Efficient terahertz-range beam control using flat optics

Abstract

The terahertz range, which spans 0.1 to 10 THz of the electromagnetic spectrum, has significant potential for numerous diverse uses including high-volume short-range communications, non-invasive and non-destructive sub-dermal medical imaging, and safe imaging of personnel and postal items for security applications. These capabilities are identified due to the unique properties of terahertz radiation; terahertz waves are of high carrier frequency relative to conventional wireless communications, are able to transmit through dry, non-polar substances, and yet are non-ionising. However, owing to factors including a lack of available power and significant atmospheric attenuation, it is challenging to maintain sufficient signal power over a realistic propagation distance for terahertz waves. For this reason, the terahertz range is presently lacking in practical applications, and hence it occupies an under-utilised portion of the electromagnetic spectrum. As unused spectrum is a valuable resource, the development of technologies to exploit the terahertz range is a highly desirable goal. Beam-control techniques—the capacity to shape and steer electromagnetic radiation— can prevent radiated power from being lost to undesired directions. Thus, techniques of this variety have the capacity to address the aforementioned obstacles to the realisation of practical terahertz technologies. This thesis is therefore centred around the development of terahertz beam-control devices that satisfy two criteria. Firstly, the beam manipulation operation must be highly efficient, as much of the motivation of this work is to mitigate the constraints upon power. Secondly, planar devices are preferable, as this is a requirement for compact systems. With these restrictions in mind, various techniques are explored for their viability in future applications of terahertz technology, including various forms of metallic and dielectric resonators, 3D printing, and composite materials with effective properties. The advantages and drawbacks of each approach are evaluated.