# Ultra-high sensitivity gas sensors employing Bloch-like surface waves in a metal-dielectric one-dimensional photonic crystal

## TL;DR

This paper introduces a new gas sensor design using metal-dielectric photonic crystals that achieves ultra-high sensitivity for detecting gases.

## Contribution

The novel use of metal-dielectric 1DPhCs in Bloch-like surface wave sensors significantly improves sensitivity and detection limits for gaseous analytes.

## Key findings

- A sensitivity of 10,900 nm/RIU and a figure of merit of 474 RIU⁻¹ were achieved for TE waves.
- Modified TiO₂ layer thicknesses enabled a sensitivity range of 10,680–28,000 nm/RIU and a very low LOD of 3.6 × 10⁻⁶ RIU for TM waves.
- The sensor design demonstrates exceptional performance for detecting a wide range of gaseous analytes.

## Abstract

Bloch surface waves (BSWs), generated at the interface of a truncated one-dimensional photonic crystal (1DPhC) and the adjacent medium (analyte), are accompanied by narrow resonance dips that are very advantageous compared to too wide resonance dips associated with the surface plasmon resonance (SPR) phenomenon. Consequently, BSW-based sensors have been thoroughly studied and applied in the field of optical sensors, but their sensitivity to gaseous analytes does not outperform the sensitivity of the SPR-based sensors. One of the possible solutions to enhance the sensitivity represents a metal-dielectric 1DPhC. We report on a sensing concept for gaseous analytes based on the wavelength interrogation and resonances supported by a metal-dielectric 1DPhC in the Kretschmann configuration. For a metal-dielectric 1DPhC comprising bilayers of TiO\documentclass[12pt]{minimal}
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\begin{document}$$_2$$\end{document}, we show that the Bloch-like SW-based resonances are resolved for both TE and TM waves. For the TE wave and the refractive index (RI) in a range of 1–1.0015, a sensitivity of 10,900 nm/RIU, a figure of merit (FOM) of 474 RIU\documentclass[12pt]{minimal}
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\begin{document}$$^{-6}$$\end{document} RIU were reached. The analysis extended to the 1DPhC with the modified thicknesses of TiO\documentclass[12pt]{minimal}
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\begin{document}$$_2$$\end{document} layers and gas, whose RI changes in a range of 1.0002–1.0022, leads to the sensitivity and FOM in a range of 10,680–28,000 nm/RIU and 434–1217 RIU\documentclass[12pt]{minimal}
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\begin{document}$$^{-6}$$\end{document} RIU for the TM wave. This research is the demonstration of exceptional properties of the Bloch-like SW-based sensors employing metal-dielectric 1DPhCs that can be used in a simple sensing of a wide range of gaseous analytes.