Journal ArticleStrong optomechanical interactions with long-lived fundamental acoustic wavesXu, Wendao; Iyer, Arjun; Jin, Lei; Set, Sze Y.; Renninger, William H.<p>Traveling-wave optomechanical interactions, known as Brillouin interactions, have now been established as a powerful and versatile resource for photonic sources, sensors, and radio-frequency processors. However, established Brillouin-based interactions with sufficient interaction strengths involve short phonon lifetimes, which critically limit their performance for applications, including radio-frequency filtering and optomechanical storage devices. Here, we investigate a new paradigm of optomechanical interactions with tightly confined fundamental acoustic modes, which enables the unique and desirable combination of high optomechanical coupling, long phonon lifetimes, tunable phonon frequencies, and single-sideband amplification. Using sensitive four-wave mixing spectroscopy controlling for noise and spatial mode coupling, optomechanical interactions with long<inline-formula><math display='inline'><mrow class='MJX-TeXAtom-ORD'><mo>><#comment/></mo></mrow><mrow class='MJX-TeXAtom-ORD'><mrow class='MJX-TeXAtom-ORD'><mn>2</mn></mrow></mrow><mspace width='thickmathspace'/><mtext>µ<#comment/></mtext><mrow class='MJX-TeXAtom-ORD'><mrow class='MJX-TeXAtom-ORD'><mi mathvariant='normal'>s</mi></mrow></mrow></math></inline-formula>phonon lifetimes and strong<inline-formula><math display='inline'><mrow class='MJX-TeXAtom-ORD'><mo>><#comment/></mo></mrow><mrow class='MJX-TeXAtom-ORD'><mrow class='MJX-TeXAtom-ORD'><mn>400</mn></mrow></mrow><mspace width='thickmathspace'/><mrow class='MJX-TeXAtom-ORD'><msup><mrow class='MJX-TeXAtom-ORD'><mrow class='MJX-TeXAtom-ORD'><mi mathvariant='normal'>W</mi></mrow></mrow><mrow class='MJX-TeXAtom-ORD'><mo>−<#comment/></mo><mn>1</mn></mrow></msup></mrow><mspace width='thickmathspace'/><mrow class='MJX-TeXAtom-ORD'><msup><mrow class='MJX-TeXAtom-ORD'><mrow class='MJX-TeXAtom-ORD'><mi mathvariant='normal'>m</mi></mrow></mrow><mrow class='MJX-TeXAtom-ORD'><mo>−<#comment/></mo><mn>1</mn></mrow></msup></mrow></math></inline-formula>coupling are observed in a tapered fiber. In addition, we demonstrate novel phonon self-interference effects resulting from the unique combination of an axially varying device geometry with long phonon lifetimes. A generalized theoretical model, in excellent agreement with experiments, is developed with broad applicability to inhomogeneous optomechanical systems.</p>Optica2023-01-0110479618Optica1022062334-2536https://doi.org/10.1364/OPTICA.4767641943658National Science Foundation