Mechanically Exfoliated Graphite Onto D-Shaped Optical Fiber for Femtosecond Mode-Locked Erbium-Doped Fiber Laser

For the first time, we report a femtosecond mode-locked Erbium-doped fiber laser (EDFL) by using mechanically exfoliated graphite deposited onto a D-shaped optical fiber. The exfoliated graphite flakes were deposited onto a stacked polyvinyl alcohol/polymethyl methacrylate thick layers, and then transferred directly to the polished surface of the D-shaped optical fiber. The characterization of the exfoliated graphite sample was performed by using optical microscope and Raman spectroscopy. By measuring its polarization performance, polarization relative extinction ratio about 5.30 dB (70%) was obtained, which resulted in the broadest bandwidth of 21 nm and the shortest pulse duration of 220 fs generation as saturable absorber (SA) into an EDFL cavity. For our knowledge, these are the best mode-locking performances ever reported in the literature for all-fiber-based graphite SA in EDFL.