Optical fiber sensor and manufacturing method therefor, and optical fiber sensing system

Abstract

An optical fiber sensor, comprising an optical fiber microstructure comprising an evanescent wave leakage portion, and an inducing sensing layer. The inducing sensing layer is used for inducing the evanescent wave leakage portion to generate a lossy mode resonance (LMR) effect and binding or adsorbing a sensed target. The inducing sensing layer is made of UIO-66-NH2, and the inducing sensing layer is bound to the outer surface of the evanescent wave leakage portion by means of a chemical modification method. The outer surface of an evanescent wave leakage portion in an optical fiber microstructure is bound to an inducing sensing layer of a metal-organic framework thin film by means of a chemical modification method. The inducing sensing layer can induce the evanescent wave leakage portion to generate an LMR effect, and can bind or adsorb a sensed target, so that a sensing thin film corresponding to a target object to be measured does not need to be coated during subsequent biosensing or other sensing, thereby further reducing the manufacturing costs of an LMR effect-based optical fiber sensor. Also provided are a manufacturing method for the optical fiber sensor and an optical fiber sensing system.

Description

A fiber optic sensor and its fabrication method, and a fiber optic sensing system. Technical Field

[0001] This invention relates to the field of optical sensing technology, and in particular to an optical fiber sensor and its fabrication method, as well as an optical fiber sensing system. Background Technology

[0002] When the propagation constant of the waveguide layer is close to that of the high-refractive-index thin film layer, and there is a large overlap between the loss mode field in the thin film and the mode field in the waveguide, a large amount of light in the waveguide will couple to the high-refractive-index thin film, resulting in a large loss of waveguide energy. As a result, a significant loss trough will appear in the transmission spectrum, which is known as loss mode resonance (LMR).

[0003] Loss-mode resonance (SMR) requires a high-refractive-index thin film coated on an optical waveguide. When a mode leaks from the waveguide into the thin film and propagates stably within it, the waveguide and thin film modes couple, inducing SMR. Fiber optic sensors based on SMR offer advantages such as high sensitivity, label-free detection, portability, low cost, and real-time monitoring, making them particularly advantageous in biosensing applications. Currently, thin films used to induce SMR are typically semiconductor or polymer materials. Coating these materials onto optical fibers usually requires expensive equipment, and subsequent biosensing or other sensing applications necessitate the coating of a corresponding sensing film for the target analyte, undoubtedly increasing manufacturing time and cost.

[0004] Therefore, there is an urgent need for an optical fiber sensor and its fabrication method, as well as an optical fiber sensing system, to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide an optical fiber sensor and its fabrication method, as well as an optical fiber sensing system, to solve the technical problem of excessively high manufacturing costs of existing optical fiber sensors based on the LMR effect.

[0006] To solve the above-mentioned technical problems, the present invention provides an optical fiber sensor, including an optical fiber microstructure with an evanescent wave leakage section and an induced sensing layer. The induced sensing layer is used to induce the evanescent wave leakage section to generate a loss mode resonance effect and to bind or adsorb the sensing target.

[0007] The induced sensing layer is made of UIO-66-NH2 material and is bonded to the outer surface of the evanescent wave leakage part through a chemical modification method.

[0008] Preferably, the optical fiber microstructure further includes a base connected to the evanescent wave leakage section. The base includes a core layer, a cladding layer, and a coating layer arranged radially from the inside to the outside. The evanescent wave leakage section includes a core layer and a cladding layer arranged radially from the inside to the outside.

[0009] Preferably, the shape of the optical fiber microstructure is any one of tapered, D-shaped, and U-shaped, and the optical fiber microstructure is a single-mode optical fiber or a multimode optical fiber.

[0010] Preferably, the refractive index of the induced sensing layer is greater than the refractive index of the evanescent wave leakage part.

[0011] Preferably, the outer surface of the evanescent wave leakage part is modified with hydroxyl groups, and the induced sensing layer includes amino groups, and the induced sensing layer is combined with the hydroxyl groups of the evanescent wave leakage part through the amino groups.

[0012] Preferably, the particle diameter of the induced sensing layer is 300 nm to 500 nm.

