Optical fiber sensor, preparation method thereof and optical fiber sensing system

Abstract

The invention provides an optical fiber sensor, a preparation method thereof and an optical fiber sensing system.The optical fiber sensor comprises an optical fiber microstructure with an evanescent wave leakage part and an induction sensing layer, the induction sensing layer is used for inducing the evanescent wave leakage part to generate a loss mode resonance effect and conducting combination or adsorption on a sensing target, the induction sensing layer is made of a UIO-66-NH2 material, and the induction sensing layer is combined to the outer surface of the evanescent wave leakage part through a chemical modification method; the induction sensing layer of the metal organic framework film is combined on the outer surface of the evanescent wave leakage part in the optical fiber microstructure through a chemical modification method, and the induction sensing layer can induce the evanescent wave leakage part to generate a loss mode resonance effect and can also combine or adsorb a sensing target. Therefore, a sensing film corresponding to the target detection object does not need to be coated during subsequent biological sensing or other sensing, and the manufacturing cost of the optical fiber sensor based on the LMR effect is further reduced.

Description

Technical Field

[0001] The present invention relates to the field of optical sensing technology, and in particular to an optical fiber sensor and a preparation method thereof, and an optical fiber sensing system. Background Art

[0002] When the propagation constant of the waveguide layer is close to that of the high-refractive-index film layer, and there is a large overlap between the loss mode field in the film and the mode field in the waveguide, the light in the waveguide will be coupled to the high-refractive-index film in large quantities, causing a large amount of energy loss in the waveguide, and finally an obvious loss trough will appear in the transmission spectrum. This is loss mode resonance (LMR).

[0003] The occurrence of loss mode resonance requires coating the optical waveguide with a high refractive index film. When the mode in the optical waveguide leaks into the film and is stably transmitted in the film, the mode in the optical waveguide couples with the mode in the film, inducing a loss mode resonance effect. Fiber optic sensors based on the loss mode resonance effect have the advantages of high sensitivity, label-free detection, portability, low cost, and real-time monitoring, and have shown advantages in biosensing applications. Currently, the films used to induce the loss mode resonance effect are generally divided into semiconductor materials and polymer materials. Coating these materials on optical fibers usually requires expensive equipment, and subsequent biosensing or other sensing requires coating of a sensing film corresponding to the target detection object, which undoubtedly increases the production time and cost.

[0004] Therefore, there is an urgent need for an optical fiber sensor and a preparation method thereof, and an optical fiber sensing system to solve the above technical problems. Summary of the invention

[0005] The object of the present invention is to provide an optical fiber sensor and a preparation method thereof, and an optical fiber sensing system, so as to solve the technical problem that the manufacturing cost of the existing optical fiber sensors based on the LMR effect is too high.

[0006] In order to solve the above technical problems, the present invention provides an optical fiber sensor, comprising an optical fiber microstructure having an evanescent wave leakage part and an induced sensing layer, wherein the induced sensing layer is used to induce the evanescent wave leakage part to produce a loss mode resonance effect and to bind or adsorb a sensing target; The induced sensing layer is made of UIO-66-NH2 material, and the induced sensing layer is combined with the outer surface of the evanescent wave leakage part by a chemical modification method.

[0007] Preferably, the optical fiber microstructure also includes a base connected to the evanescent wave leakage part, the base includes a core layer, a cladding and a coating layer arranged in sequence from the inside to the outside along the radial direction, and the evanescent wave leakage part includes a core layer and a cladding arranged in sequence from the inside to the outside along the radial direction.

[0008] Preferably, the shape of the optical fiber microstructure is any one of a cone shape, a D shape and a U shape, and the optical fiber microstructure is a single-mode optical fiber or a multi-mode optical fiber.

[0009] Preferably, the refractive index of the induced sensing layer is greater than the refractive index of the evanescent wave leakage portion.

