CN207540970U - A kind of humidity sensor based on graphene oxide coating optical fiber - Google Patents

Abstract

The utility model relates to the technical field of optical fibers, in particular to a preparation method of graphene oxide coated optical fibers, a humidity sensor and applications thereof. The optical fiber humidity sensor based on graphene oxide of the utility model comprises: a broadband light source, an optical fiber sensing head, graphene oxide, and a spectrometer; the first input port of the optical fiber sensing head is connected to the broadband light source through an optical fiber, and the first output The port is connected to the spectrometer through an optical fiber; the optical fiber sensing head is composed of three sections of optical fibers, and the three sections of optical fibers are dislocated to form a Mach-Zehnder interferometer structure, wherein the second section of optical fiber is located in the middle; the second section of the optical fiber sensing head The surface of the segment fiber is coated with a layer of graphene oxide coating. The sensor of the utility model has the advantages of simple structure, low cost, convenient operation, large measuring range, high measuring precision, high resolution and wide application range.

Description

A Humidity Sensor Based on Graphene Oxide Coated Optical Fiber

technical field

The utility model relates to the technical field of humidity sensors, in particular to a preparation method of a graphene oxide coated optical fiber, a humidity sensor based on the graphene oxide coated optical fiber and a method for measuring humidity by using the humidity sensor.

Background technique

As an important physical quantity, humidity is closely related to human life and national production. On the one hand, environmental humidity has a great impact on human health. On the other hand, in the fields of industrial and agricultural production, meteorology, environmental protection, life, aerospace, national defense, etc., it is also necessary to detect and control the ambient humidity. It is based on such a wide range of needs that the humidity measurement method has been continuously expanded and strengthened. Conventional methods for measuring humidity include telescopic method, wet and dry bulb method, condensation dew point method, lithium chloride dew point method, resistance capacitance method, electrolysis method and gravimetric method. However, these conventional measurement methods are relatively complex and have limited sensitivity, and it is difficult to measure humidity in relatively harsh environments. In scientific research with increasingly sophisticated measurement techniques, this deviation often has a greater impact on the research results. At present, these problems can be well avoided by using optical fiber to measure humidity. For example, Mach-Zehnder optical fiber interferometer, Michelson optical fiber interferometer, Fabry-Perot interferometric sensor and optical fiber Sagnac interferometric sensor can be used to measure humidity.

However, existing optical fiber instruments for measuring humidity have the problem of low detection sensitivity.

Utility model content

In view of this, it is necessary to provide a humidity sensor based on graphene oxide coated optical fiber and its application to address the above problems.

In order to achieve the above object, the utility model takes the following technical solutions:

The humidity sensor based on the graphene oxide coated optical fiber of the present utility model comprises: a broadband light source, an optical fiber sensing head, graphene oxide, and a spectrometer;

The first input port of the optical fiber sensor head is connected to the broadband light source through an optical fiber, and the first output port is connected to the spectrometer through an optical fiber; the two beams of light in the Mach-Zehnder interferometer inside the optical fiber sensor head interfere during transmission, and then transmitted to the spectrometer;

The optical fiber sensing head is composed of three sections of optical fibers, and the three sections of optical fibers are phase-displaced to form a Mach-Zehnder interferometer structure, wherein the second section of optical fiber is located in the middle, and the first section of optical fiber and the third section of optical fiber are located at both ends of the second section of optical fiber ;

A layer of graphene oxide is coated on the surface of the second section of optical fiber of the optical fiber sensing head.

Further, the optical fiber humidity sensor also includes a computer, and the computer is communicatively connected to the output end of the spectrometer. The computer is used to receive the output data of the spectrometer and calculate the refractive index and temperature.

Further, the Mach-Zehnder interferometer structure inside the optical fiber sensing head is an optical fiber pigtail.

Further, the central axes of the first section of optical fiber and the third section of optical fiber coincide.

Further, in consideration of cost and economy, the optical fibers mentioned in the three sections are common optical fibers, and the optical fiber pigtails are common optical fiber pigtails. And the ordinary optical fiber can be selected as a single-mode optical fiber.

Further, the broadband light source is a C-band 1520nm-1570nm optical fiber broadband light source, and the transmission fibers between the components are common single-mode fibers.

