Investigation of polarization tuning mechanism in fiber ring cavity laser

Ring cavity lasers employ an Er doped or a semiconductor gain medium including a wavelength selective element for tuning a lasing wavelength. For a wavelength tuner, a tunable optical filter can be realized using a rotatable grating, Fabry-Perot cavity or an acousto-optic element. In the paper, we demonstrate the fiber ring laser tuned by controlling polarization states along the birefringent optical fiber loop. The ring laser consists of a semiconductor optical amplifier, a polarization controller combined with a rotatable intra-cavity polarizer for a wavelength selective element, and a 9:1 coupler. The ring also includes a polarization independent in-line optical isolator for providing unidirectional operation and an attenuator to adjust a loop loss.