科研之友
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摘要
A photonic nanojet (PNJ) is a highly confined light beam formed by a transparent particle under light wave illumination. Here, we propose and numerically investigate the PNJ formed by a dielectric circular toroid with micro dimensions and a homogenous refractive index. Three-dimensional finite-difference time-domain (FDTD) simulations are conducted and demonstrate that ultralong PNJs can be formed by the doughnut-like structure. Besides, microtoroid structures can allow high-index materials (n = 3.5) for PNJ generation. Various PNJ properties, including the focal distance, PNJ length, full width at half-maximum, and maximum intensity, can be flexibly tuned by modifying the geometry of the proposed structure.
