A 1- $\mu$ m Cylindrical Vector Beam Fiber Ring Laser Based on a Mode Selective Coupler

We propose and demonstrate a continuous-wave all-fiber ring laser generating cylindrical vector beams (CVBs) using a mode selective coupler (MSC) as transverse mode converter and mode splitter. The MSC is fabricated by a novel method free of pre-tapering, achieving LP11 mode with a high purity of >96% near the wavelength of 1064 nm. The CVB fiber laser operates at a center wavelength of 1053.9 nm, with a 3-dB linewidth of less than 0.04 nm and a signal-to-background ratio of >60 dB. The laser slope efficiency is >9%. The radially and azimuthally polarized beams can be switched by adjusting the polarization controllers in the fiber ring cavity, with a high mode purity measured to be >96%.