Precise correction of integrated optical power splitters based on lithium niobate substrates by photorefractive effect local excitation

A method for precise adjustment of the power splitting ratio for integrated optical splitters fabricated on lithium niobate substrates is proposed. The method is based on a local refractive index change caused by the photorefractive effect under external illumination of certain areas of waveguide power splitters. A fiber optic probe was used for precise positioning of an external illumination spot. Predictable tuning of the splitting ratio for two basic splitter configurations (directional couplers and y-branches) was demonstrated. Precise adjustment of the power splitting ratio in a relatively narrow range (2%) led to a significant growth in the Mach–Zehnder modulator extinction ratio (as high as 17 dB, from 30 to 47 dB). The proposed method is simple and can prove to be a very promising additive technique for improvement of lithium niobate integrated optical schemes.