A Theoretical Study On Dual Sensitive Mode Refractive Index Sensor Utilizing Fibonacci Sequence-based Aperiodic Photonic Crystals

In this study we present a novel method for constructing a refractive-index sensor utilizing hybrid modes within a dual ‘Ag-photonic quasi-crystal’ geometry, adhering to the conventional Fibonacci sequence. The reflection spectrum of the geometry demonstrates the presence of three interconnected minima in reflectivity, occurring within the photonic-bandgap of a quasi-crystal. These hybrid modes emerge from the interplay between individual Tamm plasmon mode at the metal-photonic quasi crystal interface and the Fabry–Perot resonant cavity mode formed between two metal layers. The low wavelength dip (Mode-2) and high wavelength dip (Mode-3) display pronounced dispersive characteristics due to the substantial presence of mode-field in the sensing medium. Conversely, the mode situated between them (Mode-1) remains largely unaffected by variations in the refractive index of the sensing layer. Thus, our proposed method offers a wide range of wavelengths linked to Mode 2 and Mode 3, facilitating the concurrent utilization of dual wavelengths for sensor parameter analysis. We investigate the foundational parameters of a bio-photonic sensor, laying the foundation for a dual mode refractive-index sensing mechanism. At a normal angle of incidence, Mode -2 exhibits a maximum sensitivity of 401.4 nm/RIU and a Figure of Merit of 42.8 RIU-1. Meanwhile, for Mode -3, the highest sensitivity and Figure of Merit are 448.87 nm/RIU and 28.89 RIU-1, respectively. Additionally, we propose enhancing the hybrid-mode sensor characteristics by strategically optimizing the photonic quasi-crystal structures to increase the dispersion observed in hybrid Tamm plasmon modes, thus improving sensitivity. Utilization of the dual sensitive mode shows potential for enhancing modern biochemical sensors and optoelectronic devices, with possible applications in detecting diverse blood-related disorders distinguished by refractive index fluctuations in blood components.