Creating discrete cylindrical vector beams using coherently combined fiber arrays

Abstract

A novel method is presented for beam shaping far field intensity distributions using coherently combined fiber arrays. Traditionally, coherent arrays have been composed of linearly polarized elements having their polarization vector along a common axis. In this novel method, the fibers are arranged uniformly on the perimeter of a circle, and the linearly polarized beams are oriented with their polarization vectors arranged in a cylindrical fashion such that each subsequent vector is rotated by 2π/N where N is the number of elements on the circle. The elements each have the same Gaussian intensity distribution and power. The ensemble yields a far field intensity pattern that is a good approximation to a cylindrical vector (CV) beam which is characterized by a nonuniform polarization distribution and a null in the center of the beam. These synthetically created CV beams, or discrete cylindrical vector (DCV) beams, can be represented in a closed form solution to predict the far field intensity distributions. This solution is shown to agree with experimental results where several values of N, the number of elements, were tested. In addition, some more complex geometries such as nested geometries, fractal geometries, and some nonuniform geometries have been simulated, all of which also have a central null in the beam and have a nonuniform polarization distribution. These results are in contrast to linearly polarized beams, where the intensity peaks on axis, and from traditional cylindrical vector beams, which are generated by a single laser cavity.