Large longitudinal electric fields (Ez) in silicon nanowire waveguides.

We demonstrate the presence of strong longitudinal electric fields (E(z)) in silicon nanowire waveguides through numerical computation. These waveguide fields can be engineered through choice of waveguide geometry to exhibit amplitudes as high as 97% that of the dominant transverse field component. We show even larger longitudinal fields created in free space by a terminated waveguide can become the dominant electric field component, and demonstrate E(z) has a large effect on waveguide nonlinearity. We discuss the possibility of controlling the strength and symmetry of E(z) using a dual waveguide design, and show that the resulting longitudinal field is sharply peaked beyond the diffraction limit.