Strong Linewidth Reduction by Compact Brillouin/Erbium Fiber Laser

We demonstrate the strong linewidth reduction by a compact Brillouin/erbium fiber laser (BEFL), in which 4-m erbium-doped fiber (EDF) acts as both the Brillouin and linear gain media. Due to the assistance of the linear gain in the EDF with the acoustic damping and the cavity feedback in the resonator, the proposed BEFL transferred the 20-MHz Brillouin pump (BP) into the 950-Hz Brillouin Stokes laser emission, demonstrating that the laser linewidth is reduced by over 2 × 10⁴ times through this BEFL. The linewidth reduction is independent of the 980-nm pump power or the BP wavelength. The BEFL keeps strong linewidth reduction over the whole C-band. This effect of the BEFL provides a simple but effective way to obtain highly coherent light for many applications.