Refractive index sensor based on graphene-coated photonic surface-wave resonance.

We propose a graphene-coated photonic system with the excitation of Bloch surface waves (BSWs) for refractive index sensing. Through manipulation of the BSW resonance in the truncated photonic crystal under a Kretschmann configuration, the absorption in a graphene monolayer is significantly enhanced, assisted by the strong electromagnetic confinement of BSWs. The sharp and low reflectivity dip and the strong wave-environment interaction enable highly sensitive optical sensing. First-order perturbation theory and transfer-matrix calculation indicate that the system sensitivity is strongly related to the ratio of the electric field energy in the detection area, operation wavelength, and incident angle. Study shows that the wavelength sensitivity and figure of merit of the optimized system can reach 7023  nm/RIU and 196.44, respectively. More generalized BSW system configurations, e.g., aperiodic BSW design, are proposed for refractive index sensing application.