The method for removing splits in the phase singularity of an optical vortex generated by a spiral mirror

This study discusses method for removing splits in the phase singularity of an optical vortex generated by the spiral mirror in the millimeter-wave regime from a numerical calculation perspective. The splits of the phase singularity occurs when the mirror surface has a structure where the height varies linearly with azimuthal angle theta. It is demonstrated that a new design method can eliminate the phase singularity split. This mirror surface is formed by satisfing the condition where the difference between the incident equiphase front of Gaussian beam and the desired reflected equiphase front of optical vortex is constant. Furthermore, this method can also generate optical vortices with arbitrary focal point.