An organic molecular fiber detection system and its applications

Abstract

The application discloses an organic molecule optical fiber detection system, which comprises an optical wave multimeter (1), a transmission optical fiber (2), a detection chamber (3) and an optical fiber sensor (4), the optical wave multimeter (1) comprises a wavelength-adjustable light source and a power detection detector, the transmission optical fiber (2) is a single-mode optical fiber, the optical fiber sensor (4) is composed of a tapered optical fiber (5) and a MOF nanometer film (6) grown on the surface of the tapered waist region of the tapered optical fiber (5), the two ends of the tapered optical fiber (5) are connected with the optical wave multimeter (1) through the transmission optical fiber (2) respectively, and the optical fiber sensor (4) is placed in the detection chamber (3). The application further discloses an application of the organic molecule optical fiber detection system, which is used for detecting the concentration of ethanol. The organic molecule optical fiber detection system and the application thereof can solve the problem of low sensitivity of the current organic molecule detection technology, and improve the detection range and sensitivity of organic molecules.

Description

TECHNICAL FIELD

[0001] The present application relates to an organic molecule optical fiber detection system and its application, and belongs to the technical field of optical fiber detection. BACKGROUND

[0002] The demand for disinfectant is increasing. In the wide use of disinfectant, it is easy to produce organic molecule pollution. At present, the detection methods for organic molecules mainly include PID detection (photoionization detector), FID detection (flame ionization detector) and chromatograph. The PID detection method cannot be used in a relatively complex environment and can only detect organic molecules in a specific environment. The flame ionization detector (FID) chemically ionizes the detected substance, and this process is irreversible, so it is a destructive detector. The chromatograph detection technology is restricted in application due to high cost of detection instrument, complex operation and high requirement for operators. In addition, the methods for detecting organic molecules also include infrared spectrophotometry and fluorescence detection method, but these methods have different defects in stability and sensitivity.

[0003] Metal organic framework (MOF) material is a new type of porous material, which has super high specific surface area, adjustable pore structure, high crystallinity and designable organic ligand. Among them, zeolitic imidazolate framework (ZIF) is a subclass of metal organic framework with zeolite or similar zeolite topology. Among various ZIF materials, ZIF-8 is a tetrahedral framework formed by zinc ions and imidazole ligands, which has sodalite topology. ZIF-8 has the advantages of hydrophobicity, high porosity and high adsorption capacity, and is also used for detection of detected molecules.

[0004] Optical fiber sensing is a device that uses optical fiber as a medium to detect the change of light transmission characteristics caused by the change of the environment of the optical fiber when light propagates in the optical fiber. Optical fiber is widely used in sensing and detection due to its small size, light weight and strong anti-electromagnetic interference ability. The combination of MOF and optical fiber not only meets the performance of optical fiber sensing, but also realizes the specific detection of a substance in a complex environment. However, previous research on the combination of MOF and optical fiber has considerable difficulty in preparation and use, which requires magnetron sputtering, etching grating and other processes on the optical fiber, and has high cost and great difficulty. It also needs to meet certain conditions, such as excitation of plasmonic resonance, to carry out the next detection work, and these optical fibers are not sensitive enough to the change of external environment. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the defects of the prior art and provide an organic molecule optical fiber detection system, which can solve the problem of low sensitivity of current organic molecule detection technology and improve the detection range and sensitivity of organic molecules.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is:

[0007] An organic molecule optical fiber detection system, comprising an optical universal meter, a transmission optical fiber, a detection chamber and an optical fiber sensor, the optical universal meter comprising a wavelength adjustable light source and a power detector, the transmission optical fiber being a single-mode optical fiber, the optical fiber sensor being composed of a tapered optical fiber and a MOF nanofilm grown on the surface of the tapered optical fiber waist region, the two ends of the tapered optical fiber being connected with the optical universal meter through the transmission optical fiber respectively, and the optical fiber sensor being placed in the detection chamber.

