Light confinement effect of non-spherical nanoscale solid immersion lenses

We report on the light confinement effect observed in non-ideally shaped (i.e., non-spherical) nanoscale solid immersion lenses (SILs). To investigate this effect, nanostructures of various shapes are fabricated by electron-beam lithography. When completely melted in reflow, these non-circular pillars become spherical, while incomplete melting results in non-spherically shaped SILs. Optical characterization shows that non-ideal SILs exhibit a spot size reduction comparable to that of spherical SILs. When the SIL size is wavelength scale or smaller, aberrations are negligible due to the short optical path length. This insensitivity to minor variations in shape implies a large tolerance in nano-SIL fabrication.