A Direct Formula for Ultra-Large Effective Area Fibers Design With Top-Hat Intensity Profile

In this paper, we present a new refractive index profile, in simple easy to use equation form, which allows the design of large mode area (LMA) single mode (SM) optical fibers with the special property of supporting “perfect top-hat” mode profiles. The few parameters of this formula define the refractive index profile of such fibers. We show the effect the parameters of the refractive index profile have on the desired mode field. By applying this direct formula, we avoid the use of complex inverse refractive index reconstruction methods, or time-consuming iterative design processes. We demonstrate this formula with a number of example designs of LMA SM optical fibers with perfect flat-top electric field profile and an effective mode area (Aeff) size that in some cases exceeds the 4800 μm
²
. We expect such LMA SM top-hat fiber design to be useful for the mitigation of non-linear effects and catastrophic optical damage, as well as for achieving uniform intensity deposition on the target (material, biological tissue, and so on) in high-power applications. The results presented here are testing the validity of the refractive index profiles for non-ideal designs so as we can determine the tolerance to manufacturing such fibers.