[0008] The detection chamber is a closed container or a gas chamber.

[0009] The wavelength adjustable light source ranges from 1507 to 1600 nm, and the tuning step is 1 pm, the dynamic range of the power detector is -100 to 0 dB, and the resolution is 0.001 dB.

[0010] The transmission optical fiber is a single-mode optical fiber, the core refractive index of the single-mode optical fiber is 1.4457, and the cladding refractive index of the single-mode optical fiber is 1.4378.

[0011] The length, width and height of the detection chamber are all 20 cm.

[0012] The total length of the tapered optical fiber is 12000-13500 μm.

[0013] The diameter of the tapered waist region of the tapered optical fiber is 15-23 μm.

[0014] The MOF nanofilm is a ZIF-8 nanofilm, the large pore diameter of the ZIF-8 nanofilm is 11.6 angstroms, the small pore diameter is 3.4 angstroms, and the thickness of the ZIF-8 nanofilm is 200 nm.

[0015] For detecting the concentration of ethanol, the detection range of ethanol is 0.8%-30% in terms of volume percentage.

[0016] The sensitivity of the optical fiber sensor is 1.68 nm / %.

[0017] The application has the advantages that the organic molecule optical fiber detection system provided by the application adopts an optical wave universal meter instead of a light source and a spectrometer, so that the system is more convenient and fast; part of the light energy transmitted in the tapered optical fiber exists in the form of a strong evanescent field in the waist region, which makes the optical fiber very sensitive to changes in the external environment; the use of the porosity and specific adsorption performance of the MOF nanofilm to the molecules to be measured can detect organic molecule pollutants in water solution and air; in a complex environment with very small concentration of organic molecules, the specific adsorption of the MOF nanofilm will increase the local concentration of the target molecules at the film, which will result in a large change in the refractive index of the film, so that the detection of the target molecules with lower concentration can be realized; the growth of the MOF nanofilm on the waist region of the tapered optical fiber combines the adsorption capacity of the MOF nanofilm and the high sensitivity of the tapered optical fiber to the external environment, so that the detection range and sensitivity are improved; the optical fiber detection system has the advantages of small size, light weight and strong anti-electromagnetic interference capability. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Fig. 1 is a structural schematic diagram of the organic molecule optical fiber detection system of the application;

[0019] Figure 2 Fig. 2 is a structural schematic diagram of the optical fiber sensor in Fig. 1; Figure 1

[0020] Figure 3 Fig. 4 is a cross-sectional view of the tapered optical fiber after the surface growth of the ZIF-8 nanofilm under the scanning electron microscope;

[0021] Figure 4 Fig. 5 is a side view of the tapered optical fiber after the surface growth of the ZIF-8 nanofilm under the scanning electron microscope;

[0022] Figure 5 Fig. 6 is a relationship between the effective refractive index of the first two modes in the tapered optical fiber and the fiber radius in the application;

[0023] Figure 6 Fig. 7 is a transmission spectrum of the tapered optical fiber sensing structure with the growth of the ZIF-8 nanofilm in different concentrations of ethanol solution in the application;

[0024] Figure 7 Fig. 8 is a dip near 1540nm in the transmission spectrum in Fig. 7 selected as a reference point to calculate the sensitivity, which is 1.68nm / %. Figure 6

[0025] ​​The reference signs in the figure are as follows: 1-optical universal meter; 2-transmission optical fiber; 3-detection chamber; 4-optical fiber sensor; 5-tapered optical fiber; 6-MOF nanofilm; 21-single-mode optical fiber core; 22-single-mode optical fiber cladding. DETAILED DESCRIPTION

[0026] The application will be further described below with reference to the accompanying drawings, and the following examples are only used to more clearly illustrate the technical solutions of the application, and cannot be used to limit the protection scope of the application.

