A mode-locked fiber laser comprising a multicomponent glass fiber doped with a trivalent rare-earth ion of thulium and/or holmium and including a fiber-optic based passive saturable absorber that contains an adhesive material mixed with a saturable absorbing components and is disposed along the length of an optical fiber such as to assure that a mode propagating within the fiber spatially overlaps with the volume occupied by the saturable absorbing components.