Integrated electro-optic platform using ferroelectric crystals with the point symmetry of orthorhombic mm2

We theoretically and numerically investigate the modulation efficiencies of integrated electro-optic (EO) modulators based on ferroelectric crystals with the point symmetry of orthorhombic mm2. An analytical expression describing the index-ellipsoid under the EO effect is derived, where all 5 non-zero linear EO coefficients of mm2-crystals are considered. As practical candidates for integrated EO platform, three mm2-crystals (KNbO3, KTiOPO4, and Ba2NaNb5O15) that are well-established and commercially available are chosen for numerical simulations. The refractive-index (RI) changes caused by an external electric field applied to each crystal with an arbitrary direction are analyzed in detail for the given optical polarization states of input light wave. For each crystal, the modulation efficiency is evaluated in terms of the half-wave voltage required for a pi-phase shift of input wave, which is compared with the established counterpart based on LiNbO3. The results indicate that higher modulation efficiencies are achievable in the two schemes using KNbO3 and Ba-2 NaNb5O15 than those for other cases, meaning that either lower power-consuming or larger beam-window integrated EO devices are feasible.