Variable wavefronts of light beam caused by phase-polarization electro-optic modulation of BaTiO3 crystal thin-film waveguide

Abstract

This work investigates the characteristics of a birefringence electro-optic (EO) modulator based on a c-axis barium titanate (BaTiO3) crystal film rib waveguide and a pair of electrodes embedded in the crystal film applying a modulation electric field along the x-direction via a drive voltage. We derive the wavefront dependence of the output light wave under phase-polarization modulation (PPM) on multiple parameters such as EO coefficient, birefringence, and electric–optic field interaction length, so both the phase and polarization of the output beam are simultaneously changed with modulation voltage. The numerical simulations show that the variable helical wavefronts of a full-wave are obtained under a drive voltage of 7.0 V with a sub-millimeter-scale interaction length and a high EO coefficient (∼600 pm/V). Furthermore, the elliptical wavefront is variable in both amplitude and principal axis orientation to form a tunable helical wavefront. Consequently, the PPM effect induced variable helical wavefront evolutions of output light beam are testified by experiments. This study systematically elucidates the phase-polarization modulation mechanism and quantitatively presents the correspondence among the drive voltage, phase shift, and polarization state of the output light beam.