• Slow light;
  • coupled resonators;
  • optical cavities;
  • optical waveguides;
  • ring resonators;
  • integrated optic technologies;
  • integrated optical devices.


A century after the first optical cavity, coupled resonator optical waveguides (CROWs) were conceived as a new way to guide light on a photonic chip. Controlling chains of coupled resonators to let light propagate through, with a reduced speed and enhanced intensity, boosting light-matter interaction while keeping information undistorted: this was the fascinating promise of CROWs, but also one of the most ambitious challenges ever set for integrated optics. The first decade of the history of CROWs is discussed in this review, from the original idea to recent applications, panning through the technological platforms that have been employed to realize these structures. Design criteria and management issues, fundamental limits, and sensitivity to fabrication tolerances are discussed to make the reader aware of the performance of state-of-the-art CROWs and to provide a realistic perspective of future applicative horizons.