We predict that singular photonic Bloch modes with extremely narrow bandwid
ths occur in dual-periodic dielectric multilayer structures. The electromag
netic field of these modes is shown to be strongly localized around the tro
ughs of undulated periodic dielectric structures, which leads to an extraor
dinary high-Q value effect in the dual-periodic one-dimensional photonic cr
ystals. We also propose several real systems suitable for experimental conf
irmation of the features predicted. (C) 2001 American Institute of Physics.