Light Injection into Thin Nonabsorbing Dielectric Slabs with Graphene as Coupler

Evanescent TE electromagnetic fields produced by the Attenuated Total Reflection (ATR) technique fail to excite guided modes of a thin dielectric slab. However, we found that wave guidance arises when such slab is coated on graphene. The complex optical conductivity of (the zero thickness) graphene modifies the effective dielectric constant of the dielectric slab giving place to the physical mechanism for the mode coupling. We demonstrate that in slabs as thin as 1 $\mu$m of dielectric constant of order of 2.25, the modes are excited by fields in the 30 -- 70 THz regime. This is, up and down of the threshold frequency of the interband absorption, $f_{th}$ $\sim$ 48 THz, which is a characteristic of the optical conductivity of high doped graphene. The effect is not related to the surface TE plasmons of graphene because the phenomenon exists beyond the plasmonic frequency regime (41 -- 48 THz). A complete theoretical study including dispersion relations and field profiles of the excited modes is presented.