Erasure of ferroelectric domain inversion in Ti-diffused LiNbO3 optical waveguide by Li-rich vapor-transport equilibration

It is demonstrated that ferroelectric domain inversion layer in a LiNbO3 plate caused by high-temperature Ti diffusion process as well as by heat treatment without diffusing Ti can be erased by Li-rich vapor-transport equilibration. It is figured out that the formation or erasing of inverted domain should be attributed to an internal electrical field, caused by the coupling of lithium, niobium or titanium diffusion rate based on ambipolar model. Moreover, specific domain-inversion mechanism is also discussed. A near-stoichiometric Ti-diffused LiNbO3 waveguide was fabricated by indiffusion of Ti-strips into a congruent LiNbO3 (i.e., standard Ti diffusion procedure) and vapor-transport equilibration treatment in this paper. The resultant Ti-diffused LiNbO3 waveguide supports a TM mode at 1553 nm with the aid of prism couplers. Different with the usual Ti-diffused LiNbO3 waveguides fabricated on +Z face, no inverted domain was observed on the Ti-diffused region of this waveguide. This achievement can also be applied in ferroelectric domain engineering of single crystal lithium niobate.