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

Titanium dioxide (TiO2) 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, TiO2 is deposited on the platforms to form the TiO2 waveguides and devices. TiO2 MRRs with different bending radii, waveguide widths, and gaps in the bus waveguide are fabricated and measured. The intrinsic Q(Qint) is achieved to be ∼1.1×105 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 Qint of ∼105. These results not only unfold the feasibilities of the proposed bottom-up method for fabricating TiO2 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.