Abstract-A flexible, multifunctional, active terahertz modulator with an ultra-low triggering threshold

He Ma,   Yu Wang,   Rong Lu,   Fangrui Tan,  Yulan Fu,  Guang Wang,  Dayong Wang,  Kai Liu,   Shoushan Fan,  Kaili Jiang  Xinping Zhang 

https://pubs.rsc.org/en/content/articlelanding/2020/tc/d0tc02446e#!divAbstract

Active terahertz (THz) modulators play an essential role in THz technology. Because of the excellent THz modulation properties bestowed by its intrinsic metal-insulator transition (MIT) at 68 °C, vanadium dioxide (VO2) is an appealing active THz modulator material. Current active THz modulator designs based on pure VO2 films or metasurfaces deposited on traditional semiconductor substrates are typically subject to high triggering thresholds and slow responses. Therefore, further development of VO2 active THz modulators for superior performance requires new material and device designs. In this paper, we develop a flexible active THz modulator based on an aligned carbon nanotube thin film coated with VO2. THz wave modulation driven by the MIT of VO2 presents a giant modulation depth up to 91% and broad bandwidth (>2.3 THz). Various stimuli can be utilized to trigger the THz modulator. The response time of the THz modulator is 27 ms, which can be further shortened by decreasing the device size. In addition, the light-triggering threshold is quite low (0.58 mW/mm2). Optical anisotropy enables polarization of the THz modulator. Since they combine superior modulation performance, responsive stimuli diversity, versatility, and flexibility, these active THz modulators find applications in THz communication, THz imaging, etc.

Abstract-Highly Efficient Active All-Dielectric Metasurfaces Based on Hybrid Structures Integrated with Phase-Change Materials: From Terahertz to Optical Ranges

Chuwen Lan, He Ma, Manting Wang, Zehua Gao, Kai Liu, Ke Bi, Ji Zhou and Xiangjun Xin

https://pubs.acs.org/doi/abs/10.1021/acsami.8b22466?mi=aayia761&af=R&AllField=nano&target=default&targetTab=std

Recently, all-dielectric metasurfaces (AMs) have emerged as a promising platform for high-efficiency devices ranging from the terahertz to optical ranges. However, active and fast tuning of their properties, such as amplitude, phase and operating frequency, remains challenging. Here, a generic method is proposed for obtaining high-efficiency active AMs from the terahertz to optical ranges by using “hybrid structures” integrated with phase-change materials. Various phase-change mechanisms including metal–insulator phase change, nonvolatile phase change, and ferroelectric phase change are investigated. We first experimentally demonstrate several high-efficiency active AMs operating in the terahertz range based on hybrid structures composed of free standing silicon microstructures covered with ultrathin phase-change nanofilms (thickness d << λ). We show that both the frequencies and the strength of the Mie resonances can be efficiently tuned, resulting in unprecedented modulation depth. Furthermore, detailed analyses of available phase-change materials and their properties are provided to offer more options for active AMs. Finally, several feasible hybrid structures for active AMs in the optical range are proposed and confirmed numerically. The broad platform built in this work for active manipulation of waves from the terahertz to optical ranges may have numerous potential applications in optical devices including switches, modulators and sensors.