Coupling regimes of high-index dimer

We analyze coupling regimes in photonic structures. The simplest system composed of two high-index rods is under consideration. We derive the optical theorem for the two dimensional (2D) case, which is different from the three dimensional case. The study of scattering spectra allows us to identify three coupling regimes: strong coupling, weak coupling and a free-space coupling through Fabry-Perot resonances.