Wideband nanocrescent plasmonic antenna with engineered spectral response

A novel nantenna is presented in this article. It is formed by locating a gold circular patch inside a circular aperture etched from a gold plate. The centers of the two objects are shifted from each other, which results in having a “crescent‐shaped” aperture. Each of the circular patch and aperture has its own resonance wavelength whose location can be controlled by varying the corresponding diameter. It has been demonstrated that the working bands around these two resonances can be made slightly overlapping at their inner edges. This results in a remarkably wideband behavior characterized by a full‐width half‐maximum of more than 2000 nm centered around 2500 nm, which is equivalent to more than 80% fractional bandwidth. The proposed nantenna with 20‐nm gap width is capable of providing maximum electric field intensity enhancement of about 3000. It can confine the incident radiation within a volume well below the diffraction limit.