26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Stimulated Brillouin Scattering in InGaP-on-SiO2 Waveguides

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral ANZOS | Photonics and Optics (ANZCOP)

Description

We present the simulation, fabrication, and experimental demonstration of on-chip stimulated Brillouin scattering (SBS) in InGaP-on-SiO₂ waveguides opera􀆟ng near 1550 nm. Brillouin scattering is a third-order nonlinear interaction between optical and acoustic waves that produces narrow linewidth microwave signals through the Brillouin gain process, desired for applications such as narrow-linewidth lasers, microwave photonic filters and sensors.
InGaP is a single-crystalline material that benefits from high second- and third-order optical nonlinearities, a wide bandgap of 1.9 eV that avoids two-photon absorption at 1550 nm wavelength, a high refractive index of 3.11, and relatively low acoustic velocity compared to SiO₂. These proper􀆟es support long phonon life􀆟me, ensure efficient acousto-optic coupling, and provide simultaneous optical and acoustic confinement. This makes the InGaP-on-SiO₂ a promising platform for SBS.
We perform Numerical simulations using the finite-element NumBAT tool to evaluate backward intra-modal SBS using counter-propagating pump and probe optical waves at 1550 nm. Here, we assume both optical fields are coupled to fundamental TE mode of the waveguide and find the mechanical mode with maximum Brillouin gain coefficient at microwave frequency of 9.339 GHz, with 80% transverse and 20% longitudinal acoustic displacements.
We fabricate the waveguides through wafer-scale bonding of a 250 nm InGaP layer onto an oxidized silicon substrate, followed by substrate removal, electron-beam lithography and dry etching.
We demonstrate experimental backward SBS in a 49.8 mm long, 1000 nm wide InGaP waveguide with at 9.346 GHz with an ultra-narrow linewidth of 5.2 MHz. This corresponds to mechanical quality factor of 1797.3. Additional measurements on micro-ring resonators fabricated on the same platform, showed intrinsic optical quality factors ranging 1.1×10⁵ to 4.2×10⁵ for waveguide widths of 500 nm to 1300 nm. The corresponding propagation loss ranges from 6.7 dB/cm to 1.4 dB/cm.
This work paves the way for future Brillouin-enabled photonic devices on III-V-on-insulator systems.