A terahertz absorption spectrum device based on one-dimensional defect photonic crystal stack and its preparation method

Abstract

The present invention provides a terahertz absorption spectrum device based on a stack of one-dimensional defective photonic crystals and a preparation method thereof, belonging to the field of terahertz technology. From top to bottom, grating layers and defective one-dimensional photonic crystal layers are alternately stacked; the outermost layer is a grating layer; a single defective one-dimensional photonic crystal layer contains two identical Bragg reflection structures; the two identical Bragg reflection structures are symmetrically distributed; a defect cavity is located between the two identical Bragg reflection structures; a single Bragg reflection structure is an alternating stack of silicon layers and air layers; the outermost layer is a silicon layer; the width of the defect cavity decreases from top to bottom; a substrate is vertically arranged at the center of the defect cavity; and a thin film analysis layer is coated on one side of the substrate. The device provided by the present invention can identify a 0.1μm thick thin film analysis layer, has an absorption enhancement factor of 303 times, and can simply and effectively detect trace analytes in a wide frequency band of 0.49 to 0.57THz.

Description

Technical Field

[0001] The present invention relates to the field of terahertz technology, and in particular to a terahertz absorption spectrum device based on a one-dimensional defect photonic crystal stack and a preparation method thereof. Background Art

[0002] The terahertz (THz) band (0.1–10 THz, 3000–30 μm), located between the microwave and infrared spectra, possesses many unique properties, such as low energy, non-destructive detection, and interaction with biomacromolecules. This makes THz waves potentially applicable in a wide range of fields, such as fingerprint detection, biomedicine, imaging technology, and security sensing. However, the application of THz waves also faces several challenges, one of which is the limitation in detecting trace amounts of analytes, primarily due to the low scattering and transmittance of THz waves. Precisely because of these low scattering and transmittance, traditional absorption spectroscopy detection systems require the use of large amounts of analytical sample. In practical applications, it is necessary to measure and analyze the THz absorption spectral characteristics of trace samples. This is because large amounts of sample will affect the efficiency of the interaction between THz waves and analytes. To address the challenge of enhancing the detection of the characteristic THz absorption spectra of trace analytes, researchers have utilized various supergratings and metasurface structures to enhance the local electric field. These structures enhance terahertz absorption spectra using multiplexing techniques such as geometric multiplexing and angular multiplexing. However, in practical applications, achieving enhanced absorption spectra by slightly adjusting the incident angle is difficult, and fabricating various unit structures with small variations in thickness and resolution is also challenging. Furthermore, due to the complex unit cell structure, samples loaded onto structures such as metasurfaces and supergratings are often non-uniform. An ideal alternative to enhancement structures like supergratings and metasurfaces is a one-dimensional photonic crystal. Defective 1D-PC structures, as an important means of localizing the electric field, have been widely used for terahertz refractive index sensing and in the design of micro- and nanoscale devices such as lasers, optical waveguides, optical modulators, and sensors. By varying the width of the defect cavity, high-quality Q-factor resonance peaks can be easily tuned, offering great potential for enhancing the interaction between terahertz waves and trace samples. However, existing multiplexing techniques and defective 1D photonic crystal structures may require the preparation of more complex samples or experimental materials, increasing experimental costs and requiring multiple experiments to measure the different resonant frequencies corresponding to defect cavities of different widths, which is time-consuming. Summary of the Invention

[0003] The purpose of the present invention is to provide a terahertz absorption spectrum device based on a one-dimensional defect photonic crystal stack and a preparation method thereof, so as to solve the problem in the prior art that multiple experiments are required to separately process the measurement of different resonant frequencies corresponding to defect cavities of different widths, resulting in excessively long time.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a terahertz absorption spectrum device based on a stack of one-dimensional defective photonic crystals, which comprises alternately stacked grating layers and defective one-dimensional photonic crystal layers from top to bottom; the outermost layer is a grating layer;

[0006] A single defective one-dimensional photonic crystal layer contains two identical Bragg reflection structures;

[0007] Two identical Bragg reflection structures are symmetrically distributed;

[0008] There is a defect cavity between two identical Bragg reflection structures;

[0009] The single Bragg reflection structure is composed of alternately stacked silicon layers and air layers; the air layers are sandwiched between adjacent silicon layers;

[0010] The width of the defect cavity decreases from top to bottom, with the step length of each layer decreasing from 8 to 12 μm;

[0011] A substrate is vertically arranged at the center of the defect cavity; and a thin film analysis layer is coated on one side surface of the substrate.

