Strong coupling of in-plane propagating plasmon modes and its control.

We show anti-crossings due to strong in-plane coupling of grating excited propagating plasmon modes in dielectric-metal-dielectric structure with 2D dielectric pattern on top. Grating coupled propagating plasmon modes along with their complete dispersion in the measurement range and all different sample orientations are calculated first. Further a coupled mode theory is presented for the specific geometry presented here. Experimentally measured anti-crossing widths are compared with those calculated by coupled mode theory. It is shown that the coupling strength of the plasmon modes and thus the anti-crossing width can be controlled by the orientation of the sample.