A dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature and its fabrication process

Abstract

This invention relates to the field of fiber optic sensor technology, and in particular to a dual-D structure fiber optic sensor for simultaneous refractive index and temperature detection and its fabrication process. The fiber optic sensor includes a cladding layer, within which a fiber core is disposed. A first channel is located at the bottom of the fiber core, and a second channel is located at the top of the fiber core. An inner hexagonal vent ring is disposed within the fiber core, and an outer hexagonal vent ring is formed outside the inner hexagonal vent ring. A first circular hole is formed at the bottom of the fiber core, directly above the first channel, and a second circular hole is formed at the top of the fiber core, directly below the second channel. This invention combines the microstructure design of photonic crystal fibers with the high-sensitivity technology of surface plasmon resonance, offering advantages such as real-time monitoring, no need for marking, and low interference. Replacing ordinary optical fibers with photonic crystal fibers as sensors can solve the phase matching problem, thereby achieving high-sensitivity and multifunctional real-time sensing measurements.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensor technology, and in particular to a dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature, and its fabrication process. Background Technology

[0002] Surface plasmon resonance (SPR) refers to evanescent electron waves propagating along the surface of a metal, generated by the interaction of freely vibrating electrons and photons. SPR has attracted widespread attention as an optical technique for measuring molecular interactions. Due to its advantages of high sensitivity, small size, and real-time detection, this technology has been applied in environmental monitoring, gas detection, and medical diagnostics. However, traditional fiber-optic-based SPR sensors face severe limitations in application due to the small number of active particles and low electromagnetic power in the sensing region.

[0003] Photonic crystal fiber (CCF) consists of regularly arranged air holes in silica fiber, with large air holes or solid silica defect structures introduced into the fiber core to disrupt the cladding periodicity. CCF sensors do not require additional coupling devices and can effectively solve the phase matching problem through the arrangement of air holes, achieving mode coupling between the core mode and the surface plasmon polariton mode, thus converting changes in the refractive index of the analyte into shifts in the absorption peak. Due to their unique advantages, CCF sensors offer remote real-time detection, small size, easy integration, high sensitivity, and flexible design.

[0004] However, filling the pores with a metal layer is extremely difficult for conventional photonic crystal fiber structures. To overcome this problem, D-shaped planar polished photonic crystal fibers have been proposed to activate surface plasmon resonance (SPR) and achieve sensing of the analyte. D-channel structures are simple, have low processing costs, and high fabrication efficiency. For example, Chinese patent CN214426731U proposes a novel dual-channel SPR fiber sensor, which uses time-division multiplexing technology to achieve parallel dual channels, but its structure is more complex.

[0005] Meanwhile, for water quality measurement, biomedical monitoring, and industrial production, measuring the refractive index and temperature of the substance under study is crucial. D-channel sensors suffer from cross-sensitivity issues when measuring refractive index, temperature, and other parameters, which are typically addressed using temperature compensation, temperature-insensitive elements, or multi-channel sensing. For example, Chinese patent CN111239076B discloses a surface plasmon resonance fiber optic sensor. This sensor has a simple structure and can achieve polarization-insensitive sensing, but it cannot simultaneously detect multiple substances and has a narrow detection range. Summary of the Invention

[0006] Therefore, it is necessary to provide a dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature, and its fabrication process, to address the aforementioned technical issues.

[0007] In a first aspect, the present invention provides a dual-D structure optical fiber sensor for simultaneous detection of refractive index and temperature. The optical fiber sensor includes a cladding, and a fiber core is disposed inside the cladding. A first channel is disposed at the bottom end of the fiber core, and a second channel is disposed at the top end of the fiber core. An inner hexagonal vent ring is disposed inside the fiber core, and an outer hexagonal vent ring is disposed outside the inner hexagonal vent ring. A first circular hole is disposed at the bottom of the fiber core and directly above the first channel, and a second circular hole is disposed at the top of the fiber core and directly below the second channel.

