Generation and modulation of off-axis photonic nanojets via gradient-index microcylinders

This work presents an innovative exploration of generating and modulating off-axis photonic nanojets (PNJs) using gradient refractive index (GRIN) microcylinders with asymmetric profiles. The modulation effects of refractive index gradient, average refractive index, environmental factors, and microcylinder rotation on off-axis PNJ properties are systematically investigated. Results show that the refractive index gradient is the core parameter for controlling PNJ deflection angles: increasing the gradient enhances off-axis displacement while reducing peak intensity and extending decay length. The average refractive index primarily influences PNJ spatial distribution, with higher values creating more compact jets and stronger field intensities. Dynamic modulating of off-axis PNJ is achieved by rotating the GRIN orientation. In low-refractive-index-contrast liquid environments, PNJs exhibit abnormal phenomena such as curved beams, revealing significant environmental influences. This work expands the control dimensions of PNJs beyond traditional axial constraints, providing new, to the best of our knowledge, solutions for multi-angle optical detection, optofluidic tweezers, and micro/nano-fabrication.