Optical EngineeringToward optical sensing with hyperbolic metamaterials
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A possible means of optical sensing, based on a porous hyperbolic material that is infiltrated by a fluid containing an analyte to be sensed, was theoretically investigated. The sensing mechanism relies on the observation that extraordinary plane waves propagate in the infiltrated hyperbolic material only in directions enclosed by a cone aligned with the optic axis of the infiltrated hyperbolic material. The angle this cone subtends to the plane perpendicular to the optic axis is θc. The sensitivity of θc to changes in the refractive index of the infiltrating fluid, namely nb, was explored; also considered were the permittivity parameters and porosity of the hyperbolic material, as well as the shape and size of its pores. Sensitivity was gauged by the derivative dθc/dnb. In parametric numerical studies, values of dθc/dnb in excess of 500 deg per refractive index unit were computed, depending upon the constitutive parameters of the porous hyperbolic material and infiltrating fluid and the nature of the porosity. In particular, it was observed that exceeding large values of dθc/dnb could be attained as the negative-valued eigenvalue of the infiltrated hyperbolic material approached zero.