Subdiffraction light focusing using a cross sectional ridge waveguide nanoscale aperture.

We report a new type of plasmonic nanoscale ridge aperture and its fabrication process which is based on layer-by-layer planar lithography. This new fabrication method allows us to create desired nanoscale features of a plasmonic ridge waveguide nanoscale aperture, which helps to confine a near-field spot to sub-wavelength dimensions. Numerical simulations using Finite Element Method (FEM) are performed to calculate the near-field distribution around the exit of the aperture. Measurements using scattering near-field scanning optical microscopy (s-NSOM) confirm the design and demonstrate that the aperture is capable of producing focused spots in the ridge gap at the exit of the aperture. The planar lithography process is a step toward mass production of such plasmonic structures for applications including heat-assisted magnetic recording (HAMR).