Widely Tunable Erbium-Doped Fiber Laser Based on Superimposed Core-Cladding-Mode and Sagnac Interferences

A widely tunable erbium-doped fiber laser based on superimposed core-cladding-mode and Sagnac interferences is proposed and demonstrated. The core-cladding-mode interference is elicited by cascading two well-fabricated single mode fiber tapers, which are inserted into the Sagnac loop with one section of polarization maintaining fiber and one polarization controller (PC). By adjusting only the PC in the Sagnac loop, the lasing line may be tuned at a discrete step defined by the core-cladding-mode interference, and its covering range depends on the Sagnac interference. The tunable laser operation is obtained with a discrete step of about 2.5 nm, tuning range more than 50 nm, side mode suppression ratio higher than 45 dB, and 3-dB spectral linewidth narrower than 0.1 nm.