The graphene oxide coating on the surface of the second segment optical fiber of the optical fiber sensing head of the utility model adopts the following method to carry out coating:

Step 1, at room temperature, use 0.5-2mol/L acetone and 0.5-2mol/L hydrochloric acid to clean the surface of the optical fiber for 5-15 minutes respectively;

Step 2, wash again with deionized water and dry;

Step 3, soak the second section of optical fiber in 3-aminopropyltriethoxysilane (APTES) aqueous solution for 1-3 hours;

Step 4, cleaning the optical fiber with ethanol, and drying it in an environment with a temperature of 50-55°C after cleaning;

Step 5, immerse the second section of optical fiber processed in step 4 in a graphene oxide aqueous solution of 0.01-0.1mg/mL), and the temperature is controlled at 50-55°C; when it can be observed that the graphene oxide is successfully plated on the second section After the optical fiber, remove the second section of optical fiber; after drying it naturally at room temperature, the entire coating process is completed.

Further, the second optical fiber treated in step 2 is immersed in 0.8-1.5 mol/L NaOH solution for 0.5-2 hours.

Preferably, the concentration of the 3-aminopropyltriethoxysilane (APTES) in water is 5%.

Further, the graphene oxide coating on the surface of the second section of optical fiber of the optical fiber sensing head is coated with a graphene oxide aqueous solution with a concentration of 0.06 mg/mL.

According to the optical fiber humidity sensor based on Mach-Zehnder interferometer and graphene oxide coating of the utility model, the computer calculates the humidity of the space environment to be measured according to the rule that the valley wavelength of the interference fringes changes with the humidity of the space environment to be measured.

The method for measuring humidity using the above-mentioned humidity sensor based on graphene oxide-coated optical fiber is specifically: put the optical fiber sensor head into the space environment to be measured, and interfere with the two light beams transmitted inside the optical fiber, and the wavelength of the interference fringe trough is transmitted along with the optical fiber. The humidity of the space to be measured where the sensing head is located changes. The moving range of the valley wavelength of the interference fringes is measured by the spectrometer and the computer, and then the humidity of the space to be measured is calculated by the computer.

In the above measurement method, when the humidity of the environment space to be measured changes, the moving range of the interference fringe valley wavelength is detected by a spectrometer, and the humidity of the space environment to be measured is obtained after calculation by a computer.

When the phase difference between the core mode and the excited i-order cladding mode When , the valley wavelength is:

Among them, λmin _,k represents the valley wavelength of the interference output spectrum generated by the interference between the i-order cladding mode and the fiber core mode. and Respectively represent the effective refractive index of the core and the effective refractive index of the excited i-order cladding mode.

The beneficial effects of the utility model are:

The sensor of the utility model has the advantages of simple structure, low cost, convenient operation, large measuring range, high measuring precision, high resolution and wide application range.

The sensor of the utility model is not only used for the humidity measurement of the general environment space, but also can be used for the humidity measurement of the environment space under the small change and dangerous environment. The utility model can also measure the humidity in real time.

Description of drawings

Fig. 1 is the structural representation of the humidity sensor based on the graphene oxide coated optical fiber;

Fig. 2 is a schematic diagram of measuring the structure of the optical fiber sensing head and the interface with the solution substance to be measured;

Fig. 3 is the transmission spectrum of the optical fiber sensor in the space environment where the humidity is RH=30%;

Figure 4 is the transmission spectrum of the Mach-Zehnder interferometer when the humidity of the space environment is 30%, 40%, 50%, and 60% respectively;

Figure 5 shows the movement fitting law when the sensor interference fringe valley wavelength is 1545.7nm when the humidity of the space environment changes from 30% to 60%.

Reference signs: 1, broadband light source; 2, optical fiber sensing head; 202, the first segment of optical fiber; 203, the third segment of optical fiber; 204, the second segment of optical fiber; 3, graphene oxide; 4, spectrometer; 5, computer ; 6. Cladding; 7. Space environment to be tested.

Detailed ways

In order to make the purpose, technical solution and advantages of the utility model clearer, the technical solution of the utility model will be further clearly and completely described below in conjunction with the embodiments of the utility model. It should be noted that the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present utility model, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of the present utility model.

Example

Referring to FIG. 1 , the optical fiber humidity sensor based on Mach-Zehnder interferometer and graphene oxide includes a broadband light source 1 , an optical fiber sensing head 2 , graphene oxide 3 , and a spectrometer 4 . Wherein, the broadband light source 1 is connected to the first input port of the optical fiber sensing head 2 , and the first output port of the optical fiber sensing head 2 is connected to the spectrometer 4 . As a preference, a computer 5 can be set as a data processor, and the computer 5 is communicatively connected with the spectrometer 4 to perform data processing.

