  The role of a prominent photonic bandgap (PBG) on the phenomenon of
transverse localization of light in a semi-infinite lossless waveguide lattice
consisting of evanescently coupled disordered one-dimensional optical
waveguides has been investigated numerically. The interplay between the
underlying photonic bandgap due to inherent periodicity of the optical system
and various levels of deliberately induced transverse disorder in its
refractive index periodicity has been studied. We show that the PBG indeed
plays an important role and its simultaneous presence could catalyze
realization of localized light even when strength of disorder is not
sufficiently strong to independently cause localization of light. An important
outcome of this study revealed that PBG could be gainfully exploited to tailor
the spectral window for localization of light in potential applications like
lasing in a disordered optical lattice.
