Highly sensitive photonic crystal fiber sensor for simultaneous detection of two samples

Abstract

The invention discloses a high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection, comprising a substrate, small air holes arranged around the center of the substrate, the center of the substrate being a fiber core, an upper large air hole A being arranged on the substrate above the small air hole, a lower large air hole B being arranged on the substrate below the small air hole, the small air holes being arranged in three layers radially from the inside to the top with the center of the substrate as the center, the first layer of small air holes being the closest to the center, and the second layer of small air holes and the third layer of small air holes being arranged outwards in sequence, the second layer of small air holes being elliptical holes, the first layer of small air holes and the third layer of small air holes being circular holes, and a layer of gold nanofilm of the same thickness being deposited on the planes of the upper large air hole A and the lower large air hole B. The invention has the characteristics of high sensitivity, convenient preparation, high detection efficiency, etc., and is more conducive to use in sensor production practice.

Description

Technical Field

[0001] The invention relates to the field of photonic crystal optical fibers, and in particular to a photonic crystal optical fiber sensor for dual-sample synchronous detection based on surface plasma resonance. Background Art

[0002] Photonic Crystal Fiber (PCF) is a special optical fiber developed on the basis of two-dimensional photonic crystals. It is also a new type of optical fiber that is currently being widely studied. Compared with traditional optical fibers, PCF has a large degree of freedom in design, which makes it flexible in terms of birefringence, flatness and negative dispersion, effective area and nonlinearity. Therefore, PCF has become a research focus in the field of sensors. In the early days, PCF could not be applied on a large scale due to the influence of drawing process and drawing accuracy. Due to the maturity of the process in recent years, circular optical fibers can be made into D-type optical fibers, and then gold film can be coated on the plane. Since the metal coating on the plane can better contact the liquid to be measured, the sensing effect is more prominent. This is also one of the hot areas of current research.

[0003] Surface Plasmon Resonance (SPR) is a physical optical phenomenon. The reason for SPR is that when light is totally internally reflected on the surface of a medium, an evanescent wave is generated. The evanescent wave can excite the oscillation of free electrons on the metal surface and generate surface plasmon. SPR is formed when the frequency and wave number of the surface plasmon are equal to those of the evanescent wave. Since the resonant oscillation is very sensitive to any tiny change in the refractive index near the boundary, SPR is a very promising sensing detection method. With the in-depth development of science and technology, people have combined PCF and SPR technology and used them for environmental monitoring, water testing, cancer detection, food quality control, etc., and have conducted a lot of research in the past few decades. Summary of the invention

[0004] Based on the application of SPR-PCF in sensors, researchers have made many achievements, but there are also some problems. For example, people blindly pursue the novelty of PCF structure, which leads to the overly complex structure design and difficult preparation; the detectable range of the refractive index of the analyte is narrow; the sensitivity of sensor detection is low; there is only one detection channel for the liquid to be tested; these have greatly limited the application scope and function of PCF sensors, and seeking breakthroughs is imminent.

[0005] The purpose of the present invention is to propose a photonic crystal fiber sensor based on dual-sample synchronous detection with a simple structure, which has the characteristics of high sensitivity, convenient preparation, high detection efficiency, etc. and is more conducive to use in sensor production practice.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A high-sensitivity photonic crystal optical fiber sensor for dual-sample synchronous detection comprises a substrate, small air holes are arranged around the center of the substrate, the center of the substrate is a fiber core, an upper large air hole A is arranged on the substrate above the small air hole, and a lower large air hole B is arranged on the substrate below the small air hole. The small air holes are radially arranged in three layers from the inside to the top with the center of the substrate as the center, the small air holes closest to the center are the first layer of small air holes, and the small air holes of the second layer and the third layer are arranged outwards in sequence, the small air holes of the second layer are elliptical holes, and the small air holes of the first layer and the small air holes of the third layer are circular holes, and a layer of gold nanofilm with the same thickness is deposited on the planes of the upper large air hole A and the lower large air hole B.

