Metamaterial terahertz photoconductive antenna

Abstract

The application discloses a super-structured terahertz photoconductive antenna, which comprises a micro-scale metal rod and a metal open resonant ring, wherein the micro-scale metal rod and the metal open resonant ring are respectively integrated on the inner side and the outer side of a coplanar transmission line and are directly connected with the coplanar transmission line; the metal rod and the open resonant ring constitute a super-structured atomic microstructure; the introduction of the super-structured atomic microstructure effectively couples terahertz energy propagating along the coplanar transmission line into electromagnetic resonance modes of the super-structured antenna itself, radiates the stored energy to a far field in the form of resonance scattering, converts the terahertz wave of the transmission line mode into a far field radiation mode, and realizes radiation enhancement in a full frequency band.

Description

Technical Field

[0001] This invention relates to the field of optimizing the radiation performance of terahertz transmitting antennas, and more particularly to a meta-terahertz photoconductive antenna, specifically by introducing micron-scale metallic metamaterial electrodes into the photoconductive transmitting antenna to enhance its radiation power and broaden its spectrum. Background Technology

[0002] Photoconductive antennas, due to their unique advantages such as room temperature operation, low power consumption, wide spectrum, and compact size, have become the most widely used commercial terahertz radiation source in terahertz technology. [1-4] Its basic structure includes a semiconductor substrate (gallium arsenide, silicon, etc.) and a pair of metal electrodes attached to it. When a femtosecond light pulse with photon energy greater than the bandgap of the substrate material is focused onto the substrate in the central region of the metal electrodes, the substrate absorbs the photon energy and generates photogenerated carriers (electron-hole pairs). At this time, the DC bias field applied to the metal electrodes drives the photogenerated carriers to accelerate, thereby generating a transient photocurrent. Finally, the terahertz wave is radiated outward through the metal electrodes. [5] According to the process of terahertz wave radiation by a photoconductive antenna, in addition to the far-field radiation mode that propagates perpendicular to the substrate surface, there is also a mode that propagates parallel to the substrate surface along the coplanar transmission lines of the metal. However, for classical terahertz time-domain spectroscopy systems, only the portion of terahertz energy propagating into free space in the far-field radiation mode is effectively utilized. [6] .

[0003] Furthermore, although photoconductive antennas exhibit good performance in terahertz radiation, providing an advantage for optical generation of terahertz waves, they lack the ability to flexibly control the characteristics of the radiation spectrum, such as adjusting the intensity, direction, and polarization of the radiation, and have low radiation power. This largely limits their potential for more diversified applications in commercial terahertz technology.

[0004] References

[0005] [1]S. Preu, GH Dohler, S. Malzer, LJ Wang, and AC Gossard, Tunable, continuous-wave terahertz photomixer sources and applications, J.Appl. Phys. 109(6), 061301 (2011).

[0006] [2]Park, Sang-Gil et al. “Terahertz photoconductive antenna with metal nanoislands.”

[0007] Optics express 20 23 (2012): 25530-5.

[0008] [3]Xingwei Yan, Zhiqiang Wei, Chunhua Li, Progress on the terahertzwave radiation properties of Photoconductive Antenna, Journal of TerahertzScience and Electronic Information Technology, Vol.13(6):870-876(2015).

[0009] [4]Burford NM, El-Shenawee M O. Review of terahertz photoconductiveantenna technology[J]. Optical Engineering, 2017, 56(1): 010901-010901.

[0010] [5]Mourou G, Stancampiano CV, Blumenthal D. Picosecond microwavepulse generation [J]. Appl Phys Lett, 1981, 38(6):470-472.