[0012] Preferably, the thickness of the grating layer is 2-5 μm, and the material of the grating layer is stainless steel.

[0013] Preferably, the number of silicon layers in the Bragg reflection structure is ≥2.

[0014] Preferably, the substrate is made of polytetrafluoroethylene.

[0015] Preferably, the width of the top defect cavity is ≤390 μm; the width of the defect cavity decreases from top to bottom, and the shortest width of the defect cavity is ≥250 μm.

[0016] Preferably, the thin film analysis layer is an α-lactose thin film, and the thickness of the thin film analysis layer is 0.1 to 0.5 μm.

[0017] The present invention also provides a method for preparing the terahertz absorption spectrum device based on the one-dimensional defect photonic crystal stack, comprising the following steps:

[0018] Grating layers and defective one-dimensional photonic crystal layers are alternately stacked from top to bottom; the outermost layer is the grating layer;

[0019] A single defective one-dimensional photonic crystal layer contains two identical Bragg reflection structures, which are symmetrically distributed.

[0020] A defect cavity is left between two identical Bragg reflection structures;

[0021] The single Bragg reflection structure is composed of alternately stacked silicon layers and air layers; the air layers are sandwiched between adjacent silicon layers;

[0022] The width of the defect cavity decreases from top to bottom;

[0023] A substrate is vertically arranged at the center of the defect cavity; and a thin film analysis layer is coated on one side surface of the substrate.

[0024] The present invention has the following beneficial effects:

[0025] The present invention provides a terahertz absorption spectrum device based on a stack of one-dimensional defective photonic crystals. From top to bottom, the device comprises alternating grating layers and defective one-dimensional photonic crystal layers; the outermost layer is a grating layer; a single defective one-dimensional photonic crystal layer contains two identical Bragg reflection structures; the two identical Bragg reflection structures are symmetrically distributed; a defect cavity is located between the two identical Bragg reflection structures; a single Bragg reflection structure comprises alternating silicon layers and air layers; the air layers are sandwiched between adjacent silicon layers; the width of the defect cavity decreases from top to bottom, with each layer decreasing in steps of 8 to 12 μm; a substrate is vertically disposed at the center of the defect cavity; and a thin film analysis layer is coated on one side of the substrate. The device provided by the present invention has a simple structure, is easy to design, has low experimental costs, requires minimal work, and is easy to operate.

[0026] The present invention overcomes the problems of high experimental cost and large experimental workload by adopting a stacking approach. The staggered stacking of defective one-dimensional photonic crystals and grating layers will also guide and control the propagation of terahertz waves to undergo multiple reflections and transmissions inside the structure, thereby regulating the interaction between the terahertz waves and the same trace sample to be tested in the defect cavity perpendicular to the wave propagation direction, thereby promoting the sample's absorption of terahertz waves.

[0027] The terahertz absorption spectrum device provided by the present invention can identify thin film analysis layers as thin as 0.1 μm thick, with an absorption enhancement factor of approximately 303 times. It can simply and effectively detect trace analytes in a wide frequency band of 0.49 THz to 0.57 THz, providing a good case for the subsequent detection of trace biomacromolecules in terahertz (THz).

[0028] When a terahertz wave is incident perpendicular to the thin film analysis layer, it resonates within defect cavities of varying widths, generating multiple resonant frequencies and corresponding resonant absorption peaks simultaneously. By connecting each resonant absorption peak to form an envelope, an enhanced terahertz absorption spectrum can be obtained, enabling terahertz fingerprint detection of trace amounts of analytes. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the structure of the terahertz absorption spectrum device provided in Example 1;

[0030] Among them, 1 is the thin film analysis layer, 2 is the substrate, 3 is the grating layer, 4 is the defect cavity, and 5 is the silicon layer;

[0031] Figure 2 Graph showing the reflectivity and transmittance of the terahertz absorption spectrum device in Example 1;

[0032] Figure 3 Graph showing the reflectivity and transmittance of the terahertz absorption spectrum device in Comparative Example 1;

[0033] Figure 4 is a graph showing the absorption rate of the terahertz absorption spectrum device to terahertz in Example 1;

[0034] Figure 5 This is a comparison chart of the absorbance of the 0.1 μm lactose film in Example 1, the enhanced 0.1 μm lactose film, and the 303-fold unenhanced 0.1 μm lactose film. DETAILED DESCRIPTION

