CN210037606U

CN210037606U - Interference type optical fiber humidity sensor based on graphene

Info

Publication number: CN210037606U
Application number: CN201920605055.3U
Authority: CN
Inventors: 肖毅; 余健辉; 钟永春; 罗云瀚
Original assignee: Jinan University
Current assignee: Jinan University; University of Jinan
Priority date: 2019-04-29
Filing date: 2019-04-29
Publication date: 2020-02-07
Anticipated expiration: 2029-04-29

Abstract

The utility model relates to an interference type optic fibre humidity transducer based on graphite alkene, include: be stained with metal cylinder's slide glass and two single mode fiber, two single mode fiber pass through metal cylinder's both sides respectively and crooked in opposite directions, form two cross coupling points, and single mode fiber's both ends are fixed on the slide glass, single mode fiber middle part tapering, the awl waist region is located between two cross coupling points, and the awl waist region of one of them single mode fiber covers reduction oxidation graphite alkene rete to the both ends of covering reduction oxidation graphite alkene's single mode fiber are regarded as input and output respectively. The scheme has simple and compact structure and easy preparation, does not need mutual fusion of special optical fibers, and has low cost. The optical fiber interference structure provided by the scheme is also suitable for sensing other kinds of gases and biological and chemical sensing.

Description

Interference type optical fiber humidity sensor based on graphene

Technical Field

The utility model relates to an optic fibre humidity sensing technical field especially relates to an interference type optic fibre humidity transducer based on graphite alkene.

