Enhanced sensitivity to surface plasmon resonance phase in wavelength-modulated heterodyne interferometry

An alternative wavelength-modulated heterodyne interferometry based on surface plasmon resonance is proposed for in-situ monitoring of variations in the refractive index of a test sample. Phase variations in surface plasmon resonance are detected by the heterodyne detection system, which uses a wavelength-modulated light source and an unequal-path-length optical configuration. The measurement sensitivity and resolution of the refractive index are greatly enhanced by inserting a quarter-wave plate with a suitable azimuthal angle in front of the SPR sensor. The experimental results indicate that the resolution is better than 3×10−7 RIU.