In this work we demonstrate comprehensive studies on graphene oxide (GO) and reduced graphene oxide (rGO) based saturable absorbers (SA) for mode-locking of Er-doped fiber lasers. The paper describes the fabrication process of both saturable absorbers and detailed comparison of their parameters. Our results show, that there is no significant difference in the laser performance between the investigated SA. Both provided stable, mode-locked operation with sub-400 fs soliton pulses and more than 9 nm optical bandwidth at 1560 nm center wavelength. It has been shown that GO might be successfully used as an efficient SA without the need of its reduction to rGO. Taking into account simpler manufacturing technology and the possibility of mass production, GO seems to be a good candidate as a cost-effective material for saturable absorbers for Er-doped fiber lasers.

Low-dimensional materials, due to their versatile properties are very interesting for numerous electronics and optoelectronics applications. Recently rediscovered black phosphorus, with a graphite-like structure can be exfoliated up to the single atomic layer. In contrary to graphene it possesses a direct band gap controllable by the number of stacked atomic layers. For those reasons, it is now intensively investigated. Here we demonstrate, that black phosphorus can serve as a broadband saturable absorber and can be used for ultrashort optical pulse generation.The mechanically exfoliated ~300 nm thick layers of black phosphorus were transferred onto the fiber core and under pulsed excitation at 1560 nm wavelength its transmission increases by 4.4%.It was used to generate 272 fs-short pulses at 1550 nm and 739 fs at 1910 nm. The obtained results shows that black phosphorus can be effectively used for ultrashort pulse generation and proves its great potential to future applications.

We report, for the first time to our knowledge, the usage of black phosphorus (BP) as a saturable absorber for the mode locking of a thulium-doped fiber laser. We have experimentally shown that BP exhibits saturable absorption in the 2 μm wavelength range and supports ultrashort pulse generation. The saturable absorber was based on mechanically exfoliated BP deposited on a fiber connector tip. The laser was capable of generating 739 fs pulses centered at 1910 nm. Our results show that BP might be considered as a universal broadband saturable absorber that could successfully compete with graphene or other low-dimension nanomaterials.

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