Fig. 5: Arbitrary configuration of 2D optical skyrmion topological states and skyrmion numbers.
From: Topological state and number transitions of optical skyrmions upon free-space beam propagation

a, b Simulated the topological state of 2D optical skyrmion at different longitudinal positions z = 7.5 cm, z = 15 cm, z = 22.5 cm. c, d The corresponding simulated results of skyrmion number variation as a function of the propagation distance for a and b.