Bloch waves at the surface of a single-layer coating D-shaped photonic crystal fiber.

Bloch surface wave (BSW) platforms are particularly interesting for light confinement and surface sensitivity, as an alternative to the metal-based surface plasmon polaritons (SPP). However, most of the reported BSW platforms require depositing a large number of alternating dielectric layers to realize the excitation of the surface waves. In this Letter, we demonstrate an experimentally feasible D-shaped photonic crystal fiber (PCF) platform consisting of only a single dielectric layer on its flat surface, which can sustain Bloch waves at the boundary between the dielectric layer and the PCF cladding. The presence of the dielectric layer modifies the local effective refractive index, enabling a direct manipulation of the BSWs. In addition, the D-shaped structure provides direct contact with the external medium for sensing applications with an ultrahigh sensing figure of merit ($2451\;{{\rm RIU}^{ - 1}}$2451RIU-1) and has the potential to be used over a wide range of analyte refractive indices.