Backward stimulated Brillouin scattering (SBS) is widely exploited for various applications in optics and optoelectronics. It typically features a narrow gain bandwidth of a few tens of megahertz in fluoride crystals. Here we report a hundredfold increase of SBS bandwidth in whispering-gallery mode resonators. The crystalline orientation results in a large variation of the acoustic phase velocity upon propagation along the periphery, from which a broad Brillouin gain is formed. Over 2.5 GHz wide Brillouin gain profile is theoretically found and experimentally validated. SBS phenomena with Brillouin shift frequencies ranging from 11.73 to 14.47 GHz in ultrahigh Q Z-cut magnesium fluoride cavities pumped at the telecommunication wavelength are demonstrated. Furthermore, the Brillouin–Kerr comb in this device is demonstrated. Over 400 comb lines spanning across a spectral window of 120 nm are observed. Our finding paves a new way for tailoring and harnessing the Brillouin gain in crystals.

中文翻译：

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回音壁模式谐振器中受激布里渊散射带宽增加百倍

后向受激布里渊散射 (SBS) 被广泛用于光学和光电子学的各种应用。它通常在氟化物晶体中具有几十兆赫兹的窄增益带宽。在这里，我们报告了回音壁模式谐振器中 SBS 带宽增加了百倍。晶体取向导致沿周边传播时声相速度的大变化，由此形成宽布里渊增益。理论上发现并通过实验验证了超过 2.5 GHz 宽的布里渊增益分布。超高Q Z中布里渊频移范围为 11.73 至 14.47 GHz 的 SBS 现象展示了以电信波长泵浦的切氟化镁空腔。此外，还演示了该设备中的布里渊-克尔梳。观察到跨越 120 nm 光谱窗口的 400 多条梳状线。我们的发现为定制和利用晶体中的布里渊增益铺平了一条新途径。