Enhanced subwavelength photonic nanojet focusing via a graded-index round-head microcylinder

Abstract

Photonic nanojet is a sub-wavelength focus generated by a dielectric microparticle, like microsphere and microcylinder. The formation of nanojet can be tuned by changing the refractive index distribution and geometrical parameters of the structure. Many applications based on photonic nanojet have been explored based on the special property of dielectric microparticles. In this letter, a graded-index structure that combines hemisphere and microcylinder is proposed, which can generate a sub-wavelength nanojet with a full width at a half maximum of 120.9 nm (0.24 λ with 500 nm illumination wavelength). The influences of refraction index distribution and the length of cylinder on the properties of photonic nanojet are simulated and discussed. Moreover, the sensitivity of fabrication errors is analyzed to verify the feasibility of this structure.