Numerical study of an efficient light focusing nano-coupler based on C-shaped waveguides

Abstract

International audienceWe present an FDTD simulation study of a new design of light focusing nano-coupler consisting of a tapered succession of C-shaped silver waveguides. Its operation is based on the use of the fundamental guided mode <span class="mathjax-tex"&gt<span class="MathJax_Preview" style=""&gt</span&gt<span class="MathJax" id="MathJax-Element-1-Frame" tabindex="0" style="position: relative;" data-mathml="<math xmlns=&quot;http://www.w3.org/1998/Math/MathML&quot;&gt<mi&gtT</mi&gt<msub&gt<mi&gtE</mi&gt<mrow class=&quot;MJX-TeXAtom-ORD&quot;&gt<mn&gt10</mn&gt</mrow&gt</msub&gt</math&gt" role="presentation"&gt<nobr aria-hidden="true"&gt<span class="math" id="MathJax-Span-1" style="width: 2.455em; display: inline-block;"&gt<span style="display: inline-block; position: relative; width: 2.202em; height: 0px; font-size: 111%;"&gt<span style="position: absolute; clip: rect(1.422em, 1002.2em, 2.568em, -1000em); top: -2.252em; left: 0em;"&gt<span class="mrow" id="MathJax-Span-2"&gt<span class="mi" id="MathJax-Span-3" style="font-family: MathJax_Math; font-style: italic;"&gtT<span style="display: inline-block; overflow: hidden; height: 1px; width: 0.12em;"&gt</span&gt</span&gt<span class="msubsup" id="MathJax-Span-4"&gt<span style="display: inline-block; position: relative; width: 1.52em; height: 0px;"&gt<span style="position: absolute; clip: rect(3.174em, 1000.76em, 4.154em, -1000em); top: -4.004em; left: 0em;"&gt<span class="mi" id="MathJax-Span-5" style="font-family: MathJax_Math; font-style: italic;"&gtE<span style="display: inline-block; overflow: hidden; height: 1px; width: 0.026em;"&gt</span&gt</span&gt<span style="display: inline-block; width: 0px; height: 4.004em;"&gt</span&gt</span&gt<span style="position: absolute; top: -3.854em; left: 0.738em;"&gt<span class="texatom" id="MathJax-Span-6"&gt<span class="mrow" id="MathJax-Span-7"&gt<span class="mn" id="MathJax-Span-8" style="font-size: 70.7%; font-family: MathJax_Main;"&gt10</span&gt</span&gt</span&gt<span style="display: inline-block; width: 0px; height: 4.004em;"&gt</span&gt</span&gt</span&gt</span&gt</span&gt<span style="display: inline-block; width: 0px; height: 2.252em;"&gt</span&gt</span&gt</span&gt<span style="display: inline-block; overflow: hidden; vertical-align: -0.239em; border-left: 0px solid; width: 0px; height: 1.05em;"&gt</span&gt</span&gt</nobr&gt</span&gt</span&gt<span class="mathjax-tex"&gt</span&gt. Thanks to the optimization of the structural design parameters, we have demonstrated numerically that this compact coupler enables a sub-wavelength light focusing with a transmission coefficient of 65% and a coupling efficiency of 77% that have higher values than the optimized designs reported in the literature. We also show that our structure is an efficient functional coupler at multiple wavelengths when used in a periodic grating as well as an isolated device. This could pave the way for the development of a new generation of metamaterials for guidance and detection applications