Ultra-Narrow SPP Generation from Ag Grating

• Published in: Sensors (Basel, Switzerland) Vol. 21; no. 21; p. 6993
• Main Authors: Stocker, Gerald, Spettel, Jasmin, Dao, Thang Duy, Tortschanoff, Andreas, Jannesari, Reyhaneh, Pühringer, Gerald, Saeidi, Parviz, Dubois, Florian, Fleury, Clement, Consani, Cristina, Grille, Thomas, Aschauer, Elmar, Jakoby, Bernhard
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 21-10-2021; MDPI
• Subjects: Aluminum; Figure of merit; Gases; Indoor air quality; Interfaces; Investigations; Lasers; Optical properties; Physical properties; plasmonic grating; Plasmonics; Propagation; Quantum cascade lasers; reflection measurement; refractive index sensing; Refractivity; Sensors; Silicon substrates; Silicon wafers; Silver; surface plasmon polaritons; Tunable lasers; Wave attenuation
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s21216993

In this study, we investigate the potential of one-dimensional plasmonic grating structures to serve as a platform for, e.g., sensitive refractive index sensing. This is achieved by comparing numerical simulations to experimental results with respect to the excitation of surface plasmon polaritons (SPPs) in the mid-infrared region. The samples, silver-coated poly-silicon gratings, cover different grating depths in the range of 50 nm–375 nm. This variation of the depth, at a fixed grating geometry, allows the active tuning of the bandwidth of the SPP resonance according to the requirements of particular applications. The experimental setup employs a tunable quantum cascade laser (QCL) and allows the retrieval of angle-resolved experimental wavelength spectra to characterize the wavelength and angle dependence of the SPP resonance of the specular reflectance. The experimental results are in good agreement with the simulations. As a tendency, shallower gratings reveal narrower SPP resonances in reflection. In particular, we report on 2.9 nm full width at half maximum (FWHM) at a wavelength of 4.12 µm and a signal attenuation of 21%. According to a numerical investigation with respect to a change of the refractive index of the dielectric above the grating structure, a spectral shift of 4122nmRIU can be expected, which translates to a figure of merit (FOM) of about 1421 RIU−1. The fabrication of the suggested structures is performed on eight-inch silicon substrates, entirely accomplished within an industrial fabrication environment using standard microfabrication processes. This in turn represents a decisive step towards plasmonic sensor technologies suitable for semiconductor mass-production.