Terahertz absorption spectrum enhancing device based on photonic crystal defect mode structure on coplanar waveguide and preparation method of terahertz absorption spectrum enhancing device

Abstract

The invention belongs to the technical field of terahertz, and discloses a terahertz absorption spectrum enhancing device based on a photonic crystal defect mode structure on a coplanar waveguide and a preparation method of the terahertz absorption spectrum enhancing device. The device comprises two identical Bragg reflection structures, a defect cavity is inserted between the Bragg reflection structures, and filling materials are liquid crystals. A coplanar waveguide is added above the two Bragg structures and the liquid crystal; and the thin film analysis layer is coated on the coplanar waveguide. The device is simple in structure, low in manufacturing cost and suitable for enhanced measurement of terahertz absorption characteristic spectrums of different to-be-measured objects at different frequencies; and by adopting the polymer material substrate, the manufacturing difficulty is reduced, and the universality is higher. A series of harmonic peaks can be obtained by changing the refractive index of the liquid crystal from 1.3 to 1.82, so that a series of narrow-band absorption spectrums are obtained, and the peak values of the narrow-band absorption spectrums form enhanced characteristic absorption spectrums with envelope lines being thin film objects to be detected, so that terahertz fingerprint detection of trace objects to be detected is realized.

Description

Technical Field

[0001] The present invention relates to the field of terahertz technology, and in particular to a terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide and a preparation method thereof. Background Art

[0002] The terahertz (THz) band (0.1-10 THz, 1 THz = 1012 Hz) lies between the microwave and infrared spectra. Most organic and biological macromolecules, such as amino acids, fats, DNA, RNA, and proteins, exhibit characteristic absorption spectra, or fingerprints, in this band. These spectra reveal information about the substance's molecular vibrations, lattice structure, and electronic transitions. This information can be used to analyze the sample's properties and structure, information not available in other electromagnetic bands. However, in practical applications, traditional sensing schemes face inevitable limitations in analyzing trace samples. Therefore, in practical applications, additional microstructures, such as metasurfaces and gratings, are needed to enhance the interaction between trace analytes and electromagnetic waves. Enhancing the interaction between trace analytes and electromagnetic waves through angle and parameter multiplexing often has a number of drawbacks, such as high cost, complex optical paths, difficult machining precision, and large sample requirements. Therefore, addressing the challenge of detecting the THz absorption spectra of trace analytes and developing a THz absorption spectrum enhancement device has become an urgent technical challenge for those skilled in the art. Summary of the Invention

[0003] The purpose of the present invention is to provide a terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide and a preparation method thereof, so as to solve the defects in the prior art.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions: The present invention provides a terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide, comprising two identical Bragg reflection structures, a coplanar waveguide, and a thin film analysis layer; A defect cavity is formed between the two Bragg reflection structures; the defect cavity is filled with liquid crystal; and the liquid crystal is supported by a substrate; The coplanar waveguide is located above two identical Bragg reflection structures and liquid crystal.

[0005] Preferably, the Bragg reflector structure comprises a plastic layer, an air layer, and a protective frame; the plastic layer and the air layer are alternately stacked; and the outermost layer of the Bragg reflector structure is the air layer.

[0006] Preferably, the refractive index of the liquid crystal is 1.3~1.82.

[0007] Preferably, the number of the plastic layers is ≥3, and the length along the x-axis is 105 μm; the number of the air layers is ≥3, and the length along the x-axis is 150 μm.

[0008] Preferably, the plastic layer is made of high-density polyethylene, has a width of 600 μm along the y-axis direction, and a height of 75 μm along the z-axis direction.

[0009] Preferably, the material of the coplanar waveguide is metallic copper; the width of the central guide band of the coplanar waveguide along the y-axis direction is 190 μm; the width of the ground lines on both sides of the coplanar waveguide along the y-axis direction is 155 μm; the width of the air slot of the coplanar waveguide along the y-axis direction is 50 μm.

[0010] Preferably, the material of the thin film analysis layer is α-lactose; the thin film analysis layer is arranged on the coplanar waveguide and is consistent with the length of the defect cavity along the x-axis; the length of the thin film analysis layer along the x-axis is 390 μm, the width along the y-axis is 345 μm, and the thickness along the z-axis is 0.2~1 μm.