[0008] In the high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection, the three layers of small air holes are arranged in a regular hexagonal shape.

[0009] In the high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection, the radius of the first layer of small air holes and the third layer of small air holes are both 0.4 μm, and the spacing between adjacent small air holes is 2 μm, that is, the spacing between the centers of two adjacent small air holes is 2 μm.

[0010] In the high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection, the major axis radius and minor axis radius of the second layer of small air holes are 0.6 μm and 0.4 μm respectively, wherein the major axis is parallel to the plane of the upper large air hole.

[0011] In the high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection, the upper large air hole and the lower large air hole are respectively located just above and just below the fiber core, with a radius of 5.3 μm and a vertical distance of 6 μm from the fiber core.

[0012] In the high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection, the thickness of the gold-plated nanofilm on the plane of the upper large air hole and the thickness of the gold-plated nanofilm on the plane of the lower large air hole are both 40 nm.

[0013] In the high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection, the upper large air hole and the lower large air hole are both D-type holes, but the plane parts of the D-type holes are arranged corresponding to the small air holes.

[0014] By adopting the above technical solution, the beneficial effects of the present invention are:

[0015] The present invention adopts a typical hexagonal double cladding structure, and the vertical distance H between the large air hole channel and the fiber core is larger than that of the conventional PCF sensor. The effective refractive index of the SPP mode is improved, which is conducive to the coupling of the SPP mode and the fiber core mode, and can effectively improve the wavelength sensitivity of the sensor. The sensor is more suitable for the detection of high refractive index samples. The wavelength sensitivity of the sensor reaches up to 16200nm / RIU and 15800nm / RIU, and the refractive index detection range is 1.35-1.41.

[0016] In the present invention, the second layer of the small air hole array is an elliptical air hole, which destroys the rotational symmetry of the optical fiber. Most of the energy of the PCF is confined to the core for transmission, the energy leaked to the gold film surface is reduced, and the energy loss of the core is greatly reduced accordingly. Therefore, there is no need to add an additional high refractive index medium layer in the large air hole channel, which can effectively reduce the operational complexity and make the present invention more feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of the present invention

[0018] Figure 2 This is a schematic diagram of the electric field distribution in the core mode.

[0019] Figure 3 This is the absorption curve of the sensor when the refractive index of the liquid A to be tested is 1.33 and the refractive index of the liquid B to be tested is between 1.35 and 1.41.

[0020] Figure 4 This is a curve of the resonance wavelength and sensitivity changing with the refractive index of the liquid B to be tested when the refractive index of the liquid A to be tested is 1.33.

[0021] Figure 5 This is the absorption curve of the sensor when the refractive index of the measured liquid B is 1.40 and the refractive index of the measured liquid A is between 1.35 and 1.41.

[0022] Figure 6 This is a curve diagram of the resonance wavelength and sensitivity changing with the refractive index of the liquid A to be measured when the refractive index of the liquid B to be measured is 1.40. DETAILED DESCRIPTION

[0023] The following is combined with Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 The structure and working process of the present invention are specifically described in detail.

[0024] A high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection comprises a substrate 1, wherein the substrate material is selected from silicon dioxide with stable performance, and the refractive index is 1.45, small air holes 3 are arranged around the center of the substrate, the center of the substrate is a fiber core, and a large air hole 5 is also provided, the large air hole is a microfluid channel, an upper large air hole A is provided on the substrate above the small air hole, and a lower large air hole B is provided on the substrate below the small air hole, wherein the small air holes are radially arranged from the inside to the top with the fiber core center as the center, the first layer of small air holes is the closest to the center, and the second layer of small air holes 4 and the third layer of small air holes are arranged outwards in sequence, the second layer of small air holes is an elliptical hole, and the first layer of small air holes and the third layer of small air holes are circular holes, and a layer of gold nanofilm 2 of the same thickness is deposited on the plane of the upper large air hole A and the lower large air hole B. During use of the sensor, flat polishing is performed along the plane side of the upper large air hole channel and the plane side of the lower large air hole, so that the optical fiber can be directly immersed in the microfluid, reducing the difficulty of the manufacturing process.

