Terahertz absorption spectrum enhancing device based on sawtooth structure on coplanar waveguide

Abstract

The invention relates to a terahertz absorption spectrum enhancing device based on a sawtooth structure on a coplanar waveguide, and relates to the technical field of terahertz. Comprising a dielectric substrate, a photoconductive antenna structure and a coplanar waveguide arranged on the dielectric substrate, the grounding wires on the two sides of the middle of the coplanar waveguide are provided with sawtooth structures and are symmetrically distributed relative to the middle signal line. A photoconductive antenna structure is embedded in one side of the middle signal line, and direct-current bias voltage is arranged at the two ends of the middle signal line. According to the invention, local electric field enhancement can be realized, interaction between terahertz waves and an object to be detected is enhanced, and high-sensitivity detection in a terahertz range is realized.

Description

Technical Field

[0001] The invention relates to the field of terahertz technology, in particular to a terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide. Background Art

[0002] Terahertz waves usually refer to electromagnetic waves with a frequency range of 0.1-10THz, which is between microwaves and infrared waves. The characteristics of this frequency range make it have broad application prospects in many fields. Especially in the field of biochemistry, terahertz waves have been shown to be highly sensitive to the rotation and low-frequency vibration of a large number of molecules, especially for organic biomacromolecules. These molecules show strong absorption and dispersion characteristics to terahertz waves, resulting in unique characteristics of the absorption spectrum of terahertz waves, which can be used to form characteristic fingerprint spectra and to detect and identify these molecules. However, the application of terahertz waves is also subject to some challenges. When the volume of the target material is very small relative to the incident terahertz wavelength, it becomes difficult to use traditional free-space terahertz time-domain spectroscopy (THz-TDS) to detect the spectral fingerprint of these trace analytes, because the scattering cross section between the analyte and the terahertz wave is very small. Existing biosensors have low sensitivity, and biosensors are easy to damage the analytes, and cannot achieve non-destructive quantitative detection of biological samples, and cannot meet people's use needs well. Therefore, in order to solve the problem of enhanced detection of terahertz characteristic absorption spectra of trace amounts of analytes, how to provide a terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide has become a technical problem that technicians in this field urgently need to solve. Summary of the invention

[0003] In order to solve at least one technical problem in the background technology, the present invention provides a terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide, which can realize local electric field enhancement, enhance the interaction between terahertz waves and the object to be detected, and realize high-sensitivity detection in the terahertz range.

[0004] To achieve the above-mentioned purpose, the present invention provides a terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide, comprising: a dielectric substrate, a photoconductive antenna structure and a coplanar waveguide arranged on the dielectric substrate; the grounding wires on both sides of the middle of the coplanar waveguide are constructed with a sawtooth structure and are symmetrically distributed relative to the middle signal line; the photoconductive antenna structure is embedded on one side of the middle signal line, and a DC bias voltage is provided at both ends of the middle signal line.

[0005] Furthermore, the length of the coplanar waveguide is 2 mm, the metal thickness is 0.2 um, the width of the middle signal line is 30 um, the width of the ground lines on both sides is 500 um, and the width of the air slot between the signal line and the ground line is 20 um.

[0006] Furthermore, the depth and height of the sawtooth grooves on the coplanar waveguide are both 25um, and the period is 50um.

[0007] Furthermore, the number of teeth in the sawtooth structure of the ground wire structure on the coplanar waveguide is 6.

[0008] Furthermore, the surface of the coplanar waveguide including the sawtooth structure is completely covered with a thin film of the object to be tested.

[0009] Furthermore, the dielectric substrate material is gallium arsenide, and the dielectric constant is 12.7.

[0010] Furthermore, a femtosecond laser emits a femtosecond laser pulse to generate a terahertz time domain pulse in the photoconductive antenna structure. The probe light detects the terahertz pulse in the air slots before and after the sawtooth structure. After Fourier transform and comparison, the scattering parameters of the coplanar waveguide containing the sawtooth structure are obtained, which are used to enhance the terahertz absorption spectrum of the film to be tested.

[0011] The beneficial effects of the present invention are:

[0012] The present invention provides a terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide. By combining the coplanar waveguide with a photoconductive antenna structure, low-loss propagation of terahertz waves in a planar transmission line is achieved, and a strong interaction is generated at the sawtooth slot structure of the sawtooth structure, thereby improving the detection sensitivity and realizing terahertz fingerprint detection of trace objects to be tested.

