Dual-monitoring-range d-shaped photonic crystal fiber refractive index sensor and application

Abstract

This invention relates to the field of fiber optic sensing technology, and provides a D-type photonic crystal fiber refractive index sensor with dual monitoring ranges and its applications. The sensor includes a substrate material, a first cladding air hole, a second cladding air hole, a gold film, and a matching layer. The sensor has a D-shaped cross-section, with a platform at the top and an arc at the bottom. The substrate material is located inside the D-shaped structure, and the matching layer is disposed around the periphery of the substrate material. The first and second cladding air holes are sequentially disposed in the substrate material. The first cladding air hole is located on the upper part near the platform, and the second cladding air hole is located below the first cladding air hole. A gold film is deposited on the outer side of the platform. The sensor of this invention has different liquid refractive index monitoring ranges in the X-polarization direction and the Y-polarization direction. The liquid refractive index monitoring range of the sensor in the X-polarization direction is 1.340–1.580, and the liquid refractive index monitoring range in the Y-polarization direction is 1.340–1.390.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a D-type photonic crystal fiber refractive index sensor with dual monitoring ranges and its applications. Background Technology

[0002] Surface plasmon resonance (SPR) sensors based on photonic crystal fiber (PCF) have attracted much attention due to their high sensitivity and wide measurement range. Surface plasmon resonance (SPR) is an optical phenomenon in which the resonance wavelength varies with the effective refractive index. SPR sensors utilize the evanescent wave of light during total internal reflection to excite free electrons on a metal surface, generating a plasma surface wave. When the evanescent wave and the plasma surface wave propagation constant are equal, resonance occurs, disrupting the total internal reflection condition at the interface and causing a sharp drop in the energy of the reflected light, resulting in a resonance peak in the reflection spectrum. SPR sensors offer advantages such as light weight, compact structure, high signal-to-noise ratio, remote sensing capability, ability to perform in vivo measurements, and ease of adjustment. SPR sensors have wide applications in biological and chemical analysis, medical diagnostics, and food quality control.

[0003] Currently, SPR sensors mainly come in two forms: one involves selectively or completely filling photonic crystal fibers with gold films and liquids; the other involves removing a portion of the photonic crystal fiber to form a D-shape, while simultaneously coating the sides with a thin metal film. Each approach has its advantages. Xia Yu et al. proposed a surface plasmon resonance sensor based on selectively coated photonic crystal fibers, achieving a refractive index sensitivity as high as 5500 nm / RIU. Fan Zhenkai et al. achieved a sensitivity of 7040 nm / RIU based on an analyte-filled PCF sensor. In this type of sensor, filling photonic crystal fibers with metals and liquids of different refractive indices is very difficult. Rahul Kumar Ganhwar et al. proposed a high-sensitivity D-shaped PCF refractive index sensor based on SPR, with an average sensitivity of 7700 nm / RIU, ranging from 1.43 to 1.46. It should be noted that existing D-shaped photonic crystal fiber SPR sensors are mostly single-polarization direction detection refractive index sensors. While these sensors have high sensitivity, their measurement range is limited, making them difficult to widely apply in large-range liquid refractive index monitoring. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a D-type photonic crystal fiber refractive index sensor with dual monitoring ranges and its application. This sensor has different liquid refractive index monitoring ranges in the X-polarization direction and the Y-polarization direction.

[0005] The present invention adopts the following technical solution:

[0006] On one hand, the present invention provides a D-type photonic crystal fiber refractive index sensor with dual monitoring range, comprising a substrate material, a first cladding air hole, a second cladding air hole, a gold film, and a matching layer;

[0007] The sensor has a D-shaped cross-section, with a platform at the top and an arc at the bottom; the interior of the D-shaped structure is a substrate material, and the matching layer is disposed around the substrate material.

[0008] The first cladding air hole and the second cladding air hole are sequentially disposed in the substrate material; the first cladding air hole is located on the upper side near the platform, and the second cladding air hole is located below the first cladding air hole;

[0009] A layer of gold film is deposited on the outer side of the platform.

[0010] In addition to any of the possible implementations described above, a further implementation is provided in which the diameter of the second cladding air hole is larger than the diameter of the first cladding air hole.

