  One of the most appealing aspects of photonic crystal structures is the
photonic bandgap created in structures with sufficiently high dielectric
contrasts between constituent materials. Understanding how specific photonic
crystal structures and their associated stopband positions can selectively
interfere with incoming light is vital for implementing these structured
dielectrics in a range of optical applications. Metallo-dielectric photonic
crystals act to incorporate metal particles into the ordered arrangement of
these structures. We examined copper, nickel and gold metal infiltration into
polystyrene opals and TiO2 inverse opals. We report a consistent optical
phenomena directly associated with the creation of metallo-dielectric photonic
crystal structures. More pronounced and numerous diffraction resonances emerge
in opal photonic crystals with a metal deposited across the top layer. Common
to both opal and inverse opal structures, was a blue-shift in the position of
the (111) photonic stopband which increased in magnitude with greater metal
content in the structure. We investigate the origin of the photonic stopband
blue-shift by variation of the metal content and the placement of metal in the
photonic crystal structure. Metal introduced to structured dielectric media
tunes the photonic stopband by altering the effective dielectric constant of
the photonic crystal.
