All-fiber wavelength tunable passively mode-locked erbium-doped ring laser

An all-fiber, wavelength-tunable, passively mode-locked erbium-doped ring laser is presented. Erbium-doped fibers (EDF) are used as the gain media because of their large gain bandwidth. Nonlinear polarization rotation (NPR) plays the dual role of realizing mode-locking and effectively adjusting the intensity-dependent loss of the cavity. An unbalanced Mach-Zehnder interferometer (UMZI) is used as a tunable optical beam filter. By using the UMZI and adjusting the polarization controllers (PCs), a sub-picosecond mode-locking laser is realized that is self-starting with central lasing wavelengths that can be accurately tuned over a range of about ~ sim 30 nm and also has controllable spacings between different tunable wavelengths.