[0013] Accordingly, the present invention also provides a method for fabricating an optical fiber sensor as described in any of the above claims, the method comprising:

[0014] S10 provides an optical fiber microstructure, the optical fiber microstructure including an evanescent wave leakage section;

[0015] S20, the induced sensing layer is bonded to the outer surface of the evanescent wave leakage part by chemical modification;

[0016] The induced sensing layer is made of UIO-66-NH2 material. It is used to induce loss mode resonance in the evanescent wave leakage part and to bind or adsorb the sensing target.

[0017] Preferably, step S20 specifically includes:

[0018] S201, after uniformly mixing metal salt, organic ligand and solvent, heat treatment is carried out and cooled to room temperature to obtain the synthesized product. Then, the synthesized product is centrifuged to obtain supernatant and precipitate. The precipitate is then vacuum dried to obtain metal-organic framework powder.

[0019] S202, a suspension is obtained by mixing metal-organic framework powder with distilled water and then subjecting it to ultrasonic treatment.

[0020] S203 involves soaking the evanescent wave leak portion of the optical fiber microstructure in a piranha solution, drying it, and then immersing the evanescent wave leak portion in a suspension until an induced sensing layer is bonded to the outer surface of the evanescent wave leak portion.

[0021] Preferably, in step S201: the metal salt is zirconium oxychloride, the organic ligand is 2-aminoterephthalic acid, and the heat treatment temperature is 100℃~140℃.

[0022] Accordingly, the present invention also provides an optical fiber sensing system, including a light source, a spectrometer, and an optical fiber sensor as described above;

[0023] In this invention, one end of the fiber optic sensor is connected to a light source, and the other end is connected to a spectrometer. The advantages of this invention are: unlike existing technologies, this invention provides a fiber optic sensor and its fabrication method, as well as a fiber optic sensing system. The fiber optic sensor includes a fiber optic microstructure with an evanescent wave leakage section and an induced sensing layer. The induced sensing layer is used to induce a loss mode resonance effect in the evanescent wave leakage section and to bind or adsorb the sensing target. The induced sensing layer is made of UIO-66-NH2 material and is chemically modified to adhere to the outer surface of the evanescent wave leakage section. The fiber optic sensor provided by this invention uses a chemical modification method to attach a UIO-66-NH2 material induced sensing layer to the outer surface of the evanescent wave leakage section in the fiber optic microstructure. This induced sensing layer not only induces a loss mode resonance effect in the evanescent wave leakage section but also binds or adsorbs the sensing target. Therefore, subsequent biosensing or other sensing does not require coating with a sensing film corresponding to the target analyte, further reducing the manufacturing cost of fiber optic sensors based on the LMR effect. Attached Figure Description

[0024] Figure 1 is a process flow diagram of the fabrication method of the optical fiber sensor provided in an embodiment of the present invention;

[0025] Figure 2 is a schematic diagram of the fabrication process of the fiber optic sensor with UIO-66-NH2-induced LMR effect provided in Embodiment 1 of the present invention. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] In a first aspect, the present invention provides an optical fiber sensor, comprising an optical fiber microstructure having an evanescent wave leakage section and an induced sensing layer, wherein the induced sensing layer is used to induce a loss mode resonance effect in the evanescent wave leakage section and to bind or adsorb the sensing target.

[0028] The induced sensing layer is made of UIO-66-NH2 material and is bonded to the outer surface of the evanescent wave leakage part through a chemical modification method.

[0029] In this embodiment of the invention, the fiber optic microstructure with an evanescent wave leakage section is a key component of the sensor. Traditional optical fibers primarily rely on total internal reflection to transmit optical signals, while this specially designed fiber introduces an evanescent wave leakage section, allowing some optical energy to leak out of the fiber in the form of an evanescent wave. This design overcomes the limitations of traditional optical fibers, providing a channel for interaction with the external environment, thereby enabling the detection of sensing targets in the surrounding environment.

