Bidirectional single-mode Er-doped fiber-ring laser

A Faraday rotator is used in a laser cavity to eliminate spatial hole burning in a bidirectional Er-doped fiber-ring laser. A stable operation is achieved in single longitudinal mode with comparable intensities for both clockwise and counter-clockwise directions. A beat signal between the clockwise and the counter-clockwise laser outputs of 40 dB above noise and of about 30% fringe visibility is observed.