Nonlinear optical waveguides produced by MeV metal ion beam implantation of lithium niobate

We report linear and nonlinear optical properties of planar waveguides produced by implantation of MeV Ag ions into LiNbO₃. The linear optical properties include spectrum of propagation modes and optical extinction spectrum. The nonlinear properties include optical spectrum of nonlinear refractive index and nonlinear absorption. Light guiding in the implanted crystal is associated with the modification of the linear refractive index. The modification is a result of two concurrent processes such as crystal damage in the nuclear stopping region producing a low index optical barrier between the top light guiding layer and the bulk crystal and the diffusion of the implanted ions into the top layer causing its index increase. Relatively high nonlinear refractive index (up to 10^-10 cm²/W) is a result of enhancement of intrinsic third order nonlinearity of the implant by the mechanism of surface plasmon resonance. The intrinsic nonlinearity is associated primarily with intraband and interband electron transitions. The spectrum of the nonlinear index correlates with the spectrum of optical extinction featuring prominent peak due to surface plasmon resonance. Possible applications of the waveguides include ultra-fast photonic switches and modulators.