An intrinsic fiber ring laser based sensor with saturable absorber

A novel configuration of fiber ring laser acoustic sensor, which adopts single-mode fiber as sensing element, is proposed and demonstrated. Linewidth less than 1 kHz is achieved by introducing a segment of erbium-doped fiber in the reflecting arm as saturable absorber. A polarization independent unbalanced Michelson interrogation interferometer and phase generated carrier demodulation technique are adopted to recover signal. Experiments demonstrate that the phase sensitivity is 0.018 rad/nm in good linearity and equivalent minimum detect able length change reaches 19.1 pm.