Submicron domain engineering in periodically poled lithium niobate on insulator

Lithium niobate on insulator (LNOI) is extensively researched for potential applications in telecommunication, sensing and quantum technology. Low-loss waveguides in LNOI have been demonstrated in recent years, with further works investigating their nonlinear optical properties via electric field poling. The fabrication imperfections and minimum feature size of inverted ferroelectric domains currently limit the efficiency and application of nonlinear processes in LNOI. This work looks into focused ion beam poling and demonstrates its potential to overcome the limitations of electric field poling. We numerically investigate the susceptibility of quasi-phase-matching condition to the fabrication flaws in poling periods and waveguide geometry showing its extreme sensitivity. We demonstrate the precise fabrication of poling periods down to 200 nm consistent over 3 mm length. Submicron poling of low loss LNOI waveguides will unlock unprecedentedly efficient nonlinear interactions by the use of uncomplicated LNOI components and enable the realization of mirrorless optical parametric oscillators.