Abstract
Abstract. Plasmonic waveguides have attracted much attention owing to the associated high field intensity at the metal–dielectric interface and their ability to confine the modes at the nanometer scale. At the same time, they suffer from relatively high propagation loss, which is due to the presence of metal. Several alternative materials have been introduced to replace noble metals, such as transparent conductive oxides (TCOs). A particularly popular TCO is indium tin oxide (ITO), which is compatible with standard microelectromechanical systems (MEMS) technology. In this work, the feasibility of ITO as an alternative plasmonic material is investigated for infrared absorption sensing applications: we numerically design and optimize an ITO-based plasmonic slot waveguide for a wavelength of 4.26 µm, which is the absorption line of CO2. Our optimization is based on a figure of merit (FOM), which is defined as the confinement factor divided by the imaginary part of the effective mode index (i.e., the intrinsic damping of the mode). The obtained optimal FOM is 3.2, which corresponds to 9 µm and 49 % for the propagation length (characterizing the intrinsic damping) and the confinement factor, respectively.
Highlights
In recent years, plasmonic effects and devices have commanded increased attention, as they enable sub-wavelength photonics applications
We investigated the feasibility of indium tin oxide (ITO) as an alternative plasmonic material to replace noble metals for sensing applications in the mid-infrared region
The plasmonic slot waveguide was optimized based on a figure of merit (FOM) composed of the product of the propagation length and the confinement factor, which are two crucial quantities in sensing applications
Summary
Plasmonic effects and devices have commanded increased attention, as they enable sub-wavelength photonics applications. The maximum intensity occurs at the metal–dielectric interface where the field amplitudes decay exponentially in the direction perpendicular to the interface (Dionne et al, 2006). This so-called evanescent field represents the bound, non-radiative nature of SPPs (Barnes et al, 2003). A plasmonic device that has attracted particular attention is the plasmonic waveguide. Plasmonic slot waveguides are attractive due to the provided lateral confinement and the capability of guiding the mode in low-index materials, which can be an asset in the fabrication of miniaturized optical circuits. As plasmonic slot waveguides allow for a high-energy fraction in low-index material, they promise high sensitivity with respect to absorption in a gaseous sensing medium, acting as a low-index medium in such a sensor
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