Nano-Optical Microlens with Ultra-Short Focal Length using Negative Refraction
B. D. F. Casse, W. T. Lu, Y. J. Huang, and S. Sridhar
Applied Physics Letters, V.93, P.053111 (2008)
We have experimentally realized an ultrashort focal length planoconcave microlens in an InP/InGaAsP semiconductor two-dimensional photonic crystal with negative index of refraction n = -0.7. At wavelength 1.5 microns, the lens exhibits ultrashort focal lengths of 12 microns (~ 8x wanelength) and numerical aperture close to unity. The focused beam has a near diffraction-limited spot size of 1.05 microns (~ 0.68 wavelength) 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 emiconductor heterostructure platforms for next-generation optoelectronic applications.