Improving the beam quality in LMA fibers

The paper presents the results concerning with beam quality improvement by concurrently modifying the index and the doping profile in LMA fibers. Further, the mode effective area is maximized by providing a passive ring in the cladding. The influence of the index profile over the distribution of the optical power among various modes is presented. The aim is to favor the fundamental mode by concurrently rejecting the higher modes, i.e. generating a quality beam. Simulation results and manufacturer's tests led to a novel design which consists in providing a passive ring in the cladding. That was of great help in rejecting the higher-order modes, and it can be applied to a large range of LMA fibers. The cladding ring procedure is of interest for Liekki, and it is very likely that it would be put into production.