Characteristic Impedance Model for Plasmonic Metal Slot Waveguides

We investigate the transmission properties of a subwavelength plasmonic slot waveguide. We show that the transmission can be accurately calculated using the characteristic impedance of the propagating mode. Using such a model, we show that it is possible to design devices without extensive 3-D finite-difference time-domain (FDTD) computer simulations. We illustrate the approach with calculations of an asymmetric Fabry-Perot germanium photodetector based on the slot waveguide geometry, showing predicted detector efficiencies as high as 69% despite metallic losses.