[0035] The present invention provides a terahertz absorption spectrum device based on a stack of one-dimensional defective photonic crystals, which comprises alternately stacked grating layers and defective one-dimensional photonic crystal layers from top to bottom; the outermost layer is a grating layer;

[0036] A single defective one-dimensional photonic crystal layer contains two identical Bragg reflection structures;

[0037] Two identical Bragg reflection structures are symmetrically distributed;

[0038] There is a defect cavity between two identical Bragg reflection structures;

[0039] The single Bragg reflection structure is composed of alternately stacked silicon layers and air layers; the air layers are sandwiched between adjacent silicon layers;

[0040] The width of the defect cavity decreases from top to bottom, with the step length of each layer decreasing from 8 to 12 μm;

[0041] A substrate is vertically arranged at the center of the defect cavity; and a thin film analysis layer is coated on one side surface of the substrate.

[0042] In the present invention, the decreasing step length of each layer of the defect cavity is preferably 9 to 11 μm, and more preferably 10 μm.

[0043] In the present invention, the thickness of the grating layer is preferably 2 to 5 μm, more preferably 2.5 to 4.5 μm, and even more preferably 3 to 4 μm. The material of the grating layer is preferably stainless steel.

[0044] In the present invention, the number of silicon layers in the Bragg reflection structure is preferably ≥2.

[0045] In the present invention, the material of the substrate is preferably polytetrafluoroethylene.

[0046] In the present invention, the width of the top defect cavity is preferably ≤390 μm, further preferably ≤388 μm, and more preferably ≤385 μm; the width of the defect cavity decreases from top to bottom, and the shortest width of the defect cavity is preferably ≥250 μm, further preferably ≥255 μm, and more preferably ≥260 μm.

[0047] In the present invention, the widths of the defect cavities decrease in sequence, and the width of the bottom layer needs to be ≥250 μm.

[0048] In the present invention, the thin film analysis layer is preferably an α-lactose thin film, and the thickness of the thin film analysis layer is preferably 0.1 to 0.5 μm.

[0049] The present invention also provides a method for preparing the terahertz absorption spectrum device based on the one-dimensional defect photonic crystal stack, comprising the following steps:

[0050] Grating layers and defective one-dimensional photonic crystal layers are alternately stacked from top to bottom; the outermost layer is the grating layer;

[0051] A single defective one-dimensional photonic crystal layer contains two identical Bragg reflection structures, which are symmetrically distributed.

[0052] A defect cavity is left between two identical Bragg reflection structures;

[0053] The single Bragg reflection structure is composed of alternately stacked silicon layers and air layers; the air layers are sandwiched between adjacent silicon layers;

[0054] The width of the defect cavity decreases from top to bottom;

[0055] A substrate is vertically arranged at the center of the defect cavity; and a thin film analysis layer is coated on one side surface of the substrate.

[0056] In the above-mentioned device of the present invention, the number and width of silicon layers, the width of the air layer, the thickness of the grating layer and the width of the defect cavity in the defect one-dimensional photonic crystal will affect the change of the resonant frequency. The width df of the defect cavity, the number and width of the silicon layers, the width of the air layer and the thickness of the grating layer can be optimized according to different thin film analytes to meet the characteristic resonance of the corresponding thin film analytes. The resonant frequency of the defect one-dimensional photonic crystal structure will change with the change of the width df of the defect cavity. The different defect cavity widths df of each layer in the stacked defect one-dimensional grating photonic crystal structure have an important influence on the resonant frequency in the structure. The polytetrafluoroethylene substrate can be used as a supporting platform for the thin film analysis layer to be measured, and a thin film analysis layer of a certain thickness can be coated on the substrate before measurement.

[0057] In the present invention, unless otherwise specified, the raw materials required for preparation are all commercially available products well known to those skilled in the art.

[0058] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0059] Example 1

[0060] The structure of the terahertz absorption spectrum device based on one-dimensional defect photonic crystal stack is as follows: Figure 1 As shown, from top to bottom are alternately stacked grating layers 3 and defective one-dimensional photonic crystal layers;

[0061] A single defective one-dimensional photonic crystal layer contains two identical Bragg reflection structures, and the two identical Bragg reflection structures are symmetrically distributed.

