Fe: LiNbO₃ is a kind of common used photorefractive materials with large electro-optic (E-O) coefficients, high photorefractive sensitivity and high diffraction efficiency. It is easy operation and storage, low cost and large size availability, Fe:LiNbO₃ is a kind of common used photorefractive materials with large electro-optic (E-O) coefficients, high photorefractive sensitivity and high diffraction efficiency. It is easy operation and storage, low cost and large size availability, which make it more suitable for volume fabrication and practical devices.

 When an electric field (E) is applied to an electro-optic (E-O) crystal, the refractive index of E-O crystal will change linearly to electric field. The phenomenon is called linear electro-optic effect. For KD*P crystal, for example, the change of the refractive index (Dn) is Dn = 0.5no3r63E if both the directions of light propagation and electric field are along the z-axis, where no is refractive index without electric field and r63 is electro-optic coefficient of KD*P.There are two kinds of E-O modulations. One is longitudinal E-O modulation if the directions of electric field and light propagation are the same. The KDP isomorphic crystals are normally used in this scheme. If the directions of electric field and light propagation are perpendicular, it is called transverse E-O modulation. The LiNbO₃, MgO:LiNbO₃, ZnO:LiNbO₃, BBO and KTP crystals are usually employed in this scheme.