Background

The Optical Fiber Humidity Sensor (OFHS) has the advantages of small volume, high precision, corrosion resistance, electromagnetic interference resistance, capacity of being placed in a space which is difficult to reach, multiplexing, remote sensing and the like, and is generally concerned by people. The optical fiber humidity sensor can be divided into a plurality of implementation types such as a light absorption type, a fiber grating type, an interference type and a resonance absorption type. The light absorption type is based on the interaction of an optical fiber evanescent wave field and a humidity-sensitive substance, and the absorption of the humidity-sensitive substance to light responds to the change of the environmental humidity, so that the power or the light intensity of the light transmitted by the optical fiber can be used as a sensing parameter. The moisture sensitive substances used include: agarose gels [ Sensors and modulators B: Chemical 69,127-]Phenol red-doped PMMA [ Sensors and activators B: Chemical 80,132-135,2001]Doped CoCl₂(ii) polymer film [ Sensors and activators B: Chemical 104,217-222,2005]HEC/PVDF hydrogels [ Sensors and initiators A: Physical190,1-5,2013]And tungsten disulfide [ Optics Express 24(8), 8956-]And the like. The weakness of the light absorption sensor is that the measurement of the light power is susceptible to factors such as fluctuation of the light source power. A fiber grating is a fiber device made by forming a periodic refractive index modulation in the core. If the period of the refractive index modulation is in the submicron (100nm-1 μm) range, the optical fiber is called Bragg fiber grating (FBG); if the period of the refractive index modulation is in the range of 100 μm-1mm, it is called long period fiber grating (LPG). The fiber grating area is covered with the humidity sensitive material, so that the wavelength of the reflection peak of the fiber grating can respond to the change of the environmental humidity, and the fiber grating type humidity sensor is formed. The maximum sensitivity of 31 pm/% RH achieved by Bragg fiber grating humidity Sensors reported in the literature is achieved by using Bragg fiber gratings coated with etched claddings of Carbon Nanotubes (CNTs) [ IEEE Sensors Journal 14(8) ], 2615-]. Greater sensitivity can be achieved with long period fiber gratings, and the sensitivity of hydrogel-coated long period fiber gratings reaches 0.2 nm/% RH [ IEEE Photonics technology Letters19(12), 880-]And CaCl₂The sensitivity of the covered air gap long-period fiber grating in humidity sensing reaches 1.36 nm/% RH [ Optical Review 18(1), 93-95, 2011]. The main drawback of the fiber grating type OFHS is cross-sensitivity to temperature, deformation, etc. The interference type optical fiber humidity sensor based on the graphene can be classified into Fabry-Perot interference (FPI), Sagnac interference, Mach-Zehnder interference (MZI), Michelson Interference (MI) and other types. A tiny resonant cavity is manufactured on the end face of an optical fiber by utilizing a humidity sensitive material film layer to form a Fabry-Perot interferometer, and the prepared OFHS can achieve higher sensitivity generally. The end face of the single mode fiber uses perfluorosulfonic acid film as resonant cavity, and its humidity sensing sensitivity can reach 3.5 nm/% RH [ Sensors and Actuators B: Chemical 196,99-105,2014]. Different types of optical fibers (tapered or expanded optical fibers, hollow optical fibers, photonic crystal optical fibers and the like) are welded together to cause interference among different transmission modes in the optical fibers, and the interference phase difference is regulated and controlled by a humidity sensitive material to prepare various interference OFHS. A section of photonic crystal fiber covered with polyvinyl alcohol (PVA) and with air holes collapsed at two ends is welded at one end of a single-mode fiber to form the Michelson interference type OFHS, and the sensing sensitivity of the Michelson interference type OFHS reaches 0.6 nm/% RH [ Sensors and Actuators B: Chemical 174,563-]. The sensitivity of Mach-Zehnder interference (MZI) type sensor formed by covering the photonic crystal fibers with collapsed air holes at two ends with agarose and then welding single-mode fibers at two ends can reach 0.57 nm/% RH within the range of 40% -80% humidity, and even reach 1.43 nm/% RH within the range of 80% -95% (Applied Optics 52(16), 3884-]. A multimode optical fiber covered with polyvinyl alcohol is welded at its two ends to a single mode optical fiber and has an expanded weld, and its humidity sensing sensitivity reaches 0.223 nm/% RH [ IEEE Sensors Journal 14(8), 2683-]. Bending the optical fiber into U-shape, without adding any humidity sensitive material, to form interference type OFHS with sensitivity up to 114.7 pm/% RH [ IEEE Sensors Journal 17(3), 644-]. When the high-order conduction mode of some humidity sensitive material film layer and the effective refractive index of the conduction mode of a certain wavelength in the optical fiber are matched with each other, resonance absorption is formed on the wave field of the wavelength evanescent wave, and therefore the resonance absorption type OFHS can be manufactured. In SnO₂The maximum sensing sensitivity of the resonant absorption OFHS fabricated on the coated etched clad fiber can reach 1.9 nm/% RH [ Sensors and modulators B: Chemical 233,7-16, 20% in the humidity range of 20% -90%16]。

In recent years, graphene-based nanomaterials, including CVD graphene, Reduced Graphene Oxide (RGO), Graphene Oxide (GO), etc., have attracted increasing attention as moisture-sensitive materials. The graphene nano material is combined with the optical fiber to prepare the OFHS. A light absorption OFHS [ Optics Express22(25), 31555-. The graphene oxide covers the inclined Bragg fiber grating, and the sensing sensitivity of the intensity of the cladding mode interference peak to humidity reaches 0.129 dB/% RH [ Applied Physics Letters 109, 031107, 2016 ]. The sensitivity of the interference type OFHS prepared by using the hollow fiber covered with the reduced graphene oxide to humidity reaches 0.22 dB/% RH [ Sensors and activators B: Chemical 222,618-624,2016 ]. One end of a polarization maintaining optical fiber covered with the graphene oxide film layer is connected with a single mode optical fiber through an expanded welding part, the other end of the polarization maintaining optical fiber is connected with the single mode optical fiber to realize the welding of the fiber core with slight deviation, and the sensing sensitivity of the interference peak intensity to humidity reaches 0.349 dB/% RH [ Sensors and Actuators B: Chemical 234, 503-. The two ends of a single-mode fiber covered with the graphene oxide/PVA film layer are connected with the single-mode fiber through an expansion welding part to form an interference type OFHS, and the sensing sensitivity of the interference peak intensity to humidity is 0.193 dB/% RH [ Optics Communications 372, 229-234, 2016 ]. SPF coated with graphene oxide film layer can be made into resonance absorption type OFHS with the sensitivity of the wavelength of the resonance absorption peak to 32% -85% and 85% -97.6% humidity ranges of 0.145 nm/% RH and 0.915 nm/% RH [ Sensors and CatuatorsB: Chemical 255,57-69,2018], respectively.

