Design and Analysis of Passive and Active Terahertz Metasurface

Abstract

Terahertz science and technology have been extensively researched during the last decade. Terahertz waves have the unique property of penetrating a variety of visually opaque materials, with possible applications in product inspection, spectroscopy, material characterization and others. Despite the recent progress, the development of metamaterial based THz active and passive devices such as filters, polarizers, and modulators are still required in order to make terahertz more viable for different applications and industries. Also, as the demand for terahertz components increase, faster and more efficient design methods will eventually become a necessity in the near future. In this thesis we propose a dual-band terahertz filter based on self-complementary metasurfaces, twodimensional arrays of unit cells consisting of an artificial resonator and its complementary counterpart. The unit cell of the self-complementary metamaterial utilized to realize the dual-band filter is based on a combination of a Jerusalem cross and its complementary structure designed to resonate in the THz regime. The use of selfcomplementary structures enables the design of a 2-in-1 THz filter device whose function can be chosen between band-pass filter and band-stop filter. Besides the filtering function, they can also act as THz quarter wave plates. Also, we introduce a new method for terahertz filter design using deep neural network. Through the inverse design, where the geometric parameters of the device are obtained for an on-demand filter response, we offer a faster and more efficient solution to the current time-consuming and computationally-demanding design process. Last, in order to design active devices, we focus on the characterization and modelling of ferroelectric thin film materials, crystalline materials that exhibit spontaneous electrical polarizations switchable by an external electric field. By combining the dielectric characterization with electromagnetic simulation we show the design of tunable devices. Through this work we contribute to fill the so-called “terahertz gap” and bring terahertz technology one step closer to becoming a common technology in our daily lives.