[0030] Specifically, an evanescent wave is an electromagnetic wave that propagates at the interface between two different media, and its intensity decreases exponentially with increasing distance from the interface. In fiber optic sensors, the presence of evanescent wave leakage allows the optical signal in the fiber to have closer contact with the external environment. When the evanescent wave interacts with the external induced sensing layer, it produces a series of unique optical effects, providing a foundation for achieving high-sensitivity sensing.

[0031] Specifically, the optical fiber microstructure also includes a base connected to the evanescent wave leakage section. The base includes a core layer, a cladding layer, and a coating layer arranged radially from the inside to the outside. The evanescent wave leakage section includes a core layer and a cladding layer arranged radially from the inside to the outside.

[0032] Furthermore, the primary function of the coating layer is to protect the fiber core and cladding from external environmental interference, such as preventing mechanical damage and chemical corrosion. However, for the evanescent wave leakage section, the purpose is to allow the evanescent wave of light to effectively leak out of the fiber and interact with the surrounding environment. The coating layer hinders the direct contact between the evanescent wave and the external environment. This is because the optical properties and structure of the coating material cause reflection and scattering of the evanescent wave, reducing the energy of the evanescent wave leaking into the external environment, thereby reducing the efficiency of the fiber optic sensor's interaction with the external sensing target.

[0033] Preferably, the shape of the optical fiber microstructure is any one of tapered, D-shaped, and U-shaped, and the optical fiber microstructure is a single-mode fiber, a multimode fiber, or a special fiber.

[0034] In this embodiment of the invention, the UIO-66-NH2 material, used as the induced sensing layer, possesses numerous unique properties. UIO-66-NH2 is a metal-organic framework material, a porous material formed by the self-assembly of metal ions or metal clusters with organic ligands through coordination bonds, exhibiting high crystallinity and a well-ordered pore structure. This material has an extremely high specific surface area, providing a large number of active sites for efficient binding or adsorption to sensing targets. Furthermore, its tunable pore size and chemical properties allow for customized design to meet different sensing needs.

[0035] In this embodiment of the invention, UIO-66-NH2 material is bonded to the outer surface of the evanescent wave leakage section through a chemical modification method, ensuring a tight bond between the induced sensing layer and the fiber microstructure. This bonding method not only improves the stability and reliability of the sensor but also enhances the interaction between the evanescent wave and the induced sensing layer.

[0036] In this embodiment of the invention, the UIO-66-NH2 material can induce a loss-mode resonance effect in the evanescent wave leakage region. This effect arises from the interaction between the propagation characteristics of light in the optical fiber and the optical properties of the metal-organic framework film. When light of a specific wavelength propagates in the optical fiber, the evanescent wave interacts with the metal-organic framework film, causing the light energy to be absorbed or scattered at specific frequencies, thereby producing a resonance phenomenon. This resonance effect significantly changes the transmission characteristics of light in the optical fiber, and the presence and concentration of the sensing target can be detected by monitoring these changes.

[0037] Specifically, the UIO-66-NH2 material possesses a highly developed porous structure, forming a vast internal surface area. This high specific surface area is retained even when fabricated as a thin film. This high specific surface area means more surface sites that can interact with the sensing target, providing ample space and opportunities for the binding or adsorption of the target substance. For example, for small molecule sensing targets such as gas molecules, the pores of the metal-organic framework film can accommodate these molecules, allowing them to adhere to the inner surface of the pores. Simultaneously, the porosity results in numerous pore channels within the film, through which the sensing target can enter and be adsorbed. This porous structure not only increases the adsorption contact area but also promotes the adsorption of the sensing target through physical processes such as capillary action and molecular diffusion, thereby enhancing the adsorption capacity for the sensing target.

[0038] Furthermore, the metal ions in the UIO-66-NH2 material possess unsaturated coordination bonds and high chemical activity. The sensing target can coordinate with the metal ions to form a metal-target molecule complex, thereby achieving binding to the sensing target. Besides metal ions, metal-organic framework films also contain other active sites, such as unsaturated organic ligands and defect sites. These active sites can interact with the sensing target, further enhancing its adsorption capacity. For example, unsaturated organic ligands can undergo π-π stacking interactions with the sensing target, increasing adsorption stability.

