Fig. 1. (a) Schematic diagram of the all-dielectric nanoantenna-microtoroid structure. The x-polarized quantum emitter is located at the gap of the nanoantenna. (b) Electric field distribution of the microtoroid at the azimuthal mode number m = 21. (c) Electric field distribution and energy flow of the nanoantenna.

Fig. 2. Large Purcell enhancement with a narrow linewidth. (a) Purcell factors of the emitter in the hybrid structure, as well as in the bare nanoantenna and bare microtoroid. Inset, the linewidth of the Purcell factor in the hybrid structure at m = 20. (b) Electric field of the x–y plane (wavelength at 553.74 nm) in a hybrid structure at m = 20. The white streamlines indicate the direction of the energy flow (top part). Large Purcell enhancement with a narrow linewidth can be achieved in the hybrid structure, with a Purcell factor up to 1000–1700 and a linewidth maintained at the order of hundreds of picometers. (c) Normalized electric field values along the x axis in the hybrid structure at m = 20 under background field excitation.

Fig. 3. Influence of the dielectric nanoantenna radius R on the Purcell factor. Nanoantenna radius: (a) R = 20 nm, (b) R = 30 nm, and (c) R = 40 nm. The insets are electric field distributions in the x–y plane of the hybrid structure at m = 20 (all these electric distributions share the same colorbar). The Purcell factor decreases with the increment of R due to the lower Q.

Fig. 4. (a) Purcell factors when the nanoantenna is rotated around the z axis by an angle θ. Here, the polarization of the emitter is along the x axis. The electric field patterns of the nanoantenna at (b) θ = 10°, (c) θ = 20°, and (d) θ = 30°, λ = 553.72 nm. The Purcell factors decrease with the increase of θ, while the linewidths of the hybrid structure are maintained at about 100 pm.