## 5 MTEFL Experimental Results and Discussion  
Stability tests were conducted to evaluate the performance of the MTEFL ring-type array at room temperature (25 \({}^{\circ}\)C). A total of 31 recordings were taken over 90 min to assess stability. The results of the stability test for the corresponding tuning and switchable emission lines are summarized for single, dual-narrow, and dual configurations in Table 1 and for quadruple and triple lines in Table 2. For the tunable emission lines (Figures 11-13), stability analysis focuses on the initial and final lines. In Table 1, we observe that during the tuning process, the fluctuations in power and wavelength are as follows: for single  
Figure 10: Double-emission signal (state-e). (**a**) Tuning and most significant power peaks, (**b**) separation comparison, (**c**) peaks power comparison, (**d**) sensitivity generated with the curvature/ wavelength samples. lines, less than 0.87 dB and 0.26 nm; for dual-narrow lines, 1.11 dB and 0.2 nm; and for dual lines, 1.01 dB and 2.57 nm. In Table 2, the stability measurements for the switchable lines (Figures 14 and 15) show power and wavelength fluctuations of less than 2.85 dB and 0.53 nm for quadruple lines and 2.86 dB and 0.68 nm for triple lines, respectively. Table 3 presents a comparison of the reported performance of fiber lasers with other studies on tunable and multi-wavelength fiber lasers. [PERSON] et al. [11] reported single- and dual-line emissions using a thulium-doped ring-cavity fiber laser based on a Sagnac loop. This setup involved 1.6 m of TCF in an MZI filter, achieving a tunable range of 40 nm and 13 nm, with an SMSR of 32.68 dB and 33.5 dB, respectively. In another study, [PERSON], [PERSON] et al. [36] achieved a range of 12.6 nm for a single line, boasting an SMSR of 55.2 dB, and they reported five emission lines. The primary characteristics of our \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**State**} & \multirow{2}{*}{**Figure**} & \multirow{2}{*}{**Curvature** (\(\mathbf{m^{-1}}\))} & \multirow{2}{*}{**Emission** **Lines**} & \multirow{2}{*}{**Wavelength** (\(\mathbf{nm}\))} & \multicolumn{2}{c}{**Max Wavelength**} & \multicolumn{1}{c}{**Max Peak Power**} \\  & & & & **(nm)** & & **Fluctuation** (\(\mathbf{nm}\))} & **Fluctuation** (dB)** \\ \hline a & Figure 11 & 2.5871 & Single & \(\lambda_{1}\) & 1556.40 & 0.10 & 0.87 \\  & & & \(\lambda_{89}\) & 1564.50 & 0.26 & 0.78 \\ d & Figure 12 & 0.2670 & Dual & \(\lambda_{1\text{A}}\) & 1573.70 & 0.20 & 0.78 \\  & & & Dual & \(\lambda_{1\text{B}}\) & 1564.50 & 0.10 & 1.11 \\  & & & narrow & \(\lambda_{14\text{A}}\) & 1561.30 & 0.09 & 0.81 \\  & & & & \(\lambda_{14\text{B}}\) & 1562.20 & 0.08 & 0.78 \\ e & Figure 13 & 0.7453 & Dual & \(\lambda_{1\text{A}}\) & 1572.53 & 2.00 & 0.67 \\  & & & & \(\lambda_{1\text{B}}\) & 1585.69 & 2.26 & 0.68 \\  & & & & \(\lambda_{1\text{A}}\) & 1563.68 & 1.97 & 1.01 \\  & & & & \(\lambda_{41\text{B}}\) & 1576.88 & 2.57 & 0.78 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Tunable laser emission lines, stability testing guidance and highlights. Figure 11: (**a**) Stability test of the single initial and final emission, (**b**) power variation, (**c**) wavelength variation.