Fundamental and Harmonic Self Mode-locking in Mid IR Heavily Doped Fiber Lasers

Abstract

Harmonic self mode-locking effects are observed in heavily doped fiber lasers operating near 3 μm. The temporal profiles for the output of an Er-ZBLAN fiber laser operating at ~2.7 μm and an Ho, Pr-ZBLAN fiber laser operating at ~2.87 μm are reported. Stable second harmonic mode-locking is observed in the Er-ZBLAN fiber laser under 970nm pumping for an Er concentration of 50000 ppm, while unstable harmonic modelocking of order of between 1-1/7 times the round cavity round trip time was observed for the higher concentration of 80000 ppm and for all pump powers. Unstable harmonic modelocking is observed in the Ho, Pr-ZBLAN fiber laser when pumped at 1064nm, for fiber lengths up to 13m and for all pump powers. The experimental mode-locked pulse train periods are found to be consistent with theoretical analysis. The origin and properties of harmonic self mode-locking in heavily doped ZBLAN fiber lasers operated near 3 μm are discussed.

Keywords: Er-ZBLAN fiber laser, Ho, Pr-ZBLAN fiber laser, Self mode-locking, Harmonic self mode-locking.

PACS: Fiber lasers, 42.55.Wd, Mode locking, 42.60.Fc.