Intersecting of circular apertures to measure integer and fractional topological charge of vortex beams

Diffraction patterns of optical vortex beams (VBs) by differently shaped apertures are used to determine their topological charge (TC). In this paper, we show by simulations and experiments that diffraction of a Laguerre-Gaussian (LG) beam by intersecting circular apertures can be used to reveal the TC. The presented aperture structure has the advantage of the measurement of fractional TC in addition to the integer, sensitivity to the sign of TC, and low sensitivity to adjusting apertures. Accordingly, in addition to the integer TC up to 8, the fractional TC is measured with a step of 0.1 by two intersecting circular apertures (TICA). By examining a wide range of similarity criteria between the diffraction pattern of the fractional TC and the pattern of the lower integer TC, three metrics for measuring the fractional TC are found. Furthermore, the determination of integer TC up to 6 for three intersecting circular apertures (THICA) is demonstrated.