Fig. 2 is a schematic diagram of the structure of the measuring fiber sensing head and the interface with the substance to be measured. The optical fiber sensing head 2 is composed of three dislocated optical fibers to form a Mach-Zehnder interferometer structure. Preferably, the central axes of the first section of ordinary optical fiber 202 and the third section of ordinary optical fiber 203 located at both ends of the second section of ordinary optical fiber 204 coincide, and the surface of the second section of ordinary optical fiber 204 is coated with a layer of graphene oxide 3 . The interior of the space environment 7 to be tested is filled with air with a certain humidity.

In the present utility model, the broadband light source 1 is a broadband light source 1 in the C-band (1520nm-1570nm). The transmission fiber is a single-mode fiber.

When measuring, the optical fiber sensor head 2 is placed in the space environment 7 to be measured, and the corresponding data detected by it is input to the computer 5, and the moving range of the interference fringe valley wavelength is obtained by calculation, and the measured space is obtained according to the fitting curve. The humidity of the environment. The principle of the change of the interference fringe valley wavelength with the change of the ambient humidity of the space to be measured where the optical fiber sensor head is located is as follows:

Due to the misalignment of the fiber, a Mach-Zehnder interferometer is formed, so that the light beam transmitted in the single-mode fiber is divided into two beams, one in the core and one in the cladding 6 . The paths of the two beams of light transmission are different, and there will be a cumulative phase difference 2πΔnL ₁ /λ between them, where Δn is the refractive index difference of the beam transmitted between the core and the cladding 6, L ₁ is the length of the fiber misalignment, λ is the input wavelength. When the humidity of the space environment to be measured by the optical fiber sensor changes, the path of the light beam transmission in the cladding 6 will change, and the phase difference between the two light beams will also change, making the valley of the interference fringe between them The value wavelength shifts accordingly.

Graphene oxide3 is an important derivative of graphene, which is rich in oxygen-containing functional groups, such as hydroxyl, carboxyl, epoxide, and carbonyl. This gives it many unique properties, such as: dispersibility, hydrophilicity, and a very large specific surface area. It is these characteristics that allow graphene oxide 3 to interact with external water molecules, so it can be plated on the surface of an optical fiber to make an optical fiber sensor. The effective refractive index of graphene oxide 3 will change with the change of the humidity of the external environment, resulting in a corresponding shift in the valley wavelength of the spectrum. The humidity sensitivity of the sensor is obtained by detecting the shift of the valley wavelength.

Among them, K is the fringe visibility, I _core and I _clad are the light intensity of the core and the cladding 6, respectively.

As shown in Figure 2, the light emitted by the light source enters the optical fiber sensor head 2 from the first section of optical fiber 202, most of the light in the first section of optical fiber 202 is transmitted in the fiber core, and part of the light is coupled to the package after passing through the first dislocation structure. In layer 6, the remaining part of the light is still transmitted in the fiber core. Due to the different propagation paths of the two beams of light, a stable phase difference will be generated after a certain distance. After the second dislocation, the cladding layer 6 is coupled to the fiber core. interferes with the core mode of the fiber. As shown in Figure 3, it is the transmission spectrum of light when the air humidity is 30%. Therefore, the change in interference intensity can be expressed by the following formula:

Among them, K is the fringe visibility, I _core and I _clad are the light intensity of the core and the cladding 6, respectively.

Theoretically, K reaches its maximum value when I _core ≈ I _clad . Therefore, it is particularly important to control the dislocation length. The phase difference between the core mode and the excited cladding mode will change with the external environment. It can be represented by the following formula:

in, and are the effective refractive index of the core mode and the i-order cladding 6, respectively, d is the distance between two dislocation structures, λ is the working wavelength in vacuum, is the effective refractive index difference between the core fundamental mode and the i-order cladding 6.

when The minimum light intensity wavelength can be expressed as:

When coating the optical fiber sensor head 2 with graphene oxide 3, the surface of the optical fiber must first be treated with chemical methods, so that the graphene oxide 3 can be more easily and uniformly adsorbed on the surface of the optical fiber, and more importantly, it can improve the performance of the sensor. Humidity measurement sensitivity, that is, at room temperature, use acetone and hydrochloric acid (both at a concentration of 1mol/L) to clean the surface of the optical fiber for 10 minutes. Another purpose is to remove organic pollutants on the surface of the optical fiber. Then, rinse again with deionized water and dry. In order to increase the number of silanol groups on the fiber surface, the sensing head was immersed in NaOH (1mol/L) solution for 1 hour. Next, immerse the optical fiber in a 3-aminopropyltriethoxysilane (APTES) solution for 2 hours, and 3-aminopropyltriethoxysilane (APTES) interacts with the hydroxyl groups on the surface of the optical fiber silica to form Si -O-Si covalent bond. Then clean the optical fiber with ethanol, and dry it for 30 minutes in an environment with a temperature of 50°C after cleaning. The environment with a temperature of 50°C is realized by a constant temperature and humidity chamber. Finally, the treated optical fiber sensing head 2 was immersed in a 0.06 mg/mL graphene oxide 3 solution, and the temperature was controlled at 50 °C. After it can be observed that the graphene oxide 3 is successfully plated on the optical fiber sensing head 2, the optical fiber sensing head 2 is removed from the graphene oxide 3 solution. The entire coating process was completed after allowing it to dry naturally at room temperature for 12 hours.

