Investigation and analysis of a single-mode waveguide formed by multienergy-implanted LiNbO3

We demonstrate a single-mode waveguide in LiNbO3 by use of both prism and end-face coupling methods. The waveguide is formed by multienergy megaelectron-volt O2+ implantation at room temperature. A bright line is observed only when moderate postimplant annealing was performed. The possible index profile of the waveguide is constructed according to the damage profile of the lattice structure caused by the implantation. Although dark-mode measurement shows that the effective extraordinary index of LiNbO3 is raised in the waveguide layer, results of the analysis indicate that the single guiding mode could be supported by a synergetic effect from both the raised index layer and the low-index barrier. The reduced loss of the waveguide can be attributed to the widened low-index barrier from multienergy implantation.