The synthetic crystal Lithium Niobate (LN) plays a key role in integrated optical devices for electro-optic (EO) signal modulation and frequency conversion. Unfortunately use on LN for the realization of commercial nonlinear optical devices is hindered by the presence of photorefractivity in such crystals [1]. It is well known that photorefractivity can be strongly reduced by maintaining the LN devices at high temperature (e.g. >100°C), or using MgO-doped LN substrates. Even if both these strategies are currently used they are not completely satisfactory as keeping the device at high temperature may reduce the components reliability and life-time, while using MgO-doped LN several processes, as crystal poling and waveguide fabrication must be completely modified, as the presence if Mg in concentrations close to 6% drastically changes the substrate characteristics.
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