Passively Mode-Locked Ytterbium-Doped Fiber Laser With Cylindrical Vector Beam Generation Based on Mode Selective Coupler

We propose and demonstrate, for the first time to the best of our knowledge, a passively mode-locked ytterbium-doped fiber laser generating cylindrical vector beams (CVBs) using a mode selective coupler (MSC) as the transverse mode converter and splitter, and a semiconductor saturable absorber mirror for mode-locking. According to the coupling mode theory and the phase matching principle, the MSC was fabricated by weakly fused technology, having a low loss of about 0.5 dB and achieving LP11 mode with a high purity of >96%. The CVB fiber laser operates at a center wavelength of 1042.3 nm, with a 3 dB spectral width of 1.5 nm. The repetition rate of the mode-locked laser pulses is 18.58 MHz. The radially and azimuthally polarized vector beams can be switched by adjusting the polarization controllers in the fiber ring cavity, with a high mode purity measured to be >95%. The mode-locked CVB ytterbium-doped fiber laser has potential applications in optical tweezers, optical imaging, etc.