L-Band switchable dual-wavelength erbium-doped fiber laser based on a multimode fiber Bragg grating

In this letter, a simple, switchable dual-wavelength erbiumdoped fiber laser operating in L-band is successfully proposed and demonstrated. The two wavelengths are specified by a Bragg grating formed in multimode fiber and the wavelength separation is 1.7 nm. The multimode section including the multimode fiber grating selects not only the lasing wavelengths but also the polarization states of the lasing lines. Stable dualwavelength operation can be achieved due to the spatial mode beating effect induced by a single-mode /multimode/ single-mode fiber combination structure. By simple adjustment of a polarization controller, the proposed laser can operate in stable dual-wavelength or switch between two wavelengths, all at room temperature.