Ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect

Abstract

The utility model discloses a ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect, which comprises a photonic crystal fiber, the photonic crystal fiber comprises a fiber core and a cladding layer coated on the fiber core, and the fiber core is a core air hole positioned in the center of the fiber; three layers of air holes are formed in the cladding, the first layer of air holes comprises ten air holes, and the air holes are arranged in a regular decagon dot matrix on the periphery of the fiber core; the second layer of air holes comprises ten air holes, all the air holes are arranged in a regular decagonal dot matrix mode on the periphery of the first layer of air holes, and the second layer of air holes and the first layer of air holes are arranged in a staggered mode; the third layer of air holes comprises 20 air holes, and the air holes are arranged on the periphery of the second layer of air holes in a regular twenty-side dot matrix; the radius of each air hole is the same as that of the fiber core; and the circle center of the fiber core, the central point of the regular decagon and the central point of the regular twenty-polygon coincide with each other. The sensor provided by the utility model has higher maximum spectral sensitivity and maximum refractive index resolution.

Description

Technical Field

[0001] The utility model relates to the field of optical fiber sensing, and in particular to a ten-core photonic crystal optical fiber refractive index sensor based on plasmon resonance effect. Background Art

[0002] Fiber optic sensing technology is an important branch of current sensing technology. Fiber optic sensors have the advantages of small size, strong anti-electromagnetic interference ability, good electrical insulation performance and high reliability. Photonic crystal fiber has more advantages than traditional optical fiber in the field of fiber optic communication, but the actual process is still far from the theory, so photonic crystal fiber still has a lot of room for improvement in the field of fiber optic communication.

[0003] Photonic Crystal Fiber (PCF) sensors have derived a variety of sensor structure types based on different sensing principles. Among them, the combination of surface plasmon resonance (SPR) technology and PCF technology has received good response in the detection of material concentrations in solutions, gases and other fields, and has application value in medical testing, biosensing and other fields. Sensors based on SPR technology have the advantages of high sensitivity, wide detection range and continuous detection. Researchers have combined PCF and SPR to develop photonic crystal fiber surface plasmon resonance (PCF-SPR) sensors, which have become a research hotspot. Such sensors have a wide range of applications and can measure data such as temperature, refractive index, magnetic field, and biological concentration parameters.

[0004] In PCF-SPR, the relationship between wavelength and loss is used to detect parameters. In the relationship diagram between the loss spectrum and wavelength of the PCF-SPR sensor, the loss spectrum has an obvious resonance peak. The wavelength corresponding to the maximum loss is called the resonance wavelength. The resonance wavelength and the refractive index of the solution to be tested are matched one by one. In the experiment, the refractive index of the solution to be tested can be known by observing the wavelength of the loss spectrum. In addition, the maximum value of the loss is called the resonance intensity, and the corresponding relationship between this intensity and the refractive index can also be used for sensing.

[0005] The invention patent with the publication number CN114252168A discloses a photonic crystal fiber sensor based on the surface plasmon resonance effect, including a photonic crystal fiber, wherein the radial cross section of the photonic crystal fiber is arranged in an array by a plurality of channels, one of the channels in the channel array is set as a sensing channel, a metal film is set on the outer wall of the sensing channel, and a temperature sensitive layer is set on the inner wall of the sensing channel, and the sensing channel is a hollow structure. The invention utilizes the interaction between the incident light wave and the metal material film on the outer wall of the sensing channel (i.e., the outer side of the core) when the total reflection effect of the incident light wave occurs inside the fiber core for transmission, and the surface plasmon resonance phenomenon occurs when the phase matching condition is met, and the output light wave is detected and analyzed at the output port of the optical fiber to realize sensing. By setting a quartz glass support layer on the surface of the temperature sensitive layer, it has high spectral transmission performance, reduces radiation damage, has high heat resistance, has excellent optical performance and excellent transmittance, and thus supports the temperature sensitive layer without affecting the sensing effect. The metal film provided on the outer wall of the sensing channel can cause surface plasma resonance, and in coordination with the temperature sensitive layer, temperature sensing can be achieved by detecting the output light wave. It can be seen that the above invention improves the sensitivity of the sensor and improves its large nonlinear effect by providing a hollow structure sensing channel and a quartz glass support layer. However, the sensor described in the invention will continue to decrease with increasing temperature, and the solid channel loss will continue to decrease, so its detection range is very limited and it is difficult to meet the requirements of wide range temperature detection. Utility Model Content

[0006] The technical problem to be solved by the utility model is to provide a novel structured ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect, the sensor having higher maximum spectral sensitivity and maximum refractive index resolution.

