Near-Field Enhancement Through a Single Subwavelength Aperture with Gaps Inside

Structured subwavelength apertures have been studied widely to enhance the transmission or obtain super resolution, such as bull's eye hole, H-shaped aperture, and bowtie aperture. In this letter, we present another structured aperture with two gaps inside, which can also lead to near-field enhancement. And the resonance wavelength can be tuned by the geometric parameters of the gaps. The enhancement of this gap-aperture depends strongly on the polarization of the incident wave. Only the polarization perpendicular to the connecting line of the two gaps can realize the enhancement. We attribute the near-field enhancement of this structured aperture to the resonance excitation of the localized surface plasmon. We combine the tooth-aperture and our gap-aperture together and this special aperture can achieve stronger enhancement and super resolution simultaneously.