Design of multicore photonic crystal fibers to generate cylindrical vector beams

We propose a method to generate cylindrical vector beams (CVBs) using a specially designed multicore photonic crystal fiber (PCF). In a PCF with six cores arranged symmetrically around the fiber axis, the light fields in the cores present different polarization states, promising the compositions of vector modes. By introducing small defect airholes in the cladding region and enlarging airholes around the cores to control the mode polarizations, azimuthally and radially polarized modes are obtained separately with low propagation loss and high mode selectivity. In addition, the operation wavelength range of the vector beams can be tuned simply by adjusting the diameters of air-holes inside the cladding defect. The far fields of the fiber outputs are studied as well, which show perfect CVBs with hollow-core intensity profiles. The PCF-based CVB-generator could make the applications of vector beams much more convenient by extending it into the all-fiber structure.