Dark pulses with tunable repetition rate emission from fiber ring laser

We demonstrated the experimental observation of the dark pulses with tunable repetition rate from an erbium-doped fiber ring laser. A considerable length of high nonlinear fiber is incorporated into the fiber ring laser to enhance the nonlinear intensity. In our experiment, both bright and dark pulses can be observed under the conditions of appropriately setting of the device in the cavity. Further study showed that the dark pulse is formed due to the cross coupling between two different lasing wavelengths. Particularly, dark pulse-train with multiple repetition rates was observed from the laser cavity and the repetition rate switchable operation can be realized by simply adjusting the polarization controller (PC) in the cavity. The operation of multiple repetition rates of dark pulses was further experimentally investigated and detected as a result of pulse splitting of each component with different wavelength.