Table 1 lists the maximum sensitivity and dynamic range obtained in various types of OFHS based on non-graphene based moisture sensitive materials. Table 2 lists the sensitivity and dynamic range of various types of OFHS based on graphene-based nanomaterials.

TABLE 1

TABLE 2

In summary, the aforementioned OFHS has its advantages and disadvantages. Such as: most of the fiber grating type and interference type OFHS require special optical fibers or optical fiber structures, require complicated preparation techniques and special equipment, and have high cost. The quality of the resonant absorption type OFHS depends on the quality and the thickness of the humidity sensitive material film layer, and the resonant absorption type OFHS has high randomness. In the research of OFHS using graphene nano material as humidity sensitive material, except for the literature [ Sens. activators B255, 57-69,2018], the light transmission power or the intensity change of the interference peak is basically used as a sensing parameter, and the wavelength position shift of the interference peak is usually very small and difficult to observe. Therefore, there is a need in the industry to develop an interference type optical fiber humidity sensor based on graphene and using wavelength position shift as a sensing parameter.

SUMMERY OF THE UTILITY MODEL

To the above-mentioned problem that prior art exists, the utility model provides an interference type optic fibre humidity transducer based on graphite alkene.

The specific scheme of the application is as follows:

a graphene-based interferometric optical fiber humidity sensor comprising: be stained with metal cylinder's slide glass and two single mode fiber, two single mode fiber pass through metal cylinder's both sides respectively and crooked in opposite directions, form two cross coupling points, and single mode fiber's both ends are fixed on the slide glass, single mode fiber middle part tapering, the awl waist region is located between two cross coupling points, and the awl waist region of one of them single mode fiber covers reduction oxidation graphite alkene rete to the both ends of covering reduction oxidation graphite alkene's single mode fiber are regarded as input and output respectively.

Preferably, the cone waist region has a diameter of 20 μm.

Preferably, the metal cylinder has a diameter of 3mm and a height of 5 mm.

Preferably, both ends of the single-mode fiber are fixed on the glass slide by ultraviolet glue, and the metal cylinder is fixed on the glass slide by ultraviolet glue.

Preferably, the thickness of the reduced graphene oxide film layer is 216nm, and the linear distance between the two cross-coupling points is 1.5 cm.

Compared with the prior art, the utility model discloses following beneficial effect has:

(1) the scheme has simple and compact structure and easy preparation, does not need mutual fusion of special optical fibers, and has low cost. The optical fiber interference structure provided by the scheme is also suitable for sensing other kinds of gases and biological and chemical sensing.

(2) The scheme provides a reliable technological method for covering RGO on an optical fiber, namely, a GO film layer is covered on the optical fiber by a natural evaporation method, and then the RGO film layer covered on the optical fiber is obtained by heating and reducing under an argon environment. SEM photo shows that RGO film layer on optical fiber has good film forming property; the tested results of Raman spectrum, XRD detection and XPS detection show that the content of oxygen elements of the RGO film layer on the sensor is greatly reduced compared with the content of oxygen elements of the GO film layer, and the higher reduction degree is achieved.

(3) Compare with other interference type optic fibre humidity transducer based on graphite alkene class nano-material's based on graphite alkene in the literature, the utility model provides a sensor has great interference peak wavelength position and removes, and the phenomenon is obvious, easily observes.

Drawings

Fig. 1 is a structural diagram of an interference type optical fiber humidity sensor based on graphene according to example 1.

