A fiber ring laser is provided, which includes an optic amplifier, a first optical coupler (OCP), a second OCP, a first fiber ring, a second fiber ring, a first polarization controller (PC), and a second PC. The first fiber ring is coupled to the optic amplifier, the first and the second OCPs. The second fiber ring is coupled to the first and the second OCPs. The optic amplifier amplifies a first laser beam with a specified wavelength range. The first fiber ring receives the first laser beam. The first and the second fiber rings respectively provide a first and a second resonant cavities. The first and the second PCs respectively control polarization states of the first and second resonant cavities. The first laser beam resonates in the first and the second resonant cavities to generate a second laser beam with a first and a second wavelengths.