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Abstract
Active broadband terahertz (THz) polarization manipulation devices are challenging to realize, but also of great demand in broadband terahertz systems. Vanadium dioxide (VO2) shows a promising phase transition for active control of THz waves and provides broadband polarization characteristics when integrated within grating-type structures. We creatively combine a VO2-based grating structure with a total internal reflection (TIR) geometry providing a novel interaction mechanism between the electromagnetic waves and the device, to realize a powerful active broadband THz polarization-controlling device. The device is based on a Si-substrate coated with a VO2 layer and a metal grating structure on top, attached to a prism for generating the TIR condition on the Si-VO2-grating interface. The grating is connected to electrodes for electrically switching the VO2 between its insulating and conducting phases. By properly selecting the incident angle of the THz waves, the grating direction, and the incident polarization state, we first achieved a broadband intensity modulator under a fused silica prism with an average modulation depth of 99.75% in the 0.2-1.1 THz region. Additionally, we realized an active ultra-broadband quarter-wave converter under a Si prism that can be switched between a 45° linear rotator and a quarter wave converter in the 0.8-1.5 THz region. This is the first demonstration of an active quarter-wave converter with ultra-broad bandwidth performance. Our work shows a highly flexible and multifunctional polarization-controlling device for broadband THz applications.
Highlights
Terahertz technology has shown versatility as an academic tool to study a wide range of systems, including chemical systems in both solid and liquid forms, medical imaging and spectroscopy, and industrial process control and testing.[1,2,3,4,5] A key element in the growing interest of the terahertz field has been the continued improvement in the development of robust terahertz sources and detectors, such as the air-plasma techniques pioneered over the last decade,[6,7] which have unlocked ever higher powers and broader spectral ranges
We further developed the concept of a passive THz polarization converter to active devices by incorporating a VO2 thin film with a grating in total internal reflection (TIR) geometry
The device is built as a 100 nm thick VO2 layer on a Si substrate combined with a metal grating structure on top of the VO2 layer
Summary
Parrott,[1] Chunrui Han,[1] Georges Humbert,[2] Aurelian Crunteanu,[2] and Emma Pickwell-MacPherson1,3,b 1Department of Electronic Engineering, The Chinese University of Hong Kong, Hong Kong 2XLIM Research Institute, UMR 7252 CNRS/University of Limoges, Limoges, France 3Department of Physics and Astronomy, Warwick University, Coventry, United Kingdom (Received 27 October 2017; accepted 4 January 2018; published online 9 February 2018)
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