In this article a microscopic electronic non-equilibrium effect, highly nonlinear polaritonics, is proposed to mediate an ultrafast all-optical switching. The electronic band structure within gold (Au) nano grains shall be modified by external laser light, namely the Franz-Keldysh effect, and the modified electronic density of states within the Au grains are coupled to a single mode photonic waveguide. Using this microscopic polaritonic coupling without ever including any macroscopic influences due to the geometric arrangement a strong transmission reduction originating from the established quantum interference is derived. The lifetime of the coupled states is heavily dependent on the Fano resonance type binding and the amplitude of the applied electric field. Besides the Fano signatures the microscopic coupling photon-electron-photon leads to a gaped electronic density of states within the Au nano-grains.