Nano-optical microlens with ultrashort focal length using negative refraction

Abstract

We have experimentally realized an ultrashort focal length planoconcave microlens in an InP/InGaAsP semiconductor two-dimensional (2D) photonic crystal with negative index of refraction (−0.7). At λ=1.5 μm, the lens exhibits ultrashort focal lengths of 12 μm (∼8λ) and numerical aperture close to unity. The focused beam has a near diffraction-limited spot size of 1.05 μm (∼0.68λ) at full width at half maximum. The negative refractive index and focusing properties of the microlens are confirmed by 2D finite-difference time-domain simulations. Such ultrarefractive negative-index nano-optical microlenses can be integrated into existing semiconductor heterostructure platforms for next-generation optoelectronic applications.