Figure 1.

a) Schematic representation of cascade strong coupling successively with the donor resonant with a cavity modem $\hslash {\omega }_c$ , and then the acceptor, leading to the formation of three new eigen hybrid light–matter states: the upper (UP), middle (MP), and lower (LP), polaritonic states. b) Schematic diagram of the strongly coupled Fabry–Pérot cavity with spatial separated donor and acceptor. The spacer thickness h can be tuned from 10 nm to 75 nm. c) Temporal picture of the dipole allowed energy transfer processes from an initial state $\left|i\right.⟩$ where D is excited and A is in the ground state, to a final state $\left|f\right.⟩$ where A is excited and D is in the ground state. Those processes involve an intermediate state $\left|I\right.⟩$ in which a cavity photon of frequency ${\omega }_c$  , wavevector $k_c$ and polarization, ${\overrightarrow{ϵ}}_C$ is exchanged.