Directly exfoliated and imprinted graphite nano-particle saturable absorber for passive mode-locking erbium-doped fiber laser

By directly brushing and scribing an ultra-thin (< 5-μm thick) polymer polyvinyl alcohol (PVA) film on one end-face of a FC/APC connector in erbium-doped fiber laser (EDFL), and then imprinting it with the graphite nano-particles exfoliated from a graphite foil, the intra-cavity graphite nano-particle based saturable absorber can be formed to induce passive mode-locking effect in the EDFL. Such a novel approach greatly suppresses the film-thickness induced laser-beam divergent loss to 3.4%, thus enhancing the intra-cavity circulating power to promote the shortening on mode-locking pulsewidth. The saturable absorber with area coverage ratio of graphite nano-particles is detuned from 70 to 25% to provide the modulation depth enhancing from 11 to 20% and the saturated transmittance from 27 to 60%. Optimizing the coverage ratio reduces the non-saturable loss to 40% and enhances the modulation depth to 21%, such that the sub-ps soliton mode-locking can be initiated to provide a chirped pulsewidth of 482 fs and a linewidth of 2.87 nm