The linear-circular polarization transfer in a caustic vector optical field

Manipulating an optical field is especially required when light can be controlled by light itself, with novel properties emerging in connection with the optical beam having complex structures. Research on a structured light and the optical angular momentum has cultivated a new, vigorous and distinctive interdisciplinary area, with strong interest and activity worldwide. In this work, a caustic vector optical field is experimentally generated and demonstrated by the caustic-based approach. In our approach, we enable the caustic vector optical field to be space-variantly modulated in both phase and arbitrary polarization states in the field cross-section with acceleration trajectories during propagation. The optical field propagates in the curve trajectory during propagation due to the effect of the caustic phase. The dynamic inversion of the linear-circular polarization in a caustic vector optical field under free-space propagation is analyzed in detail. The underlying physics of the phenomenon is discussed according to the coherent superposition of the polarization. Our study reveals that the different spin angular momentum flux distributions (including opposite directions) in different positions in the cross-section of the caustic vector optical field can be dynamically managed during propagation by purposely choosing the initial polarization state distribution and the initial caustic phase. This work provides an approach to dynamically manipulate the evolution of the polarization state distribution in the cross-section of an optical field during propagation. The presented approach opens the possibility of multi-manipulating the spin optical angular momentum fluxes and the polarization state in the field cross-section, leading to more complex manipulation of the optical field scenarios, and thus further expanding the functionality of an optical system.