Fig. 2 is a cross-sectional SEM image of a single-mode optical fiber covered with a layer of reduced graphene oxide film of example 1.

Fig. 3(a) is an XRD spectrum of the graphene oxide film coated on the sensor fiber of example 1 before reduction.

Fig. 3(b) is an XRD spectrum of the graphene oxide film coated on the sensor fiber of example 1 after reduction.

Fig. 3(c) is a graph comparing raman spectra of the graphene oxide film covered on the sensor fiber of example 1 before and after reduction.

Fig. 3(d) is a comparison graph of XPS spectra of the graphene oxide film covered on the sensor fiber of example 1 before and after reduction.

FIG. 4 is a diagram of a sensing experiment apparatus of the interferometric fiber optic humidity sensor based on graphene in example 1;

FIG. 5 is a transmission light interference spectrum of the sensor of example 1 at 25 ℃ and 65% RH.

FIG. 6 is a graph of the spectrum of the sample of example 2 over the range of 45% -95% relative humidity.

FIG. 7 is a graph of the wavelength of the interference peak of the sample of example 2 as a function of humidity.

FIG. 8 is a chart of the spectrum of the sample of example 3 over the range of 45% -95% relative humidity

FIG. 9 is a graph of the wavelength of the interference peak of the sample of example 3 as a function of humidity.

Fig. 10 is a flowchart of a method for manufacturing the interferometric fiber optic humidity sensor based on graphene of example 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts belong to the protection scope of the present invention.

Example 1

Referring to fig. 1, a graphene-based interferometric optical fiber humidity sensor includes: glass slide 1 and two single mode fiber (3, 4) that are stained with metal cylinder 2, two single mode fiber are respectively through metal cylinder 2's both sides and crooked in opposite directions, form two cross coupling points, and single mode fiber's both ends are fixed on glass slide 1, single mode fiber middle part tapering, the awl waist region is located between two cross coupling points, and the awl waist region of one of them single mode fiber covers reduction oxidation graphite alkene rete 5 to the both ends of covering the single mode fiber of reduction oxidation graphite alkene are regarded as input and output respectively. In fig. 1, the optical fiber 4 is covered with reduced graphene oxide, with the end B as the input end and the end D as the output end.

In this embodiment, the taper waist region has a diameter of 20 μm. The diameter of the metal cylinder 2 is 3mm, and the height thereof is 5 mm. Two ends of the single-mode optical fiber are fixed on the glass slide 1 by ultraviolet glue 6, and the metal cylinder 2 is fixed on the glass slide 1 by the ultraviolet glue 6. The thickness of the reduced graphene oxide film layer 5 was 216nm, and the linear distance between the two cross-coupling points was 1.5 cm.

Referring to fig. 10, the preparation method of the interference type optical fiber humidity sensor based on graphene includes:

s1, tapering the single-mode optical fiber; two single mode fibers were drawn to a diameter of 20 μm (waist region) using flame fusion draw.

S2, bending two tapered single mode fibers oppositely through two sides of the metal cylinder 2 on the glass slide 1 to form two cross coupling points, wherein two ends of the single mode fibers are fixed on the glass slide 1;

and S3, covering the reduced graphene oxide film layer 5 on the conical waist area of one single-mode optical fiber to obtain the interference optical fiber humidity sensor based on graphene.

Further included between steps S2 and S3 is:

and (4) sequentially connecting the two ends of the single-mode optical fiber with the broadband light source 7 and the spectrum analyzer 9 respectively, sequentially testing the interference waveforms of the two single-mode optical fibers, and selecting the single-mode optical fiber with the larger interference peak extinction ratio and the larger peak distance to execute the step S31. The interference waveform is formed by two factors, namely multimode interference caused by tapering of a single optical fiber and Mach-Zehnder interference between two optical fibers. Two ends of the single-mode fiber 3 are respectively A and C, and two ends of the single-mode fiber 4 are respectively B and D.

