Midinfrared Refractive-index Sensor with High Sensitivity Based on an Optimized Photonic Crystal Coupled-cavity Waveguide

A photonic crystal coupled-cavity waveguide created on silicon-on-insulator is designed to act as a refractive-index-sensing device at midinfrared wavelengths around 4 μm. To realize high sensitivity, effort is made to engineer the structural parameters to obtain strong modal confinement, which can enhance the interaction between the resonance modes and the analyzed sample. By adjusting some parameters, including the shape of the cavity, the width of the coupling cavity, and the size of the surrounding dielectric columns, a high-sensitivity refractive-index sensor based on the optimized photonic crystal coupled-cavity waveguide is proposed, and a sensitivity of approximately 2620 nm/RIU obtained. When an analyte is measured in the range of 1.0–1.4, the sensor can always maintain a high sensitivity of greater than 2400 nm/RIU. This work demonstrates the viability of high-sensitivity photonic crystal waveguide devices in the midinfrared band.