the invention can also improve the response characteristic and the sensitivity of the interference type optical fiber sensor.
Further, the graphene film doped with the metal nano particles is adopted, and compared with the intrinsic graphene, the adsorption performance of the graphene doped with the metal element is obviously enhanced. The graphene is used as a support carrier, can be used for repeatedly embedding and extracting structural strain of the metal nano particles, can show good cycle performance, and the response characteristic of the sensor can be obviously improved due to the synergistic effect of the two materials. Meanwhile, the metal nano particles are selected to dope the graphene, so that the interlayer spacing of the graphene can be effectively increased, the interval between adjacent crystal faces of the graphene is enlarged, the graphene layer is effectively expanded, the possibility of graphene agglomeration can be effectively avoided under the condition that a dispersion liquid with proper concentration is selected, the irregular arrangement of nano composite materials is reduced, and the mechanical property and the gas-sensitive property of the material are improved.
In the preparation method of the optical fiber sensor, the Bragg grating is used as a raw material, the micro-nano optical fiber is prepared by adopting a fusion tapering method, and a device processed by the fusion tapering method comprises two tapered transition regions with gradually reduced diameters and a uniform waist region with the diameter in a micro-nano scale. Compared with the traditional dripping technology, the graphene dispersion liquid is used for coating the graphene on the waist region through vacuum suction filtration, the graphene-waist-region-based optical fiber device disclosed by the invention has the advantages that the graphene can be combined with the waist region more firmly and firmly through suction filtration, the mechanical property of the waist region is stronger, the breakage is not easy to occur, the gas-sensitive property is ensured, and meanwhile, the optical fiber device is not easy to be damaged; according to the invention, as the film is coated in the waist region by adopting the vacuum suction filtration method, solid-liquid separation can be realized by utilizing negative pressure, the graphene film prepared by the method is uniform in distribution and good in material adhesion, and compared with a method for growing graphene on a monocrystalline substrate, lattice mismatch caused by different lattice constants of two monocrystalline layers can be effectively avoided.
Drawings
FIG. 1 is a schematic drawing of a typical flame-fused optical fiber drawn according to an embodiment of the present invention;
fig. 2 is an enlarged view of a portion a in fig. 1;
FIG. 3 is a flow chart of the preparation of the graphene-based optical fiber sensor of the present invention;
FIG. 4 is an enlarged view of portion B of FIG. 3;
FIG. 5 is a schematic diagram of a light sensor according to the present invention.
In the figure, 1-stage, 2-flame heating unit, 3-Bragg grating, 3-1-cone transition zone, 3-2-waist zone, 4-beaker, 5-filter rod, 6-funnel, 7-filter paper, 8-vacuum pump, 9-silver doped graphene layer, 10-graphene film, 10-1-extension.
Detailed Description
The invention will be further described with reference to the drawings and examples.
Referring to fig. 5, the optical fiber sensor of the present invention includes a sensor body structure formed by processing a bragg grating by a fusion tapering method, wherein the diameter of a waist region 3-2 of the sensor body structure is in a micro-nano scale, a graphene film 10 is coated on the surface of the waist region 3-2, and the graphene film 10 is provided with an extension portion 10-1 along the radial direction of the waist region 3-2.
As a preferred embodiment of the present invention, the graphene film 10 employs a metal nanoparticle doped graphene film.
As a preferred embodiment of the present invention, the metal nanoparticles are silver nanoparticles.
As a preferred embodiment of the present invention, the graphene film 10 has a thickness of 20nm to 1.5 μm.
The preparation method of the optical fiber sensor comprises the following steps:
processing the Bragg grating by adopting a fusion tapering method to form a tapered transition region and a waist region with the diameter in a micro-nano scale;
and coating graphene on the waist region by using graphene dispersion liquid through vacuum suction filtration, forming a graphene film 10 on the waist region, and separating filter paper to obtain the optical fiber sensor.
According to the invention, the graphene material is coated on the waist region of the single-cone interference micro-nano optical fiber sensor by using a vacuum suction filtration preparation process, the structural characteristics and the stronger adsorption capacity of graphene are utilized, the sensitivity and the response characteristics of the sensor are improved, the selective identification and detection of harmful gas molecules by the optical fiber sensor are further improved, the stable measurement under the room temperature condition can be realized, and the reliable monitoring data can be obtained. The invention designs and prepares the micro-nano optical fiber sensor which has the advantages of simple method, novel structure, high sensitivity, convenient carrying and the like by utilizing the advantages of Ag nano particles in the aspects of improving the quick response and discrimination capability of graphene to target gas molecules, and the like.
