obtain absorption spectra directly from reflectivity spectra. Angle-resolved white light absorption spectra are hence recorded and shown in Fig. \[fig:3\] (a) and (b) for left and right circular polarizations. In each case, two strongly dispersing branches are observed, corresponding to upper and lower chiralitonic states. As detailed in the Supporing Information (Sec. A), a fit of a coupled dissipative oscillator model to the dispersions enables us to extract a branch splitting $2\sqrt{\left(\hbar\Omega_R\right)^2 - \left( \hbar\gamma_{\tiny\textrm{ex}}- \hbar\Gamma_{\tiny\textrm{OSO}}\right)^2}=40$ meV. With measured linewidths of the excitonic mode $\hbar\Gamma_{\tiny\textrm{OSO}}=80$ meV and of the plasmonic mode $\hbar\gamma_{\tiny\textrm{ex}}=26$ meV, this fitting yields a Rabi frequency of $\hbar\Omega_{\rm R}=70$ meV, close to our previous observations on non-OSO plasmonic resonators [@ShaojunWS2]. We emphasize that this value clearly fulfills the strong coupling criterion with a figure-of-merit $\Omega_{\rm R}^2/(\gamma_{\rm exc}^2+\Gamma_{\rm OSO}^2) =0.69$ larger than the $0.5$ threshold that must be reached for strong coupling [@Houdre2005; @TormaBarnes2015]. This demonstrates that our system does operate in the strong coupling regime, despite the relatively low level of visibility of the anti-crossing. This is only due $(i)$ to spatial and spectral disorders which leave, as always for collective systems, an inhomogeneous band of uncoupled states at the excitonic energy, and $(ii)$ to the fact 