Fig. 2: Comparison of nanofocusing effects of FPFP, DSP, and DSPP at an incident light wavelength of 633 nm.

a When the front cone angle is 32°, the absolute values of the electric field strength at 2 nm below the probe tip correspond to different cone heights H. The blue line represents the absolute value of the electric field strength of DSP. b Absolute values of electric field strength at 2 nm below the probe tip for DSPP corresponding to different front cone angles \({\rm{\alpha }}\) when the cone height is H = 500 nm and H = 1000 nm, which are the two cone heights with the largest enhancement effect in the simulation results in (a). (c–k) show the electric field and phase distributions under \({\text{HE}}_{11}\). (c–e) represent the electric field distribution of \({\text{HE}}_{11}-\text{SPP}\) excited on the FPFP surface in the cylindrical waveguide in the XY plane, the electric field distribution at the probe tip in the XZ plane, and the \({\text{E}}_{\text{z}}\) phase distribution corresponding to the XZ plane. (f–h) and (i–k) represent the electric field distribution of SPPs in the cylindrical waveguide in the XY plane, the electric field distribution at the tip of the probe in the XZ plane, and the corresponding \({\text{E}}_{\text{z}}\) phase distribution in the XZ plane during DSP and DSPP nanofocusing, respectively