Tunable fiber laser based on a cascaded structure consisting of in-line MZI and traditional MZI

A tunable erbium-doped fiber（EDF） laser with a cascaded structure consisting of in-line Mach-Zehnder interferometer（MZI） and traditional MZI is proposed. The transmission spectrum of the in-line MZI is modulated by the traditional MZI, which determines the period of the cascaded structure, while the in-line MZI＇s transmission spectrum is the outer envelope curve of the cascaded structure＇s transmission spectrum. A stable single-wavelength lasing operation is obtained at 1 527.14 nm. The linewidth is less than 0.07 nm with a side-mode suppression ratio（SMSR） over 48 d B. Fixing the in-line MZI structure on a furnace, when the temperature changes from 30 ℃ to 230 ℃, the central wavelength can be tuned within the range of 12.4 nm.