Graphitic carbon nitrides (CNs) have appeared as a new type of photocatalyst for water splitting, but their optical properties (e.g., nonlinear absorption), to the best of our knowledge, have been seldom explored. Here, we report the saturable absorption effects of novel 2D carbon-nitride-type nanosheets and use them as saturable absorbers to passively mode-lock Yb-doped fiber lasers. The CN-based saturable absorber is manufactured by solution coating of 2D CN nanosheets on a gold mirror and has a modulation depth and saturation intensity of 12.5% and 7.5 MW/cm2, respectively. Two different output couplers are employed to construct ring laser cavities. With the 10% coupler, the mode-locked fiber laser produces pulses with duration of ∼310 ps, average power of 1.24 mW, and repetition rate of 7.65 MHz. The laser spectrum is centered at 1066 nm with a bandwidth of 2.4 nm. Increasing the coupling ratio to 50% improves the output power to 2.58 mW but at the same time broadens the pulse width to 420 ps. As a new kind of 2D material with strong saturable absorption, CN nanosheets will open a new way for novel photonic and optoelectronic devices.
An all-fiber passively Q-switched ytterbium-doped fiber laser (YDFL) was successfully achieved by using a single-walled carbon nanotube (SWCNT) as a saturable absorber (SA). The SWCNT was fabricated by pyrolyzing tripropylamine in the one-dimensional channel of zeolite single crystal (ZnAPO-5, framework type code: AFI). Zn 2+ metal cations were doped to promote the filling density and quality of the SWCNT. Subsequently, by incorporating the SA into an YDFL ring cavity, a stable Q-switched pulse train at 1039.4 nm with a repetition rate of 54.28 kHz was obtained when the pump power elevated to the starting threshold of 245 mW. It proved that this SWCNT@AFI SA can be used as an effective passively Q-switched for operation at 1.0 µm region.
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