Second-Harmonic Generation in Silicon Nitride Ring Resonators

TL;DR

This paper demonstrates second harmonic generation in silicon nitride ring resonators by inducing a second-order nonlinearity in a centrosymmetric material, enabling new CMOS-compatible nonlinear optical functionalities.

Contribution

The authors show how to generate second harmonic signals in silicon nitride waveguides by breaking symmetry at the nanoscale, using high-Q ring resonators to enhance efficiency.

Findings

Second harmonic generation achieved in silicon nitride resonators.

Efficient SH generation with milliwatt input powers.

Induced $ ext{chi}^{(2)}$ response in centrosymmetric material.

Abstract

The emerging field of silicon photonics seeks to unify the high bandwidth of optical communications with CMOS microelectronic circuits. Many components have been demonstrated for on-chip optical communications, including those that utilize the nonlinear optical properties of silicon[1, 2], silicon dioxide[3, 4] and silicon nitride[5, 6]. Processes such as second harmonic generation, which are enabled by the second-order susceptibility, have not been developed since the bulk $\chi^{(2)}$ vanishes in these centrosymmetric CMOS materials. Generating the lowest-order nonlinearity would open the window to a new array of CMOS-compatible optical devices capable of nonlinear functionalities not achievable with the?$\chi^{(3)}$ response such as electro-optic modulation, sum frequency up-conversion, and difference frequency generation. Here we demonstrate second harmonic (SH) generation in CMOS compatible integrated silicon nitride (Si3N4) waveguides. The $\chi^{(2)}$ response is induced in the centrosymmetric material by using the nanoscale structure to break the bulk symmetry. We use a high quality factor Q ring resonator cavity to enhance the efficiency of the nonlinear optical process and detect SH output with milliwatt input powers.