Ring Fiber Lasers Based on EIT-Like Fano Resonances as a Wavelength-Selective Element

Based on strong over-coupling between a thin fiber taper and a microcylinder, electromagnetically induced transparency (EIT)-like Fano resonances resulting from a destructive interference between the microcylinder resonances and the background continuum transmission in the fiber are featured as a narrowband optical filter. The quality factor (Q factor) and the extinction ratio can be up to 2×10⁵ and 10 dB, respectively. When such an optical filter is applied in an erbium (Er)-doped fiber laser, a stable continuous-wave laser output can be generated with a 27.9-mW pump threshold and a ~20-MHz linewidth. In addition, by adjusting the polarization of the laser cavity, we demonstrate the tuning of the output wavelength of the ring laser.