Abstract-Terahertz Plasmonic Waveguide Based Thin Film Sensor

Maidul Islam, Dibakar Roy Chowdhury, Amir Ahmad, and Gagan Kumar

https://www.osapublishing.org/jlt/abstract.cfm?uri=jlt-35-23-5215

In this paper, we investigate sensing capabilities of a planar plasmonic terahertz waveguide. The waveguide is comprised of one-dimensional array of periodically arranged subwavelength scale corrugations in the form of rectangular dimples in order to ensure the plasmonic response. The terahertz waveguide transmission is observed for polyimide (as thin film) substance filling the dimples. The refractive index of the polyimide film is varied to examine various sensing parameters such as frequency shift, sensitivity, and figure of merit of the fundamental plasmonic resonance supported by the waveguide. We employ a semianalytical transmission line 𝐿𝐶$LC$ circuit model to elucidate our numerical observations. In efforts to improve sensing characteristics, we also examine sensing capabilities of a plasmonic waveguide having V-shaped corrugations and compare results with that of rectangular dimples. The proposed study could be significant in developing new terahertz sensors with improved sensitivity utilizing the plasmonic waveguides.

Abstract-Grating-coupled surface plasmons on InSb: a versatile platform for terahertz plasmonic sensing (Conference Presentation)

Diyar Talbayev, Shuai Lin

Tulane Univ. (United States)

Jiangfeng Zhou, Khagendra Bhattarai

Univ. of South Florida (United States)

Proc. SPIE 10210, Next-Generation Spectroscopic Technologies X, 102100X (June 9, 2017); doi:10.1117/12.2263717

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2632318

Detection and identification of molecular materials based on their THz frequency vibrational resonances remains an open technological challenge. The need for such technology is illustrated by its potential uses in explosives detection (e.g., RDX) or identification of large biomolecules based on their THz-frequency vibrational fingerprints. The prevailing approaches to THz sensing often rely on a form of waveguide spectroscopy, either utilizing geometric waveguides, such as metallic parallel plate, or plasmonic waveguides made of structured metallic surfaces with sub-wavelength corrugation. The sensitivity of waveguide-based sensing devices is derived from the long (1 cm or longer) propagation and interaction distance of the THz wave with the analyte. We have demonstrated that thin InSb layers with metallic gratings can support high quality factor “true” surface plasmon (SP) resonances that can be used for THz plasmonic sensing. We find two strong SP absorption resonances in normal-incidence transmission and investigate their dispersion relations, dependence on InSb thickness, and the spatial distribution of the electric field. The sensitivity of this approach relies on the frequency shift of the SP resonance when the dielectric function changes in the immediate vicinity of the sensor, in the region of deeply sub-wavelength thickness. Our computational modeling indicates that the sensor sensitivity can exceed 0.25 THz per refractive index unit. One of the SP resonances also exhibits a splitting when tuned in resonance with a vibrational mode of an analyte, which could lead to new sensing modalities for the detection of THz vibrational features of the analyte.

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