Properties of silicon integrated photonic lenses: bandwidth, chromatic aberration, and polarization dependence

We analyze the properties of silicon integrated photonic lenses based on scattering optical elements. The devices have been inverse-designed by combining genetic algorithms and the multiple scattering theory. These lenses are able to focus an infrared plane wave front on a position freely determined during the design stage. The nanofabricated silicon integrated lenses have proved effective over a large range of wavelengths, measured to be of the order of 100 nm. The lenses show chromatic aberration, with a displacement of the position of the focus measured to be higher than 1.5 mu m when the wavelength varies from 1500 to 1600 nm. Moreover, we analyze the polarization of the focused beam thanks to a polarization-sensitive scanning near-field optical microscope. The measurements show that the lenses focus on a definite point only for the design's polarization. The properties of these lenses enable them to assume the function of a nanofocusing device in silicon-on-insulator integrated optics. (C) 2013 Society of Photo-Optical Instrumentation Engineers (SPIE)