[0010] Preferably, the outer surface of the evanescent wave leakage part is modified with hydroxyl groups, 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.

[0011] Preferably, the particle diameter of the inductive sensing layer is 300nm-500nm.

[0012] Accordingly, the present invention also provides a method for preparing the optical fiber sensor as described above, the method comprising: S10, providing an optical fiber microstructure, wherein the optical fiber microstructure includes an evanescent wave leakage portion; S20, bonding the induced sensing layer to the outer surface of the evanescent wave leakage part by a chemical modification method; Among them, the induced sensing layer is UIO-66-NH2 material, and the induced sensing layer is used to induce the evanescent wave leakage part to produce a loss mode resonance effect and to bind or adsorb the sensing target.

[0013] Preferably, step S20 specifically includes: S201, mixing the metal salt, the organic ligand and the solvent uniformly and then heating them, cooling them to room temperature to obtain a synthesis product, then centrifuging the synthesis product to obtain a supernatant and a precipitate, and vacuum drying the precipitate to obtain a metal organic framework powder; S202, mixing the metal organic framework powder with distilled water and then performing ultrasonic treatment to obtain a suspension; S203, soaking the evanescent wave leakage part of the optical fiber microstructure with piranha solution, and placing the evanescent wave leakage part into the suspension after drying, until the outer surface of the evanescent wave leakage part is combined with the induced sensing layer.

[0014] Preferably, in step S201: the metal salt is zirconium oxychloride, the organic ligand is 2-aminoterephthalic acid, and the heating treatment temperature is 100°C to 140°C.

[0015] Accordingly, the present invention also provides an optical fiber sensing system, comprising a light source, a spectrometer and an optical fiber sensor as described above; One end of the optical fiber sensor is connected to the light source, and the other end of the optical fiber sensor is connected to the spectrometer.

[0016] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides an optical fiber sensor and a preparation method thereof, and an optical fiber sensing system. The optical fiber sensor comprises an optical fiber microstructure having an evanescent wave leakage part and an induced sensing layer, the induced sensing layer is used to induce the evanescent wave leakage part to produce a loss mode resonance effect, and to bind or adsorb the sensing target, wherein the induced sensing layer is a UIO-66-NH2 material, and the induced sensing layer is combined with the outer surface of the evanescent wave leakage part by a chemical modification method; the optical fiber sensor provided by the present invention combines the induced sensing layer of the UIO-66-NH2 material with the outer surface of the evanescent wave leakage part in the optical fiber microstructure by a chemical modification method, the induced sensing layer can not only induce the evanescent wave leakage part to produce a loss mode resonance effect, but also can bind or adsorb the sensing target, so that there is no need to coat a sensing film corresponding to the target detection object when performing subsequent biological sensing or other sensing, further reducing the manufacturing cost of the optical fiber sensor based on the LMR effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A process flow chart of a method for preparing an optical fiber sensor provided by an embodiment of the present invention; Figure 2 Schematic diagram of the preparation process of the optical fiber sensor with UIO-66-NH2 induced LMR effect provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] In a first aspect, the present invention provides an optical fiber sensor, comprising an optical fiber microstructure having an evanescent wave leakage portion and an induced sensing layer, wherein the induced sensing layer is used to induce the evanescent wave leakage portion to produce a loss mode resonance effect and to bind or adsorb a sensing target; The induced sensing layer is made of UIO-66-NH2 material, and the induced sensing layer is combined with the outer surface of the evanescent wave leakage part by a chemical modification method.

[0020] In the embodiment of the present invention, the optical fiber microstructure with the evanescent wave leakage part is a key component of the sensor. Conventional optical fibers mainly rely on total internal reflection to transmit optical signals, while this specially designed optical fiber introduces the evanescent wave leakage part, so that part of the light energy can leak to the outside of the optical fiber in the form of evanescent waves. This design breaks the limitations of conventional optical fibers and provides a channel for interaction with the external environment, thereby realizing the detection of sensing targets in the surrounding environment.

