Tailoring optical nonlinearities of thin-film lithium niobate via encapsulating plasmonic nanoparticles.

The development of lithium-niobate-on-insulator (LNOI) technology has sparked the advancement of numerous on-chip photonic devices for generating and manipulating light. However, the optical absorption of thin-film LNOI is very weak, especially in the near-infrared field, due to their extremely thin absorption layer and intrinsic band structure characteristics. Here, we propose a comprehensive framework to tackle these obstacles by means of ion implantation of Ag ions, which facilitates the encapsulation of plasmonic silver (Ag) nanoparticles within LNOI thin films. Through the incorporation of Ag nanoparticles, we have observed a tailored profile of optical nonlinear absorptions in LNOI thin films, transitioning from reverse saturable absorption to saturable absorption as well as optical-induced absorption to photobleaching behaviors. Moreover, the plasmonic effect elicited by the embedded Ag nanoparticles amplifies the third-order nonlinear coefficient by an order of magnitude. This work opens an avenue toward the development of high-performance on-chip photonic devices harnessing third-order nonlinearities of LNOI. [ABSTRACT FROM AUTHOR]