Abstract
This paper reports a metal stripe waveguide based sensor that functions like a
Mach–Zehnder interferometer. It consists of three sections. The first and third sections
are input and output metal stripe waveguides that support a long-range surface plasmon
polariton (LRSPP). The second section is a sensing region; it comprises a substrate,
which is common to the first and third sections, an insulator layer with a refractive
index larger than 2 (e.g., TiO<sup>2</sup>), and an Au layer much thicker than the skin depth
of gold. For sensing, it is covered by an aqueous solution with a refractive index of
about 1.3. Because of the thick Au layer, separate single-interface surface plasmon
polaritons (SPPs) propagate along the top and bottom surfaces of the Au layer. Since the
top and bottom SPPs rather than an LRSPP are used in the second section, it is not
constrained by the condition of supporting an LRSPP, which is that the substrate should
have almost the same refractive index as the solution. The top and bottom SPPs play the
roles of sensing and reference arms of an interferometer, respectively. In this paper,
the sensor is designed, and its bulk-sensing and surface-sensing characteristics are
theoretically analyzed. The design results in the compact sensor whose sensing region is
~35 μm long; the analysis demonstrates that the sensor has
sensitivity higher than or comparable to that of previous plasmonic sensors.
© 2012 IEEE
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