A Long-Period Waveguide Grating Sensor for Accurate Simultaneous Detection of Dual Analytes

To the best of our knowledge, we are the first to report the existence of two dispersion turning points (DTPs) in an optimized planar waveguide long-period grating (LPG) sensor for the lowest order cladding mode. Using numerical simulation, we investigate the potential of the sensor structure for bulk refractive index (RI) and surface sensing, with the goal of predicting its possible application as an integrated photonic biosensor. The proposed sensor exhibits an exceptionally high RI sensitivity of ≈7500 nm/RIU ( ≈ 10 000 nm/RIU) near lower (higher) DTP. The surface sensitivity, which is incredibly high in this form of structure, is found to be 6.5 nm/nm (7 nm/nm) near lower (higher) DTP for the RI relevant for biosensing. Utilizing the sensing characteristics of both the DTP, we propose a dual-slot biosensor by cascading two LPGs having different grating periods. The proposed biosensor shows two independent dual-resonance phenomena and is, therefore, capable of simultaneous detection of dual analytes. Utilizing the proposed dual-slot biosensor, we present simulation results for specific detection of Hepatitis B antigen and deoxyribonucleic acid (DNA) hybridization simultaneously. The proposed biosensor will reduce the sensor cost as well as detection time, since a single source and detector are required to sense two different analytes at once.