Numerical simulation of a sub-wavelength plasmonic THz antenna for bio-sensing applications

In the past decades, bio-sensing has become a steadily growing field in the life-sciences. Popular subjects of investigation are proteins, which for instance mediate intra-cellular transfer of substances and thus are attractive drug targets. They are also responsible for the occurence of degenerative diseases such as Alzheimer’s disease and the Creutzfeld-Jakob disease. Examining proteins to uncover their fundamental properties and behavior is important in order to advance modern health care and medicine. One way to investigate such proteins is to take advantage of their vibrational and rotational resonances in the THz regime that occur in the range from 0.2 to 2 THz. The difficulty in obtaining meaningful results from investigating proteins in this range of frequency is the difference in size between the excitation wavelength, which ranges from 1.5mm to 150µm, and the size of the protein itself. The protein including its hydration shell has a typical size of a few tens of nanometers. The interaction between incident electromagnetic wave and a protein is therefore very weak. In this work, several sensor designs employing highly doped germanium bow-tie antennas for plasmonic sensing are devised and their electromagnetic properties are investigated. Previous work is used as a basis to further explore the possibility of utilizing asymmetrical Fano resonances to improve the sensor’s properties. The designs are investigated via 3D full-wave numerical simulations solving Maxwell’s equation in the frequency domain. The results give insights to the electromagnetic properties of the systems and their constituents. In a first investigation, bow-tie antennas are placed in an array arrangement and investigated regarding their properties for use as a plasmonic sensor. The potential of utilizing the coupling of an array of bow-tie antennas to guided modes in strip- and slab waveguides is explored. The main results of this work show the presence of coupled modes in the proposed structures consisting of antenna arrays placed on strip- and slab waveguides. It is further shown that utilizing this Fano resonant coupling can improve the Q factor and thus the figure of merit of the sensor structure. Additionally, experimental results confirm the predictions and are presented and discussed as well. Part of this work has been published or is currently in process of being published, which is detailed in chapter 7.