Specifically, step S3 includes:

s31, dripping graphene oxide aqueous dispersion with the concentration of 2mg/ml in a conical waist area of the single-mode optical fiber, standing for 10 hours at normal temperature to naturally evaporate water, and covering a graphene oxide film (GO film) on the single-mode optical fiber;

and S32, placing the prepared sensor sample covered with the graphene oxide film layer in an argon environment for heating, and reducing the graphene oxide to obtain a reduced graphene oxide film layer 5(RGO film layer). The RGO film layer was 216nm thick as shown in the SEM photograph in FIG. 2. Further, step S32 includes:

s321, placing the prepared sensor sample covered with the graphene oxide film layer into a semi-closed gas chamber with a heating platform, wherein the gas chamber is provided with a gas inlet and a gas outlet;

s322, introducing argon into the semi-closed gas chamber at the flow rate of 1 liter/minute; the air content in the chamber will continue to decrease, as will the various components (nitrogen, oxygen, carbon dioxide, water vapor, etc.) contained in the air, and a hygrometer is placed in the chamber to indicate the extent of this decrease.

S323, when the relative humidity in the air chamber is reduced to be below 10% and the reduction speed is reduced, a switch of a heating platform is turned on to heat, the temperature of the heating platform is adjusted to 80 ℃, the sensor sample is heated for 1 hour, and argon with the flow rate of 1 liter/minute is continuously introduced during heating; this step is to form a relatively flat and robust RGO film layer with a low degree of reduction. If a higher temperature is used from the beginning, the formed RGO film layer is easy to wrinkle, warp, crack and the like.

S324, closing the heating switch, naturally cooling the temperature of the heating platform to room temperature, and continuously introducing argon with the flow rate of 0.5 liter/minute in the natural cooling process;

s325, adjusting the temperature of the heating platform to 250 ℃, heating the sensor sample for 1 hour, and continuously introducing argon with the flow rate of 1 liter/minute during heating;

and S326, closing the heating switch to naturally cool the temperature of the heating platform to room temperature, and continuously introducing argon with the flow rate of 0.5 liter/minute in the natural cooling process.

Fig. 3(a) is an XRD spectrum of the graphene oxide film covered by the cone waist region of the sensor of the present invention before reduction, and its characteristic peak is at about 9.9 °. Fig. 3(b) is an XRD pattern of the graphene oxide film covered by the cone waist region of the sensor after reduction, and the characteristic peak appears at about 24.8 ° while the peak at 9.9 ° disappears. Fig. 3(c) is a raman spectrum contrast chart of the graphene oxide film covered by the cone waist region of the sensor of the present invention before and after reduction, the intensity of the D peak and the G peak of RGO is significantly greater than GO, and in addition, the 2D peak appears in the raman spectrum of RGO. FIG. 3(d) is a comparison of XPS spectra of graphene oxide films covered by the cone waist region of the sensor before and after reduction, wherein the peak of RGO at 284.7eV (C-C bond spectrum) has a higher intensity than GO, and the peak of RGO at 286.9eV (C-O bond spectrum) disappears. The detection result shows that the content of oxygen element of the RGO film layer on the sensor is greatly reduced compared with that of the GO film layer.

Principle of humidity sensing: between the two cross-coupling points, the two optical fibers form two optical paths of Mach-Zehnder interference. Without the RGO covering segment, the optical path difference of the two optical paths hardly changes with humidity. When one of the channels is provided with the RGO covering section, the change of the effective refractive index of the transmission light of the covering section along with the humidity is obviously different from the change of the effective refractive index of the transmission light of the bare optical fiber section along with the humidity, so that the optical path difference of the two optical channels is obviously changed along with the humidity, and the wavelength position of an interference valley in an interference pattern is obviously changed along with the humidity. According to relevant literature, the wavelength position of the interference peak of the interference type OFHS that adopts GO moves inconspicuously, and the utility model discloses in adopt RGO, the wavelength position of interference peak (valley) moves comparatively obviously. The reason for this is that charge transfer between RGO and adsorbed water molecules causes a relatively significant change in the refractive index of RGO.

