Laser Mode Locking Using a Single-Mode-fiber Coil with Enhanced Polarization-Dependent Loss.

A laser mode-locking phenomenon based on polarization-dependent loss (PDL) using a passive fiber coil is demonstrated. We propose using a fiber coil operating in low-V-number regime to achieve an enhanced bend-induced PDL and to maintain a reasonable bend loss. A mode-locked thulium doped all-fiber laser is shown using the low-V-number fiber coil. The results indicate that a moderate amount of PDL at 1 dB is sufficient to initiate and sustain a stable CW mode-locking operation. To the best of our knowledge, this is the first demonstration of a CW mode-locked fiber laser based on PDL enabled by a fiber coil.