Photonic crystal double-coupled cavity waveguides and their application in design of slow-light delay lines

•The idea of photonic crystal double-coupled cavity waveguides is introduced.•Cavities at the intersection of two photonic crystal waveguides are coupled together both horizontally and vertically.•The coupled matrix of cavities can be used for design of ultra-compact optical delay lines.•Due to existence of two orthogonal degenerate resonance modes we were able to use each cavity twice in the path of signal.•The proposed structure has many potential applications, if Kerr-type nonlinear materials are employed. In this paper the idea of double-coupled cavity waveguides is introduced. The cavities used in this paper support two orthogonal degenerate resonance modes. These cavities are coupled together both horizontally and vertically. The obtained matrix of cavities introduces many interesting properties for design of photonic crystal devices such as phase shifters and gates. As an application, it is shown that the coupled matrix of cavities can be used for design of ultra-compact slow-light photonic crystal optical delay lines. Finite difference time domain method and plane wave expansion method are used to analyze the structures.