A method for improving the response range of LPFG

Abstract

The present invention belongs to the technical field of long-period fiber grating sensing, and mainly relates to a method for improving the response range of LPFG, especially a method for improving the response range of LPFG to liquids. The method for improving the response range of LPFG is to prepare a poly(diallyldimethylammonium chloride) / phytic acid multilayer nanofilms on the surface of LPFG by using reagents such as sodium chloride, phytic acid and poly(diallyldimethylammonium chloride), and to achieve the purpose of improving the response range of LPFG to environmental media through the regulation of the transmission spectrum of LPFG by the poly(diallyldimethylammonium chloride) / phytic acid multilayer nanofilms. This method has the advantages of low cost and simple preparation. The LPFG modified by this method can achieve highly sensitive detection of environmental media without high-resolution instruments and complex demodulation techniques.

Description

Technical Field

[0001] The present invention belongs to the technical field of long-period fiber grating sensing, and relates to a method for improving the response range of LPFG, in particular to a method for improving the response range of LPFG to liquids. Background Art

[0002] Long period fiber gratings (LPFGs) are made by periodically modulating the refractive index of the fiber core, and are the most important optical passive devices that can couple the fundamental mode of the core in the forward transmission of light to the cladding mode in the co-directional transmission. Since LPFG not only has many common characteristics of optical fibers such as anti-electromagnetic interference, corrosion resistance, light weight, small size, and easy compatibility with optoelectronic systems, but also has unique advantages such as no backward reflection, low insertion loss, and high sensitivity, it has received extensive attention in the fields of communication and sensing. In the past two decades, LPFGs have been applied to many fields such as optical fiber communication, temperature, stress, load, bending, biological analysis, and chemical sensing.

[0003] An important property of LPFG is its ability to sense changes in refractive index. By sensing the refractive index of the ambient medium, the physical and chemical properties of the ambient medium can be judged, such as the type of substance, the purity of the substance, the concentration of the substance, and other optical properties of the substance. The detection of refractive index has important research significance and wide application value in fields such as seawater, fermentation industrial engineering control, clinical inspection, drug screening, food quality monitoring, environmental monitoring, metallurgy, and scientific research. So far, many devices for refractive index measurement have emerged, mainly including Bragg fiber grating sensors, Abbe refractometers, Fabry-Perot interferometric sensors, surface plasmon resonance sensors, photonic crystal fibers, ring resonators, etc. Compared with these refractive index sensors, LPFG has unique advantages in refractive index measurement due to the above-mentioned many advantages, and is particularly suitable for measuring the refractive index of liquids or gases in harsh environments that are not easily accessible to humans.

[0004] However, usually, for refractive indices above 1.453, LPFG shows the disappearance of resonance peaks or very little wavelength shift. For refractive indices below 1.345, the resonance wavelength of LPFG hardly moves. Therefore, the response range of LPFG to refractive index has certain limitations, which greatly restricts the practical application of LPFG. Therefore, it is necessary to expand the response range of long-period fiber grating to refractive index to achieve high-sensitivity detection of refractive index by LPFG. Summary of the Invention

[0005] In view of this, the present invention provides a method for improving the response range of LPFG, in particular to a method for improving the response range of LPFG to liquids, aiming at the above-mentioned defects existing in LPFG.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The technical solution of a method for improving the response range of an LPFG in the present invention is that the improvement of the response range of the LPFG is achieved by using a method of modifying a nano-film on the surface of the LPFG.

[0008] The nano-film needs to be prepared with reagents such as sodium chloride, phytic acid, and poly(diallyldimethylammonium chloride).

[0009] Preferably, the modified nano-film is obtained by alternately depositing poly(diallyldimethylammonium chloride) and phytic acid on the surface of the long-period fiber grating;

[0010] The reason why the present invention selects poly(diallyldimethylammonium chloride) and phytic acid as the nano-film is that poly(diallyldimethylammonium chloride) and phytic acid have a strong binding force, and poly(diallyldimethylammonium chloride) has a very strong swelling ability in water, which results in a large difference in the resonance wavelength of the LPFG in water and sodium chloride solution.

[0011] Preferably, the molecular weight of the reagent poly(diallyldimethylammonium chloride) is 5000 - 3000000.

[0012] Preferably, the solution used for depositing poly(diallyldimethylammonium chloride) is a poly(diallyldimethylammonium chloride) solution containing sodium chloride; the solution used for depositing phytic acid is a phytic acid solution containing sodium chloride, where the molar concentration ratio of sodium chloride to phytic acid is 0.05 - 300.

[0013] Preferably, the molar concentration ratio of sodium chloride to poly(diallyldimethylammonium chloride) in the poly(diallyldimethylammonium chloride) solution is between 0.05 and 300.

