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

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 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 metal-dielectric 1DPhCs. We report on a new 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 ₂ /Au with a termination layer of TiO ₂ , we show that the Bloch-like SW-based resonances for both TE and TM waves are resolved for the refractive index (RI) in a range of 1–1.0015, and the sensitivity and figure of merit (FOM) for the TE wave are up to 10,900 nm/RIU and 474 RIU ⁻¹ , respectively. The analysis extended to the 1DPhC with the modified thicknesses of TiO ₂ layers and gas, whose RI changes in a range of 1.0002–1.0022, leads to the sensitivity and FOM for the TM wave in a range of 10,680–28,000 nm/RIU and 434–1217 RIU ⁻¹ , respectively. This research is the demonstration of exceptional properties of the Bloch-like SW-based sensors employing a metal-dielectric 1DPhC that can be used in a simple sensing of a wide range of gaseous analytes.