[0025] The high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection of the present invention comprises three layers of small air holes arranged in a regular hexagon, the radii of the first layer of small air holes and the third layer of small air holes are both 0.4 μm, and the spacing L between adjacent small air holes is 2 μm, that is, the spacing between the centers of two adjacent small air holes is 2 μm.

[0026] In the high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection of the present invention, the major axis radius and minor axis radius of the second layer of small air holes are 0.6 μm and 0.4 μm respectively, wherein the major axis is parallel to the plane of the upper large air hole.

[0027] In the high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection of the present invention, the upper large air hole and the lower large air hole are respectively located directly above and directly below the fiber core, with a radius of 5.3 μm and a vertical distance H from the fiber core of 6 μm.

[0028] In the high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection of the present invention, the thickness of the gold-plated nanofilm on the plane of the upper large air hole and the thickness of the gold-plated nanofilm on the plane of the lower large air hole are both 40nm.

[0029] In the high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection of the present invention, the upper large air hole and the lower large air hole are both D-type holes, but the plane parts of the D-type holes are arranged corresponding to the small air holes.

[0030] When the incident TM wave of a certain wavelength meets the phase match of the surface plasmon wave of the gold nanofilm, the core mode and the surface plasmon mode (SPP mode) will be energy coupled at the metal interface, and the light energy in the core mode will be transferred to the metal surface, that is, SPR will be generated, and an absorption peak will appear in the output spectrum. When the refractive index of the medium adjacent to the surface of the gold nanofilm changes, the position of the absorption peak will also move accordingly. Since the SPR generated on the surface of the metal nanolayer is extremely sensitive to the surrounding medium environment, the slight change in the refractive index of the material adjacent to the metal surface is converted into a measurable displacement of the absorption peak, realizing the detection of the refractive index, thereby achieving the purpose of sensing. In the present invention, the vertical distance H between the large air hole channel and the core is 6μm. Figure 2 As shown, since the H value is larger than that of the conventional PCF sensor, the effective refractive index of the SPP mode is improved, which is beneficial to the coupling of the SPP mode and the core mode, can effectively improve the wavelength sensitivity of the sensor, and the sensor is more suitable for the detection of high refractive index samples; on the other hand, most of the energy is confined to the core for transmission, the energy leaked to the gold film surface is reduced, and the core energy loss is greatly reduced accordingly. Therefore, there is no need to add an additional high refractive index medium layer in the large air hole channel, which can effectively reduce the complexity of operation and make the present invention more feasible.

[0031] From the above, we can know that when channels A and B are filled with the liquid to be tested, the gold nanofilms in channels A and B will both produce SPR, so two resonance peaks can be observed in the detection spectrum, such as Figure 3 The refractive index n of the liquid filling the upper microfluidic channel A is shown in a =1.33 remains constant, and the refractive index of the liquid filled in the lower microfluidic channel B is n b When the resonant wavelength of the upper microfluidic channel A changes, it remains near 589nm, and the resonance peak does not change significantly, and is not affected by the change in the refractive index of the liquid filled in the lower microfluidic channel B. Since the second layer of the small air hole array is an elliptical air hole, the rotational symmetry of the optical fiber is destroyed, and a large part of the energy is transmitted in the low-loss air hole, which greatly reduces the optical fiber loss. Figure 3 As shown in the illustration. b When the range of 1.35-1.41 changes, the resonance wavelength and sensitivity change as follows Figure 4 As shown in the figure, the corresponding resonance wavelengths are 621nm, 642nm, 668nm, 701nm, 744nm, 804nm, and 966nm. It can be seen that the greater the difference in the refractive index of the liquids to be tested in the two channels, the wider the corresponding resonance wavelength interval, that is, the stronger the ability to distinguish different liquids to be tested. The highest refractive index wavelength sensitivity detected by the lower microfluidic channel B is 16200nm / RIU. Assuming that the minimum resolution of the spectrometer is 0.01nm, the resolution of the sensor can reach 6.2×10 -7 RIU.