[0027] As shown in Figure 1 and Figure 2 , the application provides an organic molecule detection system, which comprises an optical universal meter 1, a transmission optical fiber 2, a detection chamber 3 and an optical fiber sensor 4. The optical universal meter 1 comprises a wavelength tunable light source and a power detector, the wavelength tunable light source of the optical universal meter 1 ranges from 1507 nm to 1600 nm, and the tuning step is 1 pm; the dynamic range of the power detector is -100-0 dB, and the resolution is 0.001 dB. The transmission optical fiber 2 is a single-mode optical fiber, the core refractive index of the transmission optical fiber 2, i.e. the single-mode optical fiber, is 1.4457, and the cladding refractive index of the single-mode optical fiber 2 is 1.4378. The detection chamber 3 is a sealed container or a gas chamber, and the length, width and height of the detection chamber 3 are all 20 cm.

[0028] The optical fiber sensor 4 is composed of a tapered optical fiber 5 and a MOF nanofilm 6 grown on the surface of the tapered waist region of the tapered optical fiber 5, and is placed in the detection chamber 3. The total length of the tapered region of the tapered optical fiber 5 is 12000-13500 μm. The MOF nanofilm 6 is a ZIF-8 nanofilm, the thickness of the nanofilm is 200 nm, and the large aperture of the MOF material is 11.6 angstroms and the small aperture is 3.4 angstroms.

[0029] Since the normalized frequency V co <2.40483, only the LP 01 mode, i.e. the fundamental mode, is excited in the SMF. The radius of the fundamental mode field reflects the constraint ability of the optical fiber core on the optical energy from the side, and assuming that the input light field from the SMF is E(r), the mode field radius of the fundamental mode can be expressed as:

[0030]

[0031] According to the Marcuse theorem, the mode field radius of the fundamental mode can be simplified as:

[0032]

[0033] As the fiber diameter decreases during the tapering process, part of the mode will enter the cladding when the mode field diameter is larger than the core diameter. Due to the change of the fiber diameter, the number of reflections n at the cladding-air interface will increase, and the corresponding incident angle a n and the exit angle θ n will change. The propagation constant β of the light can be expressed as:

[0034] β = n clad k0cosθ n (3)

[0035] where n clad is the refractive index of the cladding, and k0 is the wave number in vacuum. Therefore, when the light propagates from the large end face to the small end face of the tapered fiber, the mode characteristic angle θ n gradually increases due to the decrease of the fiber diameter, and the mode order of the light signal changes from low order to high order.

[0036] The effective penetration depth d z of the evanescent field can be expressed as:

[0037]

[0038] The cladding mode generated due to the decrease of the fiber diameter will be totally reflected between the cladding and the air, and a strong evanescent field will be generated in the waist region of the taper. The penetration depth of the evanescent field will be greatly extended in the external environment.

[0039] This formula shows that the refractive index of the external environment has an effect on the penetration depth. The smaller the waist diameter of the prepared tapered fiber, the stronger the penetration ability of the generated evanescent field, and the interaction between the sensing unit and the external parameter will be strengthened, and the change of the external environment will be more sensitive. In the evanescent field region of the tapered fiber, part of the energy will be transmitted to the outside in the form of evanescent wave, which will cause the loss of the transmitted light energy. When the material properties of the evanescent field outside are constant, the penetration depth of the evanescent wave is proportional to the light energy loss caused by the evanescent field.

[0040] When the effective refractive index of the fundamental mode decreases to less than the refractive index of the cladding, the fundamental mode is cut off, and the fundamental mode is conducted by the cladding. Due to the change of the fiber diameter, the cladding mode and the core mode will interfere with each other, and the interference intensity can be expressed as:

[0041]

[0042] where I is the total light intensity of the output light, I1 and I2 are the light intensities in the core mode 21 and the cladding mode 22 respectively, and φ is the phase difference between the two modes, which can be expressed as:

[0043] ​

[0044] Two-mode interference will occur a series of energy extremum in the transmission process, in which the minimum satisfies the following phase condition:

[0045] λ m =(2n eff L) / (2m-1) (7)

[0046]

[0047] Where, ΔL is the optical path difference, Δn eff is the change of the effective refractive index difference. The change of external parameters will cause ΔL and Δn eff corresponding changes. Thus Δλ m changes, causing the shift of interference peak in the output transmission spectrum.

