Mode areas and field-energy distribution in honeycomb photonic bandgap fibers

The field-energy distributions and effective mode areas of silica-based photonic bandgap fibers with a honeycomb air-hole structure in the cladding and an extra air hole defining the core are investigated. We present a generalization of the common effective-area definition, suitable for the problem at hand, and compare the results for the photonic bandgap, fibers with those of index-guiding microstructured fibers. While the majority of the field energy in the honeycomb photonic bandgap fibers is found to reside in the silica, a substantial fraction (up to similar to30%) can be located in the air holes. This property may show such fibers as particularly interesting for sensor applications, especially those based on nonlinear effects or interaction with other structures (e.g., Bragg gratings) in the glass. (C) 2003 Optical Society of America.