Microresonator Brillouin laser and multi-Stokes generation at 2µm

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Brillouin scattering in microresonators has emerged as the driving process for developing high-coherence lasers for applications such as coherent optical communications, optical atomic clocks, microcomb solitons, and quantum communications. However, most of the demonstrations of microresonator Brillouin lasers have been limited to a 1550 nm wavelength regime, which benefits from the development of low-loss microresonator devices on different material platforms and the availability of tunable pump lasers. The development of wide bandwidth thulium-doped fiber amplifiers and low two-photon absorption in silicon around 2µm makes this wavelength region a potential candidate for applications in future optical communications, gravitation wave sensing, and atmospheric sensing. All these applications will benefit from the development of Brillouin lasers. However, there has not been much progress on microresonator-based 2µm Brillouin lasers. Here, we present a demonstration of a 2µm microresonator Brillouin laser. We use whispering gallery mode resonances in a ∼330µm silica microsphere to demonstrate a Brillouin lasing threshold of 35 mW. We achieve generation of second- and third-order Brillouin Stokes using pump powers of ∼60mW and 104 mW, respectively. By tuning the pump laser wavelength, we demonstrate high-resolution (∼10 pm) tuning of the Brillouin laser. From the beat signal of the first- and third-order Brillouin Stokes, we estimate a Brillouin laser linewidth of ∼135kHz, which is 15 times smaller than the pump linewidth. This work may find applications in optical communications, soliton combs, and atmospheric sensing in the 2µm wavelength region. Published by the American Physical Society 2024