Long-range surface plasmons on gold-coated single-mode fibers

A standard single-mode optical fiber, coated with low-index polymer (Cytop), then a thin Au sheath, immersed in fluid, isproposedas a structure for optical (bio)chemical sensing. The highest-order EH1m cladding modes are found to couple strongly to long- or short-range surface plasmons on the Au sheath, forming coupled modes that are sensitive to the refractive index of the fluid or to a biochemical adlayer formed on the outer surface of the Au sheath. Interrogation of the modes can be achieved with the help of a tilted grating photoinduced into the core of the fiber. We demonstrate experimentally, in this manner, the excitation of these modes, and their use for bulk sensing