[0048] When the concentration of the molecules to be measured in the sensing area is changed, the ZIF-8 nanofilm has different degrees of pore filling due to different adsorption amounts, resulting in changes in the refractive index of the ZIF-8 film. According to formula 4, the penetration depth of the evanescent field changes, thereby causing the loss of output light energy. This will cause changes in the size of the spectral line in the transmission spectrum, and this phenomenon can be used to detect organic molecular pollutants in aqueous solutions. Similarly, changes in the refractive index of the film will change the effective refractive index difference between the cladding mode and the core mode of the tapered optical fiber. According to formulas 5-8, the interference intensity of the two modes changes due to the phase difference caused by the effective refractive index difference, and finally causes the movement of the transmission spectrum line at the output end. This phenomenon can also be used to detect organic molecular pollutants in aqueous solutions.

[0049] In summary, the detection principle of the present application can be summarized as follows: The tapered optical fiber is a special waveguide. When the light signal propagates from the large end face to the small end face of the tapered optical fiber transition zone, part of the light energy gradually leaks from the core to the cladding to excite the cladding mode. In the taper waist area, the energy proportion of the cladding mode reaches the maximum, and high-order modes or evanescent fields are excited in the cladding. These high-order modes and evanescent fields in the cladding are sensitive to the environment around the tapered optical fiber. The ZIF-8 nanofilm grown on the surface of the tapered optical fiber has specific adsorption capacity for certain molecules, and the refractive index of the ZIF-8 nanofilm after adsorption changes, thereby enabling real-time monitoring of specific molecules in various environments.

[0050] As Figure 3 is the cross-sectional view of the optical fiber after the ZIF-8 nanofilm is grown on the surface of the optical fiber taken by a scanning electron microscope. The electron micrograph shows that there is a layer of ZIF-8 nanofilm on the surface of the optical fiber with a thickness of about 200 nm and good uniformity.

[0051] As Figure 4This is a side view of a tapered optical fiber after ZIF-8 nanofilm growth, captured using a scanning electron microscope. The electron microscope image shows that the ZIF-8 nanofilm grown on the tapered optical fiber surface exhibits good compactness.

[0052] Taking ethanol in aqueous solution as an example, the kinetic molecular diameter of ethanol is 4.4 Å, which falls between the large pore size (11.6 Å) and small pore size (3.4 Å) of ZIF-8, satisfying the molecular sieve conditions for ZIF-8. Utilizing the adsorption properties of ZIF-8 films for ethanol molecules, combined with evanescent field and mode interference in tapered optical fibers, real-time detection of ethanol molecules at different concentrations can be achieved. Although the ethanol content in the aqueous solution is not high, the strong adsorption force of ZIF-8 nanofilms for ethanol molecules still allows for the capture and adsorption of ethanol molecules in the aqueous solution.

[0053] like Figure 5 This relates the effective refractive index of the first two modes in a tapered fiber to the fiber radius. As the radius of the tapered fiber gradually decreases, the mode field radius of the core mode gradually increases. When the effective refractive index of the core mode drops below that of the cladding mode, the core mode is cut off, and the fundamental mode is propagated by the cladding. Due to the change in the diameter of the tapered region, coupling may occur between the modes. When the distance between the two curves decreases to a certain extent, mode coupling is more likely to occur. When the diameter decreases to 23µm-15µm, the distance between the curves is the smallest, and the two modes are most likely to interfere. When the diameter is further reduced to below 15µm, the distance between the curves increases, and the coupling phenomenon no longer occurs. The core mode and cladding mode interference is only excited when the diameter of the tapered waist region of the tapered fiber is 15-23µm. Therefore, this application sets the tapered waist diameter of the tapered fiber to 15-23µm. Furthermore, the penetration depth of the evanescent field excited by the tapered fiber of this size is calculated to be 231.05-246.45nm using formula (4). When the thickness of the MOF nanofilm is less than the penetration range of the evanescent field, the tapered fiber is most sensitive to changes in the film's refractive index. Research and experiments have shown that a ZIF-8 film thickness of 200 nm exhibits the best uniformity and adsorption properties, and since its thickness is less than the penetration range of the evanescent field, a thickness of 200 nm was chosen for the ZIF-8 film in this application.