[0007] In order to solve the above technical problems, the utility model adopts the following technical solutions:

[0008] A ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect comprises a photonic crystal fiber, wherein the photonic crystal fiber comprises a core and a cladding coated on the core, wherein:

[0009] The fiber core is a core air hole located in the center of the optical fiber;

[0010] The cladding is provided with a first layer of air holes, a second layer of air holes and a third layer of air holes in sequence from the inside to the outside, the first layer of air holes includes 10 air holes, and each air hole is arranged in a regular decagonal lattice on the periphery of the fiber core; the second layer of air holes includes 10 air holes, and each air hole is arranged in a regular decagonal lattice on the periphery of the first layer of air holes, and the second layer of air holes and the first layer of air holes are arranged in a staggered manner; the third layer of air holes includes 20 air holes, and each air hole is arranged in a regular icosagonal lattice on the periphery of the second layer of air holes; the radius of each air hole is the same as the radius of the fiber core;

[0011] The center of the core, the center point of the regular decagon and the center point of the regular icosagon coincide with each other.

[0012] Preferably, the misalignment angle between the second layer of air holes and the first layer of air holes is 18°.

[0013] Preferably, the radius of the fiber core is 0.5-0.7 μm, and the diameter of each air hole in the first layer of air holes, the second layer of air holes and the third layer of air holes is also 0.5-0.7 μm; further preferably, the radius of the fiber core is 0.5 μm, and the corresponding diameter of each air hole in the first layer of air holes, the second layer of air holes and the third layer of air holes is also 0.5 μm.

[0014] Furthermore, in the first layer of air holes, the spacing between the center of each air hole and the center of the fiber core is preferably 4 μm; in the second layer of air holes, the spacing between the center of each air hole and the center of the fiber core can be 6.5 to 9 μm, more preferably 7 μm; in the third layer of air holes, the spacing between the center of each air hole and the center of the fiber core is preferably 11 μm.

[0015] In the present application, the base material of the optical fiber is silica.

[0016] A plasmon material layer is usually provided on the surface of the cladding. The plasmon material layer can be a gold film layer made of gold material, or a silver film layer made of silver material. In the present application, the plasmon material layer is preferably a silver film layer, and the thickness of the silver film layer is 35 to 55 nm.

[0017] An analyte channel to be detected is also provided on the outer side of the plasmon material layer. The analyte channel to be detected is annular in shape, and its inner diameter is preferably 13.30 μm, and its outer diameter is preferably 15.01 μm.

[0018] The refractive index analysis range of the analyte to be measured by the sensor of the utility model is 1.397-1.418.

[0019] Compared with the prior art, the sensor of the utility model has three layers of air holes with the same diameter as the core arranged from the inside to the outside of the core, and the first layer of air holes and the second layer of air holes are designed to be staggered, so that the leakage channel of light from the center of the optical fiber to the metal silver film is wider, the coupling effect is better, and the sensitivity of the obtained sensor is effectively improved. Furthermore, the sensor structure of the utility model is symmetrical up and down and left and right, which is more beneficial to increase the surface plasma resonance intensity of the optical fiber surface, so that the sensor can obtain better performance, can work in the near-infrared band of 720 to 1070nm, and has a higher maximum spectral sensitivity and a higher maximum refractive index resolution (the average spectral sensitivity of the sensor of the utility model is 10376.99nm / RIU, and the maximum spectral sensitivity is 15168.66nm / RIU at the refractive index of the solution to be tested of 1.415; the average refractive index resolution is 9.64×10 -6 RIU, the maximum refractive index resolution is 6.59×10 -6 RIU). BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the sensor described in the utility model.

[0021] Figure 2 It is a dispersion relation curve diagram of the core guided mode and the surface plasma mode of the sensor described in the utility model.

[0022] Figure 3 This is a diagram of the electric field mode distribution of the core guided mode of the sensor of the utility model at an incident wavelength of 930nm.

[0023] Figure 4 The figure is a line graph showing the relationship between the restrictive loss spectrum of the core guided mode of the sensor of the utility model and different silver film thicknesses when the silver film thickness changes from 35 nm to 55 nm in steps of 5 nm.

[0024] Figure 5 The core guided mode limitation loss spectrum corresponding to different air hole radii when the air hole radius in each layer changes from 0.5μm to 0.7μm in steps of 0.05μm.