[0014] Preferably, the deposition time for each time of the phytic acid solution is 5 - 15 minutes, and the deposition time for each time of the poly(diallyldimethylammonium chloride) solution is 10 - 30 minutes.

[0015] Preferably, the modification method includes the following main steps:

[0016] ① Immerse the LPFG into a mixture of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3, and treat it at 80 °C for 1 hour;

[0017] ② Rinse the LPFG 6 times with deionized water and dry it with nitrogen;

[0018] ③ Straighten and fix the LPFG on the liquid tank bracket;

[0019] ④ Add the poly(diallyldimethylammonium chloride) solution containing sodium chloride to the liquid cell for deposition;

[0020] ⑤ Rinse the deposited LPFG six times with secondary deionized water and dry it with nitrogen gas.

[0021] ⑥ Add the phytic acid solution containing sodium chloride to the liquid cell and soak for several minutes.

[0022] ⑦ Rinse the long-period fiber grating six times with secondary deionized water and dry it with nitrogen gas.

[0023] ⑧ Repeat the operation steps of ④ - ⑦, and a poly(diallyldimethylammonium chloride) / phytic acid multilayer nanofilms that can improve the wide response range of the long-period fiber grating to liquids can be obtained.

[0024] As can be seen from the above technical solutions, compared with the prior art, the present invention has the following beneficial effects:

[0025] The method for improving the response range of the LPFG according to the present invention has a significantly widened response range to the environmental medium and a significantly increased sensitivity to the environmental medium compared with the LPFG without modified poly(diallyldimethylammonium chloride) / phytic acid multilayer nanofilms.

[0026] The method for improving the response range of the LPFG according to the present invention can achieve highly sensitive detection of environmental media without using high-resolution instruments and complex demodulation techniques.

[0027] The method for improving the response range of the LPFG according to the present invention has the advantages of simple preparation process, low cost, and no need for professional technicians to operate.

[0028] The method for improving the response range of the LPFG according to the present invention can enhance the mechanical strength resistance of the LPFG by using poly(diallyldimethylammonium chloride) / phytic acid multilayer nanofilms modification.

[0029] The method for improving the response range of the LPFG according to the present invention has broad commercial application prospects in the fields of seawater salinity, food safety, environmental monitoring, etc., and is expected to be widely promoted and applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0031] Figure 1 It is a diagram of the transmission spectrum and detection range of the response of the LPFG without assembled poly(diallyldimethylammonium chloride) / phytic acid nanofilm to the environmental medium;

[0032] Figure 2 It is a diagram showing the transmission spectrum and detection range of the response of LPFG assembled with 50 bilayers of poly(diallyldimethylammonium chloride) / phytic acid nanofilm to environmental media;

[0033] Figure 3 It is a diagram showing the transmission spectrum and detection range of the response of LPFG assembled with 80 bilayers of poly(diallyldimethylammonium chloride) / phytic acid nanofilm to environmental media. Detailed implementation mode

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] Embodiment 1

[0036] (1) Immerse the LPFG in a mixture of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3 and treat it at 80 °C for 1 hour;

[0037] (2) Rinse the long-period grating 6 times with deionized water and dry it with nitrogen;

[0038] (3) Straighten and fix the LPFG on the liquid cell holder;

[0039] (4) Add the poly(diallyldimethylammonium chloride) solution containing sodium chloride to the liquid cell and soak for 10 minutes;

[0040] (5) Rinse the long-period grating 6 times with secondary deionized water and dry it with nitrogen;

[0041] (6) Add the phytic acid solution containing sodium chloride to the liquid cell and soak for 8 minutes;

[0042] (7) Rinse the long-period grating 6 times with secondary deionized water and dry it with nitrogen;

[0043] (8) Repeat the operation steps of (4)-(7) 50 times.

[0044] To further optimize the above technical solution, the molecular weight of poly(diallyldimethylammonium chloride) is 5000 - 3000000;

[0045] To further optimize the above technical solution, the molar concentration ratio of sodium chloride to poly(diallyldimethylammonium chloride) in the poly(diallyldimethylammonium chloride) solution is between 0.05 and 300.

[0046] AsFigure 1 As shown, when the refractive index of the environmental medium changes from 1.33303 to 1.45389, the resonant wavelength of the LPFG without assembled poly(diallyldimethylammonium chloride) / phytic acid nanofilms shifts by 88 nm. When the refractive index of the environmental medium becomes 1.45839, the resonant peak of the LPFG disappears, and in the wavelength range of 1100 - 1300, the transmission spectrum of the LPFG becomes a straight line. Therefore, the maximum range of the response of the LPFG without assembled poly(diallyldimethylammonium chloride) / phytic acid nanofilms to the environmental medium is 88 nm.

