This work for the first time reports the results on study of a polymer-free carbon nanotube (CNT) films used as a saturable absorber in an all-fibre laser. It is demonstrated that free-standing single-walled CNT films fabricated by an aerosol method are able to ensure generation of transform-limited pulses in an Er all-fibre ring laser with duration of several picoseconds and high quality of mode locking. The optimal average output power levels are identified, amounting to 0.4–0.5 mW depending on the linear transmission of the studied samples (60% or 80%). Application of polymer-free CNT films solves problems related to degradation of conventional polymer matrices of CNT-based saturable absorbers and paves the way to longer-lasting and more reliable saturable absorbers compatible with all-fibre laser configurations.

We report for the first time on study of a passively mode-locked Er-doped fibre laser with record-wide tuning (from 1524 to 1602 nm) of the central wavelength of its femtosecond output (503-940 fs). The recently proposed drop-shaped cavity topology for fibre lasers enabled a compact widely-tuneable femtosecond laser with a single discrete element, a reflective diffraction grating used for wavelength tuning of the output radiation. The key features of the proposed laser are: spectral tuning does not require adjustment of any other cavity elements; stable generation with a single pulse per round-trip is provided over the entire wavelength tuning range; the output pulses are close to transform-limited and feature relatively high (> 58 dB) signal-to-noise ratio of laser inter-mode beats indicating high quality of mode locking across the entire wavelength tuning range. The proposed laser configuration relying on the new drop-shaped cavity topology simultaneously delivers stability and reliability of mode locking, possibility of broad-range wavelength tunability, and adjustability of the output pulse repetition rate of the laser (which is important in various metrological and other applications).