[0054] like Figure 6The transmission spectrum of the invented optical fiber sensor in different concentrations of ethanol solution is shown in the following table. In this embodiment, the samples to be tested are deionized water and ethanol solutions with volume percentages of 0.8%, 5%, 10%, 15%, 20%, 25% and 30% respectively. The light source is a broadband light source with a wavelength range of 1507nm-1600nm. The ZIF-8 nanofilm is filled with different degrees of porosity due to different concentrations of ethanol solution, and the refractive index also changes to different degrees, resulting in different degrees of shift of the transmission spectrum, thereby realizing the detection of ethanol molecules in the aqueous solution. When the volume percentage of ethanol reaches 0.8%, the transmission spectrum line is shifted, so the lower limit of detection is 0.8%. When the volume percentage of ethanol reaches 30% or higher, the transmission spectrum line no longer changes, so the upper limit of detection is 30%. The detection range of the system for ethanol is 0.8%-30%.

[0055] As Figure 7 To select Figure 5 The sensitivity calculated by selecting the dip near 1540nm in the transmission spectrum as the reference point is 1.68nm / %.

[0056] The above is only a preferred embodiment of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. An organic molecular fiber detection system characterized by: The utility model provides a kind of optical wave multifunctional meter (1), transmission optical fiber (2), detection chamber (3) and optical fiber sensor (4), the optical wave multifunctional meter (1) includes wavelength adjustable light source and power detection detector, the transmission optical fiber (2) is single-mode fiber, the optical fiber sensor (4) is by taper fiber (5) and MOF nanometer film (6) grown in the conical waist area surface of taper fiber (5) is constituted, the both ends of the taper fiber (5) are connected with optical wave multifunctional meter (1) by the transmission optical fiber (2) respectively, the wavelength adjustable light source tuning step is 1pm, the dynamic range of the power detection detector is-100~0dB, resolution is 0.001dB, the diameter of the conical waist area of the taper fiber (5) is 15~23 μm, the MOF nanometer film (6) is ZIF-8 nanometer film, the large aperture of the ZIF-8 nanometer film is 11.6 angstrom, small aperture is 3.4 angstrom, the ZIF-8 nanometer film thickness is 200nm, the optical fiber sensor (4) is placed in the detection chamber (3).

2. An organic molecular fiber detection system according to claim 1, wherein: The detection chamber (3) is a closed container or a gas chamber.

3. An organic molecular fiber detection system according to claim 1, wherein: The wavelength adjustable light source ranges from 1507 to 1600 nm.

4. An organic molecular fiber detection system according to claim 1, wherein: The transmission optical fiber (2) is a single-mode fiber, the core refractive index of the single-mode fiber is 1.4457, and the cladding refractive index of the single-mode fiber is 1.4378.

5. An organic molecular fiber detection system according to claim 1, wherein: The length, width and height of the detection chamber (3) are all 20 cm.

6. An organic molecular fiber detection system according to claim 1, wherein: The total length of the taper region of the taper fiber (5) is 12000-13500 μm.

7. Use of an organic molecular fiber detection system according to any one of claims 1 to 6, characterized in that: The detection range of ethanol is 0.8%-30% by volume percentage.

8. Use of an organic molecular fiber optic sensing system according to claim 7, characterized in that: The sensitivity of the optical fiber sensor (4) is 1.68 nm / %.

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