In recent years, Q-switched multi-wavelength fiber lasers emitting at the 1-μm wavelength band have been attracting growing attentions for their broad application prospects in optical sensing, optical signal processing, wavelength division multiplexing (WDM), and accurate surface measurement [1], [2], [3], [4]. Besides utilizing the nonlinear optical effects [5], [6], [7], [8], other common approaches to generate the multiple wavelengths oscillation in fiber lasers are to integrate various types of comb filters including polarization maintaining fiber Bragg gratings (PM-FBGs) [9], [10], Mach–Zehnder interferometers [11], [12], Sagnac ring mirrors [13], [14], and fiber Fabry–Pérot filters [15], [16]. The simple and reliable PM-FBG scheme is particularly interesting as it introduces the polarization hole burning effect in the cavity, which may suppress the mode competition [17], [18] that is concerned for most multi-wavelength fiber lasers.

Q-switched multi-wavelength fiber lasers at ∼1-μm have been explored in various measures. A tri-wavelength, passively Q-switched, Yb-doped fiber laser (YDFL) was reported with a zinc-oxide-nanoparticle film as the saturable absorber (SA) in 2018 [19]. Another passively Q-switched dual-wavelength YDFL was demonstrated utilizing a SA based on carbon nanotubes that were embedded in polyethylene oxide film also in 2018 [20]. In 2019, a switchable and tunable multi-wavelength fiber laser, trigged by the black phosphorus SAs, was proposed and realized for both Q-switching and mode-locking [21]. However, the related works have been mostly focused on passive Q-switching while there is little study on multi-wavelength fiber lasers that are actively Q-switched, particularly in the 1-μm band. Comparing with passive Q-switching, the active scheme with an acousto-optic modulator (AOM) possesses the extra advantage of more precise and flexible parameter control for lasing pulsation.

In this paper, we experimentally demonstrate an all-fiber Q-switched multi-wavelength laser at ∼1064 nm with switchable combinations of wavelength. A piece of Yb-doped fiber (YDF) serves as the gain medium that is pumped by a continuous-wave (CW) laser diode at 980 nm. An AOM triggers the Q-switched laser pulses in a ring cavity. Two cascaded PM-FBGs are employed for wavelength control, resulting in a total of 15 states of emissions including single-, dual-, tri-, and quad-wavelength status in the lasing operation with excellent spectral stability. To the best of our knowledge, such an actively Q-switched, multi-wavelength YDFL based on a cascaded PM-FBG pair has not been reported to date.