As a preferred embodiment of the present invention, referring to fig. 4, the vacuum filtration process comprises the steps of:
s1.1, spreading filter paper between a filter cup and a filter flask, soaking the filter paper in water, and fixing and clamping the filter paper;
s1.2, placing and fixing the waist region of the Bragg grating processed by adopting a fusion tapering method on filter paper;
s1.3, adding graphene dispersion liquid into a filter bowl, starting suction filtration, and depositing a layer of graphene film on filter paper;
s1.4, separating the graphene film from the filter paper to obtain the optical fiber sensor.
As a preferred embodiment of the present invention, 20nm-1.5 μm graphene is deposited on filter paper. The layer-by-layer stacking structure and the order ratio of the graphene can be improved, and the oriented arranged graphene form is obtained, so that the macroscopic performance is determined.
As a preferred embodiment of the present invention, referring to fig. 3, S1.5 is further included to cut the graphene layer into a preset shape.
As a preferred embodiment of the present invention, the graphene dispersion liquid adopts a metal nanoparticle doped graphene dispersion liquid.
As a preferred embodiment of the present invention, the metal nanoparticles in the metal nanoparticle-doped graphene dispersion are silver nanoparticles. The silver nano particle doping can effectively enhance the sensitivity and the response time, has high selective detection on low-concentration gas, and can improve the detection range of target gas to below 200 ppm.
As a preferred embodiment of the present invention, the preparation of the silver nanoparticle-doped graphene dispersion liquid comprises the steps of:
s2.1, carrying out ultrasonic dispersion on graphene oxide powder in deionized water to obtain uniform graphene oxide dispersion liquid;
s2.2, adding the dimethylacetamide aqueous solution into the graphene oxide dispersion liquid, and uniformly stirring to obtain a mixed liquid;
s2.3, adding the silver nitrate aqueous solution into the mixed solution obtained in the step S2.2, and uniformly stirring to obtain a precursor solution;
s2.4, fully reacting the precursor liquid;
s2.5, carrying out suction filtration and cleaning on the precursor liquid after the full reaction, filtering to obtain a precipitate, and drying the precipitate to obtain the silver-doped graphene;
s2.6, preparing silver-doped graphene dispersion liquid by using silver-doped graphene powder.
In S2.1, the concentration of graphene oxide in the obtained graphene oxide dispersion liquid is 0.05-0.5 mg/mL;
s2.2, in the aqueous solution of the dimethylacetamide, the volume ratio of the dimethylacetamide to the deionized water is 1:1; the volume ratio of the dimethylacetamide to the graphene oxide dispersion liquid is 1 (1-1.5);
s2.3, wherein the mass percentage of solute in the silver nitrate aqueous solution is 2.5-10%; the mass ratio of the silver nitrate to the graphene oxide in the mixed solution is 10:1;
s2.4, reacting the precursor solution at 160 ℃, and continuously stirring in the reaction process, wherein the reaction time is 24-36 hours;
s2.5, filtering by a 0.45 mu m microporous filter, and vacuum drying the precipitate for 48-60 hours at 60 ℃;
in S2.6, the concentration of the silver-doped graphene in the silver-doped graphene dispersion liquid is 0.05-0.5 mg/mL.
As a preferred embodiment of the present invention, referring to fig. 1 and 2, the bragg grating is processed using flame fusion tapering.
According to the invention, a layer of graphene nanocomposite is firmly coated on the superfine waist region after the drawing of the phasiant by utilizing a vacuum suction filtration process, so that the strength of the optical fiber sensor is greatly enhanced, the difficulty in using the micro-nano optical fiber sensor in an outdoor exposure environment is solved, meanwhile, the contact area of the waist region to target molecules is greatly increased by adding the graphene layer, the response characteristic and sensitivity of the sensor are further improved, the evanescent field and the optical coupling effect of the waist region are enhanced, and the acting efficiency of the target molecules in the sensing region is improved.