[0011] The present invention also provides a method for preparing a terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide, comprising the following steps: Plastic layers and air layers are alternately stacked in a protective frame, with the outermost layer being an air layer, to obtain a Bragg reflection structure; A defect cavity is formed between two Bragg reflection structures. The defect cavity is filled with liquid crystal, which is supported by a substrate. Add a coplanar waveguide above the two Bragg reflection structures and the liquid crystal; The thin film analysis layer is coated on the coplanar waveguide to obtain a terahertz absorption spectrum enhancement device based on the photonic crystal defect mode structure on the coplanar waveguide.

[0012] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following beneficial effects: The present invention provides a terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide, comprising two identical Bragg reflection structures; a defect cavity inserted between the two Bragg reflection structures, the defect cavity being filled with liquid crystal, and the liquid crystal being supported by upper and lower plastic substrates; a coplanar waveguide being added above the two Bragg structures and the liquid crystal between them; and a thin film analysis layer being coated on the coplanar waveguide. The device has a simple structure, is easy to design and optimize, has low manufacturing costs, and is suitable for enhanced measurement of terahertz absorption characteristic spectra of different test objects at different frequencies; the use of a polymer material substrate reduces the difficulty of manufacturing, making the method more versatile. The present invention changes the refractive index of the liquid crystal from 1.3 to 1.82. By changing the refractive index of the liquid crystal, a series of resonance peaks can be obtained, thereby obtaining a series of narrowband absorption spectra. The peak values ​​of the narrowband absorption spectra are combined to form an envelope to form an enhanced characteristic absorption spectrum of the thin film test object, thereby realizing terahertz fingerprint detection of trace test objects. The device of the present invention also greatly eliminates other light absorption that interferes with the detection results; it can also identify that when N=5, the thin film analysis layer is only 1μm thick, the absorption enhancement ratio is about 19.2 times, and trace analytes are detected simply and effectively in the wide frequency band of 0.46~0.6THz, providing a good case for the subsequent detection of trace biomacromolecules in THz. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0014] Figure 1 Schematic diagram of the structure of the terahertz absorption spectrum enhancement device based on the photonic crystal defect mode structure on the coplanar waveguide of the present invention; wherein 1 is the thin film analysis layer, 2 is the coplanar waveguide, 3 is the plastic layer, 4 is the air layer, 5 is the protective frame, 6 is the liquid crystal, and 7 is the substrate; Figure 2 This is a reflectivity curve of the terahertz absorption spectrum of the unenhanced device in comparative example 1; Figure 3 This is a reflectivity curve diagram of the terahertz absorption spectrum enhancement device of Example 1; Figure 4 is an absorptivity curve diagram of the terahertz absorption spectrum enhancement device of Example 1; Figure 5 This is a comparison chart of the absorption rates of the terahertz absorption spectrum enhanced device of Example 1 and the terahertz absorption spectrum non-enhanced device of Comparative Example 1 magnified 19.2 times. DETAILED DESCRIPTION

[0015] The present invention provides a terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide, the structural schematic diagram of which is shown in FIG. Figure 1As shown, it includes two identical Bragg reflection structures, a coplanar waveguide 2, and a thin film analysis layer 1.

[0016] In the present invention, the coplanar waveguide 2 is located above two identical Bragg reflection structures and the liquid crystal 6 .

[0017] In the present invention, a defect cavity is formed between the two Bragg reflection structures; the filling material of the defect cavity is liquid crystal 6; the liquid crystal 6 is supported by a substrate 7; and the substrate 7 is a plastic substrate.

[0018] In the present invention, the refractive index of the liquid crystal 6 is 1.3~1.82. The present invention sets the refractive index of the liquid crystal to a series of different values, and the absorption spectra corresponding to the resonance frequencies obtained under different liquid crystal refractive indices are different. Under the irradiation of terahertz waves incident at a certain angle, a series of resonance peaks can be obtained by changing the refractive index of the liquid crystal, thereby obtaining a series of narrow-band absorption spectra, and the peak composition envelope of the narrow-band absorption spectrum is the enhanced characteristic absorption spectrum of the thin film to be tested, so as to realize terahertz fingerprint detection. The liquid crystal of the present invention is surrounded by a plastic substrate, and the change of the refractive index is achieved by applying a voltage between the middle conductor of the coplanar waveguide and the ground wires on both sides.

[0019] In the present invention, the length of the defect cavity along the x-axis direction is 390 μm.

