A tunable erbium-doped fiber laser based on an MZ interferometer and a birefringence fiber filter

A tunable erbium-doped fiber laser (TEDFL) is proposed and demonstrated by using a Mach–Zehnder interferometer (MZI) and a birefringence fiber filter (BFF) incorporating ∼6 cm high birefringence (Hi-Bi) fiber. Theoretical analysis of the filtering function based on the Jones matrix has been performed. In this laser system, a section of 9 m erbium doped fiber (EDF) serves as the gain medium. With the MZI defining the tuning step, the lasing wavelength can be discretely tuned by modifying the filtering characteristics of the BFF with the polarization controllers (PCs). The tuning range achieves 30 nm with a power uniformity of less than 2 dB, and a side-mode suppression ratio (SMSR) of ∼40 dB. The power fluctuation and wavelength variation at 1556.26 nm are observed to be less than 0.5 dB and 0.04 nm, respectively.