Gain-type fiber-optic surface plasmon sensor and its detection sensing system

Abstract

The application discloses a gain type optical fiber surface plasmon sensor and a detection sensing system thereof, and comprises a multimode optical fiber with an optical fiber end face at one end, which comprises a noble metal layer, a plasmon active layer and a perfect absorber array from outside the optical fiber end face in sequence; wherein the noble metal layer is solidified on the optical fiber end face of the multimode optical fiber; the plasmon active layer is solidified on the upper surface of the noble metal layer; and the perfect absorber array is solidified on the upper surface of the plasmon active layer and is composed of a plurality of regularly arranged cross-shaped nanometer gold units. The plasmon sensor of the application can produce strong local surface plasmon resonance at the absorption wavelength by using the MIM perfect absorber composed of metal-dielectric layer-metal, and at this time, the incident light is effectively captured in the middle layer, so that the incident light has enough time to dissipate through the ohmic loss of the gold film and the cross-shaped nanometer gold array, thereby achieving the purpose of perfect absorption.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fiber surface plasmon resonance sensing, and particularly relates to a gain type optical fiber surface plasmon sensor and a detection sensing system thereof. BACKGROUND

[0002] Surface plasmon is a phenomenon of collective resonance of free electrons induced by incident light on metal micro-nano structures, which is mainly divided into two modes: propagating surface plasmon and localized surface plasmon. The carrier of surface plasmon is usually a metal nano structure, and the light field can be localized in the nanometer scale region on the metal surface, thereby enhancing the interaction between light and matter, and thus being widely used in the sensing field. Among them, the optical fiber-based surface plasmon sensor has attracted more and more attention due to its high sensitivity, compact structure, fast response speed, and anti-electromagnetic interference, and has been widely used in the fields of biomarker detection, food allergen screening, environmental monitoring, medical diagnosis, etc. However, the performance of the traditional optical fiber surface plasmon sensor has been difficult to meet the needs of detection accuracy, detection repeatability and anti-interference ability in actual application. Therefore, the performance improvement method of the optical fiber surface plasmon sensor is one of the research hotspots in this field in recent years.

[0003] The metal-dielectric layer-metal (MIM) perfect absorber is composed of a top nano array, a middle dielectric layer and a bottom reflection layer. The significant magnetic resonance produced by the opposite potential displacement vectors of the top nano array and the bottom reflection layer and the electric dipole resonance produced by the charge aggregation of the top array structure and the image charge coupling work together to produce perfect absorption. At this time, the light is effectively captured in the middle layer, so that the light has enough time to dissipate through the ohmic loss of the upper and lower metal layers, thereby achieving the purpose of perfect absorption. At the same time, under the appropriate combination of the size and period of the metal nano array, the localized surface plasmon resonance in the array and the array Rayleigh anomaly coupling excite surface lattice resonance, which well confines the incident light energy in the array structure, thereby effectively suppressing the radiation loss of the system and significantly increasing the localized field strength, thereby having an ultra-narrow plasmon resonance width. Therefore, by optimizing the structural parameters of the MIM, an absorption spectrum with perfect absorption and extremely narrow linewidth can be realized.

[0004] CN107579354A discloses a switchable wideband terahertz wave perfect absorber based on a double-resonance ring structure. The invention provides a switchable wideband terahertz wave perfect absorber based on a double-resonance ring structure, including a bottom metal layer, a first dielectric layer, a first metal micro-nano structure layer, a second dielectric layer, and a second metal micro-nano structure layer, wherein the first dielectric layer and the first metal micro-nano structure layer include a vanadium dioxide layer. The invention realizes wide-spectrum perfect absorption of terahertz waves, and also utilizes the phase change property of vanadium dioxide with temperature change to realize switchable perfect absorption of terahertz waves in two wide frequency bands. CN208636211U discloses an optical fiber sensor including a transition layer and a nano metal array. The optical fiber sensor end is provided with a nano gold hole array, and the refractive index of the optical fiber end face can be accurately determined by the spectral peak shift of the spectrum. However, the nano gold hole and the micro-nano structure layer of the two structures are complex to prepare, and the detection precision is not high.

