  Internet of Things (IoT) employs a large number of spatially distributed
wireless sen-sors to monitor physical environments, e.g., temperature,
humidity, and air pressure, have found wide applications including
environmental monitoring, health care monitoring, smart cities and precision
agriculture. A wireless sensor can collect, analyze, and transmit measurements
of its environment. To date, wireless sensors used in IoT are predominately
based on electronic devices that may suffer from electromagnetic interference
in many circumstances. Immune to the electromagnetic interference, optical
sensors provide a significant advantage in harsh environments. Furthermore, by
introducing optical resonance to enhanced light-matter interactions, optical
sensors based on resonators exhibit small footprints, extreme sensitivity and
versatile functionalities, which can signifi-cantly enhance the capability and
flexibility of wireless sensors. Here we provide the first demonstration of a
wireless photonic sensor node based on whispering-gallery-mode (WGM) optical
resonators. The sensor node is controlled via a customized iOS app. Its
per-formance was studied in two practical scenarios: (1) real-time measurement
of air tempera-ture over 12 hours and (2) aerial mapping of temperature
distribution by a sensor node mounted on an unmanned drone. Our work
demonstrates the capability of WGM optical sensors in practical applications
and may pave the way for large-scale deployments of WGM sensors in IoT.