Examples
The embodiment adopts nano silver doped graphene to prepare the optical fiber sensor, and comprises the following specific steps:
preparation of Ag nanoparticle doped graphene composite material
The specific method comprises the following steps:
(1) putting the purchased GO powder into deionized water, and performing ultrasonic dispersion for 1h to prepare a GO uniform dispersion liquid with the concentration of 0.5mg/mL, wherein the graphene oxide content in the graphene oxide dispersion liquid is 0.5mg/mL;
(2) adding 35mL of dimethylacetamide aqueous solution into 35mL of graphene oxide dispersion liquid prepared in the step (1), and magnetically stirring for 1.5h; dimethylacetamide (DMAc) and H in aqueous dimethylacetamide solution 2 The volume ratio of O is 1:1, a step of;
(3) 3g of silver nitrate (AgNO) 3 ) Adding the silver nitrate into water to form silver nitrate solution with solute mass percent of 5 percent, and AgNO 3 The mass ratio of the content to the GO in the GO aqueous dispersion is 10:1, at this time, agNO is rapidly released 3 Dropwise adding the water solution into the solution, stirring for 10min, and completely mixing to obtain the precursor solution.
(4) Transferring the precursor liquid into 160 ℃ oil bath for magnetic stirring for 24 hours, so that the precursor liquid fully reacts;
(5) repeatedly carrying out suction filtration and cleaning on silver-doped graphene serving as a silver-doped graphene precursor reactant by using deionized water, filtering by using a 0.45 mu m microporous filter, and vacuum drying the obtained precipitate for 48 hours at the temperature of 60 ℃;
(6) and performing ultrasonic dispersion and centrifugal treatment on the silver-doped graphene powder in deionized water to form silver-doped graphene dispersion liquid with the concentration of 0.5mg/mL.
2. Preparation of single-cone interference type micro-nano optical fiber device
In many methods for preparing micro-nano optical fibers, in order to prepare micro-nano optical fibers with smooth surfaces, low loss and controllable cone areas, a flame fusion tapering method is adopted in the embodiment. The system has the advantages of simple structure, convenient preparation, low cost and better repeatability, and the SCS-4000 type optical fiber flame melting tapering system adopted in the experiment mainly comprises a host control system, a motor stretching unit, a hydrogen generating device, a flame heating unit, a packaging unit and a loss detection unit. As shown in fig. 1:
and stripping the coating layer of the prestretched optical fiber by using a stripper for 20mm, cleaning the part from which the coating layer is removed by using alcohol, and setting the parameters of fusion tapering. The whole tapering system is controlled by a computer, and parameters such as the position, the moving speed, the tapering length, the hydrogen flow and the like of the displacement platform are adjusted by entering a melting tapering operation interface. As shown in fig. 1 and 2, after the required parameters are adjusted, the prepared bragg fiber is fixed on the fiber holder, the center of the fiber except the coating layer section is positioned under the flame head, hydrogen is ignited by the electronic ignition equipment, the hydrogen is automatically operated according to a set tapering program after the hydrogen burns stably, the hydrogen is closed after the computer tapering program is operated, and finally the prepared micro-nano fiber is transferred to a substrate (glass substrate or magnesium fluoride substrate) with clean surface for measurement and subsequent processing.