[0005] To this end, an optimization model is considered to be established by comprehensively considering indexes such as localized surface plasmon resonance, surface lattice resonance and MIM structure characteristics, so as to solve the problems of low sensitivity, small absorption intensity and wide half-peak full width of the traditional optical fiber surface plasmon sensor by using a two-photon 3D printing technology. SUMMARY

[0006] The present application aims to overcome the deficiencies in the prior art and proposes a gain-type optical fiber surface plasmon sensor and a detection sensing system thereof. The plasmonic sensor sequentially includes a noble metal layer, a plasmonic active layer and a perfect absorber array on a flat optical fiber end face. The metal-dielectric layer-metal (MIM) structure produces strong localized surface plasmon resonance at the absorption wavelength, the local electric field of the metal and the nano array surface is significantly enhanced, and the sensor sensitivity is improved. At this time, the incident light is effectively captured in the plasmonic active layer located in the middle layer, so that the incident light has enough time to dissipate through the ohmic loss of the noble metal layer and the perfect absorber array, thereby achieving the purpose of perfect absorption. The scattered light of each cross-shaped nano gold particle in the perfect absorber array enters the array plane and has the same phase as the plasmonic resonance excited by the incident light of the adjacent particles, surface lattice resonance is excited, the surface lattice resonance can strengthen the resonance between adjacent particles and offset the radiation damping of the single particle response, the absorption rate and the local electric field around the array are significantly enhanced, and the absorption peak of the resonance spectrum is significantly narrowed.

[0007] The first aspect of the present application is to propose a gain-type optical fiber surface plasmon sensor, which includes a multi-mode optical fiber. One end surface of the multi-mode optical fiber is ground flat, and the ground flat end face is an optical fiber end face. The optical fiber end face outwardly includes a noble metal layer, a plasmonic active layer and a perfect absorber array in sequence. The noble metal layer is solidified on the optical fiber end face of the multi-mode optical fiber.

[0008] The plasmonic active layer is solidified on the upper surface of the noble metal layer;

[0009] The perfect absorber array is solidified on the upper surface of the plasmonic active layer; the perfect absorber array is composed of a plurality of regularly arranged cross-shaped gold nanometer units; wherein the arrangement of the gold nanometer units in the perfect absorber array is respectively dispersed along the X-axis and Y-axis with the center of the plasmonic active layer as the center.

[0010] The perfect absorber array at the end of the plasmonic sensor can produce localized surface plasmon resonance, which can change the absorption and reflection wavelength according to the refractive index of the surface.

[0011] Further, the gold nanometer units in the perfect absorber array are arranged in a rectangular array, the spacing between each gold nanometer unit is 2400 nm, the height of the gold nanometer unit is 80 nm, the width w = 40 nm, and the length a = 400 nm.

[0012] Further, the target material for preparing the noble metal layer is selected from gold or silver.

[0013] Further, the target material for preparing the plasmonic active layer is selected from one of the following: purple phosphorus, tungsten diselenide and tungsten disulfide.

[0014] Further, the preparation of the perfect absorber array comprises the following steps:

[0015] A femtosecond laser pulse system is used as an energy source, the center of the plasmonic active layer is used as the starting position for printing, and a 3D printing technology is used to plate a plurality of regularly arranged cross-shaped gold nanometer units on the upper surface of the prepared plasmonic active layer to form a perfect absorber array.

[0016] The second aspect of the present application is to propose a detection sensing system comprising the plasmonic sensor, comprising: a broadband light source, a Y-shaped jumper, the plasmonic sensor, a spectrum analyzer and a computer; the broadband light source is connected to the end of the plasmonic sensor without a fiber end face and the spectrum analyzer through the Y-shaped jumper, the spectrum analyzer is connected to the computer through a data interface, and the fiber end face of the plasmonic sensor faces the solution to be measured; wherein the plasmonic sensor is fixed on a pulling film coating machine, and the pulling film coating machine is used to make the plasmonic sensor contact with the solution to be measured to realize detection; wherein the plasmonic sensor can realize the detection of a spectral line with a full width at half maximum less than or equal to 30 nm.

