Negative curvature hollow core fiber temperature sensor based on lspr effect

Abstract

The application belongs to the technical field of optical fiber sensing, and relates to a negative curvature hollow optical fiber temperature sensor based on LSPR effect, which comprises an outer layer structure, the radial section of the outer layer structure is circular, six cladding tubes are arranged in the inner part of the outer layer structure, the six cladding tubes are all inscribed in the inner surface of the outer layer structure, the included angle between the center lines of two adjacent cladding tubes and the center line of the outer layer structure is 60 degrees, gold nanowires are deposited on the cladding tubes in the positive direction of the y-axis, the remaining space of the outer layer structure except the cladding tubes is filled with temperature-sensitive liquid, and the region close to the center of the optical fiber and surrounded by the six cladding tubes in the center direction forms a fiber core region of the optical fiber. The optical fiber temperature sensor provided by the application introduces the localized plasmon technology into the optical fiber, can effectively improve the regulation and control of the evanescent field of the sensor, excite the LSPR effect, and further realize high-performance sensing response.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber sensing technology and relates to a negative curvature hollow optical fiber temperature sensor based on the LSPR effect. Background Technology

[0002] Surface plasmon resonance (SPR) is a phenomenon based on the electromagnetic wave coupling effect at the interface between a metal and a dielectric. When light shines on the interface between a metal and a dielectric, if the frequency of the incident light matches the oscillation frequency of electrons on the metal surface, the electromagnetic wave excites the free electrons on the metal surface to resonate, resulting in a corresponding resonance absorption peak in the detection spectrum. SPR sensing technology, due to its unique properties such as high sensitivity, label-free detection, and real-time monitoring, is widely used in environmental monitoring, medical diagnostics, and biochemistry. Traditional SPR sensors are based on the Kretschmann-Raether structure, which makes the sensors bulky and complex, hindering remote monitoring. Therefore, SPR fiber optic sensors are favored by researchers due to their strong anti-interference capabilities, high measurement accuracy, and good stability. Temperature sensors are crucial in many current applications, particularly in medicine, food safety, environmental monitoring, manufacturing, energy, military aerospace, and scientific research. Therefore, the development of temperature sensors with high sensitivity, high linearity, and a wide detection range is urgently needed. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a negative curvature hollow fiber temperature sensor based on the LSPR effect. Due to its large structural size, it is easy to perform post-processing and fixation of gold nanowires without damaging the fiber structure. In addition, the large internal size of the fiber facilitates the filling of temperature-sensitive liquid. It also has the advantages of high sensitivity, high linearity, high resolution, and narrow half-width at half-maximum.

[0004] The technical solution of this invention to solve the above problems is: a negative curvature hollow fiber temperature sensor based on the LSPR effect, which is special in that:

[0005] Includes an outer structure, wherein the radial cross-section of the outer structure is circular;

[0006] The outer structure contains six cladding tubes, all of which are tangent to the inner surface of the outer structure. The angle between the line connecting the center of two adjacent cladding tubes and the center of the outer structure is 60 degrees. Gold nanowires are deposited on the cladding tubes in the positive y-axis direction.

[0007] The space within the outer structure, excluding the cladding tubes, is filled with a temperature-sensitive liquid. The core region of the optical fiber is formed by the six cladding tubes concentrically surrounding the center of the fiber.

[0008] Furthermore, the gold nanowires in the aforementioned cladding tube are symmetrically distributed about the y-axis, and the gold nanowires are deposited on the inner wall of the cladding tube, occupying one-third of the entire circumference.

[0009] Furthermore, the number of gold nanowires in the aforementioned cladding tube is 20-80, and the radius of the gold nanowires ranges from 60-140 nm.

[0010] Furthermore, the six cladding tubes extend along the optical fiber axis and have a circular radial cross-section. The inner radius of the six cladding tubes is 11–13 μm, and the wall thickness is 2.13–3.5 μm.

[0011] Furthermore, the radius of the radial cross-section of the aforementioned outer structure ranges from 86.52 to 110.52 μm.

[0012] Furthermore, the core radius is defined as half of the minimum distance between the two cladding tubes, and the core radius ranges from 22 to 25 μm.

[0013] Furthermore, the temperature-sensitive liquid filling the aforementioned fiber core area is a mixture of ethanol and chloroform, with ethanol accounting for 50%-80%.

[0014] Furthermore, the base material of the outer layer structure is quartz, and the base material of the cladding tube wall material is quartz, whose refractive index is described by Selmayer's formula:

[0015]

[0016] Where n Si λ is the refractive index of silicon dioxide, λ is the incident wavelength, and T is the ambient temperature, all in μm and °C.