[0013] The device provided by the present invention has a simple structure, is easy to design and optimize, has a low manufacturing cost, and is suitable for enhanced measurement of terahertz absorption characteristic spectra of different objects to be measured at different frequencies. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A three-dimensional schematic diagram of the structure of the terahertz absorption spectrum enhancement device provided in Example 1;

[0015] Figure 2 A front schematic diagram of the terahertz absorption spectrum enhancement device structure provided in Example 1;

[0016] Figure 3 This is a comparison chart of the absorption rates of the terahertz absorption spectrum enhancement device with a sawtooth structure in Example 1 coated with a 300um*300um*1um lactose film and the non-sawtooth planar waveguide structure coated with a 300um*300um*1um lactose film.

[0017] Among them, in the figure:

[0018] 1 is the film to be tested, 2 is the coplanar waveguide, 3 is the dielectric substrate, 4 is the photoconductive antenna structure, 5 is the sawtooth structure, and 6 is the terahertz time domain pulse. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0021] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0022] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to specific circumstances.

[0023] In addition, the terms "installed", "set", "provided with", "connected", "connected", and "socketed" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, elements, or components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0024] In order to solve the problem of enhanced detection of terahertz characteristic absorption spectra of trace analytes, researchers have introduced surface plasmon structures such as slot antennas and photonic crystals. These structures enhance the detection sensitivity of the spectral fingerprint of the analyte by generating resonance at the absorption frequency of the target analyte. On the other hand, on-chip terahertz waveguides, such as microstrip lines, can also be used to detect the absorption spectra of polycrystalline materials in a broadband range (up to 2 THz). Compared with free-space THz-TDS spectroscopy systems, on-chip THz systems can record spectra from small sample volumes. Therefore, studying methods based on on-chip terahertz waveguides can further improve its sensitivity in detecting the absorption spectra of analytes. Applying planar transmission lines to terahertz band devices can effectively reduce the volume and increase the portability of terahertz systems, which has important application value. However, the enhanced measurement effect of simple coplanar waveguides for the terahertz absorption spectra of trace analytes is still relatively limited, and additional microstructures are needed to further improve the enhanced measurement effect of characteristic absorption spectra.

[0025] Example 1

[0026] like Figure 1-2 As shown, the present invention provides a terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide, comprising: a dielectric substrate 3, a photoconductive antenna structure 4 and a coplanar waveguide 2 arranged on the dielectric substrate 3; the grounding wires on both sides of the middle of the coplanar waveguide 2 are constructed with sawtooth structures 5 and are symmetrically distributed relative to the middle signal line; the photoconductive antenna structure 4 is embedded on one side of the middle signal line, and a DC bias voltage is provided at both ends of the middle signal line, and the coplanar waveguide 2 has low radiation loss and good high-order mode suppression effect in the high frequency band. The photoconductive antenna structure 4 can generate adjustable terahertz waves in a wide frequency range and has low loss.

[0027] To further optimize the technical solution, the length of the coplanar waveguide 2 is 2 mm, the metal thickness is 0.2 um, the width of the middle signal line is 30 um, the width of the grounding lines on both sides is 500 um, and the width of the air slot between the signal line and the grounding line is 20 um. In this way, a coplanar waveguide structure without a ground plane can be formed, and its characteristic impedance is 50 ohms, which is convenient for the propagation and detection of broadband terahertz pulses in the air slot.

[0028] To further optimize the technical solution, the sawtooth groove depth and height on the coplanar waveguide 2 are both 25um, and the period is 50um. Such a periodic sawtooth structure supports terahertz plasmons, effectively constrains the electromagnetic field, and enhances the absorption of broadband terahertz waves by the thin film test object covered on its surface.

[0029] To further optimize the technical solution, the number of teeth of the sawtooth structure 5 of the ground wire structure on the coplanar waveguide 2 is 6.

[0030] To further optimize the technical solution, the surface of the coplanar waveguide 2 including the sawtooth structure 5 is completely covered with the thin film 1 of the object to be tested, which can greatly enhance the amplitude of the terahertz characteristic absorption spectrum of the object to be tested.

[0031] To further optimize the technical solution, the dielectric substrate 3 is made of gallium arsenide with a dielectric constant of 12.7, which has the advantages of small dispersion, low loss and stable dielectric constant in the high frequency band.

[0032] To further optimize the technical solution, a femtosecond laser emits a femtosecond laser pulse to generate a terahertz time domain pulse 6 in the photoconductive antenna structure 4, and the detection light detects the terahertz pulse in the air slots before and after the sawtooth structure 5. After Fourier transform and comparison, the scattering parameters of the coplanar waveguide 2 including the sawtooth structure 5 are obtained, which are used to enhance the terahertz absorption spectrum of the film 1 to be tested.