[0021] Specifically, the evanescent wave is an electromagnetic wave that propagates at the interface of two different media, and its intensity decays exponentially with the increase of the distance from the interface. In the optical fiber sensor, the existence of the evanescent wave leakage part enables the optical signal in the optical fiber to be in closer contact with the external environment. When the evanescent wave interacts with the external induced sensing layer, a series of special optical effects will be generated, which provides the basis for realizing high-sensitivity sensing.

[0022] Specifically, the optical fiber microstructure also includes a base connected to the evanescent wave leakage part, the base includes a core layer, a cladding and a coating layer arranged in sequence from the inside to the outside along the radial direction, and the evanescent wave leakage part includes a core layer and a cladding arranged in sequence from the inside to the outside along the radial direction.

[0023] Furthermore, the main function of the coating layer is to protect the core layer and cladding of the optical fiber from interference from the external environment, such as preventing mechanical damage, chemical corrosion, etc. However, for the evanescent wave leakage part, its purpose is to allow the evanescent wave of light to effectively leak to the outside of the optical fiber to interact with the surrounding environment. The coating layer will hinder the direct contact between the evanescent wave and the external environment. Because the optical properties and structure of the coating material will reflect and scatter the evanescent wave, the energy of the evanescent wave leaking into the external environment is reduced, thereby reducing the efficiency of the interaction between the optical fiber sensor and the external sensing target.

[0024] Preferably, the shape of the optical fiber microstructure is any one of a cone, a D-shape and a U-shape, and the optical fiber microstructure is a single-mode optical fiber, a multi-mode optical fiber or a special optical fiber.

[0025] In an embodiment of the present invention, the UIO-66-NH2 material used as the induced sensing layer has many unique properties. The UIO-66-NH2 material is a metal organic framework material, which is a porous material formed by self-assembly of metal ions or metal clusters and organic ligands through coordination bonds, and has a high degree of crystallinity and a regular pore structure. This material has an extremely high specific surface area and can provide a large number of active sites for efficient binding or adsorption with the sensing target. At the same time, its adjustable pore size and chemical properties allow for customized design for different sensing requirements.

[0026] In the embodiment of the present invention, the UIO-66-NH2 material is bonded to the outer surface of the evanescent wave leakage part by a chemical modification method, ensuring the close bonding between the induced sensing layer and the optical 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.

[0027] In an embodiment of the present invention, the UIO-66-NH2 material can induce a loss mode resonance effect in the evanescent wave leakage part. This effect is caused by 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 energy of the light to be absorbed or scattered at a specific frequency, thereby generating a resonance phenomenon. This resonance effect causes a significant change in 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.

[0028] Specifically, the UIO-66-NH2 material has a highly developed pore structure, and these pores form a huge internal surface area. When prepared into a film form, this high specific surface area characteristic is still retained. The high specific surface area means that there are 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 and attach them to the inner surface of the pores. At the same time, the porosity allows a large number of pore channels to exist inside the film, through which the sensing target can enter the interior of the film and be adsorbed. This porous structure not only increases the contact area for adsorption, but also promotes the adsorption of the sensing target through physical processes such as capillary action and molecular diffusion, thereby improving the adsorption capacity of the sensing target.

[0029] Furthermore, the metal ions in the UIO-66-NH2 material have 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 the binding of the sensing target. In addition to metal ions, there are some other active sites in the metal organic framework film, such as unsaturated organic ligands, defect sites, etc. These active sites can interact with the sensing target and further enhance the adsorption capacity of the sensing target. For example, unsaturated organic ligands can have a π-π stacking effect with the sensing target to increase the stability of adsorption.

