Measuring high-order orbital angular momentum based on a Microlens Array with sectorial subaperture

In this paper, a microlens array with sector sub-aperture (MLA-S) is proposed to measure the orbital angular momentum (OAM) of the vortex beam. This device has a circularly symmetric structure, which can well match the spiral phase, whose phase slope is also circularly symmetric. Furthermore, the spiral phase is split by the MLA-S, and each sub-wavefront can be approximated as a tilted wavefront. Thus, in the far field, the spot position can characterize the OAM information, and the displacement and displacement direction of the spot can determine the magnitude and sign of the OAM. In the experiments, perfect vortex beams are generated as measurement objects, and the measurement range can be up to ± 112 orders, with absolute measurement errors around 0.1. Meanwhile, for a multi-ring perfect vortex beam, in which each ring is loaded with a different OAM mode, these rings can be separated by MLA-S, and the OAM of each ring can be measured simultaneously, which is well demonstrated in the experiments. In addition, owing to the circular symmetry structure of the MLA-S, the partial error can be counteracted as the beam deviates from the center of the MLA-S. This research introduces a new technical way to measure the OAM, which is promising for some OAM-based applications.