Monolithically Integrated Cross‐Polarized Brillouin Lasers via Engineered Nonlinear Interactions

ABSTRACT On‐chip stimulated Brillouin lasers (SBLs) are promising sources of ultra‐coherent light for precision sensing, metrology, and microwave photonics. However, their deployment has been fundamentally limited by the need for bulky optical circulators to handle the backward‐propagating Brillouin Stokes wave and by the fixed Brillouin shift that restricts the accessible lasing wavelengths. In this work, we overcome these challenges by implementing cross‐polarized stimulated Brillouin scattering (XP‐SBS) in integrated chalcogenide glass (GeSbS) microrings. Combined with specially designed dissipation‐engineered couplers, we achieve 32 dB suppression of backward lasing, enabling forward‐extracted Stokes output with a 113 Hz fundamental linewidth. A microring array with tailored widths extends XP‐SBS phase matching to realize discrete wavelength coverage from 1540 to 1580 nm on a single chip. Leveraging the large Raman and Brillouin gains of GeSbS, we further harness the nonlinear interplay between XP‐SBS and stimulated Raman scattering to simultaneously generate an SBL at 1550 nm and a Raman‐shifted SBL at 1640 nm in the phonon laser regime, producing radio‐frequency signals with intrinsic linewidths down to 15.5 Hz. The SBL delivers an output power exceeding 6 mW, representing a 30‐fold enhancement compared to previous microring devices. Our results establish a compact and material‐flexible route to multi‐wavelength, low‐noise Brillouin lasers, opening new possibilities for on‐chip microwave photonics and sensing applications.