[0025] Figure 6 When the distance between the center of each air hole in the second layer of air holes and the center of the fiber core changes from 6.5μm to 9μm, the core guided mode confinement loss spectrum corresponding to different distances.

[0026] Figure 7 This is a comparison diagram of the restrictive loss of the core guided mode corresponding to different refractive indices of the solution to be measured of the sensor of the utility model.

[0027] Figure 8The figure is a curve diagram showing the relationship between the resonance wavelength of the sensor of the utility model and the refractive index of the solution to be measured.

[0028] Fig. 9 The figure is a curve diagram showing the relationship between the quality factor of the sensor of the utility model and the refractive index of the solution to be measured.

[0029] The numbers in the figure are:

[0030] 10 substrate, 20 fiber core, 21 first layer of air holes, 22 second layer of air holes, 23 third layer of air holes, 30 plasmon material layer, 40 analyte channel to be measured, 50 perfect matching layer. DETAILED DESCRIPTION

[0031] In order to better explain the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings, but the implementation methods of the present invention are not limited thereto.

[0032] Reference Figure 1 The ten-core photonic crystal fiber refractive index sensor based on the plasmon resonance effect described in the utility model comprises a photonic crystal fiber, wherein the photonic crystal fiber comprises a core 20 and a cladding coated on the core 20, wherein the core 20 is a core air hole located in the center of the fiber, and the radial cross section of the cladding is circular, and the core 20, the cladding and the fiber are coaxial. A plasma material layer 30 is arranged on the surface of the cladding, and an annular analyte channel 40 is arranged on the outside of the plasma material layer 30, and the analyte to be measured is filled in the channel to form a refractive index sensing channel. There is also a perfect matching layer 50 on the outer layer of the annular analyte channel 40, which is a calculation boundary added when the finite element method is used for performance simulation. The cladding is provided with a first layer of air holes 21, a second layer of air holes 22 and a third layer of air holes 23 from the inside to the outside. The first layer of air holes 21, the second layer of air holes 22 and the third layer of air holes 23 are all arranged along the axial direction of the optical fiber, and the radius of the air holes in each layer is the same as the radius of the core 20, wherein:

[0033] The first layer of air holes 21 includes 10 air holes, each of which is arranged in a regular decagonal lattice on the periphery of the fiber core 20. The centers of the air holes in this layer are connected in sequence to form a regular decagon, and the center point of the regular decagon coincides with the center point of the fiber core 20.

[0034] The second layer of air holes 22 includes 10 air holes, each of which is arranged in a regular decagonal lattice on the periphery of the first layer of air holes 21, and the second layer of air holes 22 and the first layer of air holes 21 are arranged in a staggered manner; that is, the centers of the air holes in the second layer are connected in sequence to form a regular decagon, the center point of the regular decagon also coincides with the center of the fiber core 20, and the vertices of the regular decagon formed by connecting the centers of the air holes in the first layer in sequence and the regular decagon formed by connecting the centers of the air holes in the second layer in sequence are staggered with each other;

[0035] The third layer of air holes 23 includes 20 air holes, and the air holes are arranged in a regular icosagonal lattice on the periphery of the second layer of air holes 22. The centers of the air holes in this layer are connected in sequence to form a regular icosagon, and the center point of the regular icosagon coincides with the center of the fiber core 20.

[0036] The substrate 10 material of the sensor of the utility model is silicon dioxide. The first layer of air holes 21, the second layer of air holes 22 and the third layer of air holes 23 arranged regularly are introduced into the substrate 10, mainly to reduce the average refractive index of the area near the air holes, so that the average refractive index of these areas is lower than the refractive index of the inner silicon dioxide. The area with a higher refractive index is the equivalent core 20, and the area with a lower average refractive index is the equivalent cladding, forming a refractive index guided photonic crystal fiber. The first layer of air holes 21 and the second layer of air holes 22 are further designed to be staggered, so that the leakage channel of light from the center of the optical fiber to the metal silver film is wider, the coupling effect is better, and the sensitivity of the obtained sensor is effectively improved.

[0037] The radius of the fiber core 20 can be 0.5 to 0.7 μm, and the diameter of each air hole in the first layer of air holes 21, the second layer of air holes 22 and the third layer of air holes 23 is also 0.5 to 0.7 μm; it is further preferred that the radius of the fiber core 20 is 0.5 μm, and the diameter of each air hole in the first layer of air holes 21, the second layer of air holes 22 and the third layer of air holes 23 is also 0.5 μm.