[0011] [6] Gu Jianqiang, Wang Kemeng, Xu Yi, et al. Terahertz photoconductive antenna based on metamaterials [J]. Chinese Journal of Lasers, 21, 48(19):174-194. Summary of the Invention

[0012] This invention provides a meta-terahertz photoconductive antenna. The invention proposes a meta-antenna structure for increasing the far-field radiated power of the photoconductive antenna across all frequency bands, and increasing the total radiated power of the antenna by more than seven times. Details are described below:

[0013] A meta-terahertz photoconductive antenna, the antenna comprising: a micrometer-scale metal rod and a metal open-loop resonator, the micrometer-scale metal rod and the metal open-loop resonator being integrated on the inner and outer sides of a coplanar transmission line, respectively, and directly connected to the coplanar transmission line;

[0014] The metal rod and the open resonant ring constitute a meta-atomic microstructure. The introduction of the meta-atomic microstructure effectively couples the terahertz energy propagating along the coplanar transmission line into the electromagnetic resonance mode of the meta-antenna itself, and radiates the stored energy to the far field in the form of resonant scattering, transforming the terahertz wave of the transmission line mode into a far-field radiation mode, thereby achieving full-band radiation enhancement.

[0015] The meta-atomic microstructure formed by the metal rod and the open resonant ring interacts with the terahertz waves propagating along the transmission line.

[0016] Furthermore, the meta-antenna achieves enhanced radiation across all operating frequencies, with a total energy increase of 7.4 times.

[0017] The meta-atomic microstructure formed by the metal rod and the open resonant ring has a localizing effect on terahertz waves propagating in the coplanar transmission line.

[0018] The meta-atomic microstructure is arranged coplanarly with the H-type dipole antenna, and the material used is the same as that of the dipole antenna.

[0019] Furthermore, the meta-atomic microstructure has a localizing effect on terahertz waves propagating in coplanar transmission lines, weakening the terahertz energy of the transmission line mode and enhancing the terahertz energy of the far-field radiation mode.

[0020] The beneficial effects of the technical solution provided by this invention are:

[0021] 1. The design of the metal metastructure photoconductive antenna of the present invention opens up a new way to improve the power of terahertz systems. At the same time, the device is simple to manufacture and the processing is flexible and convenient, laying the foundation for the large-scale application of terahertz photoconductive antennas.

[0022] 2. The metal metamaterial photoconductive antenna of the present invention, by introducing micron-scale metal metamaterial electrodes, realizes the scattering of terahertz waves in the transmission line mode that could not be utilized to the far field, giving the metasurface photoconductive antenna a novel function, and has broad application prospects in the fields of terahertz wave spectroscopy, imaging and sensing.

[0023] 3. The metal metastructure photoconductive antenna of the present invention is used as the terahertz source of the terahertz time-domain spectroscopy system, which realizes radiation enhancement at all operating frequencies and increases the total radiation power of the antenna by 7.4 times. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a meta-terahertz photoconductive antenna;

[0025] Figure 2 This is a schematic diagram of the operation of a meta-terahertz photoconductive antenna.

[0026] Among them, (a) is a schematic diagram of a traditional antenna structure; (b) is a schematic diagram of a novel terahertz photoconductive antenna structure containing a metaatomic microstructure; and (c) is a schematic diagram of the geometric parameters of the designed metaatomic microstructure.

[0027] Figure 3 This diagram illustrates the time-domain signals obtained from the preferred example of the meta-antenna and the H-type dipole antenna using a terahertz time-domain 8F spectral system, and the amplitude spectra of the two obtained through Fourier transform.

[0028] Figure 4 The diagram shows the radiated electric field distribution of a conventional photoconductive antenna and a preferred example, simulated using the time-domain solver of the electromagnetic simulation software CST Microwave Studio.

[0029] Among them, (a)-(d) are schematic diagrams of the electric field distribution of the transmission line mode of the H-type dipole antenna and the meta-antenna at 0.34THz, 0.79THz, 1THz and 1.2THz, respectively; (e)-(h) are schematic diagrams of the electric field distribution of the back radiation mode of the H-type dipole antenna and the meta-antenna, respectively.