The sensing experimental device diagram of the sensor consists of a broadband light source 7, a constant temperature and humidity box 8 capable of adjusting humidity and a spectrum analyzer 9. As shown in fig. 4. The broadband light source 7 is a supercontinuum laser light source, light emitted by the laser light source enters the optical fiber 4 from the B port, a part of light is coupled into the optical fiber 3 at the first cross-coupling point, and the rest part of light continues to be transmitted along the optical fiber 4. The transmitted light in the second cross-coupling point fiber 3 will be partly coupled into the fiber 4 again, while the transmitted light in the fiber 4 will be partly coupled into the fiber 3. The D port is connected to the spectrum analyzer 9. The observed interference pattern is formed by the combined action of two factors, namely the Mach-Zehnder interference between the transmitted light in the optical fiber 4 and the transmitted light recoupled from the optical fiber 3, and the multimode interference caused by the tapering of the single optical fiber (the optical fiber 4). FIG. 5 is an interference pattern recorded by the sensor at 25 deg.C and 65% relative humidity. It can be seen that in the long wavelength region, the peak distance (free spectral range) is large (greater than or equal to 55 nm); in the short wavelength region, the peak distance is smaller (more than or equal to 19 nm). The reference IEEE Sensorsjournal 17(3), 644-. According to the documents [ IEEE Photonics Technology Letters 25(22), 2201-.

Example 2

The sensor of this example was identical to the sensor of example 1, except that, for different sensor samples of the same lot, the results of the humidity sensing experiment are shown in fig. 6 and 7, and the position of the interference peak indicating humidity change was selected to be around 1570 nm. The experimental temperature was 25 ℃ and remained unchanged. In the range of 45% -95% relative humidity, the sensing sensitivity to rising humidity reaches 0.1934 nm/% RH, and the sensing sensitivity to falling humidity reaches 0.2111 nm/% RH. Has better recoverability.

Example 3

The sensor of this example was performed exactly as the sensor of example 1, with the only difference that, for different sensor samples of the same lot, the results of the humidity sensing experiment are shown in fig. 8 and 9, and the position of the interference peak indicating the humidity change was selected to be around 1580 nm. The experimental temperature was 25 ℃ and remained unchanged. In the range of 45% -95% relative humidity, the sensing sensitivity to rising humidity reaches 0.1714 nm/% RH, and the sensing sensitivity to falling humidity reaches 0.2226 nm/% RH. Has better recoverability.

The above-mentioned embodiments only represent some embodiments of the present invention, and the description thereof is specific and detailed, but not to be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, without departing from the spirit of the present invention, several variations and modifications can be made, which are within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. An interference type optical fiber humidity sensor based on graphene is characterized by comprising: be stained with metal cylinder's slide glass and two single mode fiber, two single mode fiber pass through metal cylinder's both sides respectively and crooked in opposite directions, form two cross coupling points, and single mode fiber's both ends are fixed on the slide glass, single mode fiber middle part tapering, the awl waist region is located between two cross coupling points, and the awl waist region of one of them single mode fiber covers reduction oxidation graphite alkene rete to the both ends of covering reduction oxidation graphite alkene's single mode fiber are regarded as input and output respectively.

2. The graphene-based interferometric fiber optic moisture sensor of claim 1, wherein the cone waist region has a diameter of 20 μ ι η.

3. The interferometric graphene-based fiber optic moisture sensor of claim 1, wherein the metal cylinder is 3mm in diameter and 5mm in height.

4. The interferometric graphene-based fiber optic humidity sensor of claim 1, wherein the single-mode fiber is affixed to the slide at both ends by uv glue and the metal cylinder is affixed to the slide by uv glue.

5. The interferometric graphene-based fiber optic humidity sensor of claim 1, wherein the reduced graphene oxide film layer has a thickness of 216nm and the linear distance between two cross-coupling points is 1.5 cm.