High-sensitivity spectroscopic gas sensor using optimized H1 photonic crystal microcavities
Lazhar Kassa-Baghdouche
Abstract
An optimized H1 photonic crystal (PhC) microcavity with a high quality factor ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mspace width="negativethinmathspace"/> <mml:mi>Q</mml:mi> </mml:math> ), small mode volume, wide measurement range, and high sensitivity is proposed, and its possibility in spectroscopic gas sensing is theoretically demonstrated. In the proposed structure, we have taken advantage of the air holes surrounding the defect region to optimize the resonance characteristics so as to detect the target gas, which is required for designing miniaturized spectroscopic gas sensors. By fine-tuning the structural parameters of several ring air holes surrounding the defect region, the results show that the sensitivity can be up to 3303 nm/RIU, along with a high <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mspace width="negativethinmathspace"/> <mml:mi>Q</mml:mi> </mml:math> of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>4</mml:mn> </mml:msup> </mml:mrow> </mml:math> and a detection limit as low as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> RIU for gas sensing. Also, it is theoretically verified that the optimized H1 PhC microcavity has the ability to maintain RI sensitivity over a wide RI range of gases, enabling detection of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mi>e</mml:mi> </mml:msub> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">N</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">C</mml:mi> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">C</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">C</mml:mi> </mml:mrow> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mn>8</mml:mn> </mml:msub> </mml:mrow> </mml:math> gases. The main feature of this structure is that the enhanced electrical field is strongly localized in the defect region for any gas sample due to a small mode volume. Therefore, these findings provide useful design rules for applications involving compact and tunable spectroscopic gas sensor devices with high <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mspace width="negativethinmathspace"/> <mml:mi>Q</mml:mi> </mml:math> and sensitivity.