Transmitting and detecting THz pulses using graphene and metals-based photoconductive antennas

Abstract

In this paper, photoconductive antennas (PCAs) are designed using graphene ribbons (GRs) and metals at THz frequencies such that both transmitting and detecting modes for PCAs are investigated. A graphene-based PCA (GPCA) can support surface plasmon polaritons (SPPs) at either THz or optical frequencies, whereas a metal-based PCA (MPCA) only supports such waves at optical frequencies. Due to the 2D nature of graphene, its electronic modeling and electromagnetic modeling significantly differ from 3D bulk metals; consequently, some challenges appear when graphene is modeled in electronic and electromagnetic solvers. Hence, in this paper, the electronic modeling and electromagnetic modeling of graphene are comprehensively examined. We show that, through application of an electrostatic bias to a GR, its Fermi energy level can be shifted to an arbitrary value. This feature provides many striking advantages for a GPCA compared to a MPCA: supporting slow waves, reconfigurability, supporting SPPs at THz frequencies, mitigation of screening effects, and more radiated THz power. Although the supporting slow waves in a GR at THz frequencies, through excitation of a SPP propagation mode, result in a miniaturized structure for a GPCA, they cause spatial dispersion for the GR’s conductivity because the photoconductor used for a PCA usually has a high refractive index. Consequently, a more complicated analysis is required for designing a GPCA. Moreover, by studying the fabrication challenges relating to a GR, some of them are considered during its modeling. Finally, the radiated THz pulses are detected through a coherent detection scheme.