Multi-wavelength passively Q-switched laser with Co2+:ZnSe thin film coated microsphere

We experimentally demonstrate an all-fiber passively Q-switched erbium-doped laser based on a microsphere resonator coated with Co2+:ZnSe film, which can achieve multi-wavelength pulse laser. With electron beam evaporation technology, the saturable absorber (SA) with a modulation depth of 55% was prepared by depositing Co2+:ZnSe film on the microsphere for the loss modulation of the laser cavity. The passively Q-switched output pulses were obtained by inserting the SA into the laser cavity and the narrowest pulse width of similar to 3 mu s was obtained. The fiber laser can stably output quintuple-wavelength laser pulses with a 3 dB bandwidth of similar to 0.1 nm. The wavelength interval of multi-wavelengths was stably maintained at similar to 1 nm and the smallest optical signal-to-noise ratio of similar to 10 dB at the pump power of 400 mW was measured. The signal-to-noise ratio was similar to 58 dB, which confirms excellent output stability. The results prove that it is a promising SA device to achieve passively Q-switched multi-wavelength pulse fiber lasers.