Characterization of multi-wavelength Q-switched fiber laser by changing wavelength separation of filter

In this paper, we present a simple compact and low threshold laser that has characteristics of Q-switched and multi-wavelength oscillation simultaneously. Multi-wavelength Q-switched oscillation is realized by inserting a Sagnac filter as a multi-wavelength filter and a section of unpumped erbium-ytterbium co-doped fiber (EYDF) into the laser cavity as a saturable absorber (SA). The characteristics of multi-wavelength Q-switched fiber laser affected by wavelength separation of filter and pump power are investigated. The number of Q-switched wavelengths increases and the wavelength separation of the laser reduces with wavelength separation of the filter decreasing. Stable multi-wavelength oscillations at wavelength separation of 0.4–0.8 nm were obtained by increasing the length of polarization maintaining fiber (PMF) in the Sagnac filter. Moreover, the number of wavelengths and wavelength separation are increased by increasing the pump power when the filter is fixed. Further, the multi-wavelength laser is verified to have Q-switched properties at each wavelength, which is filtered from laser output through a narrow-band tunable filter outside of the cavity.