Optical imaging and sensing systems based on diffractive
elements
have seen massive advances over the last several decades. Earlier
generations of diffractive optical processors were, in general, designed
to deliver information to an independent system that was separately
optimized, primarily driven by human vision or perception. With the
recent advances in deep learning and digital neural networks, there
have been efforts to establish diffractive processors that are jointly
optimized with digital neural networks serving as their back-end.
These jointly optimized hybrid (optical + digital) processors establish
a new “diffractive language” between input electromagnetic
waves that carry analog information and neural networks that process
the digitized information at the back-end, providing the best of both
worlds. Such hybrid designs can process spatially and temporally coherent,
partially coherent, or incoherent input waves, providing universal
coverage for any spatially varying set of point spread functions that
can be optimized for a given task, executed in collaboration with
digital neural networks. In this Perspective, we highlight the utility
of this exciting collaboration between engineered and programmed
diffraction and digital neural networks for
a diverse range of applications. We survey some of the major innovations
enabled by the push–pull relationship between analogue wave
processing and digital neural networks, also covering the significant
benefits that could be reaped through the synergy between these two
complementary paradigms.