  Amorphous photonic structures are mesoscopic optical structures described by
electrical permittivity distributions with underlying spatial randomness. They
offer a unique platform for studying a broad set of electromagnetic phenomena,
including transverse Anderson localization, enhanced wave transport, and
suppressed diffusion in random media. Despite this, at a more practical level,
there is insufficient work on both understanding the nature of optical
transport and the conditions conducive to vector-wave localization in these
planar structures, as well as their potential applications to photonic
nanodevices. In this study, we fill this gap by investigating experimentally
and theoretically the characteristics of optical transport in a class of
amorphous photonic structures and by demonstrating their use to some basic
waveguiding nanostructures. We demonstrate that these 2-D structures have
unique isotropic and asymmetric band gaps for in-plane propagation, controlled
from first principles by varying the scattering strength and whose properties
are elucidated by establishing an analogy between photon and carrier transport
in amorphous semiconductors. We further observe Urbach band tails in these
random structures and uncover their relation to frequency- and
disorder-dependent Anderson-like localized modes through the modified
Ioffe-Regel criterion and their mean free path - localization length character.
Finally, we illustrate that our amorphous structures can serve as a versatile
platform in which photonic devices such as disorder-localized waveguides can be
readily implemented.
