## 1 Introduction  
Fiber lasers have been of increasing interest because of their reliability, low-cost and performance efficiency. In the 1.55 \(\upmu\)m wavelength range, fiber lasers have been extensively studied due to their advantages of relatively \"eye safe\" operation and good free-space and fiber guided transmission with low losses. These advantages make them attractive to develop high power fiber lasers for applications in industrial manufacturing, medical surgery, optical communications and light detection and ranging (LIDAR). Fiber lasers based on Erbium doped fiber (EDF) have been widely investigated [1; 2; 3]. EDF exhibits efficient laser emission with excellent beam quality in single-mode laser systems. However, the low single-mode pump power provided by laser diode sources with core-pumping techniques, limits the output power of the laser emission when single-clad fibers are used [4; 5]. The advent of double-clad fibers (DCF) allowed the development of reliable high-power fiber lasers with single-mode emission without the use of a single-mode pump source. By using cladding-pumping technique it is feasible to achieve power scaling of rare-earth doped fiber lasers with a multi-mode pump source [6]. Therefore, has been demonstrated that DCF-based lasers can provide emission with high efficiency, good beam quality and heat dissipation at high output power performance [7; 8; 9]. The aforementioned advantages make DCF-based cladding pumped fiber lasers attractive to replace bulk solid-state lasers for high power applications. Particularly, Er/Yb DCFs (EYDCF) have been attractive for high power fiber lasers operating in the 1.55 \(\upmu\)m wavelength range [4; 5; 7; 10]. In a EYDCF-based laser, the pumping absorption of erbium ions is significantly improved due to the wide cross section area of ytterbium ions and non-radiative energy transference between erbium and ytterbium ions [11]. With the use of an EYDCF as gain medium, the erbium broad emission bandwidth can provide high gain over an extended wavelength range in the 1.55 \(\upmu\)m region which makes EYDCF-based fiber lasers attractive for the design of high-power tunable sources. In EDF lasers at low pump power, the complete population inversion is not maintained over the entire length of the fiber. Then, the gain medium acts as a saturable absorber. The EYDCF core is highly co-doped with ytterbium to improve pump absorption and reduce ion pairs formation but not eliminated [10]. The erbium ion pairs excitation causes a ground state depletion resulting in laser pulsations at relaxation frequency of population inversion. The increase of pump power level replenishes the population inversion at a faster rate, then, the frequency of the SQS pulses is increased. This pulsing has typical shapes and characteristics of passive Q-switched pulses. Therefore, the technique to obtain these pulses is usually called self-Q-switching (SQS). Different approaches of SQS fiber laser have been reported [12; 13; 14]. On the other hand, efficient operation of tunable fiber lasers can be achieved by using fiber Bragg gratings (FBG) as wavelength spectral filters. The central wavelength of the FBG can be displaced by temperature or mechanical strain application [15; 16]. Then, FBGs are reliable devices for wavelength tuning of the generated laser lines of fiber lasers [17; 18; 19]. Continuous wave (CW) tunable dual-wavelength fiber lasers with high-efficiency have been of persistent interest for design of pump sources for 2 \(\upmu\)m laser emission, nonlinear effect research, free-space instrumentation and sensing, LIDAR and terahertz generation. However, rare-earth doped fibers are homogeneous gain media at room temperature resulting in a strong competition between the two generated laser lines that leads to unstable laser generation. Stable dual-wavelength laser emission can be obtained through an adjustment of intra-cavity losses.