[0017] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0018] 1. The gain-type fiber surface plasmon resonance sensor of the present invention utilizes the MIM perfect absorber composed of metal-dielectric-layer-metal (MIM) to generate strong local surface plasmon resonance at the absorption wavelength, which significantly enhances the local electric field on the surface of the gold film and the nanoarray, thereby improving the sensor sensitivity; and at this time, the incident light is effectively trapped in the intermediate layer, allowing the incident light sufficient time to dissipate through the ohmic loss of the gold film and the cross-shaped gold nanoarray, thus achieving the purpose of perfect absorption;

[0019] 2. When the size and period of the perfect absorber array of the cross-shaped gold nanostructure are appropriately combined, the scattered light of each cross-shaped gold nanoparticle enters the array plane and is in phase with the plasmon resonance excited by the incident light of the adjacent particles, thus exciting the surface lattice resonance. The surface lattice resonance can enhance the resonance between adjacent particles and cancel the radiation damping of the response of a single particle. At the same time, the absorptivity and the local electric field around the array are significantly enhanced, resulting in a significant narrowing of the absorption peak of the resonance spectrum.

[0020] 3. The end-face reflective fiber optic sensor structure formed by this invention has greater convenience for detection compared with the transmission-type fiber optic sensor structure.

[0021] In summary, the gain-type fiber surface plasmon sensor described in this invention has advantages such as high detection accuracy, high sensitivity, and high quality factor, and achieves an absorption spectrum with perfect absorption and extremely narrow linewidth. It can be used in many fields such as industry, agriculture, military, national defense, and biology. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the gain-type fiber surface plasmon sensor described in this invention.

[0023] Figure 2 for Figure 1 The cross-sectional view of the sensor shown;

[0024] Figure 3 for Figure 1 Top view of the nano-gold unit in the image;

[0025] Figure 4 for Figure 1 Top view;

[0026] Figure 5 This is a schematic diagram of the structure of the detection sensing system;

[0027] Figure 6 The image shows the resonance spectra of solutions with different refractive indices measured by the plasmonic sensor in this embodiment.

[0028] Figure 7 This is the sensitivity fitting curve of the measurement results of the plasmon sensor in the embodiment.

[0029] In the picture:

[0030] 1: Multimode fiber; 2: Fiber end face; 3: Noble metal layer

[0031] 4: Plasmon active layer; 5: Perfect absorber array; 6: Gold nanounits

[0032] 1': Broadband light source in the ultraviolet to visible light band 2': Y-type jumper

[0033] 3': Plasmon Sensor; 4': Spectrometer

[0034] 5': Computer; 6': Lifting coating machine Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments described are only for explanation and illustration of the present invention and are not intended to limit the present invention.

[0036] like Figures 1-2 As shown, a gain-type fiber optic surface plasmon resonance (SPR) sensor includes a multimode fiber 1 with a core diameter of 200 μm and a cladding diameter of 230 μm. One end surface of the multimode fiber 1 is polished flat by a polishing wheel, and this polished end face is the fiber end face 2. From the fiber end face 2 outwards, it sequentially includes a noble metal layer 3, a plasmon active layer 4, and a perfect absorber array 5. The noble metal layer 3 is a dense and flat gold film with a thickness of 70 nm, solidified on the fiber end face of the multimode fiber. The plasmon active layer 4 is a purple phosphorus layer with a thickness of 10 nm, solidified on the noble metal layer 3. The perfect absorber array 5 is solidified on the plasmon active layer 4, as shown in the image. Figures 3-4 As shown, the array consists of multiple cross-shaped gold nanoparticles arranged in a rectangular array. The array is regularly and orderly arranged, with each gold nanoparticle 6 spaced 2400 nm apart. The gold nanoparticles in the perfect absorber array 5 are arranged radiating outwards along the X and Y axes, centered on the point of the plasmon active layer 4. Each gold nanoparticle has a height of 80 nm, a width w = 40 nm, and a length a = 400 nm.

[0037] The fabrication method of the perfect absorber gain-type fiber surface plasmon sensor includes the following steps:

[0038] Step 1: Pre-processing multimode fiber 1

[0039] Select a multimode fiber with a core diameter of 200μm and a cladding diameter of 230μm, cut it to a suitable length, and grind the surface of one end of the multimode fiber with a polishing wheel to form a flat fiber end face 2.

