Nonlinear harmonic generation of terahertz waves in a topological valley polaritonic microcavity

Compact terahertz (THz) devices, especially for nonlinear THz components, have received more and more attention due to their potential applications in THz nonlinearity-based sensing, communications, and computing devices. However, effective means to enhance, control, and confine the nonlinear harmonics of THz waves remain a great challenge for micro-scale THz nonlinear devices. In this work, we have established a technique for nonlinear harmonic generation of THz waves based on phonon polariton-enhanced giant THz nonlinearity in a 2D-topologically protected valley photonic microcavity. Effective THz harmonic generation has been observed in both noncentrosymmetric and centrosymmetric nonlinear materials. These results can provide a valuable reference for the generation and control of THz high-harmonics, thus developing new nonlinear devices in the THz regime.