## 3 Experimental Results  
In this research, the FSR variation is achieved by adjusting the axial position of the prism through the movement of the micrometer head of the TDLI. The main function of the TBF is to filter out wavelengths other than 1527 nm to 1534 nm, and it is also used to ensure laser output by filtering a wider range of wavelengths when the laser wavelength spacing is small. Additionally, the power faults at the edges of the interferometric pattern indicate the areas where the TBF filters are applied. In addition, the OSA is set up with a spectral sampling range of 10 nm and 2001 points. Figure 3 shows various types of dual-wavelength lasers shaped by the Figure 1 architecture. Figure 3 shows the dual-wavelength laser with variable wavelength spacing by adjusting the interferometric pattern position and FSR size of the TDLI and filtering out the unnecessary wavelengths with the TBF. The wavelength spacing between the two wavelengths in the dual-wavelength laser varies from smallest to largest, which are 0.5 nm, 1.71 nm, 2.55 nm, and 3.35 nm. The wavelength positions of the dual-wavelength lasers are listed from smallest to largest wavelength spacing, which are 1530.15 nm and 1530.65 nm (light blue pattern); 1529.54 nm and 1531.25 nm (light green pattern); 1529.23 nm and 1531.78 nm (dark current pattern); and 1528.72 nm and 1532.07 nm (yellow pattern), respectively. Moreover, the wavelength spacing variation of the dual-wavelength laser is adjusted according to the position of 1530.4 nm as the center, and the difference between the midpoint of the wavelength intervals of the dual-wavelength lasers from the smallest to the largest wavelength spacing and 1530.4 nm is 0 nm, 0.005 nm, 0.105 nm, and 0.005 nm, respectively. It can be noticed that no matter how the FSR varies, the wavelength position of the laser is always situated at the half-upper-waist of the lobe. It is also clear that the multiple interferences generated by the BS form a burr in the main interference pattern, which is caused by the amplification of the EDFA. It is also clear from the subfigure of Figure 3 that the wavelength positions of the dual-wavelength lasers with different spacings are highly overlapped with the peaks of the multiple interferences generated by the BS. This means that the sub-interferences generated by the BS deepen the spatial hole-burning effect, and the laser generation position is more likely to fall in the node of the half-upper-waist of the lobe, where it also overlaps with the peaks of  
Figure 2: (**a**) The spectrum shows multiple FP interferences resulting from the combination of two BS and the primary interference caused by TDLI with different FSRs by virtue of reflections from the end face of the fiber head. The EDFA emits light from port 1 into the TDLI, which is then reflected by port 3 and the BS into port 2 for observation by the OSA. (**b**) Transmission spectra of two-phase complementary interferences formed by TDLI and spectral characteristics of a multi-wavelength laser capable of output in the Figure 1 framework. The EDFA emits light, which passes from ports 3 to 2 and 1, respectively, and then yellow and blue line interferograms can be obtained with the OSA, respectively. the sub-interferences. As a result, the displacement between 1530.4 nm and the center point of the interval in a dual-wavelength laser with a wavelength spacing of 2.55 nm is larger. Figure 3b illustrates a dual-wavelength laser with staggered positions of several wavelengths. The laser configurations exhibit wavelength spacings of 0.8 nm, 1.15 nm, and 1.42 nm, with corresponding wavelength positions of 1529.85 nm and 1530.65 nm (light green pattern); 1530.12 nm and 1531.27 nm (dark current pattern); and 1529.62 nm and 1531.04 nm (yellow pattern). It is noticeable that the midpoints of the wavelength intervals for the dual-wavelength lasers are distinct.