FEASIBILITY OF A CHEMICAL MICROSENSOR BASED ON SURFACE-PLASMON RESONANCE ON FIBER OPTICS MODIFIED BY MULTILAYER VAPOR-DEPOSITION

An intrinsic fiber-optic sensor is described which utilizes the surface plasmon effect to monitor the chemical environment surrounding the fiber. The device is constructed by polishing a short section of the lateral surface of a single-mode fiber to within the evanescent field surrounding the core. Then one or more thin films are deposited onto the polished surface, beginning with a thin metallic film which acts as the support for the plasmon. A highly refractive dielectric overlay is deposited on the metal film to allow the monitoring of a wide range of chemical sample indices of refraction. The final layer applied to the device is the chemical sample of interest. Under the proper conditions the single-mode propagating in the fiber core can be coupled to the surface plasmon mode on the metal film. This coupling is highly dependent on the refractive index of the chemical sample and is seen as a large attenuation of the light reaching the distal terminus of the fiber. A description of the dispersion equation describing sensor operation will be given, along with details on sensor construction and testing.