A switchable femtosecond and picosecond soliton fiber laser mode-locked by carbon nanotubes

We propose a switchable dual-scale nanotube-mode-locking fiber laser based on a fiber loop mirror and fiber Bragg grating. The loop mirror not only works as a broadband reflector, but also a birefringence-induced filter. By adjusting the polarization controller in the loop, the operation wavelength can be switched between 1530 and 1560 nm. The femtosecond soliton at 1560 nm has a bandwidth of 5.5 nm and pulse duration of 680 fs, while the picosecond soliton is centered at 1529.5 nm with the bandwidth of 0.11 nm and pulse duration of 23.3 ps. The dual-scale solitons display more than 30 times a difference of pulse width, as well as distinct spectral bandwidth, repetition rate, and pulse energy. Our study provides the flexibly switchable ultrashort pulse sources at femtosecond and picosecond scales, which are suitable for practical applications.