Synergistic modulation of edge diffraction with a coaxial OAM beam for reconfigurable photonic nanojet generation

This work presents a strategy for the dynamic generation of reconfigurable photonic nanojets (PNJs) by illuminating a dielectric microcylinder with a coaxial orbital angular momentum beam. It is demonstrated that simultaneous control of the topological charge and the beam waist enables deterministic programing of the PNJ morphology. The topological charge dictates the form: with integer <i>ℓ</i>, the PNJ evolves from a symmetric jet into a defined double-lobe structure; and with fractional <i>ℓ</i>, it produces an off-axis asymmetric PNJ for |<i>ℓ</i>|<1 and a high-intensity axial nanojet enclosed by an irregular annular field for |<i>ℓ</i>|>1. Concurrently, the dynamic adaptation of the beam waist is essential to maintain edge diffraction efficiency across all states. This synergistic modulation paradigm offers a versatile and efficient platform for dynamic optical manipulation.