[0030] In an embodiment of the present invention, the refractive index of the induced sensing layer is greater than the refractive index of the evanescent wave leakage portion. When the refractive index of the induced sensing layer is greater than the refractive index of the evanescent wave leakage portion, according to the electromagnetic field theory in optics, at the interface between the two media, the evanescent wave of light can be more effectively coupled from the evanescent wave leakage portion of the optical fiber to the induced sensing layer. This enhanced coupling effect is conducive to a stronger interaction between the induced sensing layer and the evanescent wave, thereby more easily inducing the loss mode resonance (LMR) effect.

[0031] In an embodiment of the present invention, the outer surface of the evanescent wave leakage part is modified with hydroxyl groups, 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.

[0032] Specifically, the induced sensing layer is made of UIO-66-NH2 material, and the particle diameter of the induced sensing layer is 300nm~500nm.

[0033] Furthermore, UIO-66-NH2 is a metal organic framework (MOF) material with zirconium ions (Zr 4+ ) is the metal center and 2-aminoterephthalic acid is the organic ligand. These metal ions and organic ligands are connected to each other through coordination bonds to form a highly ordered three-dimensional network structure. UIO-66-NH2 material can induce LMR, and its particle diameter is 300nm~500nm, which is suitable for biosensing, gas sensing, etc.

[0034] Accordingly, see Figure 1 The present invention also provides a method for preparing the optical fiber sensor as described above, the method comprising: S10, providing an optical fiber microstructure, wherein the optical fiber microstructure includes an evanescent wave leakage portion.

[0035] Specifically, step S10 also includes: An optical fiber microstructure is provided, which includes an evanescent wave leakage part and a base connected to the evanescent wave leakage part, the base includes a core layer, a cladding and a coating layer arranged in sequence from the inside to the outside along the radial direction, and the evanescent wave leakage part includes a core layer and a cladding arranged in sequence from the inside to the outside along the radial direction.

[0036] Preferably, the shape of the optical fiber microstructure is any one of a cone shape, a D shape and a U shape, and the optical fiber microstructure is a single-mode optical fiber or a multi-mode optical fiber.

[0037] S20, combining the induced sensing layer onto the outer surface of the evanescent wave leakage part by a chemical modification method.

[0038] Specifically, step S20 also includes: S201, mixing the metal salt, the organic ligand and the solvent uniformly and then heating them, cooling them to room temperature to obtain a synthesis product, then centrifuging the synthesis product to obtain a supernatant and a precipitate, and vacuum drying the precipitate to obtain a metal organic framework powder; S202, mixing the metal organic framework powder with distilled water and then performing ultrasonic treatment to obtain a suspension; S203, soaking the evanescent wave leakage part of the optical fiber microstructure with piranha solution, and placing the evanescent wave leakage part into the suspension after drying, until the outer surface of the evanescent wave leakage part is combined with the induced sensing layer.

[0039] Preferably, in step S201: the metal salt is zirconium oxychloride, the organic ligand is 2-aminoterephthalic acid, and the heating treatment temperature is 100°C to 140°C; at this time, the induced sensing layer obtained in step S203 is UIO-66-NH2 material.

[0040] Accordingly, the present invention also provides an optical fiber sensing system, comprising a light source, a spectrometer and an optical fiber sensor as described above; One end of the optical fiber sensor is connected to the light source, and the other end of the optical fiber sensor is connected to the spectrometer.

[0041] The technical solution of the present application is now described in conjunction with specific embodiments.

[0042] Embodiment 1: Embodiment 1 of the present invention provides a U-shaped optical fiber sensor for measuring the refractive index of an unknown solution. The U-shaped optical fiber sensor comprises an optical fiber microstructure having an evanescent wave leakage portion and an induced sensing layer. The induced sensing layer is a UIO-66-NH2 material. The induced sensing layer is bonded to the outer surface of the evanescent wave leakage portion by a chemical modification method.

