Guiding terahertz waves along subwavelength channels

We propose a feasible way of guiding terahertz waves along V grooves whose lateral dimensions are subwavelength. A plasmonic metamaterial is built by periodically corrugating these channels in such a way that the system supports the propagation of electromagnetic modes with characteristics mimicking those of channel plasmon polaritons in the optical regime. These geometrically induced guided modes present long propagation lengths and low bending losses, making them excellent candidates for routing terahertz waves at planar surfaces.

Figure 1

(Color online) Dispersion relation of the guided EM modes propagating between two corrugated PEC surfaces. Both surfaces are identical and consist of two rectangular groove arrays of period $d$. The grooves width $a$ and depth $t$ are equal to $0.5d$. Five different gap widths $\left(w\right)$ are considered: $4d$ (red solid line), $2d$ (green dashed line), $d$ (blue dotted dashed line), $0.5d$ (orange double dotted dashed line), and $0.25d$ (cyan dotted line). In the lower inset, the electric field amplitude at the band edge for the case $w=1.5d$ is depicted. The upper inset renders ${ϵ}_{\text{eff}}$ (black squares) and the propagation length (red circles) at $d/\lambda =0.25$ obtained within the SIBC approximation for Al and $d=200\mu \text{m}$.

Figure 2

(Color online) FDTD dispersion relation of the first three spoof CPP modes supported by a corrugated V channel milled on a PEC surface. A schematic picture of the structure is shown in the upper inset. Lower insets depict the amplitudes of the longitudinal component of the electric field evaluated at the band edge for the three modes. The wavelength, $\lambda$, and modal size, $\delta$, for the three cases are represented.

Figure 3

(Color online) FIT simulations of the transmittance spectrum for the lower spoof CPP mode supported by a straight corrugated PEC V channel of period $d=200\mu \text{m}$ and total length 20 mm. Red dashed arrows indicate the spectral position of the cutoff and band-edge frequencies obtained from FDTD calculations. The left insets show the electric field amplitude at 0.32 THz and the right ones at 0.42 THz. Upper (lower) insets correspond to the plane located 9.1 mm (9.2 mm) away from the illuminated end of the structure.

Figure 4

(Color online) FIT simulations of the mode propagation through four $90°$ bend channels of different $r$. All structures are comprised by 100 periods. Upper panel renders the transmission spectrum for the four channels considered. Lower panels show the electric field amplitude at 0.40 THz evaluated at a height of $100\mu \text{m}$ above the planar surface for the four structures analyzed.