Multiple gold island layers on a fiber core: A promising sensing device

Optical fibers are being used more and more as chemical sensors or biosensors. Some of these devices are based on thin film plasmon excitation in which a metal coating is evaporated onto the core or end of an etched optical fiber. A new sensor configuration is presented for detecting liquid adsorbates with different indices of refraction. Instead of exciting surface plasmon waves on a thin film, localized surface plasma waves are excited on metal islands. The fiber is coated with three very thin layers of gold. Each layer is annealed before the next layer is evaporated onto it. This is done to avoid any light leakage, a problem discovered in a prior version with only one gold coating. Different sets of fibers were tested and sensitive and reproducible results for liquids with refraction indices varying from 1.563 to 1.683 were obtained.