Low-loss planar transmission lines are required for integrated optical or plasmonic nanocircuits. Full characterization of these lines is necessary for designing nanocircuits. This paper shows a method to calculate the attenuation and propagation constants of a patch-antenna-coupled microstrip transmission line (MTL) at 28.3THz that is suitable for measurement implementation via near-field microscopy techniques. After illumination with a Gaussian beam, a standing wave is formed by the electric near field along the MTL observed at the metal-air interface. By fitting an analytical standing wave expression to the near-field standing wave, the attenuation and propagation constants are determined. With the MTL characterized, a similar technique can be applied to determine the input impedance of an unknown load fed by the MTL. The quantification of antenna impedance and transmission line parameters provide requisite information for improving impedance matching and collection efficiency. Ansys High Frequency Structure Simulator (HFSS) is implemented to predict the computational results.
In recent years, plasmonic resonant antennas have seen widespread consideration in many detection and chemistry applications due to their potential for enhancing and confining the emission and polarization of electromagnetic fields. Examples include optical couplers to ultra-compact photodetectors, high-resolution optical microscopy, enablers of single molecule Raman signal detection and heating elements that facilitate nanostructure growth. An asymmetric cross-bowtie antenna is investigated for providing a broad circular polarized frequency response in the long wave infrared (LWIR). The asymmetric cross-bowtie antenna is constructed with two perpendicular bowtie antennas with differing arm lengths. The asymmetric cross-bowtie antenna is numerically analyzed using a finite element method (FEM) solver; Ansys High Frequency Structural Simulator (HFSS). The two perpendicular bowtie antennas, under illumination, provide a wide-band localized circularly-polarized field within a shared antenna feed-gap. At the center frequency of 28.3 THz (10.6μm), a circularly-polarized state over 30% bandwidth is achieved. The antenna is then loaded with a metal-oxide-metal diode in order to design a circularly polarized antenna-coupled detector.