Narrow Tamm resonances in one-dimensional photonic crystals employed in sensor applications

One-dimensional photonic crystals (1DPhCs) combined with a thin Au layer are designed to show up the Tamm resonances with potential sensor applications. For two 1DPhCs comprising six bi-layers of TiO2/SiO2 with a termination layer, the Tamm resonances are revealed within different band gaps. The first structure is characterized by a wide band gap over the visible (VIS) and near-infrared (NIR) spectral range and the Tamm resonance is supported at the normal incidence of light from both the substrate and Au sides with the resonance depth and width depending on the thickness of the Au layer. The second structure is characterized by band gaps in both the VIS and NIR spectral ranges and deep Tamm resonances for the Au layer of a 20 nm thickness are revealed. The theoretical results for both the structures are validated by experimental data, and for the first structure, the Tamm resonance dip as narrow as 6.7 nm is resolved. The second structure is utilized in relative humidity (RH) sensing due to a porous termination layer of the 1DPhC, and it is revealed that the new Tamm resonance-based sensor outperforms some optical RH sensors in both the sensitivity and figure of merit. Tamm resonance-based sensors along with the their main advantage in coupling-prism-free operation thus represent an effective alternative to other optical sensors, such as surface plasmon resonance-and Bloch surface wave-based ones.