Photonic Cavity-Mediated Tunable Ultrafast Absorption Dynamics in BaTiO₃-Based One-Dimensional Photonic Crystal

The ultrafast absorption dynamics of photonic modes and enhanced features of electronic states have been demonstrated in a barium titanate (BaTiO3, BTO)-embedded one-dimensional photonic crystal. The photonic structure has been realized as an optical microcavity, where a BTO central layer is sandwiched between two SiO2/TiO2-distributed Bragg reflectors. Angle-dependent transient absorption behavior reveals the excited-state absorption dynamics of cavity-tuned BTO defect energies. Furthermore, the dynamic evolution of photonic minibands of both sides of the photonic cavity mode demonstrates the enormous cavity field confinement effect. The temporal evolution of nonlinear absorption dynamics is specific to cavity angle tuning and is evidenced by seven orders of two-photon absorption enhancement in BTO mid-bandgap energies. Overall, the results highlight the impact of strong optical field confinement within the BTO central layer. The simulations of spatial and angle-dependent localized optical field and energy deposition within the photonic structure further support the experimental findings. The enhanced features of ultrafast absorption dynamics and strong optical nonlinearities of the BTO-based active photonic structure offer a better understanding of electron–photon interaction, which paves the way for many novel nonlinear, hybrid optoelectronic, and photonic device applications.