[0039] In this embodiment of the invention, the refractive index of the induced sensing layer is greater than that of the evanescent wave leakage section. When the refractive index of the induced sensing layer is greater than that of the evanescent wave leakage section, according to electromagnetic field theory in optics, at the interface of the two media, the evanescent wave of light can be coupled more effectively from the evanescent wave leakage section of the optical fiber into the induced sensing layer. This enhanced coupling facilitates a stronger interaction between the induced sensing layer and the evanescent wave, thereby making it easier to induce the loss mode resonance (LMR) effect.

[0040] In this embodiment of the invention, the outer surface of the evanescent wave leakage part is modified with hydroxyl groups, and the induced sensing layer includes amino groups. The induced sensing layer is combined with the hydroxyl groups of the evanescent wave leakage part through the amino groups.

[0041] Specifically, the induced sensing layer is made of UIO-66-NH2 material, and the particle diameter of the induced sensing layer is 300nm to 500nm.

[0042] Furthermore, UIO-66-NH2 is a metal-organic framework (MOF) material that uses zirconium ions (Zr) as its constituent elements. 4+ The metal ion is the metal center, and 2-aminoterephthalic acid is the organic ligand. These metal ions and organic ligands are interconnected through coordination bonds, forming a highly ordered three-dimensional network structure. UIO-66-NH2 material can induce LMR, and its particle diameter is 300nm~500nm, making it suitable for biosensing, gas sensing, etc.

[0043] Accordingly, referring to Figure 1, the present invention also provides a method for fabricating an optical fiber sensor as described in any of the above claims, the method comprising:

[0044] S10 provides an optical fiber microstructure, the optical fiber microstructure including an evanescent wave leakage section.

[0045] Specifically, step S10 also includes:

[0046] An optical fiber microstructure is provided, the optical fiber microstructure includes an evanescent wave leakage section and a base connected to the evanescent wave leakage section, the base includes a core layer, a cladding layer and a coating layer arranged radially from the inside to the outside, and the evanescent wave leakage section includes a core layer and a cladding layer arranged radially from the inside to the outside.

[0047] Preferably, the shape of the optical fiber microstructure is any one of tapered, D-shaped, and U-shaped, and the optical fiber microstructure is a single-mode optical fiber or a multimode optical fiber.

[0048] S20, the induced sensing layer is bonded to the outer surface of the evanescent wave leakage part by chemical modification.

[0049] Specifically, step S20 also includes:

[0050] S201, after uniformly mixing metal salt, organic ligand and solvent, heat treatment is carried out and cooled to room temperature to obtain the synthesized product. Then, the synthesized product is centrifuged to obtain supernatant and precipitate. The precipitate is then vacuum dried to obtain metal-organic framework powder.

[0051] S202, a suspension is obtained by mixing metal-organic framework powder with distilled water and then subjecting it to ultrasonic treatment.

[0052] S203 involves soaking the evanescent wave leak portion of the optical fiber microstructure in a piranha solution, drying it, and then immersing the evanescent wave leak portion in a suspension until an induced sensing layer is bonded to the outer surface of the evanescent wave leak portion.

[0053] Preferably, in step S201: the metal salt is zirconium oxychloride, the organic ligand is 2-aminoterephthalic acid, and the heating temperature is 100℃~140℃; at this time, the induced sensing layer obtained in step S203 is UIO-66-NH2 material.

[0054] Accordingly, the present invention also provides an optical fiber sensing system, including a light source, a spectrometer, and an optical fiber sensor as described above;

[0055] One end of the fiber optic sensor is connected to the light source, and the other end is connected to the spectrometer.

[0056] The technical solution of this application will now be described in conjunction with specific embodiments.

[0057] Example 1:

[0058] Embodiment 1 of the present invention provides a U-shaped fiber optic sensor for measuring the refractive index of an unknown solution. The U-shaped fiber optic sensor includes a fiber optic microstructure with an evanescent wave leakage section and an induced sensing layer. The induced sensing layer is made of UIO-66-NH2 material and is bonded to the outer surface of the evanescent wave leakage section by a chemical modification method.

