  A wavelength spacing tunable, multiwavelength Q-switched mode-locked (QML)
fiber laser in an erbium-doped fiber cavity based on graphene oxide deposited
on tapered fiber is proposed by choosing the diameter and length of the taper,
graphene oxide thickness and cavity dispersion, in which the wavelength spacing
could be tuned by pump power. The evolutions of temporal and spectral with
different pump strengths are investigated. Results show that the tunability of
the multiwavelength laser can be interpreted by the bound states of QML laser
resulting from a mutual interaction of dispersion, nonlinear effect, insertion
loss, and pump power. To the best of our knowledge, it is the first
experimental observation of bound states of QML, which provides a new mechanism
to fabricate tunable multiwavelength laser.
