Observation of stimulated Brillouin scattering in silicon nitride integrated waveguides

TL;DR

This paper reports the first observation of stimulated Brillouin scattering in silicon nitride waveguides, revealing unique spectral features and quantifying the material's Brillouin gain and photoelastic constant, which impacts high-power photonic applications.

Contribution

First experimental demonstration of SBS in Si3N4 waveguides, including spectral analysis and parameter estimation, advancing understanding of nonlinear effects in integrated photonics.

Findings

Observed backward SBS in Si3N4 waveguides

Identified multi-peak Brillouin spectrum due to HBARs

Estimated Brillouin gain and photoelastic constant

Abstract

Silicon nitride (Si3N4) has emerged as a promising material for integrated nonlinear photonics and has been used for broadband soliton microcombs and low-pulse-energy supercontinuum generation. Therefore understanding all nonlinear optical properties of Si3N4 is important. So far, only stimulated Brillouin scattering (SBS) has not been reported. Here we observe, for the first time, backward SBS in fully cladded Si3N4 waveguides. The Brillouin gain spectrum exhibits an unusual multi-peak structure resulting from hybridization with with high-overtone bulk acoustic resonances (HBARs) of the silica cladding. The reported intrinsic Si3N4 Brillouin gain at 25 GHz is estimated as 7x10^-13 m/W. Moreover, the magnitude of the Si3N4 photoelastic constant is estimated as |p12| = 0.047 +/- 0.004. Since SBS imposes an optical power limitation for waveguides, our results explain the capability of Si3N4 to handle high optical power, central for integrated nonlinear photonics.