Lithium niobate (LiNbO3) is an important material for optical modulators. It is a colorless solid insoluble in water. It has a trigonal crystal system and negative uniaxial birefringence which depends slightly on the stoichiometry of the crystal and on temperature. It is transparent for wavelengths between 350 and 5200 nanometers.
MgO:LN is Lithium niobate doped by magnesium oxide, which increases its resistance to optical damage.