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Abstract A thermo-optically controllable fiberized saturable absorber (SA) that is based on a combination of graphene oxide (GO), a thermo-optic polymer adhesive, and a thermo-electric temperature controller (TEC), is proposed and experimentally demonstrated. By incorporating the SA into an all-fiberized erbium-doped fiber (EDF) ring cavity, an operation-state-switchable fiber laser is successfully implemented. The operation state of the laser is shown to be switchable from a continuous wave (CW) to the Q-switching state to the harmonic mode-locking state depending on the current that is applied to the TEC under a fixed pump-power condition. As a function of the applied current, the temporal width and the repetition rate of the Q-switched pulses varied from ~5.54 μs to ~12.35 μs and from ~ 31.02 kHz to ~17.25 kHz, respectively. The maximum pulse energy is ~52.8 nJ. In the harmonic-mode-locking state, the 19th order of the harmonic-mode-locked pulses was generated. The pulse width was measured as ~595 fs with a pulse-repetition rate of ~237.5 MHz. It is believed that the operation-mode change is due to the variations of the insertion loss and the beam-polarization status of the implemented SA that are due to the temperature-variation-induced refractive-index changes of the thermo-optic polymer. [ABSTRACT FROM AUTHOR]

The potential of Fe 3 O 4 nanoparticles as a base material for saturable absorbers (SAs) that can operate in the 2 μm-wavelength regime, was investigated. An SA was fabricated on a sandwich-structured fiber-ferrule platform through the deposition of an Fe 3 O 4 mixture with polyvinyl alcohol (PVA) onto the end surface of the fiber ferrule. Using the prepared Fe 3 O 4 /PVA-composite-based SA within a Tm-Ho codoped fiber laser, stable Q-switched pulses were readily produced at 1894 nm. The temporal characteristics of the output pulses were investigated as a function of the pump power, and the maximum energy of the output pulses was 322 nJ. The temporal width of the output pulses was measured as 2.6 µs at the maximum pulse-repetition rate of 37.2 kHz. The output performance of the passively Q-switched Tm-Ho-codoped fiber laser in this work was compared with those of recently demonstrated, passively Q-switched Tm-doped fiber lasers for which the other types of saturable-absorption materials. [ABSTRACT FROM AUTHOR]