Due to the presence of oxygen-containing functional groups, the graphene oxide 3 film has strong water absorption. When the humidity of the outside environment changes, the graphene oxide 3 film will absorb water molecules. The graphene oxide 3 film becomes larger due to the filling of water molecules into the graphene oxide 3 film. With the increase of water molecules, the effective refractive index of graphene oxide 3 will decrease accordingly. Ultimately, the effective refractive index between the cladding layer 6 and the graphene oxide 3 thin film becomes smaller.

For further checking the feasibility of the present utility model, especially carry out following experiment:

In the experiment, the optical fiber sensor of the utility model is used to measure the transmission spectrum diagram under different humidity conditions in the space environment. As shown in FIG. 4 , the four curves in the figure correspond to the transmission spectra of the optical fiber sensing head 2 placed in space environments with humidity of 30%, 40%, 50%, and 60%, respectively. Wherein, the longitudinal length of the optical fiber dislocated by the Mach-Zehnder interferometer (the length of the second section of optical fiber 204 ) is about 3.5 cm, and the lateral length (ie, the dislocation length) is 5 μm. It can be seen from FIG. 4 that the valley wavelength of the interference fringes in the Mach-Zehnder interferometer increases as the humidity of the space environment where the optical fiber sensing head 2 is placed increases.

Fig. 5 is the data result and fitting result of different humidity in the space environment to be measured using the optical fiber sensor of the present utility model. It can be seen from Fig. 5 that the fitting curve can accurately match the measurement results within the range of humidity from 30% to 60% in the space environment to be measured, and the linearity is 99.61%. From the fitting curve, it can be obtained that the detection sensitivity of the Mach-Zehnder interferometer for humidity is 0.104dB/%RH. In general scientific research, this sensitivity can meet the corresponding requirements.

It can be seen from the experiment that although the valley wavelength of the transmission spectrum interference fringes changes randomly with time, the sensor's stability is feasible because of its small change with time.

The above-mentioned embodiments only express several implementations of the utility model, and the description thereof is relatively specific and detailed, but it should not be construed as limiting the patent scope of the utility model. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the scope of protection of the utility model patent should be based on the appended claims.

Claims (5)

1. A humidity sensor based on graphene oxide coated optical fiber is characterized by comprising: the device comprises a broadband light source, an optical fiber sensing head, graphene oxide and a spectrometer;

the first input port of the optical fiber sensing head is connected with the broadband light source through an optical fiber, and the first output port of the optical fiber sensing head is connected with the spectrometer through an optical fiber; two beams of light in the Mach-Zehnder interferometer in the optical fiber sensing head interfere during transmission and then are transmitted to the spectrometer;

the optical fiber sensing head consists of three sections of optical fibers, and the three sections of optical fibers are staggered to form a Mach-Zehnder interferometer structure; the second section of optical fiber is positioned in the middle, and the first section of optical fiber and the third section of optical fiber are positioned at two ends of the second section of optical fiber;

and a layer of graphene oxide is plated on the surface of the second section of optical fiber of the optical fiber sensing head.

2. The graphene oxide coated optical fiber based humidity sensor according to claim 1, further comprising a computer, wherein the computer is in communication connection with the spectrometer output; the computer is used for receiving the output data of the spectrometer and calculating the refractive index and the temperature.

3. The graphene oxide coated optical fiber based humidity sensor according to claim 1, wherein the Mach-Zehnder interferometer structure inside the optical fiber sensing head is a fiber pigtail with a removed cladding.

4. The graphene oxide coated optical fiber based humidity sensor according to claim 1, wherein the broadband light source is a C-band 1520nm-1570nm optical fiber broadband light source, and the transmission optical fibers between the connection of the components are all common single-mode optical fibers.

5. The graphene oxide coated optical fiber based humidity sensor according to claim 1, wherein the central axes of the first and third segments of optical fibers are coincident.