[0038] In the first layer of air holes 21, the distance between the center of each air hole and the center of the fiber core 20 is preferably 4 μm; in the second layer of air holes 22, the distance between the center of each air hole and the center of the fiber core 20 can be 6.5 to 9 μm, more preferably 7 μm; in the third layer of air holes 23, the distance between the center of each air hole and the center of the fiber core 20 is preferably 11 μm.

[0039] For the plasma material layer 30 on the surface of the cladding, two plasma active materials, gold and silver, are mostly used. Compared with other plasma materials, gold shows a more obvious resonance wavelength shift, but the resonance intensity of gold is small and the half-peak width is large, which will reduce the detection accuracy of the sensor. Therefore, the utility model preferably uses silver as a plasma sensitive material in order to obtain a sharper resonance peak and improve the detection accuracy of the sensor. In the present application, the plasma material layer 30 is preferably a silver film layer, and the thickness of the silver film layer is usually 35 to 55nm. The dielectric constant of the silver film layer is defined by the Lorentzian-pole pairs (L4) after compensation of the Drude model, and the refractive index of the silicon dioxide layer is related to the incident wavelength, and its effective refractive index is determined by the Sellmeier formula, and its refractive index is greater than the refractive index of the solution to be tested on the outside. The refractive index analysis range of the analyte to be tested by the sensor of the utility model is 1.397 to 1.418. In a preferred embodiment, the radius of the core 20 is limited to 0.5 μm, and the diameter of each air hole in the first layer of air holes 21, the second layer of air holes 22 and the third layer of air holes 23 in the cladding is also 0.5 μm. In the first layer of air holes 21, the distance between the center of each air hole and the center of the core 20 is 4 μm; in the second layer of air holes 22, the distance between the center of each air hole and the center of the core 20 is 7 μm; in the third layer of air holes 23, the distance between the center of each air hole and the center of the core 20 is 11 μm. The misalignment angle between the second layer of air holes 22 and the first layer of air holes 21 is 18°. The plasmon material layer 30 on the surface of the cladding is a silver film layer made of silver material, and its thickness is 40 nm. The inner diameter of the analyte channel 40 outside the silver film layer is 13.30 μm and the outer diameter is 15.01 μm.

[0040] The evanescent wave and the surface plasmon wave generated by the incident light wave satisfy the phase matching condition in the wave vector components parallel to the interface, such as Figure 2 As shown in the figure, when the incident wavelength is 930nm, there is an intersection point between the real part curves of the core guided mode and the surface plasma effective refractive index, that is, the real part of the effective refractive index of the core 20 mode is equal to the real part of the effective refractive index of the surface plasma mode. At the same time, at this intersection point, the imaginary part curve of the effective mode refractive index of the core guided mode and the limiting loss curve have an obvious loss peak. The appearance of the intersection point and the loss peak at the same wavelength indicates that phase matching occurs in the core 20, that is, the SPR effect occurs. Figure 3 From the electric field film distribution diagram of the core guided mode at an incident wavelength of 930 nm, it can be seen that the energy is partially concentrated between the second layer of air holes 22 and the third layer of air holes 23, and then turns from the top to the bottom to the left and right sides, and gradually transfers to the silver film.

[0041] The change of the thickness of the model parameter silver film layer will cause the drift of the resonance loss peak. The change of the thickness of the silver film layer has a great influence on the performance of the sensor. Figure 4 As shown in the figure, with a step size of 5nm, the silver film thickness increases from 35nm to 55nm, and the corresponding loss peak increases first and then decreases. The loss peak reaches the maximum value when the silver film thickness is 40nm. Secondly, the size of the air hole in the cladding can meet the phase matching conditions between the fundamental mode and the plasma mode, so the size of the air hole radius will directly affect the resonance intensity and stability. The relationship between the air hole radius and the core guided mode restriction loss is shown in Figure 5 As shown. As the radius of the air hole decreases, the peak-to-peak value of the loss increases, and the wavelength at the peak also gradually increases. The smaller the air hole, the weaker the constraint on the light, the more light that can reach the metal silver film, and the stronger the resonance. The second layer of air holes 22 plays the role of dividing the core 20 area. When the distance from this layer of air holes to the center of the optical fiber changes, the position of the divided core 20 will also change. When the total energy of the light remains unchanged, the closer the core 20 is to the silver film, the greater the resonance intensity, and vice versa. Figure 6 As shown, the distance P from the second layer of air holes 22 to the center of the optical fiber increases from 6.5 μm to 9 μm, the loss peak first increases and then decreases, and the wavelength at the loss peak also first increases and then decreases.

