Passive Q-switched erbium-doped fibre laser with saturable absorber

In this paper, we report that a passive Q-switched erbium-doped fibre laser can be constructed by inserting a segment of samarium-doped fibre into the ring cavity as saturable absorber. Our result shows that when the erbium-doped fibre has a large gain coefficient and the samarium-doped fibre has sufficient absorption, self-pulsing can readily be obtained. Furthermore, if the saturable absorber has large transition cross section, narrow Q-switched pulses of very large amplitude are produced.