Fig. 1

a Schematic of the designed broadband metallic planar microlens with d = 4 μm. 1 is the glass substrate, 2 is the first gold layer with a large-scale array of nanoholes, and 3 is the second gold layer defining the lens aperture. The inset gives the top view of the microlens. b The transmissive spectra of the lens when the periodicity P of nanoholes is varied from 400 to 600 nm. c 3D FDTD simulation results of the electric-field intensity for three cases of periodicity at the working wavelength of λ = 600 nm and the graphs are on the same color scale. d 3D FDTD simulation results of the electric-field intensity for three wavelengths when P = 400 nm