Maximizing intensity in TiO2 waveguides for nonlinear optics

Titanium dioxide (TiO2) represents an attractive candidate for nonlinear optical devices due its high transparency, large refractive index, and large Kerr nonlinearity. Using electron beam lithography and a liftoff procedure, we can structure both amorphous TiO2 as well as polycrystalline anatase thin films to create photonic devices that exploit the material’s properties in order to do nonlinear optics. Nonlinear optics benefit from long interactions, necessitating large intensities along long waveguide lengths. For this reason, waveguide losses need to be minimized. We study the effects of mask materials and annealing procedures on waveguide propagation losses. We also study a variety of taper structures and optimize the insertion losses of these waveguides. For short pulses, dispersion becomes an important parameter. For nano-scale structures such as ours, it can be tailored by changing the waveguide geometry. We present finite element simulations and experiments that demonstrate the dispersion engineering that was necessary to maintain high pulse intensity, as wall as some nonlinear measurements that demonstrate the benefits of these optimizations. These techniques can readily be applied to other novel photonic devices.