Switchable multi-wavelength mode-locked linear-cavity fiber laser of cylindrical vector beam

We have proposed and demonstrated a switchable multi-wavelength passively mode-locked linear-cavity fiber laser to generate cylindrical vector beam (CVB) pulses by using a semiconductor saturable absorption mirror (SESAM). A home-made broadband long-period fiber grating (LPFG) and two cascaded polarization-maintaining fiber Bragg gratings (PMFBGs) are used as mode converter and wavelength selectors, respectively. This fiber laser can be switched among four different single-wavelength and two different dual-wavelength lasing oscillations with CVB output. The laser has a mode-locking threshold value of 33.55 mW and delivers CVB pulses with duration of hundreds of picoseconds. The purity of the CVB is measured to be 94.1%. This laser can have some important applications in mode division multiplexed (MDM) systems and wavelength division multiplexed (WDM) systems in the future.