[0033] The present invention provides a terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide. By combining the coplanar waveguide 2 with a photoconductive antenna structure 4, low-loss propagation of terahertz waves in a planar transmission line is achieved, and a strong interaction is generated at the sawtooth slot structure of the sawtooth structure 5, thereby improving the detection sensitivity and realizing terahertz fingerprint detection of trace objects to be tested.

[0034] The device provided by the present invention has a simple structure, is easy to design and optimize, has a low manufacturing cost, and is suitable for enhanced measurement of terahertz absorption characteristic spectra of different objects to be measured at different frequencies.

[0035] The process of the experiment: The femtosecond laser pulses emitted by the femtosecond laser are divided into pump light and probe light. The pump light excites the photoconductive antenna structure with voltage bias to generate terahertz time-domain pulses. The terahertz wave is transmitted with low loss along the air slot gap between the central signal line of the coplanar waveguide and the ground wires on both sides. The probe light detects the terahertz pulse in the air slots before and after the sawtooth structure. When the terahertz wave is transmitted to the coplanar waveguide sawtooth structure, a strong electromagnetic interaction is generated at the tip of the sawtooth structure. When a 1um thick α-lactose film is placed in the sawtooth slot area, the terahertz wave has a strong interaction with the α-lactose film. After Fourier transform comparison, the scattering parameters of the coplanar waveguide containing the sawtooth structure are obtained. Significant changes in the absorption spectrum can be observed. There is a large peak at 0.52THz, which contains relevant information about the α-lactose film, thereby achieving high-sensitivity detection in the terahertz range.

[0036] Comparative Example 1

[0037] The only difference from Example 1 is that there is no sawtooth structure on the coplanar waveguide. In Comparative Example 1, there is a complete coplanar waveguide structure, and other structural parameters are the same as in Example 1. A 1 um thick α-lactose film is placed on the same area as in Example 1, and the terahertz absorption spectrum without the sawtooth structure is observed.

[0038] Analytical Testing

[0039] In order to evaluate the enhancement performance of the terahertz absorption spectrum enhancement device of the sawtooth structure on the coplanar waveguide, the comparison diagram of the terahertz absorption spectrum of the device in Example 1 and Comparative Example 1 is studied, as shown in FIG. Figure 3 The frequency range is 400 GHz to 600 GHz, and the absorption spectrum amplitude of the terahertz absorption spectrum of the 1 um α-lactose film with a sawtooth structure on the coplanar waveguide at 0.529 THz is greatly enhanced than the absorption spectrum amplitude of the terahertz absorption spectrum of the 1 um α-lactose film without a sawtooth structure at 0.529 THz. Compared with the non-serrated structure, the present invention significantly improves the absorption coefficient of the same object to be tested in the terahertz absorption spectrum, so as to realize the terahertz fingerprint detection of trace objects to be tested.

[0040] The above description is only a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any slight modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide, characterized in that: include: A dielectric substrate, a photoconductive antenna structure and a coplanar waveguide arranged on the dielectric substrate; the grounding wires on both sides of the middle of the coplanar waveguide are constructed with a sawtooth structure and are symmetrically distributed relative to the middle signal line; the photoconductive antenna structure is embedded on one side of the middle signal line, and a DC bias voltage is provided at both ends of the middle signal line.

2. A terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide according to claim 1, characterized in that: The length of the coplanar waveguide is 2 mm, the metal thickness is 0.2 um, the width of the middle signal line is 30 um, the width of the ground lines on both sides is 500 um, and the width of the air slot between the signal line and the ground line is 20 um.

3. A terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide as claimed in claim 2, characterized in that: The depth and height of the sawtooth grooves on the coplanar waveguide are both 25um, and the period is 50um.

4. A terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide as claimed in claim 3, characterized in that: The number of teeth of the sawtooth structure of the ground wire structure on the coplanar waveguide is 6.

5. A terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide as claimed in claim 1 or 4, characterized in that: The surface of the coplanar waveguide including the sawtooth structure is completely covered with the thin film of the object to be tested.

6. The terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide according to claim 1, characterized in that: The dielectric substrate is made of gallium arsenide with a dielectric constant of 12.

7.

7. The terahertz absorption spectrum enhancement device based on a sawtooth structure on a coplanar waveguide according to claim 1, characterized in that: A femtosecond laser emits a femtosecond laser pulse to generate a terahertz time domain pulse in the photoconductive antenna structure. The probe light detects the terahertz pulse in the air slots before and after the sawtooth structure. After Fourier transform and comparison, the scattering parameters of the coplanar waveguide containing the sawtooth structure are obtained, which are used to enhance the terahertz absorption spectrum of the film to be tested.

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