Polycrystalline anatase titanium dioxide microring resonators with negative thermo-optic coefficient

We fabricate polycrystalline anatase TiO2 microring resonators with loaded quality factors as high as 25,000 and average losses of 0.58  dB/mm in the telecommunications band. Additionally, we measure a negative thermo-optic coefficient dn/dT of −4.9±0.5×10−5  K−1. The presented fabrication uses CMOS-compatible lithographic techniques that take advantage of substrate-independent, non-epitaxial growth. These properties make polycrystalline anatase a promising candidate for the implementation of athermal, vertically integrated, CMOS-compatible nanophotonic devices for nonlinear applications.