Abstract

Surface plasmon waves (SPWs) have recently been employed in applications such as thickness and refractive-index measurement of dielectric and metallic coatings¹ and prism-based sensing.² We introduce all-fiber sensing devices based on resonant coupling interaction between fiber guided modes and SPWs generated in a metal-dielectric interface. The configuration involves a short fiber section (sensing region) where part of the cladding is removed and replaced with thin layers of proper phase-matching dielectric buffer and surface-active metallic materials covered with a suitable superstrate sensing layer. The phase matching buffer layer is used to bias properly the sensor. The TM-polarized guided wave in the fiber can excite the SPW by resonant coupling, which is extremely sensitive to refractive-index change of the sensing layer, while the TE polarization propagates unchanged. Using the TE polarization as the reference, the sensed information impressed on the TM polarization can be recovered accurately at the fiber output. In addition to being stable and simple, this sensor configuration has the potential to sense index change as small as 10⁻⁵. Detailed results are presented.

© 1988 Optical Society of America