Characterization of third order nonlinearities in TiO₂ waveguides at 1550 nm

Abstract

Polycrystalline anatase titanium dioxide waveguides are investigated as an alternative material for all-optical switching at telecommunications C-band wavelengths. Titanium dioxide does not support two-photon absorption at 1550 nm, has a high refractive index, and a relatively low loss, which allows for high-index-contrast waveguides. The TiO₂ waveguides studied for this thesis were single-mode, with dimensions 200nm x 900nm, deposited on oxidized silicon and overclad with a transparent polymer. The optical Kerr coefficient was measured using two methods: spectral broadening studies and heterodyne pumpprobe experiments. The spectral broadening studies indicated an optical Kerr coefficient of n₂ = 1.82 x 10¹⁵ cm²/W, while the heterodyne pump-probe experiments, yielded a value of n₂ = 1.03 x 10¹⁵ cm²/W. Both techniques and their implementation are described in detail. Split-step code simulations including dispersion and linear loss as well as nonlinearity confirm the internal consistency of each experiment separately. Further experiments are needed to resolve the remaining difference.