[0043] See also Figure 1 to Figure 2 , Figure 2 The schematic diagram of the preparation process of the optical fiber sensor with LMR effect induced by UIO-66-NH2 provided in Example 1 of the present invention; specifically, the preparation process of the above-mentioned U-shaped optical fiber sensor is as follows: Step 1: first take a section of multimode optical fiber, the diameter of the core layer is 62.5μm, and the diameter of the cladding layer is 125μm; then, remove the coating layer from the middle part of the multimode optical fiber, and then use the outer flame of an alcohol lamp to heat it to form a U-shaped optical fiber microstructure, with a U-shaped radius of 1mm to 5mm. At this time, the U-shaped part is the evanescent wave leakage part, and the two ends of the optical fiber are cut flat for use; Step 2, synthesizing UIO-66-NH2 powder: first, use an electronic balance to weigh 75 mg of zirconium oxychloride (ZrOCl2) and 50 mg of 2-aminoterephthalic acid (BDC-NH2) and put them into a container bottle, and then weigh 1.25 g of benzoic acid (BA) and put them into a container bottle; add 5 mL of DMF (N,N-dimethylformamide), ultrasonicate for 90 minutes, and transfer the mixed solution into an autoclave; then, place the autoclave in a heating box and heat it at 120°C for 24 hours, and then cool it to room temperature to obtain a synthetic product; then, centrifuge the synthetic product at a centrifugal speed of 8000 r / min and a centrifugal time of 10 minutes, and wash and centrifuge it with DMF and methanol for 3 times respectively to obtain a supernatant and a precipitate; finally, dry the obtained precipitate in a vacuum drying oven at 60°C for 24 hours to obtain UIO-66-NH2 powder, and store it at room temperature for later use; Step 3, prepare UIO-66-NH2 suspension: take 5 mg UIO-66-NH2 particles into 5 mL distilled water, ultrasonicate for 30 min, and obtain UIO-66-NH2 suspension; Step 4, UIO-66-NH2 modified optical fiber: First, prepare piranha solution by mixing concentrated sulfuric acid and hydrogen peroxide solution in a volume ratio of 7:3, soak the U-shaped optical fiber prepared in step 1 in the piranha solution for at least 30 minutes to remove impurities on the optical fiber, and modify the surface of the optical fiber with -OH, and dry the optical fiber with -OH in a natural environment; then, put the U-shaped optical fiber modified with -OH into the UIO-66-NH2 suspension prepared in step 3 for 12 hours to obtain a U-shaped optical fiber sensor.

[0044] Since UIO-66-NH2 carries -NH2 functional groups, it can combine with -OH, so that UIO-66-NH2 particles can be combined with U-shaped optical fibers. Since UIO-66-NH2 has a higher refractive index than optical fibers, it can induce the LMR effect.

[0045] Furthermore, the U-shaped optical fiber sensor is placed in matching liquids with different refractive indices, and then one end of the U-shaped optical fiber is connected to a light source and the other end is connected to a spectrometer. The light emitted by the light source generates a leakage mode when passing through the U-shaped optical fiber sensor, which is mutually coupled with the mode transmitted in UIO-66-NH2 to induce LMR. The spectrometer collects and demodulates the transmitted spectrum and saves the spectral data. The resonance valley of LMR moves toward the long wavelength direction as the refractive index of the matching liquid increases.

[0046] The present invention provides a fiber optic sensor with UIO-66-NH2-induced LMR effect. Compared with the semiconductor films or polymer films currently used to realize LMR, the metal organic framework (MOF) film has porosity and abundant functional groups, and can realize a film that can induce LMR and realize biosensing and gas sensing, etc., and the chemical modification process is simple and highly sensitive.

[0047] Specifically, the UIO-66-NH2 film is coated on the optical fiber microstructure to form a sensing area to induce the LMR effect. The two ends of the optical fiber sensing area are respectively connected to the light source and the spectrometer. When the light wave passes through the optical fiber microstructure, a leakage mode is generated, which is coupled into the UIO-66-NH2 film and propagates in the film, and when the propagation mode meets certain conditions, a leakage mode resonance occurs, namely LMR. The resonant absorption wavelength changes with the external dielectric constant, so the external variables can be detected by detecting the resonance valley.