[0032] Similarly, the refractive index of the liquid filling the lower microfluidic channel B is n b =1.40 remains constant, and the refractive index of the liquid filled in the upper microfluidic channel A is n a When the resonant wavelength of the lower microfluidic channel B remains near 804 nm, the resonance peak does not change significantly, and is not affected by the change in the refractive index of the liquid filled in the upper microfluidic channel A. Figure 5 As shown. When the refractive index of the liquid to be measured is n a When the range of 1.35-1.41 changes, the resonance wavelength and sensitivity change as follows Figure 6 As shown in the figure, the corresponding resonance wavelengths are 624nm, 639nm, 668nm, 701nm, 744nm, 806nm, and 964nm. The maximum refractive index wavelength sensitivity detected by channel A is 15800nm / RIU. Assuming that the minimum resolution of the spectrometer is 0.01nm, the resolution of the sensor can reach 6.33×10 -7 RIU.

[0033] The optical fiber based on the hexagonal structure is the simplest structure on the market, and the drawing process is already very mature. The present invention combines the hexagonal double-clad air hole structure with the D-type plane structure, which ensures a simple structure and convenient manufacturing and production, while greatly improving the wavelength sensitivity. The wavelength sensitivity of the dual-sample channel can reach up to 16200nm / RIU and 15800nm / RIU, which has broad application prospects in the field of high-sensitivity detection. The sensor structure designed by the present invention can be designed according to specific actual needs. For example, in the detection of cancer cells, cancer cells are considered to be in liquid form and have their own refractive index. Therefore, cancer cells can be filled into channels A and B as liquid to be tested. (1) Cancer cell 1 can be encapsulated in channel A, and only channel B is used to realize the sensing detection of cancer cell 2, which reduces the difficulty of operation; (2) The dual sample detection of channels A and B is carried out simultaneously, and the refractive index of cancer cells 1 and 2 is determined according to the change law of the peak value in the detection spectrum, thereby improving the detection efficiency.

[0034] The above is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, several changes and improvements can be made without departing from the overall concept of the present invention. These should also be regarded as the scope of protection of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection, comprising a substrate, characterized in that: Small air holes are arranged around the center of a substrate, the center of the substrate is a fiber core, an upper large air hole A is arranged on the substrate above the small air hole, and a lower large air hole B is arranged on the substrate below the small air hole, the upper large air hole A and the lower large air hole B are both D-type holes, but the plane part of the D-type hole corresponds to the arrangement of the small air holes, the small air holes are radially arranged from the inside to the outside with the center of the substrate as the center, and the three layers of small air holes are arranged in a regular hexagon; the first layer of small air holes is closest to the center, and the second layer of small air holes and the third layer of small air holes are arranged outwards in sequence, the second layer of small air holes are elliptical holes, the major axis radius and the minor axis radius of the second layer of small air holes are 0.6μm and 0.4μm respectively, wherein the major axis is parallel to the plane of the upper large air hole A, the first layer of small air holes and the third layer of small air holes are circular holes, and a layer of gold nanofilm with the same thickness is deposited on the plane of the upper large air hole A and the lower large air hole B.

2. The high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection according to claim 1, characterized in that: The radius of the first layer of small air holes and the third layer of small air holes are both 0.4 μm, and the distance between adjacent small air holes is 2 μm.

3. The high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection according to claim 1, characterized in that: The upper large air hole A and the lower large air hole B are respectively located directly above and directly below the fiber core, with a radius of 5.3 μm and a vertical distance of 6 μm from the fiber core.

4. The high-sensitivity photonic crystal fiber sensor for dual-sample synchronous detection according to claim 1, characterized in that: The thickness of the gold nanofilm on the plane of the upper large air hole A and the thickness of the gold nanofilm on the plane of the lower large air hole B are both 40 nm.

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