Optical characterization of photonic crystal delay lines based on one-dimensional coupled defects

We performed optical characterizations of optical delay lines based on photonic crystal waveguides. The delay lines were composed of cylindrical air holes in silicon-on-silicon-dioxide ridge waveguides, defects were periodically created by means of increasing the separation of two neighboring air holes, and the structure was designed to have flat-transmittance impurity band. We clearly observed an impurity band with a bandwidth of ~30 nm and a maximum transmittance of ~0.5 at an operating wavelength of ~1.55 microm . A 600-fs delay was confirmed with a 20-microm -long delay line. A good agreement was confirmed between the experimental results and the calculations.