[0062] The single Bragg reflection structure is composed of alternately stacked silicon layers 5 and air layers 6, and the width of the defect cavity decreases from top to bottom. A substrate 2 is vertically arranged at the center of the defect cavity. A thin film analysis layer 1 is coated on one side of the substrate.

[0063] The grating layer 3 is made of stainless steel with a thickness of h=5 μm.

[0064] The number of defect one-dimensional photonic crystal layer stacking layers M=15, the number of silicon layers 5 in a single Bragg reflection is N=2 and the width is 105 μm, the width of the air layer is 150 μm, the width df of the first layer of defect cavity is 390 μm, the step length of each layer of defect cavity decreases by 10 μm, and the width df of the last layer of defect cavity is =250 μm.

[0065] The thin film analysis layer 1 is α-lactose analyte and has a thickness of 0.1 μm; the substrate material is polytetrafluoroethylene.

[0066] The experimental process: The terahertz wave 7 is vertically incident on the Bragg reflection structure on one side of the defect cavity 4 along the x-axis direction. After being guided and controlled by the multi-layer one-dimensional silicon photonic crystal and stainless steel grating, it undergoes multiple reflections and transmissions inside the structure, thereby adjusting the interaction between the terahertz wave 7 and the same α-lactose thin film analysis layer 1 in the defect cavity 4 perpendicular to the wave propagation direction, and then emitted from the Bragg reflection structure on the other side of the defect cavity 4.

[0067] Comparative Example 1

[0068] The structure is basically the same as that in Example 1, the only difference being that there is no thin film analysis layer.

[0069] Analysis and Testing

[0070] In order to evaluate the enhanced performance of the absorption spectrum, the reflection spectrum (R) and transmission spectrum (T) of the stacked defective one-dimensional grating photonic crystals in Example 1 and Comparative Example 1 at different df values ​​were studied, as shown in FIG. Figure 2 and Figure 3 As shown ( Figure 2 The left side of the middle is the reflectivity graph, and the right side is the transmittance graph; Figure 3 The left side is the reflectivity graph, and the right side is the transmittance graph).

[0071] from Figure 2 and Figure 3 It can be seen that in Example 1 coated with a 0.1μm thin film analysis layer, by varying the width df of the defect cavity 4, the resonant frequency of the defect mode shifts, and the intensities of the resonance peaks in the reflection spectrum (R) and transmission spectrum (T) also change. The refractive indices of the silicon layer 5, the polytetrafluoroethylene substrate 2, and the air layer 6 are approximately 3.44 (the square root of 11.9), 1.46, and 1, respectively. Furthermore, the amplitude of the resonance peak near 0.53THz for the 0.1μm α-lactose coating shows a changing trend. When the width df of the defect cavity 4 is varied from 250μm to 390μm in 10μm steps, the absorption peak corresponding to each different width df of the defect cavity 4 shifts between 0.49THz and 0.57THz.

[0072] The width df of the defect cavity 4 has an important influence on the resonant frequency. By placing the device on a displacement platform, the width of the defect cavity 4 can be precisely adjusted to test the effect of the width of the defect cavity 4 on the absorption rate of the terahertz wave 7. Figure 4 shown.

[0073] from Figure 4It can be seen that when the width df of the defect cavity 4 increases from 250μm to 390μm in steps of 10μm, the corresponding resonance peak decreases from 0.57THz to 0.49THz. It can be observed that when the width of the defect cavity 4 increases linearly, the resonance peak gradually shifts. Therefore, by varying the width of the defect cavity 4, the electromagnetic field enhancement effect within a specific frequency range can be adjusted. The enhanced local electric field makes it easier for the sample to absorb terahertz wave energy. After α-lactose is uniformly coated on the polytetrafluoroethylene substrate 2 to form a thin film analysis layer 1, adjusting the width of the defect cavity 4 significantly enhances the thin film analysis layer 1's absorption of terahertz waves 7.

[0074] from Figure 4 It can be seen that as the width of the defect cavity 4 increases linearly, the resonance peak gradually shifts. Therefore, by varying the width of the defect cavity 4, the electromagnetic field enhancement effect within a specific frequency range can be adjusted. This localized electric field enhancement makes the sample more susceptible to terahertz wave energy absorption. Furthermore, after uniformly coating α-lactose on a polytetrafluoroethylene substrate 2 to form a thin film analysis layer 1, adjusting the width of the defect cavity 4 significantly enhances the thin film analysis layer's absorption of terahertz waves.

