TiO2 microring resonators with high Q and compact footprint fabricated by a bottom-up method

Titanium dioxide ( T i O 2 ) microring resonators (MRRs) with high quality factors (Qs) are demonstrated by using a new, to the best of our knowledge, bottom-up fabrication method. Pattern platforms with a T-shaped cross section are first defined by etching a thin top layer of silicon nitride and a thick bottom layer of silica and partially undercutting the silica. Then, T i O 2 is deposited on the platforms to form the T i O 2 waveguides and devices. T i O 2 MRRs with different bending radii, waveguide widths, and gaps in the bus waveguide are fabricated and measured. The intrinsic Q ( Q i n ) is achieved to be ∼1.1×10 5 at the telecommunication wavelengths, corresponding to a bend waveguide loss of 3.9 dB/cm while the compact MRR with a radius of 10 µm can still sustain a Q i n of ∼10 5 . These results not only unfold the feasibilities of the proposed bottom-up method for fabricating T i O 2 waveguides and MRRs with high Qs and compact footprints but also suggest a new approach for fabricating waveguides in other materials, of which direct etching is not easily accessible.