Broadband single-mode optical fiber surface plasma wave chemical sensor

We describe a new design of optical fiber surface plasma wave chemical sensor. The sensor consists of a tapered single mode optical fiber with a thin layer of silver evaporated on to the tapered section. The gradually changing diameter of the fiber along the taper results in a distributed coupling between the guided mode of the fiber and the surface plasma wave. As a result, and in contrast to conventional plasma wave sensors, coupling to the surface plasma wave occurs over a broad spectral range, typically several hundred nm. The device shows good sensitivity to changes in the refractive index of the external environment, with refractive index changes of 10 -4 being detectable. The device is compact, simple to make, and has applications as a biochemical or immunosensor.