We demonstrate all-optical modulation based on ultrafast saturable absorption in graphene-covered-microfiber. By covering the microfiber surface with polydimethylsiloxane supported graphene film along the fiber length, a greatly enhanced interaction between the propagating light and the graphene can be obtained via the strong evanescent field of the microfiber. The strong light-graphene interaction results in high-speed, broadband all-optical modulation with maximum modulation depths of 5 dB and 13 dB for single-layer and bi-layer graphene, respectively. Such a graphene all-optical modulator is easy to fabricate, is compatible with optical fiber systems and has high potential in photonics applications such as all-optical switching and all-optical communications.

Graphene saturable absorbers (GSAs) have been widely applied in ultra-fast mode-locked fiber lasers. Thanks to the broadband advantage of graphene, we theoretically and experimentally demonstrate the variation of the modulation depth of GSA by employing the effect of cross absorption modulation. This method provides an easy and efficient way to modulate the characteristics of GSA. By varying the modulation power, we realize an all-fiber fundamental mode-locked fiber laser and a harmonic mode-locked fiber laser with tunable output pulse width. Results show that the output pulse widths of the two fiber lasers can be tuned more than 40%, and the lasers have high wide application potential on nonlinear optical bio-imaging and offer an advantageous front end for extreme-power laser technologies.

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We report a passively Q-switched and mode-locked erbium-doped fiber laser (EDFL) based on PtSe 2 , a new two-dimensional material, as a saturable absorber (SA). Self-started Q-switching at 1560 nm in the EDFL was achieved at a threshold pump power of 65 mW, and at the maximum pump power of 450 mW, the maximum single Q-switched pulse energy is 143.2 nJ. Due to the polarization-dependent characteristics of the PtSe 2-based SA, the laser can be switched from the Q-switched state to the mode-locked state by adjusting the polarization state. A mode-locked pulse train with a repetition rate of 23.3 MHz and a pulse width of 1.02 ps can be generated when the pump power increases to about 80 mW, and the stable mode-locked state is maintained until the pump power reaches its maximum 450 mW. The maximum single mode-locked pulse energy is 0.53 nJ. This is the first time to our knowledge that successful generation of stable Q-switched and mode-locked pulses in an Er-doped fiber laser has been obtained by using PtSe 2 as a saturable absorber.

We experimentally demonstrate an operation switchable Erbium-doped fiber laser by employing graphene saturable absorber (GSA) on microfiber. With the introducing of a polydimethylsiloxane layer, a graphene can be considered as a parallel plate on microfiber and induces different propagation losses to TE and TM modes. By the use of such polarization sensitive GSA on microfiber, Erbium doped fiber laser with switchable operation states such as continuous wave, stable Q-switching, Q-switched mode-locking, and continuous-wave mode-locking, can be achieved by simply tuning the polarization states in the laser cavity. Our results show that covering graphene on microfibers could be a promising method for fabricating all fiber SA, and may have high potential in wide applications.