[0047] When 50 bilayers of poly(diallyldimethylammonium chloride) / phytic acid nanofilms are assembled, the maximum range of the response of the LPFG to the environmental medium becomes 122 nm, as Figure 2 shown. Compared with the LPFG without assembled poly(diallyldimethylammonium chloride) / phytic acid nanofilms, the response range of the LPFG assembled with 50 bilayers of poly(diallyldimethylammonium chloride) / phytic acid nanofilms to the environmental medium increases by 34 nm.

[0048] Example 2

[0049] (1) Immerse the LPFG in a sulfuric acid and hydrogen peroxide mixture with a volume ratio of 7:3 and treat it at 80 °C for 1 hour;

[0050] (2) Rinse the LPFG 6 times with deionized water and dry it with nitrogen;

[0051] (3) Straighten and fix the LPFG on the liquid cell holder;

[0052] (4) Add poly(diallyldimethylammonium chloride) containing sodium chloride to the liquid cell and soak for 20 minutes;

[0053] (5) Rinse the long-period grating 6 times with secondary deionized water and dry it with nitrogen;

[0054] (6) Add a phytic acid solution containing sodium chloride to the liquid cell and soak for 10 minutes;

[0055] (7) Rinse the long-period grating 6 times with secondary deionized water and dry it with nitrogen;

[0056] (8) Repeat the operation steps of (4)-(7) 80 times.

[0057] To further optimize the above technical solution, the molecular weight of poly(diallyldimethylammonium chloride) is 5000 - 3000000;

[0058] To further optimize the above technical solution, the molar concentration ratio of sodium chloride to poly(diallyldimethylammonium chloride) in the poly(diallyldimethylammonium chloride) solution is between 0.05 - 300.

[0059] When assembling 80 bilayers of poly(diallyldimethylammonium chloride) / phytic acid nanofilms, the maximum range of the LPFG's response to environmental media becomes 157 nm, as Figure 3 shown. Compared with the LPFG without assembled poly(diallyldimethylammonium chloride) / phytic acid nanofilms, the response range of the LPFG assembled with 80 bilayers of poly(diallyldimethylammonium chloride) / phytic acid nanofilms to environmental media increases by 69 nm.

[0060] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method section.

[0061] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for improving the response range of LPFG, characterized in that, The method is as follows: modifying the surface of the LPFG with a nano-film; The modified nano-film is obtained by alternately depositing poly(diallyldimethylammonium chloride) and phytic acid on the surface of the LPFG; The solution used for depositing poly(diallyldimethylammonium chloride) is a poly(diallyldimethylammonium chloride) solution containing sodium chloride; the solution used for depositing phytic acid is a phytic acid solution containing sodium chloride, where the molar concentration ratio of sodium chloride to phytic acid is 0.05 - 300.

2. A method for improving the response range of an LPFG according to claim 1, characterized in that: The molecular weight of the poly(diallyldimethylammonium chloride) is 5000 - 3000000.

3. A method for improving the response range of LPFG according to claim 2, characterized in that: In the poly(diallyldimethylammonium chloride) solution, the molar concentration ratio of sodium chloride to poly(diallyldimethylammonium chloride) is 0.05 - 300.

4. A method for improving the response range of an LPFG according to claim 1, characterized in that: The deposition time of the phytic acid solution each time is 5 - 15 minutes, and the deposition time of the poly(diallyldimethylammonium chloride) solution each time is 10 - 30 minutes.

5. A method for improving the response range of an LPFG according to any one of claims 2-4, characterized in that The method includes the following steps: ① Immerse the LPFG into a mixed solution of concentrated sulfuric acid and hydrogen peroxide, and treat it at 80 °C for 1 hour; Among them, the volume ratio of concentrated sulfuric acid to hydrogen peroxide is 7:3; ② Rinse the treated LPFG 6 times with deionized water and dry it with nitrogen; ③ Straighten and fix the LPFG on the liquid tank support; ④ Add the poly(diallyldimethylammonium chloride) solution containing sodium chloride to the liquid cell for deposition; ⑤ Rinse the deposited LPFG 6 times with secondary deionized water and dry it with nitrogen; ⑥ Add the phytic acid solution containing sodium chloride to the liquid cell for deposition; ⑦ Rinse the deposited LPFG 6 times with secondary deionized water and dry it with nitrogen; ⑧ Repeat the operation steps of ④ - ⑦, and a poly(diallyldimethylammonium chloride) / phytic acid multi-layer nano-film that can improve the wide response range of the long-period grating to liquids can be obtained.

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