Low Contrast Sub-wavelengths Grating Lenses
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Low Contrast Sub-wavelengths Grating Lenses Mao Ye1 and Ya Sha Yi1,2* 1
Integrated Nano Optoelectronics Laboratory, University of Michigan, Dearborn, MI 48128, U.S.A. 2 Energy Institute, University of Michigan, Ann Arbor, MI 48109, U.S.A. *[email protected] ABSTRACT In this work, we have demonstrated the light concentration from zero-contrast gratings (ZCG) subwavelength structures and compared the light concentration properties of previously proposed high-contrast gratings (HCG) to the ZCG micro concentrating lenses. To address the challenges of potential HCG fabrication, the difference between ZCG and HCG micro lenses is investigated numerically and found both of these subwavelength grating structures have similar light concentration characteristics. To gain deeper understanding of this phenomenon, we have explored the light concentration formation process and discussed the concentration mechanism in detail. Our work will be promising to provide a new ZCG micro lens potentially with easier and more controllable fabrication and could be utilized for various integrated nanophotonics applications, from optical cavities, read/write heads and concentrating photovoltaics. INTRODUCTION Concentrating lens is one of the most important components for photovoltaics. The nanoscale subwavelength grating structure has been investigated widely as it promises a series of applications in integrated nanophotonics. Low contrast gratings, such as Zero-contrast gratings (ZCG) based on guided-mode resonance (GMR) structures [1,2] and high-contrast grating (HCG) [3,4], were investigated as wideband reflectors. These types of subwavelength structures have potential in many applications including optical filters [5], sensing [6, 7], and photodetectors [8], offering flexible tunability of resonance wavelength and high Q factor. Until recently, nanorod arrays (NRAs) with high aspect ratio has attracted wide attention for its potential applications such as antireflection, self-cleaning and superhydrophobicity [9-12]. Dry etching technique is one most favorable method due to its excellent controllability and compatibility with the CMOS technology. Both vertical and transverse etching in most dry etching processes, such as reactiveion-etching (RIE) technique normally requires good control of etching rate to achieve good selectivity over underneath thin film. Based on coupled-wave diffraction method [13], various micro lenses have been designed, from traditional dielectric lenses to plasmonic lenses [14]. Among all the micro lenses, subwavelength structure designs based on recently proposed HCG structures [3, 4] has gained most attention as it is compatible with planar CMOS integration process while has excellent light focusing properties. However, the HCG structures normally requires the high index contrast at
Downloaded from https:/www.cambridge.org/core. University of Arizona, on 28 Apr 2017 at 10:21:05, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2017.152
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