Low-loss sharp bends in low contrast polymer hybrid metallic waveguides

Surface plasmons polaritons have drawn significant attention in recent years not only thanks to their capability of confining the field in the dielectric/metal interface, but also thanks to their potential to produce highly efficient thermooptical or electro-optical devices such as modulators and switches due to the presence of the metal layer amidst the electromagnetic field. However, the high confinement comes at the cost of high propagation losses due to the metal’s highly absorptive nature at visible and near-IR wavelengths. In order for plasmonic devices to find a widespread use in integrated optics, an advantage over dielectric waveguides needs to be found that justifies their utilization. In this work, we present an application in which metallic waveguides perform better than their dielectric counterparts. By adding a thin metallic layer underneath the waveguide core, the total bend losses (dB/90° are reduced with respect to the bend losses of the equivalent dielectric structure without the metallic layer for a range of radii from 35 µm down to 1 µm. The results show a dramatic reduction of total bend losses in TE-polarization with values as low as 0.02 dB/90° bend for radii between 6 and 13 µm. The mechanism for the reduction of bend losses is the shielding action of the metal layer, which prevents the field to leak into the substrate. In this paper, both detailed theoretical calculations as well as experimental results for SU-8 channel waveguides will be presented.