  Optical control of graphene-based photonic devices and systems has been under
extensive explorations, nevertheless, the requirement of high power pump laser
due to incoherent modulation makes those schemes low efficient. Here, we
demonstrate coherent manipulation of the operating states of partially
mode-locked fiber laser based on coherent population oscillation in reduced
graphene oxide for the first time. We couple a much weaker continuous wave
laser into the resonator operating with parametric instability state, and
observe significant depression/enhancement of the sidebands when the coherent
population oscillation conditions are satisfied. Besides, significant
depression of partially mode-locked fiber laser is achieved. The experimental
results reveal that the coherent population oscillation in reduced graphene
oxide is highly effective in manipulating mode-locked fiber laser system, and
the induced phase variation is highly asymmetrical. The discovery of coherent
population oscillation in reduced graphene oxide facilitates coherent optical
modulation of reduced graphene oxide-based photonic devices and systems with a
much weaker controlling laser.
