  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.
