  We report a wavelength-tunable Q-switched mode-locked fiber laser based on a
compact optical tuning device, which is fabricated by coating single-layer
graphene on the surface of micro-fiber Bragg grating (MFBG). Based on
thermal-optical effect through evanescent interaction between graphene and
MFBG, the center wavelength of MFBG can be accurately controlled by adjusting
power of an external laser. By inserting the fabricated device into a compact
fiber laser cavity mode-locked by single-wall carbon nanotubes, stable
Q-switched mode-locked pulse is generated. Experimental results show that the
wavelength can be precisely optical-tuned from 1550.1 nm to 1551.9 nm with a
linear sensitivity of 6.3 pm/mW. Such an optical-controlled wavelength-tunable
Q-switched mode-locked fiber laser may find potential applications in
all-optical computing, all-optical logic gating and generation of microwave
source.
