Analysis of silicon-on-insulator slot waveguide ring resonators targeting high Q-factors

Vertical slot waveguide micro-ring resonators in silicon photonics have already been demonstrated in previous works and applied to several schemes, including sensing and hybrid nonlinear optics. Their performances, first quantified by the reachable Q-factors, are still perceived to be restrained by larger intrinsic propagation losses than those suffered by simple Si wire waveguides. In this Letter, the optical loss mechanisms of slot waveguide micro-ring resonators are thoroughly investigated with a special focus on the coupler loss contribution that turns out to be the key obstacle to achieving high Q-factors. By engineering the coupler design, slotted ring resonators with a 50 mu m radius are experienced with a loaded Q-factor up to 10 times improvement from Q = 3,000 to Q = 30,600. The intrinsic losses due to the light propagation in the bent slot ring itself are proved to be as low as 1.32 +/- 0.87 dB/cm at lambda = 1,550 nm. These investigations of slot ring resonators open high performance potentials for on-chip nonlinear optical processing or sensing in hybrid silicon photonics. (C) 2015 Optical Society of America