Interference and wave propagation in a plasmonic Al2O3-Au-Al2O3 ridge waveguide

Performance of plasmonic ridge waveguides of different length formed on fused silica substrates has been studied experimentally and theoretically. All the waveguides were single-mode ones, had a width of 70 μm, and their cross-section had a structure of Al2O3-Au-Al2O3 sandwich-10 nm-thick Au film deposited between 240 nm- and 70 nm-thick Al2O3 top layer and bottom layers. To shape sidewalls, the wave guiding sandwich was etched through its depth. The waveguides were terminated by 1D gratings etched in the sandwich for light coupling/decoupling. The optimized input grating had an elliptical shape for focusing plasmon waves upon excitation, and the output grating was a conventional one. It was found that the traveled plasmonic waves decoupled and visualized themselves as interference patterns in the output grating area. We study propagation of these waves for a set of waveguides with lengths of 0.5-1 mm and demonstrate their main characteristics-the propagation length and attenuation factor.