Discrimination of incoherent vortex states of light

Coherence vortex (CV) states provide a new way for optical manipulation and communication. As a promising option for increasing the data-transmission capacity, CV multiplexing warrants investigation. However, few studies have focused on discriminating and sorting CV states with different topological charges. In this work, we examine the cross-spectral density (CSD) of a CV state embedded in an incoherent light field and so-called incoherent vortex (ICV). Given a multiplexed ICV, we propose a method to recognize the constituting single ICVs therein. Our analytical results, which are derived according to the coherence theory and the paraxial propagation law and are given in analytical forms, show that the CSD can reveal the topological charge spectrum of a multiplexed incoherent Laguerre-Gaussian mode. This proposal can be used for free-space communication and remote sensing where light fields with low coherence are preferable to completely coherent beams.