Energy transfer of strong coupling of molecular vibrations regulated by dual bound states in the continuum

Vibrational strong coupling (VSC) enables the hybridization of molecular vibrations with confined optical modes, leading to the formation of new quasi-particles—vibrational polaritons—with modified energy transfer dynamics. However, conventional optical cavities often lack spectral tunability and compactness, while plasmonic structures suffer from significant intrinsic losses. To address these limitations, we report a novel approach using the dual quasi-bound state in the continuum (q-BIC) platform to regulate energy transfer in VSC systems. By designing double-asymmetric dielectric gratings, two high-Q q-BIC modes are excited in the mid-infrared regime and strongly coupled with the C=O stretching vibration of polymethyl methacrylate (PMMA) molecules, leading to clearly resolved Rabi splittings. We systematically investigate the dependence of mode splitting on grating parameters and reveal a sequential dual-mode strong coupling process. Detuning-dependent studies further elucidate the transition of energy transfer efficiency under different resonance conditions. In addition, we explore the evolution of q-BICs into guided-mode resonances as structural symmetry is altered and demonstrate the influence of molecular concentration on coupling strength by varying the PMMA film thickness. The observed collective coupling behavior enhances energy exchange efficiency and polariton spectral visibility. Our work introduces a tunable and integrated photonic platform based on dual q-BICs for the dynamic control of energy transfer in VSC systems, offering new prospects for infrared spectroscopy, chemical reactivity modulation, and polaritonic device integration.