Submicron optical waveguides and microring resonators fabricated by selective oxidation of tantalum

Submicron tantalum pentoxide ridge and channel optical waveguides and microring resonators are demonstrated on silicon substrates by selective oxidation of the refractory metal, tantalum. The novel method eliminates the surface roughness problem normally introduced during dry etching of waveguide sidewalls and also simplifies fabrication of directional couplers. It is shown that the measured propagation loss is independent of the waveguide structure and thereby limited by the material loss of tantalum pentoxide in waveguides core regions. The achieved microring resonators have cross-sectional dimensions of similar to 600 nm x similar to 500 nm, diameters as small as 80 mu m with a quality, Q, factor of 4.5 x 10(4), and a finesse of 120. (C) 2013 Optical Society of America