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Meta 2010 & FEM 2010 – Rome, 13-15 December 2010 Optical performances of micron-sized CMOS image sensors using metallic planar lenses Rino Marinelli and Elia Palange Università degli Studi dell’Aquila, Dipartimento di Ingegneria Elettrica e dell’Informazione L’Aquila, Italy – E-mail: rino.marinelli@univaq.it CMOS image sensors equipped with metallic planar lenses have been designed and simulated by CST Microwave Studio. The increase of the spatial resolution of CMOS image sensors implies the reduction of their pixel dimensions. It has been demonstrated that for pixel size smaller than 1.4 μm, diffraction effects become so significant to prevent the microlens from acting as a focusing element [1]. The research of different focusing components is, at present, a challenge for a further size reduction of the image sensor pixel. Recently, planar lenses based on aperiodic nanoslit arrays on metal films allowed subwavelength focusing [2]. In this communication, we will report on the design and simulation of micron-sized planar lenses simply formed by circular holes in a metallic layer. We will show that the proposed diffracting lenses with a lightpipe integrated in each pixel [3], make them suitable to replace the conventional microlenses in the CMOS image sensors and are compatible with their fabrication process. In Fig. 1 we show the CMOS image sensor model used for the simulations, the resulting pattern focusing and light confinement at �=633 nm and, finally, the normalized optical and cross-talk efficiency versus the pixel size. a) b) c) Figure 1 – a) The model of a 1.75 µm single pixel: gold layer is holed, 1.1µm in diameter. b) The z-component of the Poyting vector at λ=633 nm. c) Normalized optical and cross-talk efficiency calculated for 4 pixel model versus pixel size at 1.75-1.4-1.2-1 µm. References [1] Y. Huo, C. C. Fesenmaier, and P. B. Catrysse, “Microlens performance limits in sub-2μm pixel CMOS image sensor”, Opt. Express, 18, 5861-5872, 2010. [2] L. Verslegers, P. B. Catrysse, Z. Yu, J. S. White, E. S. Barnard, M. L. Brongersma, and S. Fan, “Planar lenses based on nanoscale slit arrays in a metal film”, Nanoletters, 9, 235- 238, 2009. [3] C. C. Fesenmaier, Y. Huo and P. B. Catrysse, “Optical confinement methods for continued scaling of CMOS image sensor pixels”, Opt. Express, 16, 20457-20470, 2008. 58
Meta 2010 & FEM 2010 – Rome, 13-15 December 2010 Second Harmonic Generation in Gold Nanoantennas Alessio Benedetti, Marco Centini, Concita Sibilia, Mario Bertolotti Dipartimento di Scienze di Base e Applicate per l'Ingegneria- Sez Fisica. Sapienza Università di Roma. Via A. Scarpa 16 00161 Roma – Italy E-mail: concita.sibilia@uniroma1.it The second order nonlinear response from flat metal screens has been widely investigated, both theoretically and experimentally, from the late 1960s–1980s [1]. The last few years witnessed renewed interest in the study of nonlinear second order properties of metal/dielectric composites thanks to the development of nanotechnologies and nanoscience. In this work we study the enhancement of SHG due to the interaction between two 3D metallic wires with sections of arbitrary shape, focusing on the effect of the surface morphology and defects. We also analyze the possibility of tailoring the emission pattern. Numerical calculations have been performed applying a Green's tensor method [2,3]. The SHG as a function of the wires cross section size is investigated in both the near and far field regimes. An accurate study of the effects related to the nonlinear surface contribution for the SHG process, and of the modification of the nonlinear scattering cross section (NLSCS) due to surface roughness in realistic samples has been performed. Figure 1a shows the sample description: we note that the shape can be arbitrarily modified to take into account for surface roughness and for discrepancies from perfect rectangular shape. In Figure 1b we plot the NLSCS for a gold nanoantenna calculated when a pump field consisting of a plane wave at 800 nm, polarized along the long axis direction of the rods is considered. e) b) Figure 1: a)Sample which takes into account the imperfections and roughnesses of the metal surface. b) 3D Nonlinear SH-Scattering Cross Section for a gold nanoantenna (λ=400nm). References [1] J. E. Sipe and G. I. Stegeman, V. M. Agranovich and D. L. Mills, eds. (North-Holland, 1982). [2] M. Paulus and O. J. F. Martin, J. Opt. Soc. Am. A 18, 854–861 (2001). [3] A. Benedetti et al., JOSA B 27, 3, 408-416 (2010)). 59
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Abstracts - Dipartimento di Elettronica Applicata

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