  Lithium Niobate (LN) is an important nonlinear optical material. Here we
demonstrate LN microdisk resonators that feature optical quality factor ~
100,000, realized using robust and scalable fabrication techniques, that
operate over a wide wavelength range spanning visible and near infrared. Using
our resonators, and leveraging LN's large second order optical nonlinearity, we
demonstrate on-chip second harmonic generation with a conversion efficiency of
0.109 W-1.