3. Graphene-based optical fiber sensor prepared by utilizing traditional vacuum suction filtration technology
The graphene-based composite material is coated on the waist region of the optical fiber sensor by using the prepared Ag-doped graphene dispersion liquid through a traditional vacuum suction filtration technology. The vacuum suction filtration technology can realize solid-liquid separation by utilizing negative pressure, and the graphene film prepared by the method has the characteristics of uniform distribution, good material adhesion and self-organization, and can easily control the thickness of a film by controlling the concentration, the volume and the like of dispersion liquid to be suction filtered. The preparation method specifically by vacuum filtration comprises the following steps:
(1) Cleaning filter cups, filter bottles and other devices;
(2) Selecting medium-speed filter paper with the aperture of 0.45 mu m, paving the filter paper between a filter cup and a filter bottle, soaking the filter paper in water, and fixing and clamping the filter paper by using a metal clamp;
(3) Slowly transferring the prepared micro-nano optical fiber device to a funnel, adjusting the position of the waist region of the optical fiber, ensuring that the waist region can be horizontally arranged above filter paper and is stuck to the filter paper after the optical fiber enters the funnel, fixing the optical fiber device at two sides of a funnel opening by using a clamp at the moment, and placing a layer of soft cloth in front of the metal clamp and the optical fiber to prevent the optical fiber from breaking;
(4) Injecting 10-200mL of the prepared Ag doped graphene dispersion liquid into a filter bowl, starting a vacuum pump, performing suction filtration for 5-20min, depositing a layer of graphene with the thickness of 20nm-1.5 mu m on filter paper, and performing suction filtration for longer time as the thickness of the deposited film is larger;
(5) Carefully taking down the fixing devices at the two ends of the funnel opening, and slowly taking out the prepared graphene-based optical fiber;
(6) If the graphene layer is adhered with the filter paper, the prepared optical fiber device can be gently peeled off from the filter paper by using tweezers;
(7) Finally, according to the sensor test requirement and the use environment requirement, the waist region graphene coating layer is cut, and the preparation process is shown in fig. 3 and 4.
According to the invention, the graphene composite material is used for coating the micro-nano optical fiber waist region by using a vacuum suction filtration preparation process; the graphene nanocomposite increases the gas contact area in the waist region. In addition, as the optical fiber after being subjected to the drawing in the invention has the waist area which is as thin as a few micrometers or nanometers, is almost invisible to naked eyes, is very easy to break and can not be used in other environments, and the graphene has very strong toughness and very high mechanical strength, after being subjected to vacuum filtration and film coating, the waist area is completely coated in the graphene layer and is completely protected, so that the mechanical property of the optical fiber is well improved, the exposable property of the sensor is enhanced, the composite structure of the graphene and the optical fiber sensor is more compact, the self-assembly performance is better, the graphene is not easy to damage even in severe environments, and the repeatability of optical fiber sensing is enhanced. Ag doped graphene enhances the gas molecule sensing resolution and the response speed of the sensor; the FBG grating after the fused and pulled phase can realize gas-sensitive sensing under the environment of extremely low concentration, colorless and odorless gas.
According to the invention, the Ag nano particle doped graphene can effectively improve the gas molecule adsorption characteristic of the optical fiber sensor, and the resolution of the sensor on target gas molecules is improved. Meanwhile, the Ag nano particle localized plasmon can enhance the absorption of the sensor to visible light, enhance the evanescent field and the optical coupling effect, improve the action efficiency of gas molecules in a sensing area, shorten the response time of the sensor, and improve the sensitivity, stability and service life of the sensor. When an optical fiber is divided into a fiber core and a cladding, an optical signal is propagated in the optical fiber, a refractive wave of an x component and a refractive wave of a z component are necessarily generated at the interface of two media according to boundary conditions, the wave along the x direction is attenuated exponentially and is very weak, however, when the Bragg optical fiber is pulled to be a phasiant, only a micro-nano level superfine fiber core exists in the waist region, the wavelength of the micro-nano level superfine fiber core is in the same order as that of the light, the cladding becomes air at the moment, the energy proportion of the internal and external transmission of the optical fiber exceeds 70%, and the evanescent wave plays an important role in the situation, so that an obvious evanescent field is formed. The bare optical fiber has low sensitivity, and the graphene layer is added, so that the contact area of the optical fiber and target gas molecules is increased, the operation range of an evanescent field is widened, the sensitivity of the optical fiber is improved, the graphene can obviously influence the intensity distribution and the phase change of the evanescent field, when the evanescent wave passes through the fiber core to reach the graphene layer, the generated fluorescent signal and the intensity of the evanescent wave can be effectively gathered by the graphene layer, the property and the concentration of the target gas in the surface evanescent field range can be rapidly detected, and the response sensitivity of the optical fiber sensor is greatly enhanced. In summary, the invention uses the interference type micro-nano optical fiber device as a carrier, and makes the interference type micro-nano optical fiber device become a device with high refractive index and high sensitivity by means of the strong interaction between the strong evanescent field of the micro-nano optical fiber and the external environment. In addition, the target molecule concentration measurement is realized by combining the composite material (GO-Ag) of the Ag modified reduced graphene oxide, and the sensitization sensing with high sensitivity and high selectivity is realized.