[0059] Please refer to Figures 1 and 2. Figure 2 is a schematic diagram of the fabrication process of the UIO-66-NH2-induced LMR effect fiber optic sensor provided in Embodiment 1 of the present invention. Specifically, the fabrication process of the above-mentioned U-shaped fiber optic sensor is as follows:

[0060] Step 1: First, take a section of multimode fiber with a core diameter of 62.5 μm and a cladding diameter of 125 μm. Then, strip the coating from the middle part of the multimode fiber and heat it with the outer flame of an alcohol lamp to form a U-shaped fiber microstructure with a U-shaped radius of 1 mm to 5 mm. At this point, the U-shaped part is the evanescent wave leakage part. Cut the two ends of the fiber flat for later use.

[0061] Step 2, Synthesis of UIO-66-NH2 Powder: First, weigh 75 mg of zirconium dichloride (ZrOCl2) and 50 mg of 2-aminoterephthalic acid (BDC-NH2) into a container using an electronic balance, then weigh 1.25 g of benzoic acid (BA) into the container. Add 5 mL of DMF (N,N-dimethylformamide), sonicate for 90 min, and transfer the mixture to an autoclave. Then, place the autoclave in a heating oven at 120℃ for 24 h, and cool to room temperature to obtain the synthesized product. Next, centrifuge the synthesized product at 8000 r / min for 10 min, and wash with DMF and methanol three times each by centrifugation to obtain the supernatant and precipitate. Finally, dry the obtained precipitate in a vacuum drying oven at 60℃ for 24 h to obtain UIO-66-NH2 powder, which is stored at room temperature for later use.

[0062] Step 3, prepare UIO-66-NH2 suspension: take 5 mg of UIO-66-NH2 particles and put them into 5 mL of distilled water, sonicate for 30 min to obtain UIO-66-NH2 suspension;

[0063] Step 4, UIO-66-NH2 modification of optical fiber: First, a piranha solution was prepared by mixing concentrated sulfuric acid and hydrogen peroxide solution at a volume ratio of 7:3. The U-shaped optical fiber prepared in Step 1 was soaked in the piranha solution for at least 30 minutes to remove impurities on the optical fiber and to modify the surface of the optical fiber with -OH. The optical fiber with -OH was then dried in a natural environment. After that, the U-shaped optical fiber modified with -OH was placed in the UIO-66-NH2 suspension prepared in Step 3 for 12 hours to obtain a U-shaped optical fiber sensor.

[0064] Because UIO-66-NH2 has a -NH2 functional group, it can combine with -OH, thus allowing UIO-66-NH2 particles to be bonded to U-shaped optical fibers. Since UIO-66-NH2 has a higher refractive index than optical fibers, it can induce the LMR effect.

[0065] Furthermore, the U-shaped fiber optic sensor is placed in matching solutions with different refractive indices. One end of the U-shaped fiber is connected to a light source, and the other end is connected to a spectrometer. The light emitted from the light source passes through the U-shaped fiber optic sensor, generating a leakage mode. This mode couples with the mode transmitted in UIO-66-NH2, inducing LMR. The spectrometer collects and demodulates the transmitted spectrum and saves the spectral data. The resonance valley of LMR shifts towards longer wavelengths as the refractive index of the matching solution increases.

[0066] This invention provides a fiber optic sensor that induces LMR effect with UIO-66-NH2. Compared with semiconductor thin films or polymer thin films that currently achieve LMR, metal-organic framework (MOF) thin films have porosity and abundant functional groups, which can realize a thin film that can induce LMR, as well as realize biosensing and gas sensing. Moreover, the above chemical modification process is simple and has high sensitivity.

[0067] Specifically, a UIO-66-NH2 thin film is coated on the fiber microstructure to form a sensing region to induce the LMR effect. A light source and a spectrometer are connected to the two ends of the fiber sensing region, respectively. When the light wave passes through the fiber microstructure, a leakage mode is generated, which couples into the UIO-66-NH2 thin film and propagates in the film. When the propagation mode meets certain conditions, leakage mode resonance occurs, i.e., LMR. The resonance absorption wavelength changes with the external dielectric constant, so the external variable can be detected by detecting the resonance valley.

