Surface plasmon resonance on a single mode optical fiber

A single mode optical fiber probe employing surface plasmon resonance (SPR) as the transducing mechanism is described. The fiber has one end polished at an angle relative to the longitudinal axis and coated with a thin gold film. Diffraction of the guided mode out of the fiber core, after interaction with the metallized fiber tip, enables visual observation of a spatial SPR, the latter arising as a dark strip within the light distribution of the diffracted beam pattern. Modifications induced on the SPR due to variations in material properties of the gaseous environment next to the fiber probe indicated a detection sensitivity for changes in refractive index down to 10^-5. A theoretical model that accounts for the observed diffracted light under SPR as well as the spectral dependence of light reflected back to the fiber input, allows obtaining design parameters for the construction of highly sensitive fiber probes for use in gas sensing applications