  Visible light backscatter (VLB) is an innovative optical transmission
paradigm to enable ultra low-power passive communication and localization for
the Internet of Things (IoT), by overcoming some of the limitations of
conventional (i.e., active) visible light communication (VLC) as well as
active/passive radio-frequency (RF) technologies. In this paper, we provide a
comprehensive survey of recent research activities in the VLB field. After
describing the principles of operation and the main enabling technologies, we
classify the existing VLB techniques according to several features, discussing
their merits and limitations. Moreover, we introduce the potential applications
of VLB techniques in several IoT domains. Finally, we present the main open
challenges in this area and delineate a number of future research directions
