Chongfan Technology
News
08
2024
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08
Terahertz Double-bit Regulation of Light | Color Encoding
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Recently, National University of Defense TechnologyJiangtian Research TeamCombined with optical artificial superstructure and reconfigurable terahertz metasurface, the two-bit terahertz ultrafast modulation encoded by color light excitation is realized. This work provides a new development way for optical coding terahertz modulation, further inspires the exploration of optically controlled terahertz control devices based on super surface, and is expected to promote the application of composite super surface in terahertz control.
The results of this research are based on"Color Coded Metadevices towards Programmed Terahertz SwitchingPublished online inLight： Science & Applications. The author of the paper is National University of Defense Technology.Hu Yuze Associate ResearcherandJiang Tian researcherThe first author is National University of Defense TechnologyPhD student He Weibao. This work has been supported by the National Natural Science Foundation of China, the National Key R & D Program and the National University of Defense Technology Young Innovative Talent Incubation Fund.
Terahertz has the characteristics of low energy and large bandwidth, and has great application prospects in high-speed wireless communication and non-destructive testing. However, the lack of efficient terahertz modulators limits the further development of terahertz science and technology. In recent years, reconfigurable electromagnetic metamaterials have attracted a lot of attention, which can control electromagnetic waves flexibly and dynamically in real time, and effectively make up for the lack of terahertz multifunctional devices. The so-called electromagnetic metamaterial is composed of artificial microstructures arranged periodically, which can show physical properties that natural materials do not have. According to the different working band, it can be divided into optical metamaterials, terahertz metamaterials, microwave metamaterials and so on. Metasurface is the two-dimensional counterpart of metamaterials, which has the characteristics of easy preparation and easy integration, and is widely used in the design of terahertz devices.
Recently, terahertz modulators based on optically controlled reconfigurable metasurfaces have ultra-fast response times on the order of picoseconds, which have been favored by many researchers. This light control modulation method has the advantage of no contact, and can also try to use multiple excitation beams to achieve different functions respectively. However, optical excitation often covers the entire metasurface structure, which makes it difficult to independently regulate each resonant unit and cannot achieve terahertz modulation of optical control coding. Moreover, the photon energy of the pump light is greater than the band gap of the tunable material, which can realize the effective control of the terahertz. How to apply the degree of freedom of the pump light to the terahertz modulation is a very challenging topic.
In this work, the researchers innovatively proposed a combination of optical artificial superstructure and reconfigurable terahertz supersurface to achieve light-controlled ultra-fast coding regulation of terahertz, which can achieve two-bit terahertz information coding under different color light excitation (see.Figure 1a). Optical artificial superstructures, that is, periodically arranged distributed Bragg reflectors reflecting different wavelengths (seeFigure 1b, c), which reflect 400 nm blue light and 800 nm red light respectively (seeFigure1e、f). Reconfigurable terahertz metasurfaces, composed of epitaxial silicon composite metal artificial microstructures (seeFigure 1c). The researchers designed an active metasurface of metal wires and split resonant rings of different sizes, providing two terahertz modulation channels (seeFigure 1g), under the excitation of different color optical pumps, the switches of the corresponding resonance channels can be independently controlled, thus realizing the coding regulation of terahertz and realizing the ultrafast switching of the four coding states ("00", "01", "10" and "11") of terahertz.
Figure 1: Schematic diagram of two-bit terahertz control based on color coding and design of super surface structure
The fabricated composite terahertz supersurface was tested in a self-built dual-optically pumped terahertz detection system, and the experiments confirmed four terahertz amplitude coding states under different color optical pumping (seeFigure 2a). The left low frequency resonance channel is modulated when the blue light of 400 nm is pumped, and the right high frequency resonance channel is modulated when the red light of 800 nm is pumped. When blue light/red light is excited independently, the encoding process is "00-01/10-00" (seeFigure 2b, c); When two beams are excited at the same time, the code is "00-11-00" (seeFigure 2f); If you choose to control one channel to be in the excitation state all the time and modulate the other channel, the coding regulation of "01/10-11-01/10" can be realized (seeFig. 2D, E). The response time of optically controlled switching between the four coding states is within 1 ns.
Figure 2: Light-controlled ultra-fast terahertz coded switch
This work combines optical metamaterials and reconfigurable terahertz metasurfaces, two artificial microstructures with different operating bands. Compared with the traditional control method, the scheme can independently encode the local coupling mode in a single meta-packet, provide a novel design concept for terahertz ultra-surface modulation devices, and open up a new way for multi-functional, highly integrated and programmable terahertz functional devices for various terahertz technology applications (such as wireless communication, biological sensing and non-destructive testing). This coding method can be extended to multi-bit information processing, and is expected to be applied to the field of optically controlled terahertz imaging in the future.
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