[0008] In one embodiment, the top and bottom of the fiber core are both D-shaped surfaces, and the fiber core is made of silicon dioxide.

[0009] In one embodiment, the first channel has a rectangular structure and the second channel has a semi-circular structure. A gold film is disposed on the surface of both the first channel and the second channel, and the thickness of the gold film is 40 nm.

[0010] A polydimethylsiloxane layer with a thickness of 160 nm is disposed on the surface of the gold thin film in the first channel.

[0011] In one embodiment, the inner hexagonal vent ring includes two inner top holes and four inner ring holes. The two inner top holes and four inner ring holes are arranged in a regular hexagonal structure with an adjacent spacing angle of 60°. The two inner top holes are arranged side by side on the top of the regular hexagonal structure.

[0012] In one embodiment, the distance between the two inner ring holes at the bottom of the regular hexagonal structure is 2 μm, the diameter of the inner top hole is 1.3 μm, and the diameter of the inner ring hole is 1.7 μm.

[0013] In one embodiment, the outer hexagonal vent ring includes two outer top holes and six outer ring holes, the two outer top holes and the six outer ring holes are arranged equidistantly in a D-shaped structure, and the two outer top holes are distributed side by side on the top of the D-shaped structure.

[0014] The six outer ring holes are divided into two groups and distributed on both sides of the D-shaped structure. The angle between the outer top hole and the outer ring hole on the same side is 30°, and the angle between the two outer ring holes at the bottom of the D-shaped structure is 60°.

[0015] In one embodiment, the diameter of the outer top hole is 1.3 μm, and the diameter of the outer annular hole is 1.7 μm.

[0016] In one embodiment, the first circular hole is located at the top of the regular hexagonal structure formed by the inner hexagonal vent ring, and the second circular hole is located directly below the D-shaped structure formed by the outer hexagonal vent ring; the diameter of both the first and second circular holes is 1 μm.

[0017] In one embodiment, the matrix expression for the influence of liquid refractive index and temperature changes on the first and second channels is as follows:

[0018]

[0019] In the formula, Δλ Ⅰ This represents the wavelength change of the first channel; Δλ Ⅱ This represents the wavelength change of the second channel; Δn a The change in refractive index of the liquid is represented by ΔT; the change in operating temperature is represented by K; and the sensitivity coefficient matrix is ​​represented by K. nI =2180nm / RIU; K nII =2000nm / RIU; K TI = -0.31nm / ℃; K TII =0nm / ℃.

[0020] Secondly, the present invention also provides a fabrication process for a dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature, the fabrication process comprising the following steps:

[0021] S1. The micro-nano structure of optical fiber is formed by ultrasonic stamping technology and laser drilling is used;

[0022] S2. The semi-finished photonic crystal fiber is cut into a double D-shaped microgroove structure by polishing technology;

[0023] S3. Micro-process the sensitive materials of the first and second channels to deposit gold on the polished surfaces of the microgrooves on both sides to form a gold film.

[0024] S4. Combine the first channel with the polydimethylsiloxane material and apply a polydimethylsiloxane layer on the surface of the gold film;

[0025] S5. A dual-channel photonic crystal fiber-surface plasmon resonance sensor was fabricated.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. By combining the microstructure design of photonic crystal fiber with the high-sensitivity technology of surface plasmon resonance, it has the advantages of real-time monitoring, no need for marking, and low interference. Photonic crystal fiber can replace ordinary optical fiber as a sensor to solve the phase matching problem, so as to obtain real-time sensing measurement with high sensitivity and multifunctionality. This invention effectively improves the sensing sensitivity. By optimizing the structure and adopting a novel double-parallel D-shaped photonic crystal fiber-surface plasmon resonance form, the coupling efficiency between the core guided mode and the plasma mode is improved, making its performance significantly better than that of double-parallel fiber.

