  This paper explores the integration of cross-polarized stimulated Brillouin
scattering (XP-SBS) with Kerr and quadratic nonlinearities in lithium niobate
(LN) to enhance photonic device performance. Three novel applications are
demonstrated: (i) a reconfigurable stimulated Brillouin laser (SBL) with 0.7-Hz
narrow linewidth and 40-nm tunability, enabled by XP-SBS's thermo-optic phase
matching; (ii) an efficient coherent mode converter achieving 55% conversion
efficiency via intracavity Brillouin-enhanced four-wave mixing; (iii) a
Brillouin-quadratic laser and frequency comb operational in near-infrared and
visible bands, benefiting from the interaction between XP-SBS and quadratic
nonlinearity. These advancements promise significant improvements in photonic
technologies, including narrow-linewidth laser, microcomb generation, and
optical signal processing, paving the way for more robust and versatile
applications.
