No abstract

We report unidirectional radiation of a circularly polarized dipole above planar metal surface, the radiation direction can be manipulated via changing the distance between the dipole and the surface. This phenomenon is unique for the combination of circularly polarized dipole and metal surface and does not happen for linearly polarized dipole on metal surface or circularly polarized dipole on dielectric surface. The underlying physics is analytically disclosed by the interference of two orthogonally-oriented dipole component with π/2 phase lag. A substantially different mechanism of introducing the vectorial nature of the dipole itself to control light emission distinguishes the present scheme from nanoantenna and provides a new degree of freedom in light emission engineering.

We propose an optical antenna as a unidirectional surface plasmon polariton (SPP) mode launcher. Appropriate tuning of the transverse and longitudinal resonance of the antenna makes the scattered field pattern mimic that of the rotating dipole. An extinction ratio of 110 dB is achieved for the SPP launched via the optical antenna. The steering of the SPP propagation direction can be controlled by focusing on antennas with different orientations. The universal design can also be applied to unidirectional launching of the waveguide mode.

Based on multisphere Green's function, we investigate the interaction between a dipole source and a hybrid nanoantenna. The parameter of radiation enhancement factor is introduced to characterize spontaneous emission enhancement and radiation efficiency simultaneously. We revisit the emission of silver dimers in the context of radiation enhancement factor. Then the hybrid of metallic nanoparticles (MNPs) and dielectric nanoparticles are designed for strong enhancement as well as high efficiency. Purcell factor over 2000 and radiation efficiency over 50% are achieved by the hybrid antenna. And Purcell factor above 900 with over 57% radiation efficiency is also reached for broadband operation. Such metallo-dielectric hybrid antenna may find potential applications in bright single photon sources and Raman spectroscopy.

Except for the commonly used surface plasmon polaritons (SPPs), in this letter we demonstrate that waveguide modes (WMs) can realize the large area sub-wavelength gratings. Both transverse-magnetic (TM) and transverse-electric polarized beams can be used in this method, while for the lithography based on SPPs only TM polarized beam is applicable. The WMs interference lithography has the advantages of low heat loss and much suitable for thick photo-resist films. Large area gratings were inscribed on the azo polymer film at period of 187 nm and 189 nm, which are smaller than the half wavelength of the incident beam.