Black phosphorus (BP) is a very promising two-dimensional material as a saturable absorber for ultrashort pulse generation especially in telecommunication bands due to its ultrafast dynamic response and strong resonant absorption in the near-infrared wavelength range. However, the current fabrication methods of BP saturable absorbers are very complex and not suitable for practical large-scale production. We have successfully deposited BP with a thickness of ∼25 nm onto the fiber end facet as a saturable absorber by a simple optically driven deposition method. The BP saturable absorber shows excellent mode-locking performance with a stable pulse train repetition of 1.843 MHz and pulse duration of 117.6 ns.
We have investigated the broadband saturable absorption property of graphene–Bi2Te3 heterostructures and demonstrated their applications for stable harmonic mode-locking operation in a Yb-doped fiber laser and wavelength-tunable Q-switching operation in an Er-doped fiber laser. The modulation depth of a graphene–Bi2Te3 heterostructure saturable absorber (G-Bi2Te3-SA) is dependent on the coverage of Bi2Te3 on the graphene. By using 15%-Bi2Te3-covered G-Bi2Te3-SA with a modulation depth of 23.28% and saturable intensity of 3.32 MW/cm2, the harmonic mode-locked Yb-doped fiber laser outputs the mode-locked pulses with a pulse duration down to 189.94 ps, spectral bandwidth of 3.5 nm, and repetition rate of 79.13 MHz (21st order of the fundamental frequency). After inserting the G-Bi2Te3-SA with 85% coverage of Bi2Te3 on graphene into Er-doped fiber laser cavity, whose modulation depth and saturable intensity are about 40.79% and 12.48 MW/cm2, respectively, the wavelength-tunable Q-switched pulse with tunable wavelength range over 13.2 nm has been obtained by adjusting the intracavity fiber filter. These results suggest that the graphene–Bi2Te3 heterostructure could serve as a high nonlinear photonic device for practical applications.
The optical response and plasmon coupling between graphene sheets for graphene/polymer multilayer heterostructures with controlled separation were systematically investigated. Anomalous transmission of light was experimentally observed in mid-infrared range. The position of the broad passband in the transmission spectra was observed to red-shift with the increase of the number of layers.