Ruiwen Zhang, Guodong Chen, and Junqiang Sun*

Forward stimulated Brillouin scattering (FSBS) is an acousto-optic interaction between co-propagating pump and Stokes fields through an acoustic wave. It can be enhanced greatly with the combination of electrostrictive force and radiation pressure in nanowire waveguides and hybrid waveguides. Hybrid phononic-photonic waveguides, which are studied for optical mode conversion and control of coherent information, are favorable to realize FSBS with flexible tunability of acoustic and optical modes. The compound-material device comprises two kinds of material and provides independent control of the optical and acoustic dispersion relationships. This separate control over the optical and acoustic modes improves the structural tunability.

In this paper, we present the generation of forward stimulated Brillouin scattering (FSBS) in hybrid phononic-photonic waveguides. To confine the optical and acoustic waves simultaneously, a hybrid waveguide is designed by embedding the silicon line defect in the silicon nitride phononic crystal slab. By taking into account three kinds hybrid waveguide, the appropriate structural parameters are obtained to enhance the acousto-optic interaction. We fabricate the honeycomb hybrid waveguide with a CMOS compatible technology. The forward Brillouin frequency shift is measured up to 2.425 GHz and the acoustic Q-factor of the corresponding acoustic mode is 1100. The influences of pump power, acoustic loss, nonlinear optical loss and lattice constant on the acousto-optic interaction in FSBS are analyzed and discussed. The proposed approach has important potential applications in on-chip all-optical signal processing.

The paper is published on Optical Express (Vol. 24, Issue 12, 2016.doi: 10.1364/OE.24.013051). This work is supported by the National Natural Science Foundation of China under Grant No. 61377074.