Orange, Red and Deep Red Optical Vortex Mode Operation in Pr3+:Fiber Laser

Optical vortex carries an annular spatial form and an orbital angular momentum (OAM) assigned by a topological charge
$\ell$
owing to its helical wavefront, and it has been widely studied in a variety of applications, such as optical manipulation [1], optical communications [2], and material processing [3]. Visible optical vortex, in particular, is strongly required in underwater communications [4], and optical data storage [5] with the freedom of OAM.