Design, Analysis, and Optimization of a Plasmonic Slot Waveguide for Mid-Infrared Gas Sensing

• Published in: Nanomaterials (Basel, Switzerland) Vol. 12; no. 10; p. 1732
• Main Authors: Saeidi, Parviz, Jakoby, Bernhard, Pühringer, Gerald, Tortschanoff, Andreas, Stocker, Gerald, Spettel, Jasmin, Dubois, Florian, Grille, Thomas, Jannesari, Reyhaneh
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 18.05.2022; MDPI
• Subjects: Absorption; Carbon dioxide; Communication; Design optimization; Dielectrics; Figure of merit; Gas sensors; Gases; Gold; Infrared analysis; Metals; mid-infrared region; optical simulation; Optimization; Plasmonics; Propagation; sensing applications; Sensors; Simulation; slot waveguide; Waveguides; Wavelengths; mid-infrared region; optical simulation; slot waveguide; plasmonics; sensing applications
• ISSN: 2079-4991; 2079-4991
• DOI: 10.3390/nano12101732

In this work, we investigated the optimization of a plasmonic slot waveguide (PSWG) in the mid-IR region particularly for a representative wavelength of 4.26 µm, which is the absorption line of CO and thus particularly relevant for applications. We analysed the mode features associated with metal-dielectric-metal (MDM), dielectric-metal-dielectric (DMD), and truncated metal film (TMF) structures with respect to the considered PSWG. Subsequently, the mode features of the PSWG were considered based on what we outlined for MDM, DMD, and TMF structures. Furthermore, as confinement factor and propagation length are two crucial parameters for absorption sensing applications, we optimized the PSWG based on a figure of merit (FOM) defined as the product of the aforementioned quantities. To characterize the propagation length, the imaginary part of the effective mode index of a guided mode was considered, leading to a dimensionless FOM. Finally, we investigated the PSWG also for other wavelengths and identified particularly attractive wavelengths and geometries maximizing the FOM.