Theoretical investigation of transverse electric Bloch surface modes in a radially periodic binary multilayer cylindrical waveguide.

A truncated binary multilayer cylindrical photonic crystal operating in the near-infrared is theoretically investigated to analyze transverse electric surface modes. The multilayer periodicity is chosen to be comparable to the incident wavelength, while the core diameter is kept much larger, ensuring quasi-planar propagation and effective surface-mode localization. The surface electromagnetic modes at the interface between an aqueous medium and the cylindrical structure are studied, with emphasis on the fundamental azimuthal mode (m=0) exhibiting radial light propagation. A transfer matrix formalism adapted to cylindrical geometry is employed to evaluate the photonic band structure and electromagnetic field distributions. The influence of key structural parameters on mode localization, decay length, and confinement within photonic band gaps is systematically examined. The results reveal a strong radial localization of surface modes at the interface. The optimized cap-layer thickness significantly reduces the decay length, confining the evanescent field to only a few unit cells and producing a sharp interfacial intensity peak followed by rapid attenuation. These findings demonstrate enhanced Bloch surface-mode confinement and highlight the potential of the proposed platform for integrated photonic devices and sensing applications.