[0028] 2. By designing a photonic crystal fiber with a double D-type structure based on surface plasmon resonance, the core mode and surface plasmon mode are enhanced, resulting in superior performance. It can simultaneously detect the refractive index and operating temperature of liquid analytes. Employing a unique dual-channel and asymmetrical structure, and by optimizing the fiber structure's geometric parameters, gold film thickness, and other coating material thicknesses, the cross-sensitivity problem of the sensor is effectively solved, improving detection sensitivity and measurement accuracy. Furthermore, this sensor achieves a wavelength sensitivity of 2180 nm / RIU for liquids with a refractive index between 1.31 and 1.36, and a temperature sensitivity of -0.31 nm / ℃ over an extremely wide operating temperature range of -25℃ to 150℃. Its high precision, low cost, simplicity, and real-time performance make it a novel sensing unit, providing a new solution for the design and implementation of distributed measurement systems. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0030] Figure 1 This is one of the structural cross-sectional views of a dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to an embodiment of the present invention;

[0031] Figure 2 This is a second structural cross-sectional view of a dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to an embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram of the use and experimental process of the dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to an embodiment of the present invention.

[0033] Figure 4 This is a graph showing the relationship between the resonant wavelength and confinement loss of the two channels of a dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to an embodiment of the present invention during an experimental process.

[0034] Figure 5This is a graph showing the relationship between the resonant wavelength and confinement loss of a dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to an embodiment of the present invention, as the refractive index of the analyte changes.

[0035] Figure 6 This is a fitting relationship diagram between the refractive index of the two channels and the corresponding resonant wavelength in a dual-D structure fiber optic sensor for synchronous detection of refractive index and temperature according to an embodiment of the present invention.

[0036] Figure 7 This is a graph showing the relationship between the detection temperature, confinement loss, and resonant wavelength of a dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to an embodiment of the present invention.

[0037] Figure 8 This is a linear fitting relationship between temperature and resonant wavelength of a dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to an embodiment of the present invention.

[0038] Figure 9 This is a flowchart of the fabrication process of a dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to an embodiment of the present invention.

[0039] Reference numerals: 1. Cladding; 2. Core; 3. First channel; 4. Second channel; 5. Inner hexagonal pore ring; 501. Inner top hole; 502. Inner ring hole; 6. Outer hexagonal pore ring; 601. Outer top hole; 602. Outer ring hole; 7. First circular hole; 8. Second circular hole; 9. Gold film; 10. Polydimethylsiloxane layer. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] Please see Figures 1-8 A dual-D structure fiber optic sensor for simultaneous refractive index and temperature detection is provided. This fiber optic sensor includes a cladding 1, inside which a fiber core 2 is disposed. A first channel 3 is provided at the bottom of the fiber core 2, and a second channel 4 is provided at the top of the fiber core 2. An inner hexagonal vent ring 5 is disposed inside the fiber core 2, and an outer hexagonal vent ring 6 is formed outside the inner hexagonal vent ring 5. A first circular hole 7 is formed at the bottom of the fiber core 2, directly above the first channel 3, and a second circular hole 8 is formed at the top of the fiber core 2, directly below the second channel 4.

[0042] In the description of this invention, the top and bottom of the fiber core 2 are both D-shaped surfaces, and the material of the fiber core 2 is silicon dioxide.

[0043] In the description of this invention, the first channel 3 has a rectangular structure, and the second channel 4 has a semi-arc structure. A gold thin film 9 is disposed on the surface of both the first channel 3 and the second channel 4, and the thickness of the gold thin film 9 is 40 nm. A polydimethylsiloxane layer 10 is disposed on the surface of the gold thin film 9 in the first channel 3, and the thickness of the polydimethylsiloxane layer 10 is 160 nm.

