Low-loss high-confinement terahertz guided-wave propagation along a subwavelength gap between double-dielectric-ridge-integrated gratings

Abstract

Dielectric grating-based spoof surface plasmonic (SSP) structures are among the recent low-loss and subwavelength field-concentrating solutions for realizing high-density terahertz (THz) and sub-THz integrated circuits. In this paper, we report on a novel waveguide structure capable of supporting highly confined SSP mode while exhibiting much lower propagation loss compared to other similar SSP structures. The proposed structure is composed of two perfectly aligned identical silica ridges placed on the inner faces of the metallic plates of a parallel plate waveguide with a proper plate distancing in order to leave an empty gap region between the ridges. Each of the ridges embodies a periodic arrangement of high-resistivity silicon blocks with the same height as their own, although with smaller widths compared to their width. By performing modal analysis on the 2D and 3D structures of the proposed waveguide, its propagation properties are studied. It is observed that if the gap region is properly designed, a waveguiding structure with a subwavelength cross-sectional size around λ0/3×λ0/3, where λ0 is the free-space wavelength at the maximum frequency of operation, capable of providing a high degree of field confinement over a wide frequency bandwidth of nearly two octaves and with a very low propagation loss factor compared to similar SSP structures is achieved. Moreover, the performance of the proposed waveguide for implementing a 90° waveguide bend of the radius λ0/3, and for obtaining a spectroscopy-based refractive-index sensor is addressed. The results of our assessments suggest that the proposed waveguide can bring the state-of-the-art SSP designs yet another step closer to realizing ideal waveguiding structures for various applications in THz and sub-THz regimes.