Subwavelength Grating Structure with High Aspect Ratio and Tapered Sidewall Profiles
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Subwavelength Grating Structure with High Aspect Ratio and Tapered Sidewall Profiles W. Yu1, D. Wu1, X. Duan2, and Y. Yi1, 2* 1
University of Michigan, MI
2
Massachusetts Institute of Technology, Cambridge, MA
*e-mail: [email protected]
Abstract CMOS-compatible fabrication and etching processes are often used in subwavelength grating structures manufacturing, it normally generates tapered sidewall profile of the gratings. In this work, we have studied the impacts on resonance mode characteristics of subwavelength grating structures due to the tapered sidewall profile, as well as grating with high aspect ratio. Our simulation results have revealed that both of these two factors play important roles on the resonance mode behavior of subwavelength grating devices. We also discussed the mechanism between the guided mode resonance and the grating cavity mode resonance. Our study will provide guidance for a series of integrated photonics devices applications, such as compact optical filter, photonics amplifier, and lasers, while the realistic subwavelength grating structure is considered.
INTRODUCTION The periodic subwavelength grating structure has been widely studied in the research of nanophotonics. Guided mode resonance (GMR) [1-2] or resonance utilizing high-contrast gratings (HCG) [3-5] was both investigated. This type of structure has potential in many applications including light filters [6], optical sensing [7-8], and detectors [9], by offering advantages of flexible tunability of resonance wavelength and high quality factor. In recent years, nanorod arrays (NRAs) with high aspect ratio has attracted much attention for its potential applications such as antireflection, self-cleaning and superhydrophobicity [10-11]. This type of structure can be obtained by various template-assisted etching fabrication techniques. Dry etching technique is one most favorable method due to its excellent controllability and compatibility with the CMOS technology. This method normally gives tapered sidewall profile of gratings instead of straightly vertical gratings, which was neglected mostly by previous studies. To our best knowledge, previous studies mostly focus on vertical sidewall profile and small grating height (under 400 nanometer). In this work, we have performed numerical simulation utilizing the subwavelength nanorod arrays with tapered sidewall profile and high aspect ratio on the glass substrate to study the impacts on device GMR behavior. We have numerically demonstrated that the GMR can be coupled into the grating cavity mode when increasing the grating height, and an extraordinary field enhancement with enhancement factor as large as 900 is obtained. Finite difference time domain (FDTD) simulation has been performed to investigate
1693 Downloaded from https:/www.cambridge.org/core. Cornell University Library, on 18 Apr 2017 at 08:08:02, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2015.32
the generation of the coupling resonance field
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