Two-versus-three-dimensional rigorous simulations comparison: the modal dependence of a photonic nanojet.

Photonic Nanojets (PNJ) have demonstrated their interest in many applications where sub-wavelength resolution is required. Initially achieved with dielectric micro-particles, they can now also be realized using a lensed fiber. To study these fiber microlenses, 2D electromagnetic simulations are often used as a simplified model to approximate real 3D cases. We show by rigorous electromagnetic simulation that due to the modal dependency of this light interaction, this approximation has minimal relevance. More generally, PNJ microlenses behave as an open cavity, and their modal dependency explains why the PNJ properties do not depend monotonously on the microlens properties, which is key knowledge for their design.