Characterization of underwater propagated optical singular beams through self-interference

The spatial modes of structured optical fields, especially singular beams, have attracted significant interest in optical communication due to their multiple degrees of freedom, including phase, amplitude, and polarization. However, the feasibility of their singularity characterization in underwater environments remains largely unexplored. Here, we demonstrate the underwater propagation characteristics of singular structured beams by applying a self-referenced interferometric technique for their characterization. Unlike conventional interferometry, the self-referenced approach enables stable and efficient phase characterization without requiring an external reference beam, making it particularly suitable for underwater environments. Vortex and Bessel-vortex beams were used as representative singular beams to assess the feasibility. The obtained results demonstrate the capability of self-interferometry to characterize phase singularities after underwater propagation, supporting its potential for future underwater optical communication applications.