[0044] Compared to silver and copper, metal nanoparticles are more stable and less prone to oxidation. Their localized surface plasmon resonance covers most of the visible and near-infrared wavelength range. Therefore, a gold thin film was fabricated on the surfaces of the first channel 3 and the second channel 4. Experiments were conducted to analyze and compare the limiting losses of the gold thin film within the range of 30–50 nm. When the gold thin film thickness was 40 nm, the signal-to-noise ratio of the sensor was reduced, and the coupling effect between the core mode and the surface plasmon mode was significantly enhanced, thereby improving the sensor's sensitivity.

[0045] On the gold thin film 9 of the first channel 3, a polydimethylsiloxane temperature-sensitive material is coated. Since the refractive index of polydimethylsiloxane changes with temperature in the form of n... PDMS = -4.5 × 10 -4 With a transmittance of T+1.4176, it exhibits excellent light transmittance, maintaining over 90% transmittance in the visible light wavelength range. Experiments analyzed and compared the detection sensitivity of polydimethylsiloxane within the thickness range of 150–170 nm. The highest sensitivity to the ambient temperature of the analyte was observed at a thickness of 160 nm.

[0046] Confinement loss (CL) is the decrease in light intensity when light enters from one end of an optical fiber and exits from the other. This means that some of the light energy is attenuated after the optical signal propagates through the fiber. This indicates that some material in the fiber, or for some other reason, obstructs the passage of the light signal. The greater the confinement loss, the stronger the surface plasmon resonance.

[0047] In the description of the present invention, the inner hexagonal vent ring 5 includes two inner top holes 501 and four inner ring holes 502. The two inner top holes 501 and the four inner ring holes 502 are arranged in a regular hexagonal structure with an adjacent spacing angle of 60°. The two inner top holes 501 are arranged side by side on the top of the regular hexagonal structure.

[0048] The inner top hole 501 in the inner hexagonal vent ring 5 is reduced in proportion to the outer top hole 601, so as to accumulate a stronger excitation field for the sensor and excite more surface electrons.

[0049] In the description of the present invention, the distance between the two inner ring holes 502 located at the bottom of the regular hexagonal structure is 2 μm, the diameter of the inner top hole 501 is 1.3 μm, and the diameter of the inner ring holes 502 is 1.7 μm.

[0050] The distance between the two inner ring holes 502 at the bottom of the regular hexagonal structure is denoted as Λ, i.e., Λ = 2μm. Then the diameter of the inner top hole 501 is 0.65Λ, and the diameter of the inner ring hole 502 is 0.85Λ.

[0051] In the description of the present invention, the outer hexagonal vent ring 6 includes two outer top holes 601 and six outer ring holes 602. The two outer top holes 601 and the six outer ring holes 602 are arranged at equal intervals in a D-shaped structure, and the two outer top holes 601 are distributed side by side on the top of the D-shaped structure.

[0052] Depend on Figure 2 It is known that the first exhaust hole at the top of the hexagonal ring 6, which is composed of the outer ring hexagonal vent ring, has been etched, and the remaining part forms a D-shaped structure to generate a double D-shaped photonic crystal fiber with an open channel. The two continuous vent holes on the outer ring are placed at a 30-degree angle. The diameter of the air hole (outer ring hole 602) is 1.7 μm (0.85Λ). The second exhaust hole (outer top hole 601) is reduced to 0.65Λ, or 1.3 μm, in proportion to the inner top hole 501, thereby accumulating a stronger evanescent field and exciting more surface electrons.

[0053] The six outer ring holes 602 are divided into two groups and distributed on both sides of the D-shaped structure. The angle between the outer top hole 601 and the outer ring hole 602 on the same side is 30°, and the angle between the two outer ring holes 602 at the bottom of the D-shaped structure is 60°.

[0054] In the description of the present invention, the diameter of the outer top hole 601 is 1.3 μm (0.65Λ), and the diameter of the outer annular hole 602 is 1.7 μm (0.85Λ).

