Focusing of light by negative refraction in a photonic crystal slab superlens on silicon-on-insulator substrate.

We experimentally demonstrate the light focusing by negative refraction in a photonic crystal slab superlens at wavelengths lambda of 1.26-1.42 microm. The photonic crystal slab was fabricated on silicon-on-insulator substrate with an interface structure optimized for low reflection and diffraction losses. The light focusing in the photonic crystal slab was clearly observed through the intentional out-of-plane radiation or scattering of guided light in the slab. The minimum focused spot width was limited to 1.8 microm(1.4 lambda) owing to aberrations. The focusing characteristics were in good agreement with those obtained from photonic band and finite-difference time-domain analyses.