We show theoretically and experimentally that the wavelength tunability of an Er3+–doped fiber laser is improved by using a twofold filter combining a Mach-Zehnder interferometer and a polarimetric filter. This new filter allows us to tune continuously the wavelength from 1.53 to 1.56 µm without the discontinuity associated to the narrow transmission bands of a Mach-Zehnder tuning filter.