Hexagonal close-packed arrays of optical fibers for partitioning a laser beam into individual beamlets: Analysis and prototype fabrication

Abstract

Hexagonally close-packed arrays of optical fibers were investigated for partitioning a laser beam into individual beamlets for distribution to remote and variously located regions for experimental purposes. Equations were derived giving the efficiency of coupling the laser beam into the fibers as a function of the fiber cross section geometry and the number of fibers in a given hexagonal array, assuming that the laser beam just filled the outermost fibers in the array. The analysis was done also for the case in which a small lens was used in conjunction with each fiber in the array. For the lens fiber combination, the effect of spherical aberration was calculated and equations were derived giving the location and radius of the so-called circle of least confusion as a function of the lens geometry. The effects of aberration were also compared with the calculated diffraction limited focal spot size for a lens in the array. The effect of misalignment of a lens relative to the laser beam was analyzed with regard to the efficiency of energy coupled into the mating fiber. A prototype array was fabricated utilizing a hexagonal array of 61 fibers.