A new type of Yb3+ doped fiber with an octagonal-shaped core

A new type of Yb3+ doped fiber with an octagonal-shaped core is fabricated based on MCVD and solution doping techniques. We compare this type of fiber with the traditional circle core fiber theoretically, founding that the octagonal-shaped core fiber has smaller fundamental mode area when they have the same doped area. Besides, the higher order modes almost distribute around the corner of the octagon, which is promising to couple the higher order modes out of the core if eight side cores are placed near the corners, like a 3C fiber. Based on the new type of fiber in the size of 10/130 mu m, a CW fiber laser is set up, exhibiting a 7.25W output with a slope efficiency of 80%.