Bragg gratings are fabricated in all-solid photonic bandgap fibers by forming a longitudinal periodic index modulation over the high-index rod lattice in the cladding. Due to its unique index-modulation pattern and the modal properties of the fiber, resonance couplings to the LP(01) supermodes (also known as high-index rod modes) are observed. The corresponding peak is located at the long-wavelength side of the Bragg wavelength and presents the highest depth. The asymmetric index profile over the high-index rods, which is induced by side UV illumination, leads to broadening of the supermode resonance peaks and variation with fiber orientation in the bend response of the fiber grating.