[0017] Furthermore, the aforementioned sensor achieves an average sensitivity of 10.64 nm / ℃, a linearity of 0.99817, and a resolution of 9.398 x 10⁻⁶ within a temperature range of 20℃ to 60℃. -3 At ℃, the full width at half maximum (FWHM) of the loss spectrum is in the range of 21.02-37.27 nm.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] 1. The fiber optic temperature sensor provided by this invention introduces localized plasma technology into optical fibers, which can effectively improve the sensor's control over evanescent fields, excite the LSPR effect, and thus achieve high-performance sensing response. Compared with SPR, the size and shape of the metal nanoparticles used in LSPR can be adjusted, which means that LSPR can better adjust the position and intensity of the resonance peak to adapt to specific sensing applications. Secondly, metal nanoparticles respond faster to changes in the surrounding environment and generally have higher sensitivity. Metal nanoparticles are more adaptable to rough surfaces and can also save heavy metal materials, thereby reducing manufacturing costs.

[0020] 2. The negative curvature hollow fiber structure provided by this invention has a large size, making it easy to perform post-processing operations without damaging the cladding structure. It is also convenient to fill its core region with temperature-sensitive liquid, and its hollow structure also provides a platform for flow-light interaction.

[0021] 3. Different temperatures will cause different resonance loss peaks in the spectrum at the output end of the optical fiber. The refractive index of the analyte can be determined by observing the resonance spectrum.

[0022] 4. The accuracy of the sensor of the present invention is not sensitive to minute changes in structural parameters, which greatly reduces the complexity of its manufacturing;

[0023] 5. The sensor of the present invention can achieve an average sensitivity of 10.64 nm / ℃ in the range of 20℃-60℃, a linearity of 0.99817, a resolution of 9.398x10-3℃, and a loss spectrum with a half width at half maximum (FWHM) in the range of 21.02-37.27 nm. Attached Figure Description

[0024] Figure 1 This is a cross-sectional view of the negative curvature hollow fiber temperature sensor based on the LSPR effect proposed in this invention.

[0025] Figure 2 This is a schematic diagram showing the effective refractive index and loss of the y-polarized fundamental mode of the sensor proposed in this invention, and the effective refractive index curve of the SPP mode.

[0026] Figure 3 This is a schematic diagram of the loss curve of the sensor proposed in this invention within its detection range;

[0027] Figure 4 This is a schematic diagram showing the change of the resonant wavelength of the sensor proposed in this invention with temperature.

[0028] Figure 5 The sensor proposed in this invention limits the full width at half maximum (FWHM) of the loss spectrum at different temperatures.

[0029] In the figure: 1-outer layer structure, 2-first cladding tube; 3-second cladding tube; 4-third cladding tube; 5-fourth cladding tube; 6-fifth cladding tube; 7-sixth cladding tube; 8-core region; 9-gold nanowire. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0031] Negative curvature hollow fiber (NCHCF) is a novel type of optical fiber developed in recent years. The optical guidance of NCHCF relies on the principle of anti-resonant reflection waveguide (ARROW). Sensors combining NCHCF and SPR fully utilize the inherent advantages of anti-resonance effects, generating specific resonant wavelengths over a broadband window. Sensitivity is then obtained by monitoring the displacement or intensity fluctuations of these specific resonant wavelengths. Furthermore, the relatively large size and simple structure of NCHCF make it easy to fill with temperature-sensitive liquids, and its hollow core structure also provides a platform for flow-optic interactions.

[0032] Based on this, the present invention proposes a high-resolution, high-sensitivity negative curvature hollow fiber temperature sensor based on the LSPR effect.

[0033] Example 1

[0034] See Figure 1 A negative curvature hollow fiber temperature sensor based on the LSPR effect includes an outer structure 1 with a circular radial cross-section. The outer structure 1 contains six cladding tubes: a first cladding tube 2, a second cladding tube 3, a third cladding tube 4, a fourth cladding tube 5, a fifth cladding tube 6, and a sixth cladding tube 7. The second cladding tube 3 and the fourth cladding tube 5 are located on the y-axis.

[0035] Six cladding tubes are inscribed within the inner surface of the outer structure 1, with an angle of 60 degrees between adjacent cladding tubes. Gold nanowires 9 are filled in the second cladding tube 3 in the positive y-axis direction. The remaining space within the outer structure 1, excluding the cladding tubes, is filled with a thermosensitive liquid. The region near the fiber center, enclosed by the six cladding tubes concentrically, forms the fiber core region 8. Its large size and simple structure make it easy to fill with a thermosensitive liquid, and its hollow core structure also provides a platform for flow-optic interaction.

