Rainbow light trapping in a chirped 3D woodpile photonic crystal

The so called "rainbow trapping" effect (wavelength dependent light localization) is demonstrated in a chirped 3D woodpile photonic crystal in the visible and near infrared regimes. By varying the period in the propagation direction, the 3D structure is designed to progressively slow down the incident wave and to localize different wavelengths at different positions. A first experiment in the visible range shows good qualitative results, with green localizing near the beginning of the crystal and red propagating deeper. The measurements in the infrared regime show strong localization between 1400nm and 1700nm. This localization goes deeper into the crystal as the wavelength increases, agreeing nicely with our numerical simulations.