Vibrational Strong and Ultrastrong Cocoupling in Optical Microcavities

Under resonance conditions, vibrational strong and ultrastrong cocoupling can be realized in optical microcavities. Using mixed PC–DMF solutions, we demonstrate access to this regime by first tuning the cavity into resonance with one type of molecule, producing well-separated polariton branches through ultrastrong coupling. Subsequently, one of these polariton branches strongly couples with the vibrational mode of the other type of molecule, leading to pronounced hybridization between the two molecular species and the photonic mode. A three-oscillator model successfully reproduces both the transmission spectra and polariton dispersions, showing excellent agreement with the experiment. Taken together, these results establish a robust platform and elucidate a mechanistic pathway that may play a significant role in cooperative cavity catalysis.