Narrow band filter designed from Bravais-Moiré two-dimensional photonic crystal

This work investigates the light propagation through a narrow-band filter based on a two-dimensional photonic crystal with Bravais-Moiré lattice and dielectric elements of circular cross section. We report on the corresponding gap mapping as a function of the radius of dielectric cores as well as the dispersion relations of TM modes for a sample 2D structure and for the waveguide system built of defect lines within such crystal, coupled to a microcavity. The proposed design is tested via numerical simulations, using the finite element method, aiming at its eventual biosensing performance. Cavity resonant frequencies were determined for different biological molecules, finding values of quality factor up to Q = 54,858.1. A linear response against changes in the index of refraction of different analyzed substances was found for the filter. Sensibility of up to 13086 nm/RIU (equivalent to 73.3 GHz/RIU), and figure of merit up to 3112.32 RIU⁻¹ were determined. This points at the possible use of this kind of filters for developing THz-range biosensors with label-free medical and biological applications.