Wavelength switchable all-fiber mode-locked laser based on nonlinear multimode interference

Abstract We report a switchable single wavelength and dual-wavelength all-fiber ultrafast mode-locked lasers based on nonlinear multimode interference (NL-MMI) effect of graded-index multimode fiber (GIMF). The saturable absorber (SA) used in the laser is composed of tapered fiber-GIMF-tapered fiber. The use of tapered fibers not only reduces the dependence on the length of GIMF, but also simplifies the fabrication of SA. The modulation depth of the SA was measured to be 9%. By adjusting intra-cavity loss and the polarization controllers properly, traditional switchable single wavelength and dual-wavelength mode-locking can be realized. Meanwhile, a single wavelength harmonic soliton molecule mode-locking can be observed, and the central wavelength with the same modulation period can be switched between 1558 nm and 1531 nm. Such a switchable harmonic soliton molecules mode-locked laser with wide wavelength intervals could be useful in measuring chemical reactions, and has rarely been reported.