[0020] In the present invention, the Bragg reflector structure includes a plastic layer 3, an air layer 4, and a protective frame 5; the plastic layer 3 and the air layer 4 are alternately stacked; and the outermost layer of the Bragg reflector structure is the air layer 4.

[0021] In the present invention, the number of the plastic layer 3 is ≥3, and the length along the x-axis direction is 105 μm.

[0022] In the present invention, the plastic layer 3 is made of high-density polyethylene, has a width of 600 μm along the y-axis direction, and a height of 75 μm along the z-axis direction.

[0023] In the present invention, the number of the air layers 4 is ≥3, and the length along the x-axis direction is 150 μm.

[0024] In the present invention, the coplanar waveguide 2 is made of metallic copper; the width of the central guide band of the coplanar waveguide 2 along the y-axis direction is 190 μm.

[0025] In the present invention, the coplanar waveguide 2 is provided with air slots along the x-axis direction; the width of the air slots of the coplanar waveguide 2 along the y-axis direction is 50 μm.

[0026] In the present invention, the width of the ground lines on both sides of the coplanar waveguide 2 along the y-axis direction is 155 μm.

[0027] In the present invention, the material of the thin film analysis layer 1 is α-lactose; the thin film analysis layer 1 is disposed on the coplanar waveguide 2 and has the same length as the defect cavity along the x-axis direction.

[0028] In the present invention, the thin film analysis layer 1 has a length of 390 μm along the x-axis direction, a width of 345 μm along the y-axis direction, and a thickness of 0.2-1 μm along the z-axis direction.

[0029] The present invention also provides a method for preparing a terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide, comprising the following steps: Plastic layers 3 and air layers 4 are alternately stacked in a protective frame 5, with the air layer 4 being the outermost layer, to obtain a Bragg reflection structure; A defect cavity is formed between the two Bragg reflection structures. The defect cavity is filled with liquid crystal 6, which is supported by upper and lower plastic substrates 7. Add a coplanar waveguide 2 above the two Bragg reflection structures and the liquid crystal 6; The thin film analysis layer 1 is coated on the coplanar waveguide 2 to obtain a terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on the coplanar waveguide.

[0030] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0031] Example 1

[0032] This embodiment provides a terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide, and a preparation method thereof includes the following steps: Plastic layers 3 and air layers 4 are alternately stacked in a protective frame 5, with the outermost layer being the air layer 4, to obtain a Bragg reflection structure. The number of plastic layers 3 is five, and the material is high-density polyethylene (HDPE). A defect cavity is formed between two identical Bragg reflection structures, and the defect cavity is filled with liquid crystal 6. The liquid crystal 6 is supported by upper and lower plastic substrates 7. A coplanar waveguide 2 made of metal copper is then added above the two Bragg reflection structures and the liquid crystal 6 therebetween. A thin film analysis layer 1 made of α-lactose is coated on the coplanar waveguide 2. The parameters of each structure are set as follows: the length of the plastic layer 3 along the x-axis is The length of the air layer 4 along the x-axis is 150 μm; the length of the thin film analysis layer 1 along the x-axis is 390 μm, the width along the y-axis is 345 μm, and the thickness along the z-axis is 1 μm; the length of the defect cavity along the x-axis is 390 μm; the width of the central conduction band of the coplanar waveguide 2 along the y-axis is 190 μm, the width of the ground lines on both sides along the y-axis is 155 μm, the width of the air slot along the y-axis is 50 μm, and the refractive index of the liquid crystal 6 is 1.3~1.82.

[0033] Comparative Example 1

[0034] This comparative example provides a device without enhanced terahertz absorption spectrum, which is specifically referred to Example 1, except that the thin film analysis layer 1 is not coated, and the rest is the same as Example 1.

[0035] The performance of the terahertz absorption spectrum enhanced device prepared in Example 1 and the terahertz absorption spectrum non-enhanced device prepared in Comparative Example 1 were tested, and the reflectivity curve is shown in the figure below. Figure 2 、 Figure 3 As shown, the absorption rate curve is as follows Figure 4 As shown. Figure 2 and Figure 3 It can be seen that when the refractive index of liquid crystal increases from 1.3 to 1.82, the resonance peak corresponding to the refractive index of different liquid crystals moves between 0.49 and 0.57 THz, which can be used for sensing research. Figure 4 As can be seen in the figure, as the refractive index of the liquid crystal increases linearly, the resonance peak gradually shifts. Therefore, changing the refractive index of the liquid crystal can enhance the interaction between the incident terahertz wave and the material at different frequencies. Furthermore, evenly coating the analysis layer with a thin film of α-lactose significantly enhances the absorption of terahertz waves by the analysis layer when the refractive index of the liquid crystal is altered.

