Holey fibers for evanescent field devices

Summary form only given. In a holey fiber (HF), the cladding is formed by an array of holes which run along its length, and the core is simply the absence of a hole. HFs guide light because of the effective volume average index difference between the core and the cladding. The holes provide new opportunities for exploiting the interaction of light with gases and liquids through evanescent field effects. For example, the concentration of pollutants in a gas can be determined using the absorption which occurs as light propagates through the gas for a range of wavelengths, and HFs offer an alternative which naturally provide the possibility of extremely long optical path lengths. To assess the suitability of HFs for evanescent field devices such as gas sensors, it is crucial to know the magnitude of the overlap of the modal field with the holes, and here we present what we believe to be the first such calculations.