CN108801941A - Gas identification fibre optical sensor based on metal-organic framework material and recognition methods - Google Patents

Abstract

The present invention discloses a kind of gas identification fibre optical sensor and recognition methods based on metal-organic framework material, and the coupling that sandwich layer mould arrives cladding mode, the transmission respectively of realization sandwich layer mould and cladding mode occur at the first long-period fiber grating；Cascaded optical fiber sensitive layer adsorbs known gas so that cladding mode refraction index changing；In second long-period gratings, the optical coupling of cladding mode returns to sandwich layer to interfere, and obtains interference spectrum；According to the correspondence between interference spectrum and gas with various, recognition detection gas；It is sensitive to have the advantages that fast response time identifies.

Description

Optical fiber sensor and identification method for gas identification based on metal organic framework materials

technical field

The invention belongs to the field of optical fiber sensing, in particular to an optical fiber sensor technology.

Background technique

In recent years, with the development of industrial and agricultural modernization economy, timely and accurate monitoring, forecasting and control of flammable, explosive, toxic and harmful gases has become an important problem to be solved urgently in the coal, petroleum, chemical, electric power and other departments. At the same time, with the improvement of people's living standards, human beings have higher and higher requirements for the purification of the ecological environment. It is urgent to monitor and monitor flammable, explosive, toxic and harmful gases, reduce environmental pollution, and ensure physical and mental health. Therefore, it is very important to develop a gas identification and detection system. Since the gas to be detected is usually in a dangerous environment such as high temperature, high pressure, and corrosion, the use of electrical sensors is limited. Moreover, non-optical sensors are easily affected by factors such as cross-sensitivity and surface contamination of the sensing membrane, which have slow response, short life, poor repeatability, and are difficult to monitor continuously on-line in real time.

Optical fiber has the characteristics of small size, wide frequency band, low transmission loss, strong anti-electromagnetic interference, and large amount of information. The sensor composed of it has anti-electromagnetic interference, electrical insulation, corrosion resistance, high sensitivity, and is easy to reuse into a network and many other advantages. This technology uses the change of the characteristic parameters (such as intensity, phase, wavelength, polarization, scattering, etc.) of the light propagating in the optical fiber caused by the external physical quantity to measure the external physical quantity and transmit data. It has small size, light weight, anti-electromagnetic interference, high safety (no electric spark, can work in flammable and explosive environments), no power supply is required for the detection end, high temperature resistance, and it is convenient to form a sensor network and integrate the Internet of Things, etc. advantage. Therefore, as a new type of sensing and detecting device, optical fiber sensing has attracted the attention of researchers, and has been widely studied and applied. Coating a layer of sensitive metal-organic framework material on the optical fiber will further improve the detection response speed and sensitivity of the device to gas.

Metal-organic frameworks, or MOFs for short, are a series of multi-functional materials with various structures. It is widely used in structural chemistry, and this material has potential applications in many fields, such as gas storage, gas separation, heterogeneous catalysis, chemical sensing, nonlinear optics, energy storage and conversion (batteries and solar cells ), drug delivery, bioimaging, etc.

However, there are still existing sensors: optical fiber gas recognition detection devices have corresponding deficiencies in response speed, sensitivity and other aspects.

Contents of the invention

In order to solve the above technical problems, the present invention provides a metal-organic framework material-based gas recognition optical fiber sensor and a recognition method, combined with an optical fiber gas recognition detection device whose sensitive layer is a metal-organic framework material, which has a faster response speed and a high sensitivity.

The technical solution adopted in the present invention is: a Mach-Zehnder interferometer, at least comprising: a first long-period fiber grating and a second long-period fiber grating; A cascaded optical fiber is connected in series; the core layer and the cladding layer of the cascaded optical fiber serve as two arms of the interferometer respectively, and a sensitive layer is grown on the cladding layer of the cascaded optical fiber.

Further, the sensitive layer is a layer of porous ZIF-8 metal organic framework material.

A gas recognition optical fiber sensor based on a metal organic framework material, at least including the above-mentioned Mach-Zehnder interferometer.

The present invention also provides a method for detecting organic gas, comprising the following steps:

The core light in the optical fiber is coupled from the core mode to the cladding mode at the first long-period grating, forming the separate transmission of the core mode and the cladding mode;

The sensitive layer of the cascaded optical fiber absorbs the organic gas to be detected, which changes the refractive index of the cladding mode;

In the second long-period grating, the light of the cladding mode is coupled back to the core layer to interfere, and the interference spectrum is obtained;

According to the corresponding relationship between the interference spectrum and different gases, the organic gas to be detected is identified.

Further, the establishment process of the corresponding relationship between the interference spectrum and different gases is:

The core light in the optical fiber is coupled from the core mode to the cladding mode at the first long-period grating, forming the separate transmission of the core mode and the cladding mode;

The sensitive layer of the cascaded optical fiber absorbs known gas, which changes the refractive index of the cladding mode;

In the second long-period grating, the light of the cladding mode is coupled back to the core layer to interfere, and the interference spectrum is obtained;

The corresponding relationship with the known gas is established based on several interference spectra.

