Strong Resonant Enhancement in Polarization Anisotropy in Third Harmonic Generation from MoS₂ Disks with Subtle Structural Ellipticity

Transition metal dichalcogenides (TMDC) are emerging as promising photonic platforms with favorable optical properties such as high refractive index, wide optical transparency window, and strong nonlinear optical susceptibilities. The electric field enhancement achievable within TMDC resonant subwavelength resonant structures can result in multifold enhancements in nonlinear optical processes. Herein, strong resonant enhancement in polarization anisotropy in third harmonic generation (THG) from isolated MoS 2 disk resonators is reported due to small structural ellipticity introduced during fabrication. The anisotropic optical response from the disks results in noticeable spectral shifts in the reflectance dip and THG peak for orthogonally polarized fundamental excitations. Polarization dependent THG response also reveals significant deviations from the expected isotropic behavior for circular disk with highly polarization selective double‐lobed and fourlobed profiles. The observed polarization selectivity is quantified using a contrast metric, which is as high as 47% for the THG measurements, while linear reflectance yields only 2%–4%. These observations are corroborated by electromagnetic simulations of polarization‐resolved linear and THG response considering the small structural ellipticity. Resonant tuning of nonlinear signal polarization properties through subwavelength structure perturbation can be leveraged for selective polarization state generation or detection with applications in classical and quantum photonics.