A chemical sensor based on the measurement of differential phase related to surface plasmon resonance

The optical phase change associated with the surface plasmon resonance (SPR) effect that exists in a glass-metal-dielectric stack has been studied using a differential phase imaging technique. A typical prism-coupled SPR set-up was constructed and a Mach-Zehnder interferometer was used to perform interferometric analysis between the two orthogonal polarizations in the exit beam. By stepping the phase of the reference arm, one can measure the phase change caused by the SPR effect. Since the reference and signal beams traverse identical optical paths, we expect that this scheme can be more robust in terms of noise immunity. The interrogation area can be enlarged to enable imaging of the SPR sensing surface. Initial phase measurements obtained from a salt-water mixture are presented to demonstrate the operation of the technique.