Single emitters have been considered as sources of single photons in various contexts such as cryptography, quantum computation, spectroscopy, and metrology 1,2,3 . The success of these applications will crucially rely on the efficient directional emission of photons into well-defined modes. To accomplish a high efficiency, researchers have investigated microcavities at cryogenic temperatures 4 , photonic nanowires 5, and near-field coupling to metallic nano-antennas 6 . However, despite an impressive progress, the existing realizations substantially fall short of unity collection efficiency. Here we report on a theoretical and experimental study of a dielectric planar antenna, which uses a layered structure for tailoring the angular emission of a single oriented molecule. We demonstrate a collection efficiency of 96% using a microscope objective at room temperature and obtain record detection rates of about 50 MHz. Our scheme is wavelength-insensitive and can be readily extended to other solid-state emitters such as color centers 7 and semiconductor quantum dots 8 .One of the most powerful and versatile approaches to the generation of single photons exploits the property that a single quantum mechanical two-level system cannot emit two photons simultaneously since each excitation and emission cycle requires a finite time. Unfortunately, such single-photon sources (SPS) are intrinsically inefficient because their radiation spreads over a 4π solid angle and cannot be fully captured by conventional optics. Several years ago, a simple avenue for efficient photon collection was proposed by Koyama et al. in the context of fluorescence microscopy 9 , where emitters were placed at the interface between two media with large refractive index contrast 9,10 . Such a structure can be viewed as a dielectric antenna 11 in which the dipolar radiation of the emitter is funneled into the high-index substrate. The black trace in Fig. 1a shows the angular emission of a dipole sitting close to an interface and oriented perpendicular to it. Despite the strongly modified radiation pattern, one finds that 14% of the light is still lost to the upper half-space, and more importantly, a considerable amount of light is directed to very large angles in the lower substrate, which are not accessible by the collection optics. In this Letter, we remedy these issues by embedding the emitter in a dielectric layer that we engineer on top of the highindex substrate and obtain unprecedented photon collection efficiencies, directionality, and count rates.To provide an intuitive explanation of our antenna design, let us decompose the radiation of a dipolar emitter into plane waves and consider the propagation of each component 12. This

Local distribution of the optical magnetic field is a critical parameter in developing materials with artificially engineered optical properties. Optical magnetic field characterization in nano-scale remains a challenge, because of the weak matter-optical magnetic field interactions. Here, we demonstrate an experimental visualization of the optical magnetic field profiles by raster scanning circular apertures in metal film or in a conical probe. Optical magnetic fields of surface plasmon polaritons and radially polarized beam are visualized by measuring the transmission through metallic apertures, in excellent agreements with theoretical predictions. Our results show that Bethe-Bouwkamp aperture can be used in visualizing optical magnetic field profiles.