Unidirectional optical nanoantenna with individual core–dual shells nanoparticle

We propose an optical nanoantenna, which is an individual nanosphere consisting of two identical metal strips separated by a dielectric spacer (Ag–Ge–Ag) with a notch. Such design integrates the advantages of array dielectric antenna and plasmonic antenna such as high directivity, emission direction control, and highly localized field enhancement based on excitation of electric and magnetic multipoles of high-orders and localized surface plasmons in the symmetry breaking of this nanomatryoshka. Major properties of this nanoantenna have been revealed theoretically and numerically. We compare our hybrid nanoantenna with plasmonic and dielectric nanoantenna of similar geometry, and the proposed nanoantenna exhibits better directivity and efficiency. By suitably positioning the feed inside the notch, this compact nanoantenna can spectrally sort the electromagnetic emission, together with a high value in directivity up to 13.5. In addition, we have also revealed that displacement of the emitter along the y-axis leads to beam rotation. In contrast to other conventional nanoantenna in subwavelength, the proposed nanoantenna may exhibit higher directivity and Purcell factor due to effective excitation of electric and magnetic multipoles of high-orders inside the nanoparticle and localized surface plasmons in the outmost metal shell. The ultradirectional nanoantenna may shed light to the design of compact nanoantennas, which may find various applications in biosensing and quantum communications.