Silicon based plasmonic coupler

Plasmonics is a field in which the light matter interaction can be controlled at the nanoscale by patterning the material surface to achieve enhanced optical effects. Realisation of micron sized silicon based plasmonic devices will require efficient coupling of light from an optical fibre grating coupler into silicon compatible plasmonic waveguides. In this paper we have investigated a silicon based plasmonic coupler with a very short taper length, which confines and focuses light from a broad input fibre opening into a plasmonic waveguide at the apex of the structure. A simple transfer matrix model was also developed to analyse the transmission performance of the coupler with respect to its key physical parameters. The proposed plasmonic coupler was optimised with respect to its different structural parameters using finite element simulations. A maximum coupling efficiency of 72% for light coupling from a 6.2 μm wide input opening into a 20 nm slit width was predicted. The simulated result also predicted an insertion loss of ≈ 2.0 dB for light coupling into a 300 nm single mode SOI waveguide from a plasmonic structure with a 10.4 μm input opening width and a taper length of only 3.15 μm. Furthermore, the application of the optimised plasmonic coupler as a splitter was investigated, in which the structure simultaneously splits and couples light with a predicted coupling efficiency of ≈ 37 % (or a total coupling efficiency of 73%) from a 6.22 μm input opening into two 50 nm wide plasmonic waveguides.