We experimentally confirm that graphene within fiber laser cavities can generate four-wave-mixing (FWM) by observing the laser spectral broadening and the transition from the single-longitudinal-mode oscillation to multiple-longitudinal-mode one. Then, by simultaneously exploiting the graphene-induced nonlinear FWM and its super-broadband saturable absorption, we further achieve for the first time to the best of our knowledge, multiwavelength Q-switched Yb<sup>3+</sup>- or Er<sup>3+</sup>-doped fiber lasers at 1 <i>μ</i>m and 1.5 <i>μ</i>m wavebands, respectively. Simultaneous 23-wavelength Q-switching oscillation with a wavelength spacing of 0.2 nm is stably generated at 1.5 <i>μ</i>m waveband. The multiwavelength Q-switched pulses have the minimum pulse duration of 2.5 <i>μ</i>s, the maximum pulse energy of 72.5 nJ and a wide range of pulse-repetition-rate (PRR) from 2.8 to 63.0 kHz. At 1 <i>μ</i>m waveband, we also obtain five-wavelength simultaneous lasing in Q-switching regime with the pulse duration of ~3<i>μ</i>s, pulse energy of 10.3 nJ and PRR between 39.8 and 56.2kHz.
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