Effective-Medium-Clad Dielectric Components Towards Terahertz Integrated Platform

Abstract

Over the past few decades, optics-based time-domain spectroscopic systems have significantly promoted the developments of terahertz science and technology. Despite their success in physics, the bulky and costly optical systems are not readily amendable to various applications such as communications, imaging, sensing, and radar. These applications require devices with structural compactness, integrability, and portability. Leveraging both electronic and photonic technologies, terahertz integrated circuits have emerged and gradually bridged the gap between ’concept’ and ’application’. To realise multifunctional terahertz integrated circuits, efficient and broadband platforms able to accommodate various passive and active components are in great demand, while interconnects with low loss, low dispersion, and broad bandwidth are vital. To this end, this thesis focuses on an efficient and broadband terahertz integrated platform based on silicon. Firstly, a class of self-supported substrateless dielectric waveguides are proposed based on the effective medium theory. The effective-mediumclad dielectric waveguides are purely built into a high-resistivity intrinsic float-zone silicon wafer to achieve extremely low loss and low dispersion. The effective medium is realised by periodically perforating the silicon slab with a deep subwavelength spacing, leading to a tailorable effective relative permittivity tensor. Consequently, an additional degree of freedom is granted in this design to manipulate the waveguides’ modal indices and adapt to different guiding scenarios. Through in-depth investigations of various propagation characteristics, the proposed waveguides show a potential to establish a terahertz integrated platform with a high level of design flexibility. Benefiting from the concept of effective medium to create this new waveguide platform, various fundamental building blocks and functional components are proposed including bends, crossings, directional couplers, filters, and polarisation splitters. All these components inherit high efficiency and broad bandwidth, which are much needed for terahertz applications that typically leverage a vast available bandwidth with limited source power. The proposed concepts can benefit terahertz integrated circuits at large, in analogy to the silicon-on-insulator platform for integrated photonics.