WAVE-GUIDE FORMATION MECHANISM GENERATED BY DOUBLE DOPING IN FERROELECTRIC-CRYSTALS

Physical mechanisms causing the refractive index increase an in uniaxi al oxidized ferroelectric crystals subjected to double doping are disc ussed. The analysis shows that the index changes of the two different dopants, Delta n(A) and Delta n(B) are additive only if the correspond ing changes of the spontaneous polarization are small. Ti indiffusion and proton exchange (TIPE) waveguides in LiNbO3 are considered as an e xample of the case when this condition is not fulfilled. The hydrogen- lithium substitution in such waveguides leads to a strong reduction of the spontaneous polarization of the virgin crystals and the final ind ex change Delta n is not a sum of Delta n(A) and Delta n(B). A physica l model is developed to explain light waveguiding in double-doped ferr oelectric structures. Experimental data obtained for TIPE waveguides c onfirm the model. (C) 1995 American Institute of Physics.