Engineered second-order nonlinearity in silicon nitride
Yi Zhang, Juniyali Nauriyal, Meiting Song, Marissa Granados Baez, Xiaotong He, Timothy L. Macdonald, Jaime Cárdenas
Abstract
The lack of a bulk second-order nonlinearity ( χ (2) ) in silicon nitride (Si 3 N 4 ) keeps this low-loss, CMOS-compatible platform from key active functions such as Pockels electro-optic (EO) modulation and efficient second harmonic generation (SHG). We demonstrate a successful induction of χ (2) in Si 3 N 4 through electrical poling with an externally-applied field to align the Si-N bonds. This alignment breaks the centrosymmetry of Si 3 N 4 , and enables the bulk χ (2) . The sample is heated to over 500°C to facilitate the poling. The comparison between the EO responses of poled and non-poled Si 3 N 4 , measured using a Si 3 N 4 micro-ring modulator, shows at least a 25X enhancement in the r 33 EO component. The maximum χ (2) we obtain through poling is 0.30pm/V. We observe a remarkable improvement in the speed of the measured EO responses from 3 GHz to 15 GHz (3 dB bandwidth) after the poling, which confirms the χ (2) nature of the EO response induced by poling. This work paves the way for high-speed active functions on the Si 3 N 4 platform.