Refractive index fluctuations in deformed Ti:LiNbO3 waveguides due to SiO2 overlayer deposition

During the fabrication process of Ti:LiNbO3 optical modulators, the deformation into a convex configuration of the LiNbO3 wafer occurs after the deposition of the micrometer-thick SiO2 buffer layer. This deformation remains in the modulator chip and possibly generates the strain in the waveguides. The strain induced change of refractive index (Δn) in the waveguide is estimated from consideration of the piezo-optic effect. This Δn is on the order of 10−5 and is close to that due to the electro-optic effect. The corresponding optical phase retardation is in agreement with measured values.