[0011] In addition to any of the possible implementations described above, a further implementation is provided in which the first cladding air hole includes three semi-circular air holes and four circular air holes; the three semi-circular air holes are disposed immediately adjacent to the platform and are used to fill the liquid to be tested; the four circular air holes are disposed below the three semi-circular air holes.

[0012] In addition to any of the possible implementations described above, another implementation is provided in which the second cladding air holes are multiple and arranged in several rows below the first cladding air holes.

[0013] In addition to any of the possible implementations described above, another implementation is provided in which the number of air holes in the second cladding layer is 13, arranged in 4 rows in sequence.

[0014] In addition to any of the possible implementations described above, another implementation is provided in which the substrate material is pure silicon dioxide for transmitting broadband laser light.

[0015] In addition to any of the possible implementations described above, another implementation is provided in which the material of the matching layer is silicon dioxide.

[0016] In addition to any of the possible implementations described above, another implementation is provided in which the diameter of the first cladding air hole is 1.2 μm, the diameter of the second cladding air hole is 1.6 μm, the thickness of the gold film is 30 nm, the spacing between adjacent cladding air holes is 2 μm, and the wavelength range of the broadband light source used in the test is 1.0–2.4 μm.

[0017] On the other hand, the present invention also provides an application of the above-mentioned dual-monitoring-range D-type photonic crystal fiber refractive index sensor, wherein the sensor is used for the determination of liquid refractive index, and the specific determination method includes:

[0018] S1. Place the D-type photonic crystal fiber refractive index sensor with dual monitoring range into the liquid to be tested. One side of the sensor is connected to a broadband light source, and the other side is connected to a spectrometer via a polarization filter.

[0019] S2. Turn on the broadband light source, and the laser is transmitted to the D-shaped structure of the sensor. It undergoes a plasma resonance effect with the gold film, which causes the loss of light waves of a specific wavelength in the optical fiber to increase. The spectrometer records the received light wave signal.

[0020] S3. Analyze the beam intensity signals received by the spectrometer at different wavelengths in the X-polarization or Y-polarization direction to obtain the refractive index of the liquid under test in the X-polarization or Y-polarization direction at different wavelengths.

[0021] This invention proposes a fiber optic sensor with a simple structure, easy industrial production, and adjustable liquid refractive index monitoring range. The advantages of this invention are: it combines high sensitivity and a wide monitoring range; the sensor achieves good sensing performance in both x-polarization and y-polarization modes, which is rare among similar sensors reported to date; the sensor structure is simple and easy to manufacture, and it has broad application prospects in biosensors. Attached Figure Description

[0022] Figure 1 The diagram shown is a schematic representation of the structure of a D-type photonic crystal fiber refractive index sensor with dual monitoring ranges according to an embodiment.

[0023] Figure 2 The figure shows the refractive index monitoring results in the X-polarization direction in the embodiment.

[0024] Figure 3 The figure shows the refractive index monitoring results in the Y-polarization direction in the embodiment.

[0025] In the figure: 1-substrate material; 2-first cladding air pores; 3-second cladding air pores; 4-gold film; 5-matching layer; 6-liquid to be tested. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered in isolation, but can be combined with each other to achieve better technical effects.

[0027] like Figure 1As shown, an embodiment of the present invention provides a D-type photonic crystal fiber refractive index sensor with dual monitoring ranges, comprising a substrate material, a first cladding air hole, a second cladding air hole, a gold film, and a matching layer;

[0028] The sensor has a D-shaped cross-section, with a platform at the top and an arc at the bottom; the interior of the D-shaped structure is a substrate material, and the matching layer is disposed around the substrate material.

[0029] The first cladding air hole and the second cladding air hole are sequentially disposed in the substrate material; the first cladding air hole is located on the upper side near the platform, and the second cladding air hole is located below the first cladding air hole;

[0030] A layer of gold film is deposited on the outer side of the platform.

[0031] In one specific embodiment, the diameter of the second cladding air hole is larger than the diameter of the first cladding air hole.

[0032] The optical fiber is made of silicon dioxide with a refractive index of 1.46, while air has a refractive index of 1. In this invention, the purpose of the air holes in the fiber cladding is to reduce the effective refractive index in the area where the air holes are located, thereby confining the beam to the fiber core for transmission (total internal reflection condition). Different diameters of the air holes result in different effective refractive indices; in the photonic crystal fiber used in this invention, the beam mainly propagates within the silicon dioxide (i.e., outside the air holes), and the small diameter of the upper air holes is beneficial for the beam to achieve plasmonic resonance (high intensity) with the gold film.

