Stopped microwave-rainbow in 3D chirped photonic crystals

The reported stopped rainbow concept in tapered metamaterial and plasmonic guiding microstructures has revealed the possibility to obtain local wave enhancement together with spatial chromatic resolution. Recently, this phenomenon has also been demonstrated in graded defect waveguides in photonic crystals. As the wave is stopped in such single mode defect waveguides, the energy of the stopped wave will be restricted due to the limited volume of the mode, which seriously limits the brightness (i.e. its local intensity) of the trapped rainbow. For many applications more desirable would be to stop the light in a bulk of a structure, and to harvest the energy of the stopped wave across all the structure, without any principal restrictions imposed by the mode volume. Such stopping of waves in bulk of a structure has been shown for acoustic waves in sonic crystals recently and also for electromagnetic waves in multilayer dielectric slabs. However high radiation losses in the latter case are inevitable due to the weak index confinement. Here we present a first experimental demonstration of stopped microwave in a chirped 3D photonic crystals. We show that the complete 3D photonic bandgap may significantly reduce the external losses and we also show that the local intensity can be enhanced up to two order of magnitudes. This allows an important increase of absorption/photodetection of microwave radiation. We further demonstrate that the different microwave components stop and reflect at different depths of the chirped structure, which offers a frequency-resolved microwave detection.