  Lithium niobate on insulator (LNOI) waveguides, as an emerging technology,
have proven to offer a promising platform for integrated optics, due to their
strong optical confinement comparable to silicon on insulator (SOI) waveguides,
while possessing the versatile properties of lithium niobate, such as high
electro-optic coefficients. In this paper, we show that mode hybridization, a
phenomenon widely found in vertically asymmetric waveguides, can be efficiently
modulated in an LNOI ridge waveguide by electro-optic effect, leading to a
polarization mode converter with 97% efficiency. Moreover, the proposed device
does not require tapering or periodic poling, thereby greatly simplifying the
fabrication process. It can also be actively switched by external fields. Such
a platform facilitates technological progress of photonic circuits and sensors.
