Tunable Photonic Nanojet Formed by A Two-Layer Dielectric Microcylinder

A photonic nanojets (PNJs) is a highly confined light beam that focuses from the shadow side of microparticles. In this simulation work, we report the realization of a tunable PNJ, which is formed by an engineered two-layer dielectric microcylinder. The key parameters, maximum intensity, length of PNJ and full-width at half maximum (FWHM), of photonic nanojets (PNJs) are studied. Finite difference time-domain (FDTD) analysis shows that under 400nm illumination, a PNJ with a high quality factor of 145.78 is achieved. We find that the photonic nanojets can be tuned by changing the distance between two layers of dielectric microcylinder. Because of its simple structure and flexibility, it has potential applications in optical imaging, nanolithography, and nanoparticle manipulation.