[0030] The attached diagram lists the components represented by each number as follows:

[0031] 1: The antenna section of the photoconductive antenna, that is, the point where the femtosecond laser is incident, is also the point where terahertz waves are radiated outward;

[0032] 2: Superatomic microstructure;

[0033] 3: Coplanar transmission lines;

[0034] 4: Antenna electrodes;

[0035] 5: Photoconductive substrate;

[0036] 6: A femtosecond laser pulse with a center wavelength of 780 nm, incident perpendicularly;

[0037] 7: Terahertz waves in transmission line mode propagating horizontally along a coplanar transmission line;

[0038] 8: Terahertz waves in the far-field mode propagating perpendicular to the photoconductive substrate. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0040] The emergence of the metasurface concept has opened up new avenues for overcoming the difficulties in the prior art. Because metasurfaces exhibit extremely high design freedom in electromagnetic wave manipulation, their introduction for optimizing photoconductive antenna electrodes holds promise as a new method for improving antenna radiation performance. To date, reported photoconductive antennas integrating metaatoms can only improve radiation efficiency at specific frequencies, which contradicts the broadband characteristics of photoconductive antennas. This invention proposes a technical method—designing a micrometer-scale metallic metasurface antenna—that can achieve a full-band improvement in the radiated power of the photoconductive antenna, increasing the total radiated power of the antenna by 7.4 times.

[0041] Example 1

[0042] To improve the radiation efficiency and increase the total radiated power of photoconductive antennas across the entire operating frequency band, this invention proposes a meta-antenna incorporating a metallic meta-atomic microstructure. This antenna structure includes a micrometer-scale metal rod and a metal open-loop resonant ring, directly connected to a coplanar transmission line and integrated on the inner and outer sides of the transmission line, respectively. The introduction of the meta-atomic microstructure effectively couples the terahertz energy propagating along the coplanar transmission line into the meta-antenna's own electromagnetic resonant mode, radiating the stored energy to the far field through resonant scattering. This transforms the previously unusable terahertz waves from the transmission line mode into a far-field radiation mode, thereby not only increasing the antenna's overall radiated power by more than seven times but also achieving full-band radiation enhancement.

[0043] The technical solution adopted is as follows: the above-mentioned metallic meta-atomic microstructure is arranged in the same plane as the H-type dipole antenna, and the material used is the same as that of the dipole antenna. Therefore, its fabrication process is similar to that of the traditional antenna. It is only necessary to change the mask pattern on the basis of the traditional H-type dipole antenna, which is convenient and quick.

[0044] Metaantenna structures containing metallic metaatoms are key to comprehensively enhancing radiated power and achieving spectral modulation.

[0045] The metallic metaatomic microstructure consists of two parts: a metal rod and a metal open-ended resonant ring. The metal rod is symmetrically distributed on the inner side of two coplanar transmission lines, while the open-ended resonant ring is symmetrically distributed on the outer side. The interaction between the metaatomic microstructure composed of the metal rod and the open-ended resonant ring and the terahertz modes propagating along the transmission lines is the key to achieving enhanced radiation across the entire frequency band and a significant increase in total power.

[0046] The metal rod and the metal open-loop resonant ring are directly connected to the coplanar transmission line, arranged symmetrically about the antenna section. Both microstructures have a linewidth of 10 μm, and their connection points to the transmission line are 45 μm from the center of the antenna section. Electromagnetic simulations and experimental verification demonstrate that this invention's embodiments confirm that the meta-antenna containing this meta-atomic microstructure can interact with terahertz waves in transmission line mode through electromagnetic resonance, thereby localizing some terahertz energy within its own structure. In this process, the meta-antenna radiates the coupled terahertz energy to the far field through resonant scattering, achieving not only full-band enhancement of radiated power but also an increase of more than 7 times in the total radiated power.

[0047] Example 2

[0048] The specific fabrication process of the photoconductive antenna with integrated metallic meta-atomic microstructure is as follows:

[0049] The technologies used in the embodiments of this invention mainly involve deep ultraviolet lithography and material deposition technologies. The specific processing flow of the embodiments of this invention is as follows:

[0050] First, photoresist is uniformly spin-coated onto a GaAs substrate. Then, deep ultraviolet lithography is used to selectively expose the photoresist according to the designed mask pattern. Next, development is performed to retain the unexposed parts of the photoresist on the substrate surface, thereby forming the designed photoconductive antenna pattern.

[0051] Furthermore, the pattern transfer of the designed antenna structure is completed through the deposition of metal materials. Finally, the excess photoresist and metal materials are removed by stripping to complete the fabrication of the designed photoconductive antenna.

[0052] The superconducting photoconductor antenna with integrated metallic metaatomic microstructures has a radiation bandwidth of 0.02–2.2 terahertz. It was characterized using a conventional 8F terahertz time-domain spectroscopy system, and coherent detection of terahertz pulses was performed using photoconductivity sampling.

