Wavelength switchable and tunable noise-like pulses from a 2 μm figure-eight all-fiber laser

We propose the generation of wavelength switchable and tunable noise-like pulses (NLPs) in 2 μm all-fiber laser mode-locking with nonlinear amplifier loop mirror technique. An properly segment of ultra-high numerical aperture fiber is inserted in the cavity to reduce the pump power required for achieving mode-locking at different wavelengths, and a suitable length of single mode fiber is employed to induce more intracavity birefringence. By increasing the pump power and adjusting the intracavity polarization state, the fiber laser can deliver NLPs with switchable wavelengths between 1979.4 nm and 2003.8 nm. Based on the spectral filter effect induced by fiber birefringence, continuous wavelength tunable NLP operation at these two wavebands can be achieved by adjusting polarization controllers. The center wavelength of NLP can be continuously tuned from 1952.1 nm to 1999.0 nm and from 2002.6 nm to 2014.4 nm, with corresponding spectral tuning ranges of 46.9 nm and 11.8 nm, respectively. This wavelength switchable and tunable NLP fiber laser has great potential in fiber sensing and industrial processing.