Enhancing directivity of terahertz photoconductive antennas using spoof surface plasmon structure

Abstract

Terahertz photoconductive antenna (PCA) is an important device for generating ultrabroadband terahertz radiations, being applicable in various scenarios. However, the metallic electrodes in PCAs, a pair of coplanar strip lines (CSL), always produce horizontal electrode modes in a broad THz band, thus resulting in low directivity in the vertical direction. Here, we introduce spoof surface plasmon polariton (SSPP) structures to suppress horizontal electrode modes in a broad band. The suppression principles are accounted to both the forbidden band of the fundamental SSPP mode and the orthogonality between source and higher-order SSPP modes. In the SSPP-modified PCA, we achieve around 2 dBi higher directivity in the vertical direction compared to a typical CSL PCA. Unlike the narrow bands inheriting from conventional metamaterial resonators, the relative operational band of the SSPP-modified PCA is as broad as 48%. This planar SSPP structure is compatible with the well-developed micro fabrication technologies. Thus, our scheme can be combined with the semiconductor material engineering and plasmonic nanoscale structures for further increasing THz output power.

Plasmonic grating assisted photo‐absorption enhancement in terahertz photoconductive antenna

“…A plasmonic hexagonal structure fabricated on top of a GaAs surface by using focused ion beam etching achieved reflectance lower than 10% at 1570 nm wavelength 19 . Directivity improvement was also reported by co‐designing the antenna and plasmonic structures 20 . As was noted above, the THz emission strength has been improved by the reduction of surface reflection loss of the incident laser light or plasmonic field enhancement due to the nanoscale metallic structure.…”

“…19 Directivity improvement was also reported by co-designing the antenna and plasmonic structures. 20 As was noted above, the THz emission strength has been improved by the reduction of surface reflection loss of the incident laser light or plasmonic field enhancement due to the nanoscale metallic structure. However, these performance enhancements have been demonstrated with small-area PCA.…”

Recent advances of transition radiation: Fundamentals and applications

“…Due to the recent advances in nanofabrication, artificially-engineered materials or nanostructures, such as metamaterials [109][110][111][112][113][114][115][116][117][118][119], 2D materials [120][121][122][123][124][125][126][127][128], and photonic crystals [129][130][131][132][133][134][135], begin to play an important role in the flexible manipulation of transition radiation.…”

Perspective on Meta-Boundaries

“…Apart from changing the optical properties of bulk media, the electromagnetic boundary itself can be directly tailored due to the recent advent of metasurfaces − and low-dimensional materials, − which can be well modeled by an effective two-dimensional surface without a thickness, but with a nonzero surface conductivity. − In other words, with the addition of metasurfaces or low-dimensional materials, the boundary can be featured with a nonzero surface conductivity. This way, the judicious design of surface conductivity can provide an extra degree of freedom to regulate the electromagnetic boundary conditions and thus the light-matter interaction.…”