Strong Coupling to Generate Complex Birefringence: Metasurface in the Middle Etalons

We
have measured the optical signatures of strong coupling between
the resonance of etalons and plasmon antenna arrays in transmission
and polarization. Planar etalons in the middle of which a plasmon
antenna array is placed show anticrossings in transmission between
the etalon resonances and plasmon antenna resonance, which we map
as a function of frequency, etalon opening and oscillator strengh.
We argue that the proper interpretation of strong coupling and the
magnitude of the Rabi splitting requires a “metasurface-in-the-middle”
cavity model and is distinct from strong coupling between a cavity
and a dispersive material. Furthermore, we quantitatively connect
the Rabi splitting to the electrostatic antenna polarizability, that
is, the polarizability in the absence of radiative damping corrections.
Finally, we demonstrate that the strong coupling brings very strong
polarization conversion effects, as the hybrid modes provide for a
strong retardance that can be leveraged for linear birefringence and
dichroism.