One-dimensional dielectric grating structure for plasmonic coupling and routing

We propose and demonstrate one-dimensional (1-D) TiO₂ dielectric grating structures that couple 793-nm wavelength light and two-dimensional (2-D) surface plasmon polaritons (SPPs) into guided 1-D SPPs supported by dielectric-loaded plasmonic waveguides. The 1-D grating structure consists of a central TiO₂ stripe with a periodic array of TiO₂ teeth attached to the stripe. Finite-difference time-domain (FDTD) simulations reveal that the electromagnetic boundary conditions created by the teeth bend the electric field and induce charge oscillations under the grating, enabling excitation of SPPs. The same mechanism supports the routing of 2-D SPP. In the simulation the symmetric gratings achieve a maximum coupling efficiency of 19.1 % at an optimized grating period of Λ = 600 nm, and 1.7 % for asymmetric gratings. Both types exhibit strong polarization selectivity: symmetric gratings couple only under TM excitation, whereas asymmetric gratings respond under TE excitation. Experimental confirms these behaviors, yielding a coupling efficiency of ∼13 % for optimized symmetric gratings. The structures also function as SPP routers. Asymmetric gratings route incoming 2-D SPPs into 1-D TiO₂ waveguides with a simulated routing efficiency of 5.7 %, compared to 4.0 % for symmetric designs. The devices offer a ∼14 nm bandwidth around 793 nm and a small footprint of 18.7 μm², resulting in a figure of merit (efficiency/area) of 0.71 % μm^-2, the highest among reported devices designed to couple free-space light directly into 1-D SPP waveguides. These results demonstrate that 1-D TiO₂ gratings offer a compact and multifunctional platform for efficient coupling and routing of SPPs in integrated plasmonic circuits.