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31

2024

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07

Terahertz double-bit regulation of color light coding

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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 superstructure materials 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 superstructure material 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 super-dog materials, terahertz superstructure materials, microwave superstructure materials and so on. The metasurface is the two-dimensional counterpart of the metasurface, which is easy to prepare and integrate, and is widely used in the design of terahertz devices.
Recently, terahertz modulators based on optically controlled reconfigurable supersurface have ultra-fast response time on the order of picoseconds, which are 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 superstructured surface structure, which makes it difficult to independently regulate each resonant unit and cannot achieve terahertz modulation of optically controlled 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.
Recently, the Jiang Tian research team of the National University of Defense Technology combined optical artificial superstructure with reconfigurable terahertz superstructure surface to achieve a two-bit terahertz ultrafast modulation of color light excitation coding. This work provides a new development way for optical coding terahertz modulation, further inspires the exploration of optically controlled terahertz control devices based on superstructured surfaces, and is expected to promote the application of composite superstructured surfaces in terahertz control.
The research results were published online in international high-level academic journals under the title "Color Coded Metadevices toward Programmed Terahertz Switching" Light: Science & ApplicationsOn. The author of the paper is Hu Yuze, associate researcher and Jiang Tian researcher of the National University of Defense Technology, and the first author is He Weibao, a doctoral student of the National University of Defense Technology. 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.

innovation research

In this work, the researchers innovatively proposed a combination of optical artificial superstructure and reconfigurable terahertz superstructure surface to achieve light-controlled ultra-fast coding control of terahertz, which can achieve double-bit terahertz information under different color light excitation (see Figure 1a). Optical artificial superstructures, I .e., periodically arranged distributed Bragg reflectors that reflect different wavelengths (see Figure 1b, c), reflect 400 nm blue light and 800 nm red light, respectively (see Figure 1e, f). The reconfigurable terahertz supersurface is composed of epitaxial silicon composite metal artificial microstructures (see FIG. 1c). Researchers designed the active superstructure surface of metal wire and split resonant ring with different sizes, and provided two terahertz modulation channels (see Figure 1g). Under the excitation of optical pumps of different colors, the switches of corresponding resonance channels can be independently controlled respectively, thus realizing the coding regulation of terahertz, achieve ultra-fast switching of the four coding states ("00", "01", "10", "11") of terahertz.

The composite terahertz superstructure surface was tested in the self-built dual-optical pump terahertz detection system, and the experiment confirmed the four terahertz amplitude coding states under different color optical pumps (see Figure 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 independently excited, the encoding process is "00-01/10-00" (see Figures 2b and c); When two beams of light are excited at the same time, the encoding is "00-11-00" (see Figure 2f); If one channel is controlled to be excited all the time while the other channel is modulated, the encoding regulation of "01/10-11-01/10" can be realized (see Figures 2d and E). The response time of optically controlled switching between the four coding states is within 1 ns.

Fig.1 Schematic diagram of dual-bit terahertz control based on color coding and design of superstructured surface structure

Fig.2 Opto-controlled ultrafast terahertz coded switch

Summary and Prospect

This work combines optical metamaterials and reconfigurable terahertz supersurface, two artificial microstructures with different working 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 superstructured 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, biosensing 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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