[0036] In a preferred embodiment of the present invention, the six cladding tubes extend along the optical fiber axis and have a circular radial cross-section.

[0037] In some optional embodiments, the inner radius r of the six cladding tubes ranges from 11 to 13 μm, and the tube wall thickness t is 2.13 to 3.5 μm.

[0038] In some optional embodiments, the number of gold nanowires 9 in the second cladding tube 3 is 20-80; the radius of the gold nanowires 9 in the second cladding tube 3 is 60nm-140nm.

[0039] In some alternative embodiments, the core radius of the core region is defined as half of the minimum distance between the two cladding tubes.

[0040] In a preferred embodiment of the present invention, the base material of the outer layer structure 1 is quartz; the base material of the cladding tube wall material is quartz, and its refractive index is described by the Selmayer formula:

[0041]

[0042] Where n Si λ is the refractive index of silicon dioxide, λ is the incident wavelength, and T is the ambient temperature, all in μm and °C.

[0043] The thermosensitive liquid used for filling is a mixture of ethanol and chloroform, and its refractive index can be expressed as:

[0044]

[0045] n mix =n core

[0046] Where n mix n is the refractive index of the mixture, n1 and n2 are the refractive indices of ethanol and chloroform at 20℃, and n core Let be the refractive index of the NCHCF fiber core, and m and (1-m) be the proportions of ethanol and chloroform in the mixture, respectively (0.5 ≤ m ≤ 1). dn / dT represents the thermo-optic coefficient, with the thermo-optic coefficients of ethanol and chloroform being -3.94 x 10⁻⁶. -4 ℃ -1and -6.328x10 -4 ℃ -1 .

[0047] For the negative curvature hollow-core fiber temperature sensor proposed in this invention, when the core radius is 24 μm, the cladding tube radius is 12 μm, the cladding tube wall thickness is 2.13 μm, the gold nanowire radius is 80 nm, the number of gold nanowires is 80, and T = 20℃, the finite refractive index real part of the y-polarized fundamental mode and the SPP mode, as well as the confined loss curve of the y-polarized fundamental mode, are shown in the following curves as a function of wavelength. Figure 2 As shown in the figure, the transmission relationship between the y-polarized fundamental mode and the SPP mode was analyzed using the finite element method. The figure shows that as the incident light wavelength increases, the evanescent wave generated by the fiber core and the surface plasmon wave generated by the excited gold nanowires gradually satisfy the phase-matching condition. This is reflected in the figure as the real part curve of the refractive index of the y-polarized fundamental mode gradually approaches the real part curve of the refractive index of the SPP mode, and intersects at resonance. However, as the wavelength further increases, the phase-matching condition is no longer satisfied, and the two real part curves of the refractive index gradually move away from each other. At shorter wavelengths, the fundamental mode and the SPP mode are confined to the fiber core and the metal surface. As the wavelength increases, some of the fiber core energy begins to leak more into the gold nanowire region. This energy transfer leads to light transmission loss, resulting in a resonance loss peak in the transmission spectrum at the fiber core output end. Figure 3 The images show the confinement loss spectra at different temperatures. As the temperature changes, the refractive index of the fiber core also changes. This change in refractive index alters the conditions for plasmon resonance, causing a shift in the position of the loss peak. By measuring this shift, the temperature can be determined.

[0048] Example 2

[0049] A negative curvature hollow fiber refractive index sensor based on the LSPR effect, such as Figure 1 As shown, the structure includes an outer layer 1 with a circular radial cross-section. The outer layer 1 contains six cladding tubes: a first cladding tube 2, a second cladding tube 3, a third cladding tube 4, a fourth cladding tube 5, a fifth cladding tube 6, and a sixth cladding tube 7. The second cladding tube 3 and the fourth cladding tube 5 are located on the y-axis.

[0050] Six cladding tubes are inscribed within the inner surface of the outer layer structure 1, with an angle of 60 degrees between adjacent cladding tubes. Gold nanowires 9 are filled in the second cladding tube 3 in the positive y-axis direction. The remaining space within the outer layer structure 1, excluding the cladding tubes, is filled with a thermosensitive liquid. The region near the center of the optical fiber, enclosed concentrically by the six cladding tubes, forms the fiber core region 8. In a preferred embodiment, the six cladding tubes extend along the optical fiber axis and have a circular radial cross-section. The inner radius r of the six cladding tubes ranges from 11.5 μm, and the wall thickness t is 3.0 μm. The second cladding tube 3 contains 40 gold nanowires 9; the radius of the gold nanowires 9 in the second cladding tube 3 is 100 nm. The core radius of the core region is defined as half the minimum distance between two cladding tubes, and the core radius R ranges from 23 μm. The base material of the outer layer structure 1 and the cladding tube wall material is quartz, and the filling thermosensitive liquid is a mixture of ethanol and chloroform.

