Measurement of optical loss in nanophotonic waveguides using integrated cavities

Measurement of optical loss in nanophotonic waveguides is necessary for monitoring the properties of integrated photonic devices. We propose a simple method of measuring the optical loss using integrated nanocavities. It is shown theoretically that weak coupling between the waveguide and cavities leads to a direct estimation of the optical loss by measuring light radiated from the cavities. In addition, we experimentally demonstrate the optical loss in a fabricated photonic crystal waveguide. Our method gives not only a degree of freedom in real-time monitoring of the optical properties of nanophotonic structures, but it also can be used for various waveguide-based applications.