[0075] Due to the different properties of α-lactose, the amplitudes of the absorption peaks are also different. By connecting the various absorption peaks, the enhanced absorption spectrum of the stacked defective one-dimensional grating photonic crystal structure can be obtained. Therefore, the absorption rates of the 0.1 μm lactose film, the enhanced 0.1 μm lactose film and the 303-fold unenhanced 0.1 μm lactose film in Example 1 are compared. Figure 5 shown.

[0076] from Figure 5 It can be seen that the absorption of terahertz waves by 0.1μm α-lactose is increased by 303 times, so it can be said that α-lactose has unique terahertz spectral characteristics.

[0077] It can be seen from the above embodiments that the present invention provides a terahertz absorption spectrum device based on a stack of one-dimensional defect photonic crystals, which comprises alternately stacked grating layers and defective one-dimensional photonic crystal layers from top to bottom; the outermost layer is a grating layer; a separate defective one-dimensional photonic crystal layer contains two identical Bragg reflection structures; the two identical Bragg reflection structures are symmetrically distributed; a defect cavity is located between the two identical Bragg reflection structures; a separate Bragg reflection structure is alternately stacked silicon layers and air layers; the air layer is sandwiched between adjacent silicon layers; the width of the defect cavity decreases from top to bottom; a substrate is vertically arranged at the center of the defect cavity; and a thin film analysis layer is coated on one side of the substrate. It can be seen from the test that the number of stacked layers is 15, the number of silicon layers in the Bragg reflection structure is 2, the thickness of the grating layer is 5μm, and the width of the defect cavity is increased from 250μm to 390μm in steps of 10μm. During this period, the defect cavity increases to a series of different widths, and a series of absorption spectra are obtained. Then, the peak values ​​of the resonant absorption peaks are connected to form an envelope to form an enhanced characteristic absorption spectrum of the thin film analyte, thereby realizing terahertz fingerprint detection of trace analytes.

[0078] 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 device based on a one-dimensional defect photonic crystal stack, characterized in that: From top to bottom, there are alternately stacked grating layers and defective one-dimensional photonic crystal layers; the outermost layer is the grating layer; The number of stacked layers of defective one-dimensional photonic crystal is 15; A single defective one-dimensional photonic crystal layer contains two identical Bragg reflection structures; Two identical Bragg reflection structures are symmetrically distributed; There is a defect cavity between two identical Bragg reflection structures; The single Bragg reflection structure is composed of alternately stacked silicon layers and air layers; the air layers are sandwiched between adjacent silicon layers; The width of the defect cavity decreases from top to bottom, with the step length of each layer decreasing from 8 to 12 μm; A substrate is vertically arranged at the center of the defect cavity; a thin film analysis layer is coated on one side of the substrate; The width of the top defect cavity is ≤390 μm; the width of the defect cavity decreases from top to bottom, and the shortest width of the defect cavity is ≥250 μm.

2. The terahertz absorption spectrum device based on a one-dimensional defect photonic crystal stack according to claim 1, characterized in that: The thickness of the grating layer is 2-5 μm, and the material of the grating layer is stainless steel.

3. The terahertz absorption spectrum device based on a one-dimensional defect photonic crystal stack according to claim 1 or 2, characterized in that: The number of silicon layers in the Bragg reflection structure is ≥2.

4. The terahertz absorption spectrum device based on a one-dimensional defect photonic crystal stack according to claim 3, characterized in that: The material of the substrate is polytetrafluoroethylene.

5. The terahertz absorption spectrum device based on one-dimensional defect photonic crystal stack according to claim 4, characterized in that: The thin film analysis layer is an α-lactose thin film, and the thickness of the thin film analysis layer is 0.1-0.5 μm.

6. The method for preparing a terahertz absorption spectrum device based on a one-dimensional defect photonic crystal stack according to any one of claims 1 to 5, characterized in that: It includes the following steps: Grating layers and defective one-dimensional photonic crystal layers are alternately stacked from top to bottom; the outermost layer is the grating layer; A single defective one-dimensional photonic crystal layer contains two identical Bragg reflection structures, which are symmetrically distributed. A defect cavity is left between two identical Bragg reflection structures; The single Bragg reflection structure is composed of alternately stacked silicon layers and air layers; the air layers are sandwiched between adjacent silicon layers; The width of the defect cavity decreases from top to bottom; A substrate is vertically arranged at the center of the defect cavity; and a thin film analysis layer is coated on one side surface of the substrate.

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