DESIGN AND ANALYSIS OF HYBRID WAVEGUIDES FOR LONG RANGE SURFACE PLASMON PROPAGATION

Abstract

Three different models a metal strip, a slot-based waveguide, and a hybrid plasmonic waveguide with a metal cap have been examined. Comparative analysis of some waveguide characteristics such as propagation length, effective modal area, and Figure of Merit (FOM) was made by varying waveguide dimensions using graphene and regular SiO2, incorporating the silver as a metal. This research reveals that the lower the waveguide dimension is, the better the outcome for all the models, while conventional SiO2 is replaced by graphene, which leads this work towards designing nano-scale devices. Firstly, while investigating metal strip waveguides, it was discovered that, regardless of a slight improvement in propagation length and mode area, the figure of merit (FOM) was fundamentally improved (approximately 50%) compared to traditional SiO2 subsequent to utilizing graphene with a smaller gap among strip and the metal substrate. Furthermore, the highest propagation length was 8.5 μm, which is about 75% higher than that of SiO2. Then secondly, the slot-based waveguide was examined. The largest propagation length was found as 224 μm using SiO2 when the height of silver was 50 nm, silicon layer between metal (ds) was 70 nm with a metal width of 40 nm, though the highest figure of merit was limited to 4951 by setting ds at 60nm. The results were better using SiO2 rather than graphene, which was quite the opposite of the direction of this research. Thus, the third model, a hybrid plasmonic waveguide with a graphene layer and metal cap on top, was introduced, which demonstrates an elevated propagation length 1814 µm with tight confinement of around 250 nm2. The key parameter, the figure of merit, is found in the range of 106 when we keep graphene layer 5 nm, utilized in the middle of metal and silicon, which is not only superior to that ofthe SiO2 layer but also the highest values of FOM found in previous models. In this manner, among three models, a hybrid plasmonic waveguide with a metal cap shows a better outcome regarding propagation length, modal area, and Figure of merit.