Polarization domains and self-mode-locked pulses in an erbium-doped fiber laser

We have observed various polarization domains and a giant self-mode-locked pulse in a 130 m long erbium-doped fiber laser without any mode-locking devices. By adjusting the intracavity polarization controller, we investigated the evolution process of the polarization domain with the varying cavity birefringence. When the birefringence was close to zero, the polarization domains split into multidomains, and finally a giant self-mode-locked pulse formed for the first time. We analyzed that the generation of the self-mode-locked pulse was related to the multiple subdomains ascribed to the strong coherent cross coupling between the orthogonal polarization light components in the long fiber cavity.