[0055] In the description of this invention, the first circular hole 7 is located at the top of the regular hexagonal structure formed by the inner hexagonal vent ring 5, and the second circular hole 8 is located directly below the D-shaped structure formed by the outer hexagonal vent ring 6. The diameters of the first circular hole 7 and the second circular hole 8 are both 1 μm (0.5Λ).

[0056] Two circular holes, each 1 μm in diameter, were placed near the first channel 3 and the second channel 4 to form two field strength cores. The slightly smaller diameter of these holes was designed not to obstruct the transmission path of the channel light. Two D-shaped surfaces were fabricated at the top and bottom of the photonic crystal fiber, respectively. This structure of the photonic crystal fiber greatly reduces the distance between the sensing material and the fiber core, which is more conducive to increasing the surface plasmon resonance field strength of the sensor's double D-surfaces.

[0057] Photonic crystal fiber (PCF), also known as micro-structured fiber (MSF), has a complex refractive index distribution on its cross-section and usually contains pores arranged in different ways. The size of these pores is roughly on the same order of magnitude as the wavelength of light and runs through the entire length of the device. Light waves can be confined to propagate in the low-refractive-index fiber core region.

[0058] Surface plasmon resonance (SPR) is a novel analytical technique based on optical principles. It refers to the resonance phenomenon that occurs when light undergoes total internal reflection on the surface of a prism or metal film, forming an evanescent wave that enters a less optically dense medium. Meanwhile, a plasma wave exists within the medium (hypothetically a precious metal). Based on the principle of energy conservation, these two wavebands may resonate when they meet. This technique can detect interactions between antigens and antibodies, DNA and proteins, and DNA and DNA molecules, and has been widely applied in life sciences, medical diagnostics, food safety, and environmental monitoring.

[0059] In the description of this invention, confinement loss is a crucial characteristic characterizing the properties of a surface plasmon resonance sensor; it represents the ability of an optical waveguide to confine incident light. Higher confinement loss results in greater penetration of the evanescent field into the cladding. It is defined as:

[0060]

[0061] In the formula, λ represents the incident wavelength, and Im(neff) is the imaginary part of the effective refractive index.

[0062] This invention primarily optimizes the characteristics of a surface plasmon resonance sensor operating in photonic crystal fiber at T = 50℃. Wavelength sensitivity (S w The calculation method for ) is as follows:

[0063]

[0064] In the formula, Δλ peak The wavelength shift distance between two adjacent resonance peaks, expressed in nanometers, Δn. a S represents the change in the refractive index (RI) of a liquid. w (nm / RIU) is a unit for nanometers / refractive index.

[0065] Based on structural parameters, analyte refractive index, and temperature analysis, channel 3 is significantly affected by the refractive index and temperature of the liquid analyte, while channel 4 is significantly affected by the refractive index of the analyte but almost unaffected by temperature. Therefore, the matrix expressions for the effects of liquid refractive index and temperature changes on channels 3 and 4 are as follows:

[0066]

[0067] In the formula, Δλ Ⅰ This represents the wavelength change of the first channel 3, Δλ. Ⅱ This represents the wavelength change of the second channel 4, Δn. a ΔT represents the change in refractive index of the liquid, ΔT represents the change in operating temperature, and K represents the sensitivity coefficient matrix. nI =2180nm / RIU, K nII =2000nm / RIU, K TI = -0.31nm / ℃, K TII =0 nm / ℃. Therefore, the liquid refractive index and temperature change values ​​for the two sensing channels are:

[0068]

[0069] In the description of this invention, the use of fiber optic sensors and experimental apparatus are as follows: Figure 3 As shown. (A) A light source that generates polarized incident light is coupled to (B) a polarization controller to produce X- or Y-polarized light. This light source is connected to the sensor via a fiber coupler at the output end of a single-mode fiber (F1). Next, a pump controls the injection of liquid analyte into the sensor through the inlet (C), and excess analyte sample flows out through the outlet (D). The incident light interacts with the two detection channels of the sensor, and the transmitted light is output through a fiber coupler connected to the single-mode fiber (F2) and forms a spectrum in an optical spectrometer (G). The spectrometer is connected to a computer (H) for data analysis, which can qualitatively and quantitatively analyze the injected sample and the sensor's operating temperature. When the refractive index of the analyte or the sensor's operating temperature changes, the phase matching condition and confinement loss will change, which will cause a blue shift or red shift in the resonance peaks of the two sensing channels. The shift of the resonance peaks can also be used to detect the refractive index and temperature of the analyte.

