Ordered Polar Topological Domains Enabling Giant Second-Harmonic Generation in Ferroelectric Nematic Liquid Crystals.

Abstract

Developing high-performance nonlinear optical materials that simultaneously deliver large effective nonlinearity and device-level integrability remains a longstanding challenge. Ferroelectric nematic liquid crystals (FNLC) have emerged as a promising platform owing to their intrinsic non-centrosymmetry, theoretically predicted large second-order nonlinearity, and solution processability on diverse substrates. However, realizing strong second-harmonic generation (SHG) in FNLCs has been hindered by pronounced orientational disorder inherent to fluidic systems without lattice constraints. Here, this limitation is overcome through a surface-anchoring strategy that induces highly ordered polar topological structures within self-assembled FNLC droplets. The resulting architecture yields a giant effective SHG coefficient of 56.9 pm/V-an order of magnitude higher than previously reported FNLC systems-together with SHG efficiency surpassing that of benchmark LiNbO₃ films of comparable thickness. Moreover, the system exhibits broadband SHG response, while the engineered polar topology enables passive, field-free spatial optical modulation with a contrast ratio of 330%. The combination of giant nonlinearity, outstanding SHG efficiency, broadband SHG response, spatial optical modulation, and solution processability establishes a new paradigm for integrated nonlinear photonic devices.