Thulium doped fiber lasers (TDFL) with emission around 2000 nm wavelength are attractive owing to their applications in multiple domains such as medicine, defence and spectroscopy. The inherent broad gain bandwidth makes Thulium doped silica an attractive laser gain medium for generating short pulses.

Mode-locking is the technique by which short pulses can be generated from a laser cavity. Mode-locking can be generally classified into two: passive mode-locking and active mode-locking, depending on how it is accomplished. In this thesis, we discuss the generation of short pulses from a TDFL based on these techniques. Passive mode-locking is demonstrated using a saturable absorber mirror in the cavity as the mode-locking element. The influence of various cavity parameters on the stable mode-locked operation of a passively mode-locked TDFL is investigated through numerical modeling. Using a phase modulator inside the cavity, wavelength and repetition rate tunable actively mode-locked TDFL is demonstrated in an all-fiber configuration. We further discuss the details of the self mode-locking features that are observed even in the absence of a particular mode-locking element in the laser cavity.