Figure 1. Design of surface-plasmon-based spatial differentiator.

(a) Schematic of the plasmonic spatial differentiator with the Kretschmann configuration to excite the surface plasmon polariton (SPP). The dark grey layer and the light grey area correspond to the silver film and the glass, respectively. (b) Sample photo of three deposited silver thin films with different thicknesses. (c–e) Spatial transfer function spectra of the three samples by the experimental measurement (dotted lines) and the numerical fitting (solid lines). In the numerical calculation, the thicknesses of the silver layer were 46.0, 50.0 and 55.5 nm, respectively. θ₀ corresponds to the incident angle for the phase matching. The red line in (d) corresponds to the fitting results to equation (2).