Fig. 1. (a) Schematic diagram for a PMLL. (b) Quarter enlarged view of the top of the dielectric film with air holes. (c) Transverse cross section of the intensity profile at the point ρ=R in the y direction. (d) Intensity distribution of SPPs [three-dimensional (3D) simulation] propagating along y direction and passing through a PMLL. The red circle indicates the radius R of the PMLL. The red dotted circle indicates the real area of the designed lens. The white dotted line indicates the position y=R.

Fig. 2. (a), (c), (e), and (g) Transverse cross sections of the intensity profile at the point ρ=R in the y direction. (b), (d), (f), and (h) Intensity distributions of SPPs (3D simulation) propagating along y direction and passing through the PMLL with different heights. The red circles indicate the radius R of the PMLL. The red dotted circles indicate the real area of the designed lens. The white dotted lines indicate the position y=R.

Fig. 3. (a) and (e) Schematic diagram for a PMLL. (b) and (f) Quarter enlarged view of the top of the PMMA film with air holes. (c) and (g) Transverse cross section of the intensity profile at the point ρ=R in the y direction. (d) and (h) Intensity distributions of SPPs (3D simulation) propagating along y direction and passing through a PMLL. The red circles indicate the radius R of the PMLL. The red dotted circles indicate the real area of the designed lens. The white dotted lines indicate the position y=R.

Fig. 4. (a) Schematic diagram for a taper. (b) Schematic diagram for a PMLL coupler. (c) Transverse cross section of the electric field profile at the position y=7μm. (d) Electric field profile of SPPs propagating along y direction, passing through a taper coupler, and coupled to the 40 nm wide waveguide. (e) Transverse cross section of the electric field profile at the position y=7μm. (f) Electric field profile of SPPs propagating along y direction, passing through a PMLL, and coupled to the 40 nm wide waveguide. The red circle indicates the position of the PMLL, and the white dotted line indicates the position of the monitor.

Fig. 5. The performance of the PMLL coupler and taper coupler based on 3D simulations in a broad bandwidth.