Evanescent field interaction with Fe3O4 nano-particle for passively Q-switched thulium-doped fiber laser at 1.94 μm

Abstract

We experimentally demonstrate the use of Fe3O4-based saturable absorber (SA) to generate self-starting, passively Q-switched pulses at 1943 nm. The Fe3O4 particles were characterized with scanning electron microscopy with energy dispersive spectroscopy. The size distribution of Fe3O4 particles was varied from ∼150 nm to 980 nm. The proposed SA was fabricated with combination of a side-polished fiber and the Fe3O4 particle by using evanescent field interaction between the side-polished fiber and the Fe3O4 particle. The insertion loss and polarization dependent loss of the proposed SA were measured as ∼4 dB and 0.3 dB, respectively at a wavelength of 1930 nm. The stable passively Q-switched pulses were readily generated from thulium-doped fiber laser incorporating the proposed SA at 1943 nm. The pulse width was changed from ∼8.1 μs to ∼880 ns while the repetition rate was changed from ∼61 kHz to ∼87 kHz. The tuning capability of both pulse width and repetition rate was also shown according to pump power.