Refractive index measurement based on surface plasmon resonance with optical fiber excitation structure and phase-detection using dual-frequency laser interferometry

The refractive index is an important physical characteristic that reflects material information. In this paper a refractive index measurement method based on surface plasmon resonance (SPR) with optical fiber excitation structure and phase-detection using a dual-frequency laser interferometer is presented. A four-layer fiber SPR model is built based on Kretschmann structure. Theoretical analyses indicate that the phase difference variation between p and s polarization components of the reflected light is approximately linear with the refractive index in a certain range, and thus the calculation formulae are derived. The presented optical measurement system meets the principle of the common optical path to get good anti-interference ability and stability. Signal processing adopts phase detection, which avoids the influence of light intensity fluctuation and achieves high resolution. The refractive index measurement experiments show that the results are consistent with the theoretical analysis. Comparison results with the Abbe refractometer show a good agreement. The presented method is a new attempt to combine fiber SPR with laser heterodyne interference phase measurement.