[0033] In one specific embodiment, the diameter of the second cladding air hole is larger than the diameter of the first cladding air hole.

[0034] In one specific embodiment, the first cladding air hole includes three semi-circular air holes and four circular air holes; the three semi-circular air holes are arranged in a row adjacent to the platform and are used to fill the liquid to be tested; the four circular air holes are arranged in a row below the three semi-circular air holes.

[0035] In one specific embodiment, there are multiple second cladding air holes, arranged in several rows below the first cladding air holes.

[0036] In one specific embodiment, the second cladding layer has 13 air holes arranged in four rows; the top two rows each have four air holes, the third row has three air holes, and the fourth row has two air holes. The arrangement of the air holes can vary, differing only in their ability to constrain the base film. In this embodiment, the arrangement provides the best beam confinement effect.

[0037] In one specific embodiment, the substrate material is pure silicon dioxide, used for transmitting broadband laser light.

[0038] In one specific embodiment, the matching layer is made of silicon dioxide and has a thickness of 5 μm; the function of the matching layer is to confine the light beam to the fiber core for transmission as much as possible.

[0039] The choice of air hole diameter is not random; only with air holes of a specific diameter can the fiber core allow transmission solely through the base film. The sensor principle relies on the regular change in fundamental mode intensity with the external environment. If the air hole is too small, higher-order modes will be excited in the fiber core, affecting the base film strength; if the air hole is too large, the plasma resonance effect generated by the base film and gold film in the fiber core will be very weak.

[0040] In one specific embodiment, the diameter of the first cladding air hole is 1.2 μm, the diameter of the second cladding air hole is 1.6 μm, the gold film thickness is 30 nm, and the spacing between adjacent cladding air holes is 2 μm; the wavelength range of the broadband light source used in the test is 1.0–2.4 μm. Under the air hole diameter of this embodiment, the matching effect of the base film strength and the plasmon resonance effect generated by the base film and the gold film achieves optimal results.

[0041] This invention relates to an application of the aforementioned dual-monitoring-range D-type photonic crystal fiber refractive index sensor, wherein the sensor is used for measuring the refractive index of a liquid, and the specific measurement method includes:

[0042] S1. Place the D-type photonic crystal fiber refractive index sensor with dual monitoring range into the liquid to be tested. One side of the sensor is connected to a broadband light source, and the other side is connected to a spectrometer via a polarization filter.

[0043] S2. Turn on the broadband light source, and the laser is transmitted to the D-shaped structure of the sensor. It undergoes a plasma resonance effect with the gold film, which causes the loss of light waves of a specific wavelength in the optical fiber to increase. The spectrometer records the received light wave signal.

[0044] S3. Analyze the beam intensity signals received by the spectrometer at different wavelengths in the X-polarization or Y-polarization direction to obtain the refractive index of the liquid under test in the X-polarization or Y-polarization direction at different wavelengths.

[0045] Example

[0046] The described dual-monitoring-range D-type photonic crystal fiber refractive index sensor uses pure silicon dioxide as its substrate material 1. The first cladding air holes 2 and the second cladding air holes 3 are arranged in two hexagonal layers with a spacing of 2 μm. The diameter of the first cladding air hole 2 is 1.2 μm, and the diameter of the second cladding air hole 3 is 1.6 μm. The gold film 4 has a thickness of 30 nm. The broadband light source used in the test has a wavelength range of 1.0–2.4 μm. This type of sensor is based on the surface plasmon resonance effect between the plasmon mode and the fiber core mode. Light waves in optical fibers mainly exist in two modes: X-polarization mode and Y-polarization mode. When surface plasmons resonate with the polarization mode, a large amount of energy is absorbed by the metal in the fiber core polarization mode, resulting in a loss peak in the transmission spectrum.

[0047] By adding a polarization filter to the receiving end of a D-type photonic crystal fiber refractive index sensor, the spectrometer can selectively receive light intensity in either the X-polarized or Y-polarized direction from the light source. During the fabrication of the photonic crystal fiber, by reducing the diameter of the air hole on one side, light energy can be leaked as much as possible to the gold film surface, enhancing the surface plasmon resonance effect of the sensor.

