The spatially varying polarization behavior of an optical guided mode in a Ti-indiffused lithium niobate (Ti:LiNbO \(_3\) ) waveguide is investigated. Ti indiffusion causes different rates of increase for the ordinary ( \(n_o\) ) and extraordinary ( \(n_e\) ) refractive indices in the waveguide, creating a distinct birefringence ( \(n_o \ne n_e\) ). The calculated results indicate the formation of C-points and L-lines in the generated spatially varying polarization guided modes (SVPGMs) at specific propagation lengths. Since controlling and tuning SVPGMs via propagation alone is challenging, electro-optical control and tuning of the generated SVPGMs in a Ti-indiffused periodically poled lithium niobate (Ti:PPLN) waveguide are proposed and theoretically investigated. The obtained results confirm full tunability of the SVPGMs. As an example, a 46.5 V applied voltage is required to convert an input vertical vector mode into a horizontal one, accompanied by several L-line singularities, in a 5 mm-long waveguide.