[0040] Step 2: Plating a precious metal layer 3

[0041] The pretreated multimode fiber from step one is fixed onto a fixture and placed in a magnetron sputtering apparatus. A gold target is sputtered onto the upper surface of the flat fiber end face 2, thereby forming a dense and flat noble metal layer 3 with a thickness of 70 nm. The sputtering power is set to 30 W, the sputtering time to 10 min, and the vacuum degree to 10. -4 bar;

[0042] Step 3: Depositing the plasmonic active layer 4

[0043] The multimode optical fiber 1 prepared in step two was placed on a workpiece tray and placed in a vacuum evaporation machine. The prepared purple phosphorus target was placed in the instrument, and the vacuum was evacuated to 7 × 10⁻⁶. -4 Pa, using the evaporation barrier coating mode, a purple phosphorus layer with a thickness of 10 nm is deposited on the upper surface of the noble metal layer 3 in step two, thereby forming a plasmonic active layer 4.

[0044] Step 4: Depositing a perfect absorber array 5

[0045] A perfect absorber array was deposited on the plasmonic active layer of the multimode fiber prepared in step three using two-photon 3D printing technology. A femtosecond laser pulse system was used as the energy source, and a layer-by-layer scanning and stacking method was adopted. The center of the plasmonic active layer 4 was used as the printing start position by a CCD monitoring system. The cross-shaped gold nanoarray was sliced ​​layer by layer by 3D printing control software, and control code was generated to control the photopolymerization reaction process at the micro-nano scale, thereby forming a perfect absorber array 5, namely a cross-shaped gold nanoarray with spaced distribution. The maximum size of the horizontal / vertical direction is 400 nm; the minimum size of the horizontal / vertical direction is 40 nm; the height is 80 nm; and the horizontal / vertical array spacing is 2400 nm.

[0046] This completes the fabrication of a perfect absorber gain-type fiber surface plasmon resonance sensor. The perfect absorber array 5 at the end of the fabricated plasmon sensor can generate localized surface plasmon resonance, and its absorption and reflection wavelengths will change according to the refractive index of its surface.

[0047] In use, the gain-type fiber optic surface plasmon resonance sensor is applied to a detection sensing system. For example... Figure 5As shown, the detection sensing system includes: a broadband light source 1' with a wavelength in the ultraviolet to visible light band, a Y-type jumper 2', the plasmonic sensor 3', a spectrometer 4', and a computer 5'. The broadband light source 1' is connected to the end of the plasmonic sensor 3' without the optical fiber end face 2 and the spectrometer 4' via the Y-type jumper 2'. The spectrometer 4' is connected to the computer 5' via a data interface. The optical fiber end face 2 of the plasmonic sensor 3' faces the solution to be tested. The plasmonic sensor 3' is fixed on a dip coating machine 6', and the dip coating machine 6' is used to bring the plasmonic sensor 3' into contact with the solution to be tested for detection.

[0048] When the detection and sensing system is working, the light from the broadband light source 1' is coupled into the plasmonic sensor 3' from the side without the fiber end face 2 via the Y-type jumper 2'. The evanescent field energy of the light in the multimode fiber 1 is coupled into the surface plasmons generated by the noble metal layer 3, the plasmonic active layer 4, and the local surface plasmons generated by the perfect absorber array 5. The MIM perfect absorber composed of gold film-purple phosphorus layer-cross-shaped gold nanoarray can generate strong local surface plasmon resonance at the absorption wavelength. Due to the loss of light energy, a resonance valley appears in the sensor transmission spectrum. The resonance wavelength of surface plasmon resonance (SPR) is closely related to parameters such as the dielectric constant of the metal film, the concentration of the test solution, and the refractive index. Therefore, under the condition that only the test solution is changed while other parameters remain unchanged, the refractive index of the sensor surface changes, the phase matching condition changes, and the resonance valley moves. By exploring the movement law of the resonance valley, the refractive index solution can be detected.

