3. Some configurations of plasmonic sensors on optical fibers

3.1 Multimode optical fibers

We have just seen that plasmonic sensors based on the use of a prism exploit the evanescent wave resulting from total internal reflection at the interface between a prism and a metal layer when the angle of incidence of light at this interface is greater than the critical angle.

In practice, evanescent waves are also present in optical fibers, since light guidance is based on the mechanism of total internal reflections at the core-cladding interface. As a result, the evanescent wave propagates along this interface. The optical fiber core thus acts as a prism. A plasmonic sensor is obtained by removing the optical cladding from a small portion of the fiber, as shown in figure