Engineered second-order nonlinearity in silicon nitride

TL;DR

This paper demonstrates the induction of second-order nonlinearity in silicon nitride through electrical poling, enabling high-speed electro-optic modulation and second harmonic generation on a CMOS-compatible platform.

Contribution

The authors successfully induce  in silicon nitride via electrical poling, breaking centrosymmetry and enabling active nonlinear optical functions.

Findings

At least 25X enhancement in EO response after poling

Maximum  obtained is 0.24 pm/V

EO bandwidth increased from 3 GHz to 15 GHz

Abstract

The lack of a bulk second-order nonlinearity (\c{hi}(2)) in silicon nitride (Si3N4) 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 \c{hi}(2) in Si3N4 through electrical poling with an externally-applied field to align the Si-N bonds. This alignment breaks the centrosymmetry of Si3N4, and enables the bulk \c{hi}(2). The sample is heated to over 500{\deg}C to facilitate the poling. The comparison between the EO responses of poled and non-poled Si3N4, measured using a Si3N4 micro-ring modulator, shows at least a 25X enhancement in the r33 EO component. The maximum \c{hi}(2) we obtain through poling is 0.24pm/V. We observe a remarkable improvement in the speed of the measured EO responses from 3GHz to 15GHz (3dB bandwidth) after the poling, which confirms the \c{hi}(2) nature of the EO response induced by poling. This work paves the way for high-speed active functions on the Si3N4 platform.