The ability to change the photonic band gap structure continuously and reversibly by modifying the index thermally allows the band gap features to be sensitively tuned, allowing for a thorough investigation of the various band gap guiding properties. Furthermore, it may be possible to use this type of band gap fiber as a tunable filter. Investigations of the dispersion properties of this fiber have been examined recently in our laboratory showing a change in dispersion > 10/sup 3/ ps/nm km across the band gap region suggesting that controlling the band gap position and width may also provide a sensitive method for tunable dispersion compensation.