Optical Kerr effect, altering refractive index linearly with input light intensity, enables solitons, supercontinuum spectra, and frequency combs. Terahertz Kerr effect (TKE) holds promise for high-rate computing, but faces challenges due to low power density and weak response. This work demonstrates giant TKE mediated by stimulated phonon polaritons (SPhPs) in a lithium niobate Fabry-Pérot microcavity. Power-dependent refractive index changes cause measurable frequency shifts. The nonlinear coefficient, orders of magnitude larger than in visible/infrared light, is validated experimentally and theoretically using nonlinear Huang equations. This opens avenues for TKE-based applications.

Yibo Huang, Yao Lu, Wei Li, Xitan Xu, Xinda Jiang, Ruobin Ma, Lu Chen, Ningjuan Ruan, Qiang Wu, Jingjun Xu