Switchable dual-mode all-fiber laser by using LPG and FBG

We experimentally demonstrate a ring optical fiber laser with two order transverse modes output. The mode switch is realized by a special filter which is constructed by a cascaded long period grating (LPG) and fiber Bragg grating (FBG). The LPG and FBG are all written in the same two-mode fiber (TMF). By controlling the polarization state and the pressure applied in the LPG, three transverse modes output with two switchable wavelengths is achieved.