Surface-plasmon-polariton modes in deep metallic trenches- measurement and analysis

SPP photonic waveguiding inside trenches engraved in 400nm thick gold layer and symmetrically embedded in a dielectric host was experimentally studied using excitation at λ=1.55μm. This waveguide has a similarity to a coplanar transmission line configuration, although plasmonic hybrid modes are supported (rather than TEM waves). Excitation by TE and TM polarizations was studied and the emergence of long propagating plasmonic modes was observed. Mode solving using Full Vectorial Magnetic-Field Beam Propagation Method, validated the observed results, and disclosed the nature of the fundamental long range mode, coexisting with higher order guided modes in such SPP waveguide.