According to the invention, ag nano particle doped graphene is prepared by a one-step synthesis method as a precursor material, a graphene composite material is coated on the waist region of the single-cone interference micro-nano optical fiber sensor by a vacuum suction filtration preparation process, the sensitivity and response characteristics of the sensor are improved by utilizing the structural characteristics and the stronger adsorption capacity of the doped graphene, the selective identification and detection of harmful gas molecules by the optical fiber sensor are further improved, stable measurement under the room temperature condition can be realized, and reliable monitoring data are obtained. The invention designs and prepares the micro-nano optical fiber sensor which has the advantages of simple method, novel structure, high sensitivity, convenient carrying and the like by utilizing the advantages of Ag nano particles in the aspects of improving the quick response and discrimination capability of graphene to target gas molecules, and the like.
Claims (1)
1. The optical fiber sensor is characterized by comprising a sensor body structure formed by processing a Bragg grating by adopting a fusion tapering method, wherein the diameter of a waist region (3-2) of the sensor body structure is in a micro-nano scale, a graphene film (10) is coated on the surface of the waist region (3-2), and the graphene film (10) is provided with an extension part (10-1) along the radial direction of the waist region (3-2);
the graphene film (10) adopts a graphene film doped with metal nano particles;
the metal nano-particles are silver nano-particles;
the thickness of the graphene film (10) is 20nm-1.5 mu m;
the preparation method of the optical fiber sensor comprises the following steps:
processing the Bragg grating by adopting a fusion tapering method to form a tapered transition region and a waist region with the diameter in a micro-nano scale;
coating graphene on the waist region by utilizing graphene dispersion liquid through vacuum suction filtration, forming a graphene film (10) in the waist region, and separating filter paper to obtain the optical fiber sensor;
the vacuum filtration process comprises the following steps:
s1.1, spreading filter paper between a filter cup and a filter flask, soaking the filter paper in water, and fixing and clamping the filter paper;
s1.2, placing and fixing the waist region of the Bragg grating processed by adopting a fusion tapering method on filter paper;
s1.3, adding graphene dispersion liquid into a filter bowl, starting suction filtration, and depositing a layer of graphene film on filter paper;
s1.4, separating the graphene film from the filter paper to obtain the optical fiber sensor;
the graphene dispersion liquid adopts graphene dispersion liquid doped with metal nano particles;
the metal nanoparticles in the graphene dispersion liquid doped with the metal nanoparticles are silver nanoparticles;
the preparation of the silver nanoparticle doped graphene dispersion liquid comprises the following steps:
s2.1, carrying out ultrasonic dispersion on graphene oxide powder in deionized water to obtain uniform graphene oxide dispersion liquid;
s2.2, adding the dimethylacetamide aqueous solution into the graphene oxide dispersion liquid, and uniformly stirring to obtain a mixed liquid;
s2.3, adding the silver nitrate aqueous solution into the mixed solution obtained in the step S2.2, and uniformly stirring to obtain a precursor solution;
s2.4, fully reacting the precursor liquid;
s2.5, carrying out suction filtration and cleaning on the precursor liquid after the full reaction, filtering to obtain a precipitate, and drying the precipitate to obtain the silver-doped graphene;
s2.6, preparing silver-doped graphene dispersion liquid by using silver-doped graphene powder;
s2.1, wherein the concentration of graphene oxide in the obtained graphene oxide dispersion liquid is 0.05-0.5 mg/mL;
s2.2, in the aqueous solution of the dimethylacetamide, the volume ratio of the dimethylacetamide to the deionized water is 1:1; the volume ratio of the dimethylacetamide to the graphene oxide dispersion liquid is 1 (1-1.5);
s2.3, wherein the mass percentage of solute in the silver nitrate aqueous solution is 2.5% -10%; the mass ratio of the silver nitrate to the graphene oxide in the mixed solution is 10:1;
s2.4, reacting the precursor solution at 160 ℃, and continuously stirring in the reaction process, wherein the reaction time is 24-36 hours;
s2.5, filtering by a 0.45 mu m microporous filter, and vacuum drying the precipitate for 48-60 hours at 60 ℃;
in S2.6, the concentration of the silver-doped graphene in the silver-doped graphene dispersion liquid is 0.05-0.5 mg/mL.
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