Fig. 1. Nanotoroid–nanowire system. (a) Schematic diagram of a dielectric nanotoroid close to a dielectric nanowire. (b) Electric field distribution of the nanostructure. Details of electric field distributions of the same size nanotoroid (c) without and (d) with nanowire with parameters R=500nm, r=170nm, d=5nm, ϵ1=12, ϵ2=5, D=100nm, and working wavelength λ=524.693nm.

Fig. 2. Mechanism of enhancing the coupling coefficient g and maintaining comparatively low cavity loss κ. (a) The variation of the coupling coefficient g along the X axis. g=588.69GHz with nanowire and g=106.07GHz without nanowire, respectively. (b) The variation of the normalized energy of the cavity modes Wcav with the wavelength λ. κ=70.34GHz with nanowire and κ=64.68GHz without nanowire, respectively.

Fig. 3. Results of the coupling coefficient g influenced by relevant parameters. (a), (b) g increases with the growth of ϵ1 and ϵ2. (c) g increases with the shortening of d.

Fig. 4. Results of coupling coefficient g and cavity loss κ in the nanotoroid–Ag-nanowire system. (a) The variation of the coupling coefficient g along the X axis. At the interface of the nanogap and the nanowire, the coupling coefficient g can reach its maximum g=689.40GHz. Inset in (a) shows the electric field distributions of the WGMs of the nanotoroid and the surface plasmon polariton of the nanowire. (b) Normalized energy of the cavity modes Wcav changes with wavelength λ. κ=2814.57GHz with Ag nanowire.