<inline-formula> <tex-math notation="TeX">$L_{n}$</tex-math></inline-formula> Slot Photonic Crystal Microcavity for Refractive Index Gas Sensing

Abstract

We propose and experimentally demonstrate a series of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$L_{n}$</tex-math></inline-formula> slot photonic crystal (PhC) microcavities, which operate as refractive index (RI) gas sensors. The cavities are simply composed of a silicon slab triangular photonic crystal with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$n$</tex-math></inline-formula> holes replaced by a slot, which do not require sophisticated design or high fabrication resolution. With the increase in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$n$</tex-math></inline-formula> , the quality factor of the cavity exponentially increases, which is explained by the envelope of electric field approaching a Gaussian profile. An <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$L_{9}$</tex-math></inline-formula> slot PhC microcavity with a quality factor exceeding 30 000, sensitivity of 421 nm per RI unit (RIU), and detection limit down to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$1\times 10^{-5}$</tex-math></inline-formula> RIU was experimentally demonstrated. The performance of the device is comparable with other fine-tuned PhC microcavity structures. Due to its simple structure and high fabrication tolerance, it could have wide applications in optical sensors.