Microtopography‐Guided Double‐Layer Cross Structure for a Terahertz Multiband Amplitude Modulator

Abstract

electromagnetic waves change from transmission to reflection, and the change process is reversible. Due to the phase change properties, VO 2 is often embedded in a metamaterial structure to fabricate a THz modulator, and other materials which have the same phase change properties (e.g., bismuth, graphene, and gyroelectric) can be used to fabricate the THz modulator too. [12][13][14][15][16] As ref. [17] shown, an active and smart electro-optic THz modulator based on a strongly correlated electron oxide VO 2 was proposed. The metamaterial structure of the THz modulator is composed od three layers, the materials of each layer are silver (Ag), silicon dioxide (SiO 2 ), and VO 2 , respectively. With milliampere current excitation on the VO 2 film, the transmission, reflection, absorption, and phase of THz waves can be modulated efficiently. In particular, the antireflection condition can be actively achieved and the modulation depth reaches 0.99. As ref. [18] shown, an optically and thermally controlled THz modulator based on silicon (Si) and VO 2 hybrid meta surface is proposed to improve the ability of flexibly manipulating THz waves, and the modulator can bring a deep MD of 0.97 at 0.9 THz. There are other phase-change materials used in the modulator to modulate THz waves except VO 2 . As ref. [19] shown, a faraday modulator based on graphene, gyroelectric (InSb), SiO 2 , and Si materials was proposed. Finally, the THz signal transmission can be modified from 0 to 0.8 by varying applied static magnetic fields. As ref. [20] shown, a high-performance, broadband THz modulator based on the photo-induced transparency of carbon nanotube films was proposed. The modulation depth of this modulator can reach +0.8 with modulation speeds of 340 GHz under femtosecond pulsed illumination. In summary, the metamaterial structures are used to realize the transmission and reflection, and phasechange materials (PCM) are inserted in the metamaterial structures to modulate the transmission and reflection. Generally, all the structures are prepared by photolithography, etching, or liftoff technologies. As the feature size of metamaterials reduces to micro and nano scale, the cost rises at an exponential rate, and the accuracy of insertion of PCM is difficult to control.A deep MD of the modulator will bring a large-scale modulation, which means lots of signals can be controlled, thereby the diversity of modulation can be improved. Meanwhile, high rising and falling slopes of the filtering band, leading to a short time from filtering pass to blocking thereby an improvement of transmission response. Herein, a THz multiband amplitude Terahertz (THz) modulator can be used to modulate the amplitude and frequency of THz wave. A THz multiband amplitude modulator based on temperature control is proposed in this study. The metamaterial structure of proposed modulator is a double-layer cross structure which attached on a silicon substrate, and the cross-distribution of different materials in top and middle layer is Cu @ SiO 2 and SiO 2 @ VO 2 , r...