Graphene Saturable Absorber Based on Slightly Tapered Fiber With Inner Air-Cavity

We experimentally demonstrate a passively mode-locked fiber laser operation by using a saturable absorber based on graphene deposited on slightly tapered optical fiber with inner air-cavity. Such a saturable absorber enables a strong light-graphene interaction owing to the evanescent field of the excited cladding mode, and as a result, stable passively mode-locked laser pulses with pulsewidth of 674 fs have been generated, and in addition, a harmonic mode-locking operation can also be achieved.