[0042] Combined with the above model parameter optimization results, the silver film thickness of the sensor of the utility model is selected to be 40nm, the radius of the air holes in each layer of air holes is selected to be 0.5μm, and the distance between the center of each air hole in the second layer of air holes 22 and the center of the fiber core 20 is selected to be 7μm.

[0043] The change of refractive index of different test solutions will cause the resonance wavelength to drift. Figure 7 As shown in the figure, with a step size of 0.003, the effective variation range of the refractive index of different test solutions is 1.397-1.418. As the refractive index increases, the resonance wavelength red-shifts. This is because the closer the refractive index of the test solution is to the refractive index of pure silica in the background, the stronger the resonance is. As the refractive index of the test solution increases from 1.397 to 1.418, it is closer to the refractive index of silica, the resonance intensity increases, and the wavelength at the corresponding loss peak also moves toward the larger wavelength. Figure 8 The graph is a relationship between the resonance wavelength and the refractive index of the solution to be tested, and the wavelengths corresponding to all refractive indices are fitted with a polynomial, and the R square value of the fitting curve is 0.9997, which shows that the fitting degree is quite high. Using multiple polynomial fittings, it can be calculated that the average spectral sensitivity of the sensor of the utility model is 10376.99nm / RIU, the maximum spectral sensitivity is 15168.66nm / RIU at the refractive index of the solution to be tested of 1.415, and the average refractive index resolution is 9.64×10 -6 RIU, the maximum refractive index resolution is 6.59×10- 6 In addition, the quality factors corresponding to the different refractive indices of the tested solutions were calculated. Fig. 9 is the relationship curve between the quality factor and the refractive index of the solution to be tested, Fig. 9 It can be seen that the overall trend of the quality factor increases with the increase of the refractive index of the solution to be tested, reaching a maximum at a refractive index of 1.415, at which the maximum quality factor is 445.16. It then tends to decrease, decreasing to 428.5 at a refractive index of 1.418, indicating that the detection limit of the sensor of the utility model is relatively large.

[0044] From the above experiments, it can be seen that the ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect described in the utility model has good sensitivity, high refractive index and resolution, wide detection range, wide application range, and potential application value in many fields.

Claims

1. A ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect, comprising a photonic crystal fiber, wherein the photonic crystal fiber comprises a core (20) and a cladding coated on the core (20), wherein: The fiber core (20) is a core air hole located in the center of the optical fiber; The cladding is provided with a first layer of air holes (21), a second layer of air holes (22) and a third layer of air holes (23) in sequence from the inside to the outside, the first layer of air holes (21) includes 10 air holes, each of which is arranged in a regular decagonal lattice around the periphery of the fiber core (20); the second layer of air holes (22) includes 10 air holes, each of which is arranged in a regular decagonal lattice around the periphery of the first layer of air holes (21), and the second layer of air holes (22) and the first layer of air holes (21) are arranged in a staggered manner; the third layer of air holes (23) includes 20 air holes, each of which is arranged in a regular icosagonal lattice around the periphery of the second layer of air holes (22); the radius of each of the air holes is the same as the radius of the fiber core (20); The center of the fiber core (20), the center point of the regular decagon and the center point of the regular icosagon coincide with each other.

2. The ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect according to claim 1 is characterized in that: The radius of the fiber core (20) is 0.5-0.7 μm.

3. The ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect according to claim 2 is characterized in that: In the first layer of air holes (21), the distance between the center of each air hole and the center of the fiber core (20) is 4 μm; in the second layer of air holes (22), the distance between the center of each air hole and the center of the fiber core (20) is 6.5-9 μm; in the third layer of air holes (23), the distance between the center of each air hole and the center of the fiber core (20) is 11 μm.

4. The ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect according to any one of claims 1 to 3, characterized in that: A plasmon material layer (30) is arranged on the surface of the cladding.

5. The ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect according to claim 4 is characterized in that: The plasmon material layer (30) is a silver film layer.

6. The ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect according to claim 5 is characterized in that: The thickness of the silver film layer is 35-55 nm.

7. The ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect according to claim 4 is characterized in that: An analyte channel (40) to be detected is provided on the outer side of the plasmon material layer (30).

8. The ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect according to claim 7 is characterized in that: The inner diameter of the analyte channel (40) to be detected is 13.30 μm, and the outer diameter is 15.01 μm.

9. The ten-core photonic crystal fiber refractive index sensor based on plasmon resonance effect according to any one of claims 1 to 3, characterized in that: The substrate (10) of the optical fiber is made of silicon dioxide.

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