[0068] Unlike existing technologies, the present invention has the following advantages:

[0069] 1. This invention utilizes UIO-66-NH2 as the induction film and sensing film of an LMR-based fiber optic sensor, realizing a fiber optic sensor that can both induce LMR and simultaneously bind or adsorb the sensing target with a thin film, thereby reducing the manufacturing cost of LMR-based fiber optic sensors.

[0070] 2. The UIO-66-NH2 synthesized in this invention has a large specific surface area and abundant functional groups, and exhibits stability in liquid environments, making it suitable for biosensing. Furthermore, UIO-66-NH2 is a three-dimensional porous material capable of adsorbing specific gas molecules, thus enabling gas sensing.

[0071] 3. This invention uses a chemical modification method to bond UIO-66-NH2 onto optical fiber, which reduces modification time and makes film thickness easier to control.

[0072] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0073] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An optical fiber sensor, characterized by, It includes an optical fiber microstructure with an evanescent wave leakage section and an induced sensing layer, wherein the induced sensing layer is used to induce the evanescent wave leakage section to generate a loss mode resonance effect and to bind or adsorb the sensing target. The induced sensing layer is made of UIO-66-NH2 material and is bonded to the outer surface of the evanescent wave leakage part by a chemical modification method.

2. The fiber optic sensor of claim 1, wherein, The optical fiber microstructure also includes a base connected to the evanescent wave leakage section. The base includes a core layer, a cladding layer, and a coating layer arranged radially from the inside to the outside. The evanescent wave leakage section includes the core layer and the cladding layer arranged radially from the inside to the outside.

3. The fiber optic sensor of claim 2, wherein, The shape of the optical fiber microstructure can be any one of tapered, D-shaped, and U-shaped, and the optical fiber microstructure can be single-mode or multimode optical fiber.

4. The fiber optic sensor of claim 1, wherein, The refractive index of the induced sensing layer is greater than the refractive index of the evanescent wave leakage part.

5. The fiber optic sensor of claim 4, wherein, The outer surface of the evanescent wave leak is modified with hydroxyl groups, and the induced sensing layer is combined with the hydroxyl groups of the evanescent wave leak through amino groups.

6. The fiber optic sensor of claim 5, wherein, The particle diameter of the induced sensing layer is 300nm to 500nm.

7. A method of manufacturing an optical fiber sensor according to any one of claims 1 to 6, characterized in that, The method includes: S10, providing an optical fiber microstructure, the optical fiber microstructure including an evanescent wave leakage section; S20, the induced sensing layer is bonded to the outer surface of the evanescent wave leakage part by a chemical modification method; The induced sensing layer is made of UIO-66-NH2 material. The induced sensing layer is used to induce the loss mode resonance effect in the evanescent wave leakage part and to bind or adsorb the sensing target.

8. The method of claim 7, wherein the optical fiber sensor is prepared by the steps of: The S20 step specifically includes: S201, after uniformly mixing the metal salt, organic ligand and solvent, the mixture is heated and cooled to room temperature to obtain the synthesized product. The synthesized product is then centrifuged to obtain the supernatant and precipitate. The precipitate is then vacuum dried to obtain the metal-organic framework powder. S202, the metal-organic framework powder is mixed with distilled water and then subjected to ultrasonic treatment to obtain a suspension; S203, the evanescent wave leakage part of the optical fiber microstructure is soaked in piranha solution, and after drying, the evanescent wave leakage part is placed in the suspension until the outer surface of the evanescent wave leakage part is bonded with the induced sensing layer.

9. The method of claim 7, wherein the optical fiber sensor is prepared by the steps of: In step S201: the metal salt is zirconium oxychloride, the organic ligand is 2-aminoterephthalic acid, and the temperature of the heat treatment is 100℃~140℃.

10. An optical fiber sensing system characterized by, Includes a light source, a spectrometer, and a fiber optic sensor as described in any one of claims 1 to 6; One end of the fiber optic sensor is connected to the light source, and the other end of the fiber optic sensor is connected to the spectrometer.

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