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-Highly Efficient Ultra‐Broadband Terahertz Modulation Using Bidirectional Switching of Liquid Crystals

Xuequan Chen, Kaidi Li,  Rui Zhang, Swadesh Kumar Gupta, Abhishek Kumar Srivastava, Emma Pickwell‐MacPherson,

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201901321

Accurately manipulating field strength and polarization state are essential in various terahertz applications. Such manipulations are based on the efficient modulation of the amplitude and phase of electromagnetic waves. However, there is a lack of such terahertz modulators with sufficient efficiency and bandwidth. Herein, the Brewster–critical angle is exploited for modulation by using a nematic liquid crystal. Unlike liquid crystal phase shifters that only give a narrowband phase delay via a one‐directional switch, the presented device modulates both the amplitude and phase across an ultra‐broadbandwidth via a bidirectional active switch. An average intensity modulation depth over 99.6% is achieved for 0.2–1.6 THz. Furthermore, highly accurate polarization conversion between linear and circular states is also realized for 0.4–1.8 THz, with the average degree of linear and circular polarizations as high as 0.994 and 0.998, respectively. The superior accuracy, bandwidth, and active control achieved provide great potential for multifunctional terahertz modulation.