Stretched-pulse operation of a mode-locked thulium/holmium-doped fiber laser has been demonstrated using a high numerical aperture (NA) fiber inside the laser cavity for intracavity dispersion compensation. The high NA fiber exhibits normal group-velocity dispersion allowing for the net-cavity dispersion to be positive. We experimentally investigate the laser dynamics as a function of the net-cavity dispersion, observing the transition from stretched-pulse to solitonic operation as the length of high NA fiber was reduced. In the stretched-pulse regime the laser produced pulses with a bandwidth of 30 nm and duration of 450 fs. Methods for compensating the third-order dispersion using high NA fibers are proposed. (C) 2015 Optical Society of America
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