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Photonic nanostructures for robust far-field coupling to high-Q whispering-gallery mode optical resonators (Conference Presentation)
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Paper Abstract

The light confinement properties of high quality (Q) factor microtoroid whispering-gallery mode (WGM) optical resonators prevent efficient coupling between far-field radiation and the WGM. Instead, light is most commonly evanescently coupled to the WGM using optical fibers that have been tapered to micron-scale thickness. These tapers, however, break easily and are sensitive to environmental vibrations and fluid flow fluctuations. This limits their effectiveness in mass-produced and/or field-portable biochemical sensing applications. Here we present a gold nanorod grating as an experimentally-feasible alternative for robust coupling of free-space light to a microtoroid resonator, and we simulate its performance with a novel finite-element 3D beam envelope method. 3D simulations of the full system are not tractable due to its large size. Previously, simulations of nanostructures on microtoroids have been performed on a thin wedge of the 3D system with perfect electrical conductor (mirror) boundary conditions. While these simulations provided some insight, they do not accurately model typical travelling-wave WGM experiments because they can only simulate standing waves. The standing wave nodes and antinodes significantly alter interactions between the WGM and the nanostructure. In our new method, we use a small wedge domain with custom boundary conditions that accurately simulate the travelling wave and nanophotonic interactions. Using this approach, we have designed and simulated a grating for far-field WGM coupling. With the grating, it is possible to maintain a high Q-factor of 3×10^6. We anticipate that our proposed modeling approach can solve a variety of other nanoparticle-microtoroid coupled systems in the future.

Paper Details

Date Published: 8 March 2019
Proc. SPIE 10927, Photonic and Phononic Properties of Engineered Nanostructures IX, 109270W (8 March 2019); doi: 10.1117/12.2509311
Show Author Affiliations
Lei Chen, Beijing Univ. of Posts and Telecommunications (China)
The Univ. of Arizona (United States)
Cheng Li, The Univ. of Arizona (United States)
Mohammad Hosain Teimourpour, The Univ. of Arizona (United States)
Yumin Liu, Beijing Univ. of Posts and Telecommunications (China)
Judith Su, The Univ. of Arizona (United States)
Euan McLeod, The Univ. of Arizona (United States)

Published in SPIE Proceedings Vol. 10927:
Photonic and Phononic Properties of Engineered Nanostructures IX
Ali Adibi; Shawn-Yu Lin; Axel Scherer, Editor(s)

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