3D rendering of a slot waveguide and of a monochromatic wave propagating along it. The two green regions indicate the high index volumes that embed the slot. The two evanescent tails of the electromagnetic field pile up within the slot volume and give rise to an enhanced field intensity. For clarity only the electric field component parallel to the horizontal plane is shown and projected below the waveguide structure. The field maxima (sketched in blue and red) are clearly confined within the low index region of the slot.