Passively q-switched fiber laser system and method for fabricating a saturable absorber of the system

A passively Q-switched fiber laser system comprising:

• a pump source for generating a pump beam;
• and
• a ring cavity for receiving the pump beam to generate a pulsed laser beam, wherein the ring cavity comprises a wavelength division multiplexer, a gain fiber, and a directional coupler connected in order, and a saturable absorber connected between the directional coupler and the wavelength division multiplexer, wherein the saturable absorber and the pump source are connected at the same end of the wavelength division multiplexer together,
• wherein, the gain fiber is doped with a rare earth ion and emits the pulsed laser beam at a wavelength region;
• wherein, the directional coupler has a connecting end and an output end, the connecting end is used to connect with the saturable absorber to form the ring cavity, the output end is used for the pulsed laser beam to emit out from the ring cavity,
• wherein, the saturable absorber is a lead sulfide quantum-dot polymer composite film, referred to as a PbS QD polymer composite film below, the PbS QD polymer composite film has a plurality of absorption bands comprising 1000 nm to 1100 nm and 1500 nm to 1600 nm, and the wavelength region of the gain fiber corresponds to one of the plurality of absorption bands, the PbS QD polymer composite film is fabricated by mixing a quantum dot material of lead sulfide with a colloidal polymer to form a mixture and drying the mixture, wherein, steps of drying comprise drying at a first temperature firstly and then drying at a second temperature, wherein the second temperature is higher than the first temperature.