## 4 Tunable and Switchable Performance
As depicted in Figure 9b,c, when combined with a gradual adjustment of the polarization state, this change facilitated the generation of five-wavelength (1559.59-1560.91-1561.58-1562.93-1563.61 nm) and six-wavelength (1560.25-1560.97-1561.63-1562.29-1562.98-1563.64 nm) laser oscillations with OSNR of 35 dB. The FSR between adjacent laser lines was measured to be approximately 0.66 nm. The maximum spectral distance achieved between laser lines was about 4.05 nm. Ensuring the stability of multi-wavelength laser emission is crucial for consistent performance across various applications. Stability characterization is essential for evaluating how the laser is affected by environmental conditions, which is critical to maintaining the integrity of the laser system and ensuring that outputs are consistently reliable and repeatable. For a detailed assessment of amplitude and wavelength stability, nine sequential scans of the lasing spectra were conducted at 5 min intervals, comprehensively covering all the obtained multi-wavelength spectra. Figure 10 illustrates the spectral distribution stability of a single laser oscillation at 1562.22 nm, showing high-intensity uniformity across the spectrum. Figure 10b shows a maximum wavelength shift of 0.01 nm, while Figure 10c presents output power fluctuations of less than 0.12 dB, reflecting consistent power. Figure 8: (**a**) Single-wavelength oscillation at 1562.22 nm, (**b**) dual-wavelength oscillation (1562.22–1562.875 nm), (**c**) triple-wavelength oscillation (1560.175–1562.22–1562.88 nm). Figure 11a presents the power spectrum of the dual-wavelength laser. The lasing lines centered at approximately 1562.22 nm and 1562.875 nm exhibit a wavelength shift of approximately 0.07 nm, as observed in Figure 11b. Figure 11c illustrates the power fluctuations of the two lasing lines, with maximum values of 1.11 dB and 0.25 dB, respectively. Figure 12 presents the power stability characteristics exhibited by the triple-wavelength laser system. An evaluation of the 1560.182 nm laser line reveals a maximum wavelength shift of 0.07 nm (Figure 12b) and a maximum amplitude fluctuation of 0.51 dB (Figure 12c). It is important to note that the remaining wavelengths in the triple-wavelength configura  
Figure 10: (**a**) Spectral distribution stability of a single laser oscillation at 1562.22 nm, with high-intensity uniformity across the spectrum, (**b**) a maximum wavelength shift of 0.01 nm, and (**c**) output power fluctuations of less than 0.12 dB. tion demonstrated power stability levels exceeding the measurement parameters, indicating superior performance for those specific lines. Additionally, the stability of the four-wavelength emission is presented in Figure 13. In this case, the maximum wavelength shift is approximately 0.022 nm for the wavelength at 1562.83 nm, indicated by the blue line with triangular markers in Figure 13b. This wavelength also exhibits the most considerable fluctuation in power, with a maximum variation of 3 dB, as shown in Figure 13c. Figure 11: (**a**). Stability of the dual-wavelength laser oscillation at 1562.22–1562.785 nm with uniform intensity, (**b**) a maximum wavelength shift of 0.07 nm, and (**c**) output power fluctuations of less than 0.25 dB. Figure 12: (**a**) Power stability of the triple-wavelength laser system, (**b**) maximum wavelength shift of 0.07 nm, and (**c**) maximum amplitude fluctuation of 0.51 dB for the 1562.88 nm line. Figure 13: (**a**) Power stability of the quadruple-wavelength laser system, (**b**) maximum wavelength shift of 0.22 nm, and (**c**) maximum amplitude fluctuation of 3 dB for the 1562.83 nm line. For the following quintuple-wavelength and sextuple-wavelength stability analyses, as shown in Figures 14 and 15, the maximum wavelength shift of 0.07 nm was estimated at 1562.93 nm (indicated by the pink dotted line in Figure 14b). The maximum amplitude deviation recorded was 1.7 dB for the wavelength of 1561.58 nm, as depicted in Figure 14c.