Enhanced phase sensitivity of metamaterial absorbers near the point of darkness

Abstract

Plasmonic resonances are accompanied by abrupt phase changes. Utilization of this phase signal and lower phase noises can improve the refractive index resolution of plasmonic sensors. It is shown that the maximal phase change in the frequency domain is achieved at the point of the minimal reflection—the point of darkness. Since the metamaterial absorbers have near zero reflection at their resonance by definition, their phase can be used for sensing purpose. Considered metamaterial absorbers consist of parallel gold strips separated by a dielectric spacer from a thick metallic plate. By the optimization of the spacer thickness and strip widths, and by the adjustment of the angle of incidence, the phase sensitivity above 104 deg/RIU can be achieved in the dynamic range of 2×10−2 RIU.