[0048] Different from the prior art, the present invention has the following beneficial effects: 1. The present invention uses UIO-66-NH2 as the induction film and sensing film of the optical fiber sensor based on the LMR effect, realizing an optical fiber sensor that can both induce LMR and bind or adsorb the sensing target with a thin film, thereby reducing the production cost of the optical fiber sensor based on the LMR effect.

[0049] 2. The UIO-66-NH2 synthesized by the present invention has a large specific surface area and abundant functional groups, and is stable in a liquid environment, and is suitable for biosensing. At the same time, UIO-66-NH2 is a three-dimensional porous material that can adsorb special gas molecules and realize gas sensing.

[0050] 3. The present invention combines UIO-66-NH2 on the optical fiber through a chemical modification method, which reduces the modification time and makes the film thickness easy to control.

[0051] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For matters that are not described in detail in some embodiments, reference may be made to the description in other embodiments.

[0052] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An optical fiber sensor, characterized in that: It comprises an optical fiber microstructure having an evanescent wave leakage part and an induced sensing layer, wherein the induced sensing layer is used to induce the evanescent wave leakage part to produce a loss mode resonance effect and to bind or adsorb a sensing target; Wherein, the induced sensing layer is UIO-66-NH2 material, and the induced sensing layer is combined with the outer surface of the evanescent wave leakage part by a chemical modification method.

2. The optical fiber sensor according to claim 1, characterized in that: The optical fiber microstructure also includes a base connected to the evanescent wave leakage part, the base includes a core layer, a cladding and the coating layer arranged in sequence from the inside to the outside along the radial direction, and the evanescent wave leakage part includes the core layer and the cladding arranged in sequence from the inside to the outside along the radial direction.

3. The optical fiber sensor according to claim 2, characterized in that: The shape of the optical fiber microstructure is any one of a cone, a D-shape and a U-shape, and the optical fiber microstructure is a single-mode optical fiber or a multi-mode optical fiber.

4. The optical fiber sensor according to claim 1, characterized in that: The refractive index of the induced sensing layer is greater than the refractive index of the evanescent wave leakage portion.

5. The optical fiber sensor according to claim 4, characterized in that: The outer surface of the evanescent wave leakage part is modified with hydroxyl groups, and the induced sensing layer is combined with the hydroxyl groups of the evanescent wave leakage part through amino groups.

6. The optical fiber sensor according to claim 5, characterized in that: The particle diameter of the inductive sensing layer is 300nm~500nm.

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

8. The method for preparing an optical fiber sensor according to claim 7, characterized in that: The step S20 specifically includes: S201, mixing the metal salt, the organic ligand and the solvent uniformly and then heating them, cooling them to room temperature to obtain a composite, then centrifuging the composite to obtain a supernatant and a precipitate, and vacuum drying the precipitate to obtain a metal organic framework powder; S202, mixing the metal organic framework powder with distilled water and then performing ultrasonic treatment to obtain a suspension; S203, soaking the evanescent wave leakage part of the optical fiber microstructure with piranha solution, placing the evanescent wave leakage part into the suspension after drying, until the outer surface of the evanescent wave leakage part is combined with the induced sensing layer.

9. The method for preparing an optical fiber sensor according to claim 7, characterized in that: In the step S201: the metal salt is zirconium oxychloride, the organic ligand is 2-aminoterephthalic acid, and the temperature of the heating treatment is 100°C to 140°C.

10. An optical fiber sensing system, characterized in that: It comprises a light source, a spectrometer and the optical fiber sensor according to any one of claims 1 to 6; Wherein, one end of the optical fiber sensor is connected to the light source, and the other end of the optical fiber sensor is connected to the spectrometer.

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