[0048] The experimental results are as follows:

[0049] Based on this embodiment, a D-type photonic crystal fiber refractive index sensor with dual monitoring ranges was developed. The linearity in the X-polarization direction is 0.99866, the sensitivity is 6969.8 nm / RIU, the monitoring range for the refractive index of the liquid under test is 1.340–1.580, and the relationship between the resonant wavelength and refractive index is y = 6969.78022x - 7598.18681. The results are as follows... Figure 2 As shown; the linearity in the Y-polarization direction is 0.98897, the sensitivity is 14816.7 nm / RIU, the monitoring range of the refractive index of the liquid under test is 1.340~1.390, and the relationship between the resonance wavelength and the refractive index is y=21777.08333-14816.6666x. The results are as follows. Figure 3 As shown.

[0050] While several embodiments of the present invention have been provided herein, those skilled in the art should understand that modifications can be made to these embodiments without departing from the spirit of the invention. The above embodiments are merely exemplary and should not be construed as limiting the scope of the invention.

Claims

1. A dual monitoring range D-shaped photonic crystal fiber refractive index sensor, characterized in that, The sensor includes a substrate material, a first cladding air hole, a second cladding air hole, a gold film, and a matching layer; The sensor has a D-shaped cross-section, with a platform at the top and an arc at the bottom; the interior of the D-shaped structure is a substrate material, and the matching layer is disposed around the substrate material. The first cladding air pore and the second cladding air pore are sequentially disposed in the substrate material; The first cladding air hole is located on the upper side near the platform, and the second cladding air hole is located below the first cladding air hole; and the diameter of the second cladding air hole is larger than the diameter of the first cladding air hole; the first cladding air hole includes 3 semi-circular air holes and 4 circular air holes, the 3 semi-circular air holes are located immediately adjacent to the platform; the 4 circular air holes are located below the 3 semi-circular air holes; A layer of gold film is deposited on the outer side of the platform.

2. The dual monitoring range D-shaped photonic crystal fiber refractive index sensor of claim 1, wherein, The second cladding air holes are multiple and arranged in several rows below the first cladding air holes.

3. The D-type photonic crystal fiber refractive index sensor with dual monitoring range as described in claim 2, characterized in that, The second cladding layer has 13 air holes, arranged in 4 rows.

4. The D-type photonic crystal fiber refractive index sensor with dual monitoring range as described in claim 1, characterized in that, The substrate material is silicon dioxide, which is used to transmit broadband laser light.

5. The D-type photonic crystal fiber refractive index sensor with dual monitoring range as described in claim 1, characterized in that, The matching layer is made of silicon dioxide.

6. The D-type photonic crystal fiber refractive index sensor with dual monitoring range as described in claim 1, characterized in that, The diameter of the first cladding air hole is 1.2 μm, the diameter of the second cladding air hole is 1.6 μm, the thickness of the gold film is 30 nm, and the spacing between adjacent cladding air holes is 2 μm; the wavelength range of the broadband light source used in the test is 1.0 ~ 2.4 μm.

7. The application of the dual-monitoring-range D-type photonic crystal fiber refractive index sensor as described in any one of claims 1-6, characterized in that, The sensor is used to determine the refractive index of liquids.

8. The application of the D-type photonic crystal fiber refractive index sensor with dual monitoring range as described in claim 7, characterized in that, The specific method for determining the refractive index of a liquid using the aforementioned sensor includes: S1. Place the D-type photonic crystal fiber refractive index sensor with dual monitoring range into the liquid to be tested. One side of the sensor is connected to a broadband light source, and the other side is connected to a spectrometer via a polarization filter. S2. Turn on the broadband light source, and the laser is transmitted to the D-shaped structure of the sensor. It undergoes a plasma resonance effect with the gold film, which causes the loss of light waves of a specific wavelength in the optical fiber to increase. The spectrometer records the received light wave signal. S3. Analyze the beam intensity signals received by the spectrometer at different wavelengths in the X-polarization or Y-polarization direction to obtain the refractive index of the liquid under test in the X-polarization or Y-polarization direction at different wavelengths.

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