[0070] Experiments were conducted using the aforementioned apparatus, by separately controlling the refractive index of the analyte and the operating temperature of the sensor, such as... Figure 4The diagram shows the limiting losses of the two sensing channels. When the temperature is maintained at 50°C, the refractive index decreases from 1.36 to 1.35. The peak values ​​of the first channel 3 (labeled as channel I in the figure) and the second channel 4 (labeled as channel II in the figure) show blue shifts of 20 nm and 30 nm, respectively. When the refractive index is maintained at 1.36 and the temperature decreases from 50°C to 0°C, the first channel 3 is red-shifted by 20 nm, while the second channel 4 remains unchanged. This is mainly because the polydimethylsiloxane thermosensitive material is only coated on the first channel 3, and the temperature change has no effect on the second channel 4. These two sets of experimental results and analysis demonstrate that the surface plasmon resonance sensor of this invention can simultaneously detect changes in the refractive index of the analyte and the operating temperature without mutual interference, indicating the excellent performance of the sensor.

[0071] In addition, the present invention uses the finite element method for simulation calculation, with a perfectly matched layer as the boundary condition. The sensor structure adopts a fine triangular mesh division, with the largest mesh cell size being 1.32 μm and the smallest cell size being 0.0264 μm. The complete mesh contains 38,511 degrees of freedom, 5,130 domain elements and 718 boundary elements.

[0072] Under the initial geometric conditions, T = 50℃, n a =1.36, the electric field distribution modes of various parts in the sensor of the present invention: the first channel 3 and the second channel 4 are in the basic core mode, indicating that light can be transmitted uniformly and stably in the fiber core. The gold thin film 9 is in the surface plasmon polariton mode, and it is the electric field entering the gold surface that causes the surface plasmon resonance effect in the sensor.

[0073] The surface plasmon resonance sensor of the present invention has two sensing channels, which can generate two tunable resonance peaks, enabling a strong response at the resonance wavelength (phase matching point), with a large amount of energy being converted from the basic core mode to the surface plasmon polariton mode.

[0074] like Figure 5 This shows the refractive index (n) a The relationship between the sensor's confinement loss and wavelength is shown on the x-axis, where wavelength is on the x-axis and confinement loss is on the y-axis, within the range of 1.31-1.36. It can be seen that as the refractive index increases, the resonant wavelength shifts to longer wavelengths. Simultaneously, the optical leakage of the fiber core continuously increases, and the confinement loss values ​​of both channels continue to increase. When n... a When the value is 1.36, the plasma resonance phenomenon is strongest in both channels, and the confinement loss reaches its maximum value. The first channel 3 is 463.19 dB / cm, and the second channel 4 is 204.49 dB / cm.

[0075] Figure 6The fitted relationship between the refractive index of the analyte and the corresponding resonant wavelength was plotted, with the x-axis representing the refractive index and the y-axis representing the resonant wavelength. For channel 3, the fitted polynomial between the analyte's refractive index and the resonant wavelength is λ = 16.07n. a 2 -41.53n a +28.04, R 2 The value is 0.994, indicating a very good fit and a high spectral wavelength sensitivity λ. s =32.14n a -41.53. When the refractive index of the liquid analyte is 1.36, a maximum wavelength sensitivity of 2180 nm / RIU can be obtained, with a corresponding resolution of 4.58 × 10⁻⁶. - 5 RIU.

