Light focusing on a stack of metal-insulator-metal waveguides sharp edge.

Near field light focusing by two-dimensional isosceles triangle shaped stack of silver plasmon-polaritons waveguides is being investigated numerically with full-vectorial Finite Difference Time Domain method for H-polarized light and wavelength lambda = 500 nm. For wide angle of tip, results are in good agreement with theoretically predicted propagation constant of light in stack and while discrepancy becomes significant for smaller angle. Physical phenomena of refraction and interference, similar to ones in dielectric axicons lead to conversion of a Gaussian beam incident on the flat side of the stack into a narrow light jet behind the structure sharp edge. The beam is concentrated into long focal region of 0.37 lambda width and enhancement of field amplitude is achieved in spite of significant absorption in the structure. The results are compared with bulk dielectric structure.