A differential measurement approach for improving surface plasmon resonance phase sensing performance

We propose a method to improve the performance of existing phase surface plasmon resonance (SPR) sensing system. The interferometric phase sensing technique used in SPR sensors has been investigated in terms of possible ways to improve refractive index measurement sensitivity. A typical prism-coupling scheme containing a prism/metal/dielectric sensor head and a Mach-Zehnder interferometer has been constructed to analyze the phase change caused by the SPR effect. Since the probe beam and the reference beam are required to separate into two different optical paths, mechanical drift and vibrations make the system performance become unstable and noisy. In the new scheme, we propose to use of differential phase sensing technique, which means that both the probe beam and reference beam traverse identical optical paths in the system. Experimental results show good measurement stability and we believe that our differential approach will be a very effective way for achieving high sensitivity measurement.