Continuously bandwidth-tunable pulse generation from a SWNT mode-locked fiber laser

The continuously bandwidth-tunable pulse generation in the SWNT mode-locked fiber laser is achieved by only tuning the intracavity polarization state. By introducing the in-line polarizer with 2-meter-long polarization maintaining fiber pigtails in a typical ring fiber laser, a bandwidth-tunable SWNT mode-locked fiber laser is constructed. The mode locker is the single-wall carbon nanotube saturable absorber, which is fabricated by optical deposition in the ~0.27 w.t % ultrasonic carbon nanotube alcohol solution. By only tuning the intracavity polarization controllers, the spectral bandwidth is continuously tuned in the range of 0.94 to 3.04 nm. We attribute the upper limit of the spectral bandwidth to the limit of the free spectral range determined by Lyot filter, which consists of polarization controllers and in-linepolarizer in the cavity. These results provide a simple way to achieve bandwidth-tunable subpicosecond pulse, which should be attractive to the applications requiring ultrafast sources with tunable bandwidth or pulsewidth.