Switchable dual-transverse-mode all-fiber laser with a mode selective filter

A ring optical fiber laser which can output two order transverse modes at two different wavelengths respectively is experimentally demonstrated. The mode switch and the wavelength switch are realized through a special filter which is constructed by cascading a long period grating (LPG) and a fiber Bragg grating (FBG). The LPG and the FBG are all formed in the same two-mode fiber. By controlling the polarization state of the light injected into the LPG and the pressure applied to the LPG, the outputs of the two order transverse modes at either of two switchable wavelengths are achieved in the port of Out. 2. Moreover, the ring optical fiber laser can work as a three-wavelength selective laser with the fundamental mode output when the output port is set as Out. 1.