[0036] The absorption rate comparison between the device coated with a 1 μm thin film analysis layer in Example 1 and the device not coated with a 1 μm thin film analysis layer in Comparative Example 1 magnified 19.2 times is shown in the figure below. Figure 5 As shown, from Figure 5As can be seen in the figure, due to the different properties of α-lactose, the amplitudes of the absorption peaks also vary. By connecting the absorption peaks of different liquid crystal refractive indices, we can obtain the absorption spectrum envelope corresponding to a 1µm thick α-lactose layer, which exhibits an enhancement factor of approximately 19.2. Furthermore, the solid line represents the absorption spectrum without the 1µm thick α-lactose layer, showing an enhancement factor of approximately 19.2. Therefore, it is clear that α-lactose has unique terahertz spectral characteristics.

[0037] As shown in the above examples, when no thin-film analysis layer is applied, the incident terahertz wave is not fully reflected by changing the refractive index of the liquid crystal. However, when a thin-film analysis layer is applied, the resonant frequency shifts by changing the refractive index of the liquid crystal, and the amplitude of the reflection spectrum also changes. This causes the amplitude of the resonant mode absorption spectrum (A=1-R) to vary with the refractive index of the liquid crystal. This is due to the characteristic absorption of the thin-film analysis layer. By connecting the peak values ​​of the resonant absorption peaks corresponding to a series of different liquid crystal refractive indices, the resulting envelope is the enhanced absorption spectrum of the thin-film analysis layer. Compared to the unenhanced absorption spectrum without the thin-film analysis layer, a significant enhancement effect can be achieved.

[0038] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide, characterized in that: It includes two identical Bragg reflection structures, a coplanar waveguide, and a thin film analysis layer; A defect cavity is formed between the two Bragg reflection structures; the defect cavity is filled with liquid crystal; and the liquid crystal is supported by a substrate; The coplanar waveguide is located above two identical Bragg reflection structures and liquid crystal.

2. The terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide according to claim 1, characterized in that: The Bragg reflection structure comprises a plastic layer, an air layer, and a protection frame; the plastic layer and the air layer are alternately stacked; and the outermost layer of the Bragg reflection structure is the air layer.

3. A terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide according to claim 1 or 2, characterized in that: The refractive index of the liquid crystal is 1.3-1.

82.

4. The terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide according to claim 2, characterized in that: The number of plastic layers of the Bragg reflection structure is ≥3, and the length along the x-axis is 105 μm; the number of air layers of the Bragg reflection structure is ≥3, and the length along the x-axis is 150 μm.

5. The terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide according to claim 4, characterized in that: The plastic layer is made of high-density polyethylene, has a width of 600 μm along the y-axis, and a height of 75 μm along the z-axis.

6. The terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide according to claim 3, characterized in that: The coplanar waveguide is made of metallic copper; the width of the central guide strip of the coplanar waveguide along the y-axis is 190 μm; the width of the ground lines on both sides of the coplanar waveguide along the y-axis is 155 μm; the width of the air slot of the coplanar waveguide along the y-axis is 50 μm.

7. The terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide according to claim 1, characterized in that: The material of the thin film analysis layer is α-lactose; the thin film analysis layer is arranged on the coplanar waveguide and is consistent with the length of the defect cavity along the x-axis; the length of the thin film analysis layer along the x-axis is 390 μm, the width along the y-axis is 345 μm, and the thickness along the z-axis is 0.2~1 μm.

8. The method for preparing a terahertz absorption spectrum enhancement device based on a photonic crystal defect mode structure on a coplanar waveguide according to any one of claims 1 to 7, characterized in that: The following steps are involved: Plastic layers and air layers are alternately stacked in a protective frame, with the outermost layer being an air layer, to obtain a Bragg reflection structure; A defect cavity is formed between two Bragg reflection structures. The defect cavity is filled with liquid crystal, which is supported by a substrate. Add a coplanar waveguide above the two Bragg reflection structures and the liquid crystal; The thin film analysis layer is coated on the coplanar waveguide to obtain a terahertz absorption spectrum enhancement device based on the photonic crystal defect mode structure on the coplanar waveguide.

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