Orbital angular momentum detection of vortex beams by #-type lines

OAM detection of vortex beams using #-type lines is presented. In the far-field distribution of #-type line diffraction, the primary diffraction spots associated with the OAM of the beam can be easily distinguished because these diffraction spots contain the main beam energy (over 64%) with respect to the diffraction spots formed via small apertures; the diffraction spots formed from small apertures contain less than 1% of beam energy, which remains for the beams with a topological charge above the 7th order, and are severely disturbed by second-order diffraction spots. Therefore, #-type line OAM detection is especially applicable for measuring the vortex beams with weak intensities, such as long-distance transmitted vortex beams; these beams possess the potential to greatly impact the development of remote free-space optical communication. Moreover, the structure of the #-type lines is simple and can be adjusted according to the beam size, and the OAM detection range can reach 30.