Dual-wavelength lasing in an erbium-doped fiber cavity with a nested magnesium fluoride microcavity

We demonstrate a hybrid fiber laser system utilizing an angled fiber coupler and high-Q magnesium fluoride (MgF₂) whispering gallery mode resonator (WGMR). The angled fiber coupler, with two polished facets, serves as both a coupling mechanism to the WGMR and a partial reflector, enabling lasing even without the WGMR. By integrating a 340 μm diameter MgF₂ microcavity, we create a hybrid fiber cavity nested with a WGMR. This configuration results in dual-wavelength lasing, indicating the unique capabilities of our hybrid system. Our findings highlight the potential of angled fiber coupler-WGMR systems for enhancing spectral control in fiber lasers, opening new avenues for multi-wavelength laser sources.