Beneficial effects of the present invention: the light emitted by the light source of the present invention is coupled from the core mode to the cladding mode at the first long-period fiber grating, realizing the separate transmission of the core mode and the cladding mode; The known gas makes the refractive index of the cladding mode change; in the second long period grating, the light of the cladding mode is coupled back to the core layer to interfere, and the interference spectrum is obtained; according to the corresponding relationship between the interference spectrum and different gases, Recognize and detect gas; the system and method of the present invention adopt cascaded long-period fiber gratings combined with optical fiber gas recognition and detection devices with metal organic framework materials as the sensitive layer, which has a fast response speed and high sensitivity to specific gases, and can be applied to the environment monitoring and chemical sensing; and the sensor made by adopting the structure of the present invention is more miniaturized and has higher cost performance.

Description of drawings

Fig. 1 is a basic structural diagram of cascaded long-period fiber gratings coated with metal-organic framework materials in the present invention.

Figure 2 is the transmission spectrum diagram of the device at different moments in the measured gas atmosphere;

Wherein, Fig. 2 (a) is the spectrogram obtained for testing ethanol, Fig. 2 (b) is the spectrogram obtained for testing methanol, Fig. 2 (c) is the spectrogram obtained for testing ethyl acetate, Fig. 2 (d) is the spectrogram obtained for testing The spectrogram that acetone obtains, Fig. 2 (e) is the spectrogram that testing methylene chloride obtains, and Fig. 2 (f) is the spectrogram that testing pyridine obtains, and Fig. 2 (g) is the spectrogram that testing ether obtains, Fig. 2 ( h) is the spectrogram obtained by testing toluene, and Fig. 2(i) is the spectrogram obtained by testing cyclohexane.

Detailed ways

In order to facilitate those skilled in the art to understand the technical content of the present invention, the content of the present invention will be further explained below in conjunction with the accompanying drawings.

Among various MOFs, ZIF-8 is a porous framework material polymerized by zinc nitrate hexahydrate and 2-methyl-imidazole, and the pore size The specific surface area is as high as 1947m ² g ^-1 , the chemical stability and thermal stability are very good, and the thermal decomposition temperature is above 450°C. It has potential application value in the field of gas recognition and sensing. Therefore, the long-period fiber grating thin-film gas recognition detector combined with porous material ZIF-8 has extremely excellent performance, can realize long-distance telemetry and online real-time monitoring, and can be made into a miniaturized device with high cost performance.

Figure 1 shows the basic sensing structure of cascaded long-period fiber gratings coated with metal organic framework material ZIF-8. ZIF-8 can be grown on the fiber cladding by immersing the fiber in a methanol solution of zinc nitrate hexahydrate and 2-methyl-imidazole. Figure 1B and C are scanning electron microscope images of the fiber surface and end face, respectively.

An organic gas recognition optical fiber sensor based on a metal organic framework material of the present invention consists of two separate long-period fiber gratings (LPG1 and LPG2) connected in series in the middle of a section of cascaded optical fiber with a length d (this length can be changed arbitrarily). A special combination of long-period fiber gratings. When the structural parameters of the two separate long-period fiber gratings LPG1 and LPG2 are the same, after the light emitted by the light source passes through LPG1, the core mode is partially coupled to the cladding mode, and the cladding mode and the remaining core mode are respectively along the Cladding and core transmission, at LPG2, the cladding mode is coupled back to the core to become the core mode, and interferes with the uncoupled core mode passing through LPG1. Light travels in LPG1 and LPG2 in a similar way to a Mach-Zehnder interferometer. The optical fiber with a middle length of d is coated with a layer of ZIF-8 metal-organic framework material as a gas-sensing material, and the effective refractive index of the sensitive layer can be changed by using the different adsorption strength and adsorption capacity of the material for different types of gases. The transmission constant of the cladding modes, thus changing the characteristics of the output spectrum.

If the phases of the two beams of light from the core and the cladding are the same, the light at the output interferes constructively; if the phase difference of the two beams of light is π, the interference at the output is destructive. The effective refractive index of the cladding mode of the gas-sensitive material ZIF-8 changes in different amounts after absorbing different gases, and the interference spectrum at the output end will have changes in wavelength and intensity, so that the relationship between different gases and the interference spectrum can be established. The corresponding relationship, so as to realize the gas identification.

The following is a description of the specific working principle:

The sensor works with a broadband light source (C+L band). The light is input from the input end of a single-mode fiber. When the light wave passes through the first long-period grating LPG1, part of the energy is coupled into the cladding. Due to the length of the intermediate cascaded fiber d is limited, and the light energy attenuation of the cladding part is limited, so when the light wave passes through the second long period grating LPG2, the light energy of the cladding part will be coupled into the fiber, and it will be generated with the light in the original fiber core layer The interference is output by the output port and received by the spectrometer. When the device is not in contact with the gas, the phase difference between the two beams of light transmitted by the cladding and core of the fiber remains unchanged in the part of the cascaded length in the middle of the fiber. When the device is in contact with gas, the sensitive layer ZIF-8 changes the refractive index of the sensitive layer due to the adsorption of gas, which leads to a change in the propagation constant of the cladding mode of the fiber, and the two beams of light transmitted by the cladding and core of the fiber The phase difference changes during interference, so after the device is exposed to gas, the interference spectrum of the device starts to move to the left relative to the interference spectrum when it is not exposed to gas. The concentration of the gas is the smallest when it first touches the device, and as the volatilization concentration of the gas in a specific sensing cavity increases gradually, the shift of the interference spectrum also increases gradually. Therefore, the gas concentration range can be determined according to the shift amount of the interference spectrum. The longer the device is exposed to the gas, the greater the shift of the interference spectrum; on the contrary, the shorter the time, the smaller the shift of the interference spectrum.

