Tight light localization in a hyperbolic secant planar slit lens

Abstract

We show by FDTD simulation that a photonic-crystal hyperbolic secant binary microlens in silicon (with the refractive index n=3.47) of size 2 μm × 5 μm with a slit 50 nm wide and 250 nm long can focus a plane TM-wave into a near-surface focal spot of size λ/23 with a 44% diffraction efficiency. The focus intensity is 60 times higher than the incident wave.