A Mode-Locked 1.91 μm Fiber Laser Based on Interaction between Graphene Oxide and Evanescent Field

The use of a graphene oxide (GO)-deposited D-shaped fiber as a saturable absorber for mode locking of a thulium-doped fiber laser is experimentally demonstrated. By using the evanescent field interaction of an oscillating beam with GO, a passive mode locking operation at a wavelength of ∼1.91 µm is shown to be achievable from a ring cavity. Stable picosecond pulses are readily obtained at a repetition rate of 15.9 MHz. This demonstration confirms that GO is a cost-effective saturable absorber applicable for ∼2 µm ultrafast pulse generation.