The present invention takes a section of wavelength range near C-band 1550nm as an example, and according to the structure of the designed device, a cascaded long-period grating sensor device with a grating period of 320 microns, a period number of 50, and a series length d of 6 cm is manufactured. Those skilled in the art should note that this is only for ease of understanding. In practical applications, the sensor structure proposed by the present invention, the grating period, the number of periods and the value of the series length d can be determined according to the specific situation, and are not limited to this embodiment. For this one, as shown in Figure 2, the sensor produced in this embodiment is placed in different gas environments, and the movement of the interference spectrum of the device relative to the interference spectrum when it is not exposed to gas is observed at different time points, mainly including : the spectrogram that test ethanol obtains shown in Fig. 2 (a), the spectrogram that test methanol obtains shown in Fig. 2 (b), the spectrogram that test ethyl acetate obtains shown in Fig. 2 (c), Fig. 2 (d) The spectrogram obtained by testing acetone shown in Fig. 2 (e), the spectrogram obtained by testing dichloromethane shown in Fig. 2 (e), the spectrogram obtained by testing pyridine shown in Fig. 2 (f), and the obtained spectrogram obtained by testing ether shown in Fig. 2 (g). Spectrogram, the spectrogram obtained by testing toluene shown in Fig. 2 (h), and the spectrogram obtained by testing cyclohexane shown in Fig. 2 (i); Table 1 shows the movement of the interference spectrum under different gases measured.

Table 1 Measures the movement of the interference spectrum under different gases

amount of movement ethanol Methanol acetone ethyl acetate Dichloromethane pyridine Ether toluene Cyclohexane Δλ 23.45 19.29 8.70 8.75 10.61 14.42 9.71 4.85 5.40

In summary, the present invention realizes the detection of different gas types through the cascaded long-period fiber grating structure coated with metal organic framework materials, and produces a new type of gas detection device with fast response speed and high sensitivity, which can be applied to environmental monitoring And chemical testing and many other aspects, has very good practical application value.

It should be pointed out that for those of ordinary skill in the art, on the basis of the content disclosed in the present invention, several equivalent deformations and replacements can be made, such as changes in cascaded long-period grating production parameters such as grating period, depth, etc., and sensitive material The effect of gas recognition and detection realized by the change of ZIF-8 growth thickness, etc., these equivalent deformations and replacements should also be regarded as the protection scope of the present invention; in addition, the detection of other gases not demonstrated in the present invention should also be regarded as the protection scope of the present invention.

Those skilled in the art will appreciate that the embodiments described here are to help readers understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Various modifications and variations of the present invention will occur to those skilled in the art. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of the claims of the present invention.

Claims (5)

1. a kind of Mach of increasing Dare interferometer, which is characterized in that include at least：First long-period fiber grating, the second long period Fiber grating；It connects between first long-period fiber grating and the second long-period fiber grating a cascaded optical fiber；The grade Join two-arm of the sandwich layer of optical fiber with covering respectively as interferometer, grows one layer of sensitive layer on the cascaded optical fiber covering.

2. a kind of Mach of increasing Dare interferometer according to claim 1, which is characterized in that the sensitive layer is one layer porous The metal-organic framework material of ZIF-8.

3. a kind of gas based on metal-organic framework material identifies fibre optical sensor, which is characterized in that including such as claim 2 The Mach increases Dare interferometer.

4. a kind of organic gas detection method, which is characterized in that including：

Coupling of the sandwich layer mould to cladding mode occurs at the first long-period gratings for the sandwich layer light in optical fiber, forms sandwich layer mould and covering The transmission respectively of mould；

Cascaded optical fiber sensitive layer adsorbs organic gas to be detected so that cladding mode refraction index changing；

In second long-period gratings, the optical coupling of cladding mode returns to sandwich layer to interfere, and obtains interference spectrum；

According to the correspondence between interference spectrum and gas with various, the organic gas to be detected is identified.

5. a kind of organic gas detection method according to claim 4, which is characterized in that the interference spectrum and different gas Correspondence between body establishes process：

Coupling of the sandwich layer mould to cladding mode occurs at the first long-period gratings for the sandwich layer light in optical fiber, forms sandwich layer mould and covering The transmission respectively of mould；

Cascaded optical fiber sensitive layer adsorbs known gas so that cladding mode refraction index changing；

In second long-period gratings, the optical coupling of cladding mode returns to sandwich layer to interfere, and obtains interference spectrum；

The correspondence between the known gas is established according to several interference spectrums.