Waveguide-Based Refractometers Using Bulk, Long-and Short-Range Surface Plasmon Modes: Comparative Study

We present a numerical study comparing three configurations of the waveguide-based surface plasmon resonance refractometer: without a buffer layer based on the excitation of the bulk surface plasmon mode, and with a buffer layer using the symmetric (long-range) and antisymmetric (short-range) plasmon modes. Optimal conditions ensuring the sharpest resonant dip in the refractometer's transmission spectrum are identified. Relative merits of various configurations in terms of the figure-of-merit parameter, local sensitivity to refractive index variations near the metal film, and the size of the sensing element are quantified and discussed.