Higher-order Poincaré Spheres and Spatio-Spectral Poincaré Beams

The study of fundamental optics effects has been stimulated through the increasing ability to structure light in all its degrees of freedom (DOFs) in sophisticated but simple experimental settings. However, with such an increase in experimental capabilities, it has also become important to study theoretical descriptions for a more intuitive understanding of the underlying concepts. Here, we introduce a visual representation of light that is structured in its transverse space, frequency, and polarization in the form of a higher-order Poincaré sphere and discuss interesting links to its fundamental counterpart. We further leverage this connection to discuss and experimentally generate light possessing all possible polarization states across its spatio-spectral shape, which we term spatio-spectral Poincaré beams. By invoking all DOFs of light in the powerful description of higher-order Poincaré spheres, our work can pave the way for a deeper understanding and beneficial application of structured light as a powerful tool in optics.