Abstract-Total Internal Reflection Geometry: Exploiting Total Internal Reflection Geometry for Terahertz Devices and Enhanced Sample Characterization

Qiushuo Sun, Xuequan Chen, Xudong Liu, Rayko I. Stantchev, Emma Pickwell‐MacPherson

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201900535

To promote potential applications of terahertz (THz) technology, more advanced functional THz devices with high performance are needed, including modulators, polarizers, lenses, wave retarders, and antireflection coatings. This work summarizes recent progress in THz components built on functional materials including graphene, vanadium dioxide, and metamaterials. The key message is that, while the choice of materials used in such devices is important, the geometry in which they are employed also has a significant effect on the performance achieved. In particular, devices operating in total internal reflection geometry are reviewed, and it is explained how this geometry is able to be exploited to achieve a variety of THz devices with broadband operation.

Abstract-Exploiting Total Internal Reflection Geometry for Terahertz Devices and Enhanced Sample Characterization

Qiushuo Sun, Xuequan Chen, Xudong Liu, Rayko I. Stantchev 

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201900535

To promote potential applications of terahertz (THz) technology, more advanced functional THz devices with high performance are needed, including modulators, polarizers, lenses, wave retarders, and antireflection coatings. This work summarizes recent progress in THz components built on functional materials including graphene, vanadium dioxide, and metamaterials. The key message is that, while the choice of materials used in such devices is important, the geometry in which they are employed also has a significant effect on the performance achieved. In particular, devices operating in total internal reflection geometry are reviewed, and it is explained how this geometry is able to be exploited to achieve a variety of THz devices with broadband operation.

Abstract-Graphene controlled Brewster angle device for ultra broadband terahertz modulation

Zefeng Chen, Xuequan Chen, Li Tao, Kun Chen, Mingzhu Long, Xudong Liu, Keyou Yan, Rayko I. Stantchev, Emma Pickwell-MacPherson, Jian-Bin Xu

https://www.nature.com/articles/s41467-018-07367-8


Terahertz modulators with high tunability of both intensity and phase are essential for effective control of electromagnetic properties. Due to the underlying physics behind existing approaches there is still a lack of broadband devices able to achieve deep modulation. Here, we demonstrate the effect of tunable Brewster angle controlled by graphene, and develop a highly-tunable solid-state graphene/quartz modulator based on this mechanism. The Brewster angle of the device can be tuned by varying the conductivity of the graphene through an electrical gate. In this way, we achieve near perfect intensity modulation with spectrally flat modulation depth of 99.3 to 99.9 percent and phase tunability of up to 140 degree in the frequency range from 0.5 to 1.6 THz. Different from using electromagnetic resonance effects (for example, metamaterials), this principle ensures that our device can operate in ultra-broadband. Thus it is an effective principle for terahertz modulation.

Abstract-Towards a Rapid Terahertz Liquid Crystal Phase Shifter: Terahertz In-Plane and Terahertz Out-Plane (TIP-TOP) Switching

Benjamin S.-Y. Ung,  Xudong Liu,  Edward P. J. Parrott,  Abhishek Kumar Srivastava,  Hongkyu Park, Vladimir G. Chigrinov, Emma Pickwell-MacPherson

http://ieeexplore.ieee.org/document/8283624/


Terahertz (THz) phase shifters are an essential component needed to realize many potential applications. Liquid crystals (LC) are commonly used at optical frequencies, yet to achieve an equivalent phase shift at THz frequencies the LC layer needs to be orders of magnitude thicker. Consequently, the time for the LC to relax back to its initial state is prohibitively slow. In this paper, we show for the first time how a thick, nematic phase LC cell can be switched actively in both directions, thereby achieving fast phase shifting of THz light. We call this THz in-plane and THz out-plane (TIP-TOP) switching. To achieve this, we have designed and fabricated a novel electrode structure, able to switch to and from both in- and out-plane orientations (TIP-TOP). The performance of the fabricated device provides an actively controllable phase delay with an ON–OFF cycle switching time of approximately 0.5 s: almost 100 times faster than the usual cycle time which exceeds 40 s. Furthermore, the analysis of the director distributions allows us to understand the causes of the asymmetric switching times. The TIP-TOP cell presents the capability to work as a low insertion loss, fast THz phase shifter and could be scaled up to realize a phased array device.

Abstract-Exploiting a metal wire grating in total internal reflection geometry to achieve achromatic polarization conversion

Xudong Liu, Xuequan Chen, Edward P. J. Parrott, and Emma Pickwell-MacPherson

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-5-4-299&origin=search

We demonstrate how a metal wire grating can work as a 45° polarization converter, a quarter-wave retarder, and a half-wave retarder over a broadband terahertz range when set up in total internal reflection geometry. Classical electromagnetic theory is applied to understand the mechanism, and equations to calculate the polarization state of reflected light are derived. We use a metal grating with a period of 20 μm and width of 10 μm on a fused silica surface: linearly polarized terahertz light incident from fused silica with a supercritical incident angle of 52° is totally reflected by the metal grating and air. The polarization of the terahertz light is rotated by 45°, 90°, and circularly polarized by simply rotating the wire grating. The performance is achromatic over the measured range of 0.1–0.7 THz and comparable to commercial visible light wave retarders.

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