Terahertz electrically addressable metasurfaces based on liquid crystal and phase change material

Jingbo Wu, Benwen Chen, Weili Li, Caihong Zhang, Kebin Fan, Biaobing Jin, Jian Che1, and Peiheng Wu

Research Institute of Superconductor Electronics(RISE), School of Electronic Science and Engineering, Nanjing University, Nanjing 210023, China

The burgeoning field of electrically addressable terahertz (THz) metasurfaces shows good application prospects in beamforming, compressive imaging, and adaptive optics. For example, In the landscape of 6G communication, terahertz (THz) technology stands poised to revolutionize data transmission with unprecedented speeds, and the effective beamforming techniques are imperative to compensate for the significant path loss as shown in Fig. 1a. In this paper, we present the recent development of a THz electrically addressable metasurface based on liquid crystal and phase change material (PCM).

Leveraging the electro-optic effect and birefringence of liquid crystals, we have developed a variety of THz electrically addressable metasurfaces with amplitude and phase modulation capabilities[1-3]. The metasurface antenna with pixelated phase modulators enables dynamic beam steering by altering the coding sequences on each pixel. Initially, the 1D THz beam deflection was realized using a metasurface antenna consisting of 24 elements[1]. We introduce a THz metasurface featuring a crossbar structure, effectively scaling the array to exceed 3000 elements, as displayed in Fig. 1b [3]. The coding pattern on this electrically addressable device is derived through the modulo-addition operation of coding sequences on the top and bottom layers. Through experimental validation, we demonstrate the capability of the metasurface to actively deflect beams in the upper half-space.

Figure 1: THz electrically addressable metasurface. (a) THz electrically addressable metasurface for beam steering. (b) Diagram of electrically addressable metasurface based on liquid crystal [3]. (c) Diagram of electrically addressable metasurface based on VO₂ [5].

Vanadium dioxide (VO₂) is a popular choice of PCM. Upon transitioning, its conductivity experiences a remarkable shift of over five orders of magnitude, rendering it a good choice for reconfigurable and programmable devices operating at THz frequencies. We recently developed a pixelated metasurface with memory, comprising 8×8 pixels [4]. Thermal crosstalk, a key challenge for such metasurface, is effectively mitigated in our design, enabling modulation speeds up to 1 kHz. Memory function is achieved via hysteresis in the phase transition. Diverse spatial patterns with varying greyscales are attainable using different current pulses. Furthermore, we have developed an integrated self-adaptive metasurface (SAM) endowed with THz wave detection and modulation capabilities as shown in Fig. 1c [5]. Through applying different coding sequences, the metasurface demonstrates the capacity to deflect THz beams. Furthermore, we have established a software-defined sensing-reaction system for intelligent THz beam steering. Utilizing the proposed system, the SAM exhibits self-adaptive behavior, autonomously adjusting the deflection angle of THz beams in direct response to the strength change of the detected signal.
The electrically addressable metasurfaces based on PCM and liquid crystal provide a powerful and intelligent platform for manipulating THz waves, especially in active beamforming. The advancement of THz electrically addressable metasurfaces, characterized by high efficiency, high speed, and intelligence, carries noteworthy implications for their application in THz communication, radar, and imaging.

References
[1] J. Wu, Z. Shen, S. Ge, B. Chen, Z. Shen, T. Wang, C. Zhang, W. Hu, K. Fan, W. Padilla, Y. Lu, B. Jin, J. Chen, and P. Wu, “Liquid crystal programmable metasurface for terahertz beam steering,” Appl. Phys. Lett. 116, 131104 (2020)
[2] W. Li, X. Hu, J. Wu, K. Fan, B. Chen, C. Zhang, W. Hu, X. Cao, B. Jin, Y. Lu, J. Chen, and P. Wu, “Dual-color terahertz spatial light modulator for single-pixel imaging,” Light Sci. Appl. 11, 191 (2022)
[3] W. Li, B. Chen, X. Hu, H. Guo, S. Wang, J. Wu, K. Fan, C. Zhang, H. Wang, B. Jin, J. Chen, and P. Wu, “Modulo-addition operation enables terahertz programmable metasurface for high-resolution two-dimensional beam steering,” Sci. Adv. 9, eadi7565 (2023)
[4] B. Chen, J. Wu, W. Li, C. Zhang, K. Fan, Q. Xue, Y. Chi, Q. Wen, B. Jin, J. Chen, and P. Wu, “Programmable Terahertz Metamaterials with Non‐Volatile Memory,” Laser Photon. Rev. 16, 2100472 (2022)
[5] B. Chen, X. Wang, W. Li, C. Li, Z. Wang, H. Guo, J. Wu, K. Fan, C. Zhang, Y. He, B. Jin, J. Chen, and P. Wu, “Electrically addressable integrated intelligent terahertz metasurface,” Sci. Adv. 8, eadd1296 (2022)