Ultrahigh light transmission through a C-shaped nanoaperture

Optical resolution beyond the diffraction limit can be achieved by use of a metallic nanoaperture in a near-field optical system. Conventional nanoapertures have very low power throughput. Using a numerical finite-difference time domain method, we discovered a unique C-shaped aperture that provides $\sim 3$ orders of magnitude more power throughput than a conventional square aperture with a similar near-field spot size of $\sim 0.1\lambda$ Microwave experiments at 6 GHz quantitatively confirmed the simulated transmission enhancement. The high transmission of the C-aperture—or one of the related shapes—is linked to both a propagation mode in the aperture and local surface plasmons.