Photorefractive Damage in congruent LiNbO3• Part II. Magnesium doped Lithium Niobate Crystals

The photorefractive effect in lithium niobate (LN) crystals is one the main drawback for its integration in optoelectronic devices using high light intensity. Doping congruent LN crystals by appropriate dopants like divalent ions such as Mg2+ are known, for specific concentrations, to improve their optical damage resistance. We present experimental measurements of the photorefractive damage in a series of magnesium doped congruent lithium niobate, performed with two experimental technique based on the measurement with time of the photoinduced distortion for the first one and based on the direct measurement of the photoinduced birefringence variation with time for the second. The dependences of the photorefractivity and of the photosensitivity on the power and dopant concentration have been investigated and discussed with the consideration of the electro-optic properties dependence with the defect structure of the doped crystals. We conclude that that doping above a second threshold concentration with divalent Mg ions leads to a significant decrease of the photorefraction with respect to pure congruent crystals. We conclude that doping LN congruent crystals with Mg strongly increase the photorefractive damage resistance and, in association to the interesting electro-optic coefficients, LN:Mg present an interesting alternative for modulating devices to the stoichiometric LN, which is difficult to growth in high quality and in large quantity.