  The memristors are expected to be fundamental devices for neuromorphic
systems and switching applications. For example, the device made of a
sandwiched layer of poly(N-vinylcarbazole) and reduced graphene composite
between asymmetric electrodes (ITO/PVK:rGO/Al) exhibits bistable resistive
switching behavior. Depending on the resistance state of the (ON-state or
OFF-state) at a constant applied voltage, it may show two different
resistivities. The performance of the memristor can be optimized by controlling
the doping amount of graphene oxide in the PVK polymer. To assess the
performance of the device, when it switches between ON and OFF states, optical
characterization approaches are highly promising due to their non-destructive
and remote nature. Here, we characterize the memristor device by the use of
speckle pattern (SP) analysis. The speckle pattern is the interference of
multiple light waves with random relative phases, which is generated via
different mechanisms such as scattering from diffusive materials. Therefore,
SPs can be used to investigate such samples as they include a huge amount of
information to be statistically elaborated. The experimental paradigm includes
\textit{in situ} acquisition of SPs of the PVK:rGO in different states followed
by statistical post-processing toward examining its conduction mechanism. The
variations in these statistical parameters are attributed to the resistance
state of the PVK:rGO samples under the applied voltage with regard to the
physical switching mechanism of the device. The resistance/conduction state, in
turn, depends on the activity and properties of PVK:rGO memristors as well as
the additional non-uniformities induced through the variations of density of
carriers. The present optical methodology can be potentially served as a
bench-top device for characterization purposes of similar devices while they
are operating.
