Mid-infrared Rabi splitting between transverse optical phonon and Fabry–Perot cavity mode

In this paper, we investigate the strong coupling and Rabi splitting between the transverse optical (TO) phonon and Fabry–Perot (FP) cavity mode under both transverse electric (TE) and transverse magnetic (TM) polarizations. The proposal is a prism coupling setup implementing the Otto configuration, where a highly-transmission KRS-5 prism enables phase-matched excitation of TO phonon polariton across an air gap. A layer of vanadium dioxide (VO₂) provides FP resonance, which can couple with TO phonon at almost the same wavelength. Owing to the strong coupling, the Rabi splitting reaches 58 meV. Besides, the coupling strength can be flexibly controlled by the angle of incidence, the thickness of each layer, and the phase state of VO₂. The combination of VO₂’s phase transition and its integration with FP mode introduces a powerful method for achieving strong coupling with tailored light–matter interaction strengths. As for the case of TE-polarization, the resonances of the FP mode and TO phonon polariton can still interact strongly. Our findings highlight the potential in creating adaptive photonic systems, capable of operating in a wide range of applications that demand dynamic control over coupling and resonance frequencies.