Development of thulium fiber lasers operating at 1.9 micron region

This thesis describes a thorough study on a newly developed thulium bismuth codoped fiber laser (TBDFL) in replace of a conventional thulium-doped fiber laser (TDFL). TDFL normally requires a high threshold pump power and thus cannot be pumped by a low power commercial laser diode. The fiber was fabricated using modified chemical vapour deposition (MCVD) in conjunction with the solution doping process. The experimental results revealed that the newly developed thulium bismuth co-doped fiber (TBDF) requires a comparatively shorter length for 1.9 micron lasing as compared to the conventional thulium-doped fiber (TDF). Both of the 802 nm and 1552 nm pumps can be used to generate lasing for the TBDF. The TBDFL performance is superior to the conventional TDFL with a threshold pump power of 80.1 mW and a slope efficiency of 42.23% at a fiber length of 0.4 m. The superior lasing performance exhibited by the TBDF is due to the selection of suitable fiber parameters, namely the dopants compositions, their relative proportions and the host glass composition. The Q-switched TBDFL is also demonstrated using a simple and low cost multi-walled carbon nanotubes (MWCNT) saturable absorber. It operates at the 1857.8 nm wavelength with a threshold pump power of 106 mW. It is observed that the repetition rate increases almost linearly from 12.84 kHz to 29.48 kHz with an increasing pump power of 106.6 mW to 160 mW. Meanwhile, the pulse width reduces from 9.6 μs to 6.1 μs with the increase in the pump power increases. At the maximum pump power of 160 mW, the maximum pulse energy is obtained at 61.7 nJ