An all-fiber passively wideband-tunable nanotube Q-switched low threshold erbium doped fiber laser is presented. With a low insertion loss carbon nanotube based saturable absorber, C- and L-band tunable Q-switched lasers are achieved by tuning the transmission wavelength of one C-band tunable filter and the other L-band one, respectively. The threshold of the Q-switched operation is only 12.8 mW. The self-mode-locking effect on the Q-switching can be effectively reduced by introducing a spatial hole burning effect with two optical circulators. The tunable wavelength range of the Q-switching laser can be changed by inserting a variable optical attenuator in the laser cavity to tune the gain spectrum.
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