[0076] The first channel 3 is coated with polydimethylsiloxane, which allows for simultaneous temperature detection. a =1.36 and when T ranges from -25 to 150℃, the increase in temperature causes a blue shift in the peak value of the resonance wavelength, such as Figure 7 As shown, the horizontal axis represents refractive index, and the vertical axis represents confinement loss. Simultaneously, the maximum interaction occurred between the surface plasmon polariton mode and the core mode. The resonance effect was strongest at T = 50℃, with a maximum confinement loss of 463.19 dB / cm. The polynomial fitting equation for the temperature measurement in channel 3 is λ = -4.76 × 10⁻⁶. -8 *T 2 -2.96×10 -4 *T+1.296, R 2 It is 0.973, such as Figure 8 As shown. Differentiating the fitted equation with respect to T, we get λ = -9.52 × 10⁻⁶. -8 *T-2.96×10 -4 With a maximum temperature sensitivity of approximately -0.31 nm / ℃, this sensor exhibits excellent temperature characteristics.

[0077] Please see Figure 9 It also provides a fabrication process for a dual-D structure fiber optic sensor that simultaneously detects refractive index and temperature, which includes the following steps:

[0078] S1. The micro-nano structure of the optical fiber is formed by ultrasonic stamping technology and laser drilling is used.

[0079] S2. The photonic crystal fiber semi-finished product is cut into a double D-shaped microgroove structure by polishing technology.

[0080] S3. Micro-process the sensitive materials of the first channel 3 and the second channel 4 to deposit gold on the polished surface of the microgrooves on both sides to form a gold film 9.

[0081] S4. Combine the first channel 3 with the polydimethylsiloxane material and apply a polydimethylsiloxane layer 10 on the surface of the gold film 9.

[0082] S5. A dual-channel photonic crystal fiber-surface plasmon resonance sensor was fabricated.

[0083] In summary, by combining the microstructure design of photonic crystal fiber with the high-sensitivity technology of surface plasmon resonance, the present invention offers advantages such as real-time monitoring, no need for marking, and low interference. Replacing ordinary optical fiber with photonic crystal fiber as a sensor can solve the phase matching problem, thereby achieving high-sensitivity and multifunctional real-time sensing measurements. The present invention effectively improves sensing sensitivity by optimizing the structure and employing a novel dual-parallel D-shaped photonic crystal fiber-surface plasmon resonance configuration to enhance the coupling efficiency between the core guided mode and the plasmon mode, resulting in performance significantly superior to dual-parallel optical fibers. By designing a photonic crystal fiber with a double D-type structure based on surface plasmon resonance, the core mode and surface plasmon mode are enhanced, resulting in superior performance. This allows for the simultaneous detection of the refractive index and operating temperature of liquid analytes. Employing a unique dual-channel and asymmetric structure, and optimizing the fiber's geometric parameters, gold film thickness, and other coating material thicknesses, the cross-sensitivity problem of the sensor is effectively solved, improving detection sensitivity and measurement accuracy. Furthermore, this sensor achieves a wavelength sensitivity of 2180 nm / RIU for liquids with refractive indices between 1.31 and 1.36, and a temperature sensitivity of -0.31 nm / ℃ over an extremely wide operating temperature range of -25℃ to 150℃. Its high precision, low cost, simplicity, and real-time performance make it a novel sensing unit, providing a new solution for the design and implementation of distributed measurement systems.