[0049] Experiments were conducted using the aforementioned perfect absorber gain-type fiber surface plasmon sensor to measure glycerol solutions with different refractive indices:

[0050] The plasmon sensor 3' was used to sequentially detect glycerol solutions with different refractive indices, and the resulting resonance spectra were as follows: Figure 6 As shown. When the plasmonic sensor 3' is inserted into each refractive index solution, a resonance valley immediately appears in the resonance spectrum. After changing the refractive index solution, the position of the resonance valley changes. Note that before each change of refractive index solution, the plasmonic sensor 3' should be immersed in a 95% alcohol solution to remove any residue from the previous refractive index solution. Figure 6 It can be seen that the resonance valley with a refractive index of 1.331 has a smaller full width at half maximum (FWHM) and the absorption valley of the sensor is deeper, which has a significant advantage compared with traditional fiber plasmon sensors. This indicates that the plasmon sensor 3' can achieve the detection of spectral lines with a FWHM of less than or equal to 30 nm.

[0051] The lowest point of the resonance valley corresponding to each refractive index solution, i.e., the resonance wavelength, is subjected to a quadratic fitting with the corresponding refractive index. The slope of the tangent line at each refractive index point of the quadratic fitting curve is taken as the sensor sensitivity at that refractive index point. The average value of the sensitivity at all refractive index points is taken as the average sensitivity of the sensor. The specific results are as follows: Figure 7 As shown, the average sensitivity of the sensor is 3172 nm / RIU when the refractive index ranges from 1.3331 to 1.3431 RIU.

[0052] The perfect absorber gain type fiber surface plasmon sensor proposed in this invention has higher detection accuracy, sensitivity and quality factor for detecting low refractive index solutions, and can be widely used in many fields such as industry, agriculture, military, national defense and biology.

[0053] Although preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these are within the scope of protection of the present invention.

Claims

1. A gain-type fiber surface plasmon resonance sensor, comprising a multimode fiber (1), wherein one end surface of the multimode fiber (1) is ground flat, and the ground end face is the fiber end face (2); characterized in that, The fiber end face (2) comprises, in sequence, a noble metal layer (3), a plasmonic active layer (4), and a perfect absorber array (5); wherein, the noble metal layer (3) is solidified on the fiber end face (2) of the multimode fiber (1); The plasmon active layer (4) is solidified on the upper surface of the noble metal layer (3); The perfect absorber array (5) is solidified on the upper surface of the plasmon active layer (4); the perfect absorber array (5) is composed of multiple regularly arranged cross-shaped gold nanounits; wherein, the arrangement of the gold nanounits (6) in the perfect absorber array (5) is radiating outwards along the X-axis and Y-axis with the center of the plasmon active layer (4) as the center; the perfect absorber array (5) has local surface plasmon resonance characteristics and can change the absorption and reflection wavelength according to the refractive index of its surface; moreover, the noble metal layer (3), the plasmon active layer (4) and the perfect absorber array (5) together constitute a metal-dielectric layer-metal structure; The target material for preparing the plasmon active layer (4) is selected from one of the following: purple phosphorus, tungsten diselenide and tungsten disulfide.

2. The gain-type fiber optic surface plasmon sensor according to claim 1, characterized in that, The gold nanoparticles in the perfect absorber array (5) are arranged in a rectangular array. The spacing between each gold nanoparticle (6) is 2400 nm. The height of each gold nanoparticle is 80 nm, the width is w=40 nm, and the length is a=400 nm.

3. The gain-type fiber optic surface plasmon sensor according to claim 1, characterized in that, The target material for preparing the noble metal layer (3) is selected from gold or silver.

4. The gain-type fiber optic surface plasmon sensor according to claim 1, characterized in that, The preparation of the perfect absorber array (5) includes the following steps: Using a femtosecond laser pulse system as the energy source, and taking the center of the plasmonic active layer as the starting position for printing, multiple regularly arranged cross-shaped gold nanounits are deposited on the surface of the prepared plasmonic active layer using 3D printing technology to form a perfect absorber array.

5. A detection sensing system, characterized in that, include: The system comprises a broadband light source (1'), a Y-type jumper (2'), a plasmonic sensor (3') as described in claim 1, a spectrometer (4'), and a computer (5'); the broadband light source (1') is connected to the end of the plasmonic sensor (3') without the fiber end face (2) and the spectrometer (4') respectively via the Y-type jumper (2'); the spectrometer (4') is connected to the computer (5') via a data interface; the fiber end face (2) of the plasmonic sensor (3') faces the solution to be tested; wherein the plasmonic sensor (3') is fixed on a dip coating machine (6'), and the dip coating machine (6') is used to bring the plasmonic sensor (3') into contact with the solution to be tested for detection.

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