Ultranarrow-Linewidth Brillouin/Erbium Fiber Laser Based on 45-cm Erbium-Doped Fiber

We demonstrate an ultranarrow-linewidth Brillouin/erbium fiber laser (BEFL), in which 45-cm commercialized erbium-doped fiber (EDF) acts as both the Brillouin and linear gain media. The Brillouin pump threshold of the BEFL is in submilliwatts. Its 980-nm pump threshold is only 15 mW. The BEFL presents an ultranarrow linewidth of 40 Hz. This single-frequency BEFL presents a number of applications in many high-coherence fields.