We report a ring cavity passively harmonic mode-locked fiber laser using a newly developed thuliumbismuth co-doped fiber (TBF) as a gain medium in conjunction with a carbon nanotube (CNT)-based saturable absorber. The TBF laser generates a third harmonic mode-locked soliton pulse train with a high repetition rate of 50 MHz and a pulse duration of 1.86 ps. The laser operates at 1 901.6 nm with an average power of 6.6 mW, corresponding to a pulse energy of 0.132 nJ, at a 1 552 nm pump power of 723.3 mW. OCIS codes: 320.0320, 140.0140.

We report a ring cavity passively harmonic mode-locked thulium-doped fiber laser (TDFL) using a newly developed single-wall carbon nanotube-based saturable absorber. The TDFL generates the 25 th harmonic mode-locked stretched pulse train with a high repetition rate of 213 MHz and a pulse duration of 710 fs. The laser operates at 1901.6 nm with an average power of 1.89 mW, which corresponds to the pulse energy of 0.008 nJ, at 1552 nm pump power of 719 mW. The peak-to-background ratio is measured to be 60 dB, which indicates the stability of the laser.

We demonstrate a simple, compact and low cost Q-switched thulium-doped fiber laser (TDFL) operating at 1844.1 nm by exploiting a graphene based saturable absorber (SA) in conjunction with 1552 nm pumping. The SA is fabricated by sandwiching the graphene thin film between two fiber connectors. The thin film was produced by mixing graphene flakes, synthesized by an electrochemical exfoliation process, with polyethylene oxide (PEO) solution. The TDFL generates a stable pulse train with 6.73 kHz repetition rate, 11.41 μs pulse width and 90.64 nJ pulse energy at 513 mW 1552 nm pump power. A higher performance Q-switched TDFL is expected to be achieved with the optimization of the SA and laser cavity.

A stable passive Q-switched thulium-doped fibre laser (TDFL) operating at the 1900 nm region is demonstrated by using a multi-layer graphene film-based saturable absorber (SA). The graphene is synthesised by electrochemical exfoliation of graphite at room temperature in 1% sodium dodecyl sulphate aqueous solution. Graphene flakes obtained from the process are mixed with polyethylene oxide as the host polymer to produce free standing composite thin film which acts as a passive Q-switcher in the TDFL ring cavity. At 793 nm pump power of 186 mW, the TDFL generates an optical pulse train with a repetition rate of 7.5 kHz, pulse width of 19.7 μs and a pulse energy of 66.6 nJ. A higher performance Q-switched TDFL could be achieved with the optimisation of the graphene SA and the laser cavity.