Analysis of multilevel spiral phase plates using a Dammann vortex sensing grating

Optical vortices can be easily generated using a multilevel spiral phase plate (SPP). However the quality of the generated vortex beam depends on the number of phase segments. We review the theory for this multilevel SPP using a Fourier expansion of integer topological charged vortices. We then experimentally examine the validity of this expansion using a fabricated Dammann vortex diffraction grating spectrum analyzer. The Dammann vortex diffraction grating is fabricated using SU-8 photoresist on glass substrate and yields uniform diffraction efficiency across a desired number of diffracted orders. Experimental results show the extra angular harmonics of a multilevel SPP and agree with the theory.