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 asis and coated wit h a thin gold film. Diffraction of the guided mode out of the fiber co re, after interaction with the metallized fiber tip, enables visual ob servation of a spatial SPR, the latter arising as a dark strip within the light distribution of the diffracted beam pattern. Modifications i nduced on the SPR due to variations in material properties of the gase ous environment nest to the fiber probe indicated a detection sensitiv ity for changes in refractive index down to 10(-5). A theoretical mode l that accounts for the observed diffracted light under SPR as well as the spectral dependence of light reflected back to the fiber input, a llows obtaining design parameters for the construction of highly sensi tive fiber probes for use in gas sensing applications.