High‐Frequency Stimulated Brillouin Scattering in Suspended Thin‐Film Lithium Niobate Waveguides

Stimulated Brillouin scattering (SBS) enables photonic filtering at gigahertz center frequencies with narrow linewidths at megahertz‐range, 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. Here, we show that SBS in suspended Z‐cut thin‐film lithium niobate (TFLN) waveguides satisfies these demands, exhibiting Brillouin frequency shifts exceeding 15 GHz when pumped at telecom wavelengths, nearly twice the highest values previously reported in TFLN. We observe gain coefficients up to 23.8 , among the largest achieved for such high Brillouin frequency shifts in any integrated Brillouin platform to date. For the first time, we apply spontaneous Brillouin microspectroscopy to suspended TFLN waveguides and confirm the high‐frequency acoustic mode observed in our SBS experiments. Our results unlock TFLN as a compelling material platform for scalable microwave photonics, with future applications spanning communication, sensing, and information processing.