[0051] The sensor in this embodiment can measure the refractive index based on the resonance peak shift. See [link to relevant documentation]. Figure 4 Within the temperature range of 20°C to 60°C, the average sensitivity reaches 10.64 nm / ℃, with a maximum sensitivity of 12.2 nm / ℃. The resonant wavelength of the analyte exhibits a good linear relationship with temperature, with a linearity of 0.99817. The resolution is 9.398 x 10⁻⁶. -3 ℃, within the detection range, see Figure 5 The sensor's loss spectrum exhibits a full width at half maximum (FWHM) within the range of 21.02–37.27 nm, indicating sharper signal peaks and better differentiation from other signal modes. Simulation results demonstrate that the core radius and cladding tube radius have little impact on sensor sensitivity, implying a reduction in the required manufacturing precision. Due to its excellent temperature sensing characteristics and low manufacturing difficulty, this sensor demonstrates significant advantages in temperature measurement. Therefore, the sensor developed in this study has broad potential applications in fields such as medicine, food safety, and environmental monitoring.

[0052] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related system fields, are similarly included within the scope of protection of the present invention.

Claims

1. A negative curvature hollow fiber temperature sensor based on the LSPR effect, characterized in that: Includes an outer structure, wherein the radial cross-section of the outer structure is circular; The outer structure contains six cladding tubes, all of which are tangent to the inner surface of the outer structure. The angle between the line connecting the center of two adjacent cladding tubes and the center of the outer structure is 60 degrees. Gold nanowires are deposited on the cladding tubes in the positive y-axis direction. The space within the outer structure, excluding the cladding tubes, is filled with a temperature-sensitive liquid. The core region of the optical fiber is formed by six cladding tubes concentrically surrounding the center of the fiber. The gold nanowires in the cladding tube are symmetrically distributed about the y-axis, and the gold nanowires are deposited on the inner wall of the cladding tube and occupy one-third of the entire circumference. The number of gold nanowires in the cladding tube is 20-80, and the radius of the gold nanowires is 60-140 nm. The temperature sensor achieves an average sensitivity of 10.64 nm / ℃, a linearity of 0.99817, and a resolution of 9.398 x 10⁻⁶ within a temperature range of 20℃ to 60℃. -3 At ℃, the full width at half maximum (FWHM) of the loss spectrum is in the range of 21.02-37.27 nm.

2. The negative curvature hollow fiber temperature sensor based on the LSPR effect according to claim 1, characterized in that: The six cladding tubes extend along the fiber axis and have a circular radial cross-section. The inner radius of the six cladding tubes is 11~13μm and the wall thickness is 2.13-3.5μm.

3. The negative curvature hollow fiber temperature sensor based on the LSPR effect according to claim 2, characterized in that: The radius of the radial section of the outer structure ranges from 86.52 to 110.52 μm.

4. A negative curvature hollow fiber temperature sensor based on the LSPR effect according to claim 3, characterized in that: The core radius is defined as half of the minimum distance between two cladding tubes, and the core radius ranges from 22 to 25 μm.

5. A negative curvature hollow fiber temperature sensor based on the LSPR effect according to claim 4, characterized in that: The temperature-sensitive liquid filling the fiber core area is a mixture of ethanol and chloroform, with ethanol accounting for 50%-80%.

6. A negative curvature hollow fiber temperature sensor based on the LSPR effect according to claim 5, characterized in that: The base material of the outer layer structure is quartz, and the base material of the cladding tube wall material is quartz, whose refractive index is described by Selmayer's formula: Where n Si λ is the refractive index of silicon dioxide, λ is the incident wavelength, and T is the ambient temperature, all in μm and °C.

7. A negative curvature hollow fiber temperature sensor based on the LSPR effect according to claim 6, characterized in that: The thermosensitive liquid used for filling is a mixture of ethanol and chloroform, and its refractive index can be expressed as: Where n mix n is the refractive index of the mixture, n1 and n2 are the refractive indices of ethanol and chloroform at 20℃, and n core denoted as the refractive index of the NCHCF fiber core, m and 1-m represent the proportions of ethanol and chloroform in the mixture, respectively, 0.5 ≤ m ≤ 1, and dn / dT represents the thermo-optical coefficient, with the thermo-optical coefficients of ethanol and chloroform being -3.94 x 10⁻⁶. -4 ℃ -1 and -6.328 x 10 -4 ℃ -1 .

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