This book investigates the behavior of light (light pulse) within the micro- and nano-scale device (ring resonator), which can be integrated to form the device, circuits, and systems that can be used for atom/molecule trapping and transportation, optical transistor, fast calculation devices (optical gate), nanoscale communication and networks, and energy storage, etc. The large demand of small-scale device, especially, with light signal processing is needed. This book discusses device (nano device) design and simulation, which can be useful for practice in the near future.