Description
Stimulated Brillouin scattering enables narrow-linewidth, GHz-centered photonic filtering, making it a key building block for integrated microwave photonics. Accessing radio-frequency bands beyond 15 GHz with SBS requires high frequency shifts and high gain coefficients, a combination that yet remains a challenge. Existing integrated platforms face a fundamental trade-off between Brillouin frequency shift and gain coefficient: chalcogenide waveguides deliver high gain coefficients but are constrained to lower frequencies, while silicon nitride and silicon oxynitride access higher frequencies at the cost of much weaker gain. Silicon-on-insulator offers both high Brillouin frequency shifts and gain coefficients, but is hampered by two-photon absorption. Additionally, none of these platforms natively combine high frequency shifts, strong gain, and second-order nonlinearity, the combination required for fully integrated, multifunctional microwave photonic processors.
In this work, we demonstrate that suspended Z-cut TFLN waveguides support a rich spectrum of confined acoustic modes that provide both high Brillouin frequency shifts and high gain coefficients. We observe a phonon mode at 16.8 GHz with a gain coefficient of 23.8 (mW)⁻¹, nearly doubling the highest Brillouin shifts previously reported in TFLN, and among the largest gain coefficients reported at such high shifts in any integrated Brillouin platform. We further validate these results using Brillouin microspectroscopy on nanoscale TFLN waveguides for the first time, finding good agreement between backward stimulated and spontaneous Brillouin scattering measurements.
This work presents the first experimental demonstration of confined high-frequency acoustic modes in TFLN waveguides. The Brillouin shifts demonstrated here cover new microwave bands, including the Ku-band (12–18 GHz) and K-band (18-26.5 GHz), and approach the millimeter-wave regime, opening on-chip filtering for satellite, 5G/6G, and radar systems at frequencies previously inaccessible to integrated Brillouin platforms. Our results unlock TFLN as a compelling material platform for scalable microwave photonics, with future applications spanning communication, sensing, and information processing.
| I am the presenting author | Yes |
|---|