[0053] Example 3

[0054] The solutions in Examples 1 and 2 will be further described below with specific examples:

[0055] Figure 2 This schematically illustrates a preferred embodiment of the present invention: a meta-photoconductive antenna integrating a metallic meta-atomic microstructure. For example... Figure 2 As shown in (b), the terahertz photoconductive antenna with integrated meta-atomic microstructure includes: antenna section 1, the designed metal meta-atomic microstructure 2, coplanar transmission line 3, antenna electrode 4, and photoconductive substrate 5.

[0056] Among them, the photoconductive substrate is an intrinsic gallium arsenide with uniform thickness (…). Figure 2 (b) As shown in 5), its function is as an attachment layer for dipole antennas and metaatoms; the metallic metaantenna is based on an H-type dipole ( Figure 2 (a)), H-type dipoles are introduced on both sides of the antenna section ( Figure 2 (a) The same metallic material is composed of superatomic atoms ( Figure 2 (b) As shown in 2), the metaatomic microstructure consists of 4 pairs of identical metallic subwavelength microstructures ( Figure 2 (b) As shown in 2, the antenna sections are symmetrically arranged in the antenna section ( Figure 2 (b) As shown in 1) It consists of two sides, 90 μm apart, and the specific dimensions of the metal metaatoms are as follows. Figure 2 As shown in (c), its function is to radiate terahertz waves outwards. Its usage is as follows: Figure 1 As shown, antenna section ( Figure 2 (b) As shown in Figure 1) the gallium arsenide substrate layer corresponding to the center is the pumping position of the femtosecond laser pulse, which rapidly generates photogenerated carriers in response to the femtosecond pulse and radiates terahertz pulses in the opposite direction; coplanar transmission lines ( Figure 2 (b) (shown in section 3) is connected to the metallic metastructure antenna, and its function is to feed the antenna; the antenna electrodes are located at both ends of the coplanar transmission line, and their function is to connect to the packaged circuit through the electrodes ( Figure 2 (b) As shown in 4).

[0057] Specifically, the geometric parameters of antenna section 1 of the photoconductive antenna are as follows: Figure 2 As shown in (a), it is positioned at the center of the antenna; the geometric parameters of the metallic metaatomic microstructure 2 designed in this embodiment of the invention are as follows: Figure 2 As shown in (c), the linewidth is 10 μm; the linewidth of coplanar transmission line 3 is 10 μm, and the spacing is 80 μm; the area of ​​electrode 4 is 2 mm². 2 The antenna elements 1, 2, 3, and 4 are arranged at the four corners of the antenna and connected to both ends of the coplanar transmission line; the photoconductive substrate 5 is an intrinsic gallium arsenide with a thickness of 650 μm; the antenna section 1, the designed "meta-atomic" microstructure 2, the coplanar transmission line 3, and the antenna electrode 4 are all made of 10 nm chromium / 200 nm gold and are arranged on the surface of the photoconductive substrate. As a preferred embodiment of the present invention, its working schematic diagram is as follows: Figure 1 As shown, a femtosecond laser pulse 6 with a center wavelength of 780 nm is incident perpendicularly on the surface of the photoconductive substrate 5 at the center of the antenna section 1, exciting it to generate a transmission line mode terahertz wave 7 propagating along the direction of the coplanar transmission line 3 and a far-field mode terahertz wave 8 propagating perpendicular to the substrate direction.

[0058] In this embodiment of the invention, the performance of a conventional H-type dipole photoconductive antenna and a published meta-photoconductive antenna integrating a metallic meta-atomic microstructure were characterized under the same test conditions using a terahertz 8F time-domain spectroscopy system. The results are as follows: Figure 3 As shown, in the time domain, the terahertz wave pulse radiated by the meta-electro-optical antenna with integrated metallic meta-atomic microstructure has a significantly different time-domain waveform compared to that of a conventional H-type dipole photoconductive antenna; in the frequency domain, compared to a conventional H-type dipole photoconductive antenna, the meta-electro-optical antenna with this structure achieves radiation enhancement across the entire frequency band, with a total radiated power increase of 7.4 times. Figure 3 This effectively demonstrates the effectiveness of the design in this embodiment of the invention for enhancing the far-field radiated power of terahertz photoconductive antennas across the entire frequency band, and for significantly enhancing the total radiated power of photoconductive antennas.