[0084] It should be understood that although the steps in the flowcharts of the accompanying figures are shown sequentially as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the accompanying figures may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

Claims

1. A dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature, characterized in that, The fiber optic sensor includes a cladding (1) and a fiber core (2) is disposed inside the cladding (1). The fiber core (2) has a first channel (3) at the bottom end and a second channel (4) at the top end. The fiber core (2) has an inner hexagonal air hole ring (5) inside and an outer hexagonal air hole ring (6) outside the inner hexagonal air hole ring (5). A first circular hole (7) is provided at the bottom of the fiber core (2) and directly above the first channel (3), and a second circular hole (8) is provided at the top of the fiber core (2) and directly below the second channel (4). The top and bottom of the fiber core (2) are both D-shaped surfaces, and the material of the fiber core (2) is silicon dioxide; The first channel (3) is a rectangular structure, and the second channel (4) is a semi-arc structure. Both the first channel (3) and the second channel (4) are provided with a gold film (9), and the thickness of the gold film (9) is 40nm. A polydimethylsiloxane layer (10) is provided on the surface of the gold film (9) in the first channel (3), and the thickness of the polydimethylsiloxane layer (10) is 160 nm. The first circular hole (7) is located at the top of the regular hexagonal structure formed by the inner hexagonal vent ring (5), and the second circular hole (8) is located directly below the D-shaped structure formed by the outer hexagonal vent ring (6). The diameters of the first circular hole (7) and the second circular hole (8) are both 1 μm.

2. The dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to claim 1, characterized in that: The inner hexagonal vent ring (5) includes two inner top holes (501) and four inner ring holes (502). The two inner top holes (501) and the four inner ring holes (502) are arranged in a regular hexagonal structure with an adjacent spacing angle of 60°. The two inner top holes (501) are arranged side by side on the top of the regular hexagonal structure.

3. The dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to claim 2, characterized in that: The distance between the two inner ring holes (502) located at the bottom of the regular hexagonal structure is 2μm, the diameter of the inner top hole (501) is 1.35μm, and the diameter of the inner ring hole (502) is 1.7μm.

4. The dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to claim 3, characterized in that: The outer hexagonal vent ring (6) includes two outer top holes (601) and six outer ring holes (602). The two outer top holes (601) and the six outer ring holes (602) are arranged at equal intervals in a D-shaped structure. The two outer top holes (601) are distributed side by side on the top of the D-shaped structure. The six outer ring holes (602) are divided into two groups and distributed on both sides of the D-shaped structure. The angle between the outer top hole (601) and the outer ring hole (602) on the same side is 30°, and the angle between the two outer ring holes (602) at the bottom of the D-shaped structure is 60°.

5. The dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to claim 4, characterized in that: The diameter of the outer top hole (601) is 1.3 μm, and the diameter of the outer ring hole (602) is 1.7 μm.

6. The dual-D structure fiber optic sensor for simultaneous detection of refractive index and temperature according to claim 1, characterized in that: The matrix expressions for the influence of liquid refractive index and temperature changes on the first channel (3) and the second channel (4) are as follows: ； In the formula, This indicates the wavelength change of the first channel (3); This indicates the wavelength change of the second channel (4); It represents the change in the refractive index of a liquid; Indicates changes in operating temperature; K represents the sensitivity coefficient matrix; K nI =2180nm / RIU; K nII =2000nm / RIU; K TI =-0.31nm / ℃; K TII =0nm / ℃。 7. A fabrication process for a dual-D structure fiber optic sensor for simultaneous refractive index and temperature detection, used to fabricate the dual-D structure fiber optic sensor for simultaneous refractive index and temperature detection as described in any one of claims 1-6, characterized in that, The manufacturing process includes the following steps: S1. The micro-nano structure of optical fiber is formed by ultrasonic stamping technology and laser drilling is used; S2. The semi-finished photonic crystal fiber is cut into a double D-shaped microgroove structure by polishing technology; S3. Micro-process the sensitive materials of the first channel (3) and the second channel (4) to deposit gold on the polished surface of the microgrooves on both sides to form a gold film (9). S4. Combine the first channel (3) with polydimethylsiloxane material and coat the surface of the gold film (9) with a polydimethylsiloxane layer (10). S5. A dual-channel photonic crystal fiber-surface plasmon resonance sensor was fabricated.

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