Optical Biosensors Based On Topological Photonic Crystals

In recent years,topological physics has developed rapidly with the discovery of the quantum Hall effect.The introduction of topological concept provides a new platform for physics research,many achievements have been made in the condensed matter system of topological states.Therefore,driven by advances in condensed matter physics,a large number of studies of topological states in optical,acoustic and mechanical systems have recently emerged.Topological photonics provides a new way to realize exotic topological models and explore topological effects due to its great potential in flexible structural design and energy transfer.Photonic crystal is an artificial metamaterial composed of periodic arrangement of media with different refractive indices.When light waves propagate in the photonic crystal,due to the modulation of the periodic potential field,the eigenvalue of the photon forms an energy band structure.Since photonic crystals have a wide wavelength range and weak interactions,artificial structures can easily satisfy any desired symmetry,and thus are a good platform for the study of topological photonics.The most important property in photonic topology is the bulk-boundary correspondence,which originates from the quantum Hall effect’s directional conduction mode at the boundary,and has great application prospects due to its low dissipation and anti-interference transport properties.Two square photonic crystals with the same band structure were used in the paper.The topological phase transition of the structure is achieved by adjusting the distribution distance of the dielectric cylinders,and a helical edge state is formed at the interface of the two square crystals.At the same time,changing the radius of the dielectric cylinder in the photonic crystal produces a cavity mode whose frequency is in the band gap,and the topological edge state forms a special coupling-transport mode with the optical cavity.This paper innovatively realizes the combination of topological photonics and biodetection,and the designed optical biosensor can achieve very high sensitivity without sacrificing the low detection limit,breaking through the opposing limitations of the two properties in traditional biosensors.At the same time,the system adopts topologically protected boundary state transmission,which is more resistant to scattering and general manufacturing defects,and can distinguish multiple disease markers in a single detection.