Large optical transmission through a single subwavelength hole associated with a sharp-apex grating

The effect of grating shapes on optical transmission in a bull's eye structure (a single subwavelength hole surrounded by a concentric grating in a metal) is discussed. Finite-difference time-domain calculations predict that a sharp-apex shape gives as high a reflective structure to the propagating surface plasmon polaritons (SPPs) as does a rectangular shape. Fabricated samples with a sharp-apex grating actually show large optical transmission (a factor of 400 greater than that of samples with a single hole) even when the number of corrugations is three. This result indicates that a sharp-apex grating acts as an effective SPP reflector to confine the energy around the hole, resulting in high optical throughput.