Switchable L‑band dual‑wavelength dark–bright pulse pair generation from an Er‑doped mode‑locked fber laser with SMF–GIMF–SMF as the saturable absorber

We have demonstrated the dual-wavelength domain-wall pulse operation in an Er-doped mode-locked fber laser based on single-mode fber (SMF)–graded index multimode fber (GIMF)–SMF as the saturable absorber for the frst time. The domain-wall dark–bright pulse pairs exhibited two peaks, which were located at 1604.6 and 1606 nm. The pulse repetition rate was maintained at 16.5 MHz throughout the dark–bright pulse pairs operation. Besides, dark–bright pulse pairs operation was demonstrated at a relative stability with the signal to noise ratio of 55.3 dB. Moreover, the dark–bright pulse pairs could be converted into bright–dark pulse pairs by adjusting the polarization state, which has potential advantages for the development of wavelength division multiplexing and optical fber sensing technology.