[0059] Example 4

[0060] The feasibility of the scheme in Example 1 is verified by specific experiments, as detailed below:

[0061] (1) The distribution of terahertz electric fields at 0.34 THz, 0.79 THz, 1 THz and 1.2 THz was numerically simulated using CST electromagnetic simulation software, realizing the following: Figure 4 The simulation results show that this structure has a strong localization effect on terahertz waves propagating in coplanar transmission lines, achieving the expected effect of reducing the terahertz energy of transmission line modes while enhancing the terahertz energy of far-field radiation modes.

[0062] (2) The radiation performance of traditional photoconductive antennas and photoconductive antennas containing metaatoms was characterized using a terahertz time-domain spectroscopy system, and the results were as follows: Figure 3 The effect shown. Based on the measured time-domain signal ( Figure 3 The Fourier transform amplitude spectrum of the middle left figure ( Figure 3 The right-hand figure in the middle verifies the effectiveness of this design in the embodiment of the present invention. Under the same experimental conditions, compared with the H-type dipole photoconductive antenna without metaatoms, the meta-antenna achieves radiation enhancement across the entire operating frequency range and the total energy is enhanced by 7.4 times.

[0063] Unless otherwise specified, the model numbers of the various devices in this embodiment of the invention are not limited, and any device that can perform the above functions is acceptable.

[0064] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A meta-terahertz photoconductive antenna, characterized in that, The antenna includes: a micrometer-sized metal rod and a metal open-loop resonant ring, which are respectively integrated on the inner and outer sides of the coplanar transmission line and directly connected to the coplanar transmission line. The metal rod and the open resonant ring constitute a meta-atomic microstructure. The introduction of the meta-atomic microstructure effectively couples the terahertz energy propagating along the coplanar transmission line into the electromagnetic resonance mode of the meta-antenna itself, and radiates the stored energy to the far field in the form of resonant scattering, transforming the terahertz wave of the transmission line mode into a far-field radiation mode, thereby achieving full-band radiation enhancement. The metaatomic microstructure formed by the metal rod and the open resonant ring interacts with the terahertz waves propagating along the transmission line. The meta-atomic microstructure formed by the metal rod and the open resonant ring has a localizing effect on terahertz waves propagating in the coplanar transmission line. The meta-atomic microstructure is arranged coplanarly with the H-type dipole antenna, and the material used is the same as that of the dipole antenna. The meta-atomic microstructure has a localizing effect on terahertz waves propagating in coplanar transmission lines, weakening the terahertz energy of the transmission line mode and enhancing the terahertz energy of the far-field radiation mode. The metallic meta-antenna is based on an H-type dipole. Metallic metaatoms of the same metallic material as the H-type dipole are introduced on both sides of the antenna section. The metaatomic microstructure consists of four pairs of identical subwavelength metallic microstructures symmetrically arranged on both sides of the antenna section, 90 μm apart. The gallium arsenide substrate at the center of the antenna section serves as the pumping position for the femtosecond laser pulse. It rapidly responds to the femtosecond pulse, generating photogenerated carriers and radiating terahertz pulses in the opposite direction. A coplanar transmission line is connected to the metallic meta-antenna, serving as the antenna feed. Antenna electrodes are located at both ends of the coplanar transmission line, connecting to the packaging circuitry via the electrodes. The performance of a conventional H-type dipole photoconductive antenna and a published meta-photoconductive antenna integrating a metallic meta-atomic microstructure were characterized using a terahertz 8F time-domain spectroscopy system under the same test conditions. In the time domain, the terahertz pulse waveform radiated by the meta-photoconductive antenna integrating the metallic meta-atomic microstructure showed significant differences compared to that of the conventional H-type dipole photoconductive antenna. In the frequency domain, compared to the conventional H-type dipole photoconductive antenna, the meta-photoconductive antenna integrating this structure achieved radiation enhancement across the entire frequency band, with a total radiated power increase of 7.4 times.

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