Localization in silicon nanophotonic slow-light waveguides

Slowing down light on a chip can lead to the development of optical buffers1, filters2,3 and memory elements4 useful for optical interconnects and for resonantly enhanced chip-based nonlinear optics5,6. Several approaches to slow light rely on the phenomenon of light interference in a sequence of coupled resonators1,2,3,4,7,8,9,10,11; however, light interference is also responsible, in disordered structures, for the localization of light, an effect particularly prominent in one-dimensional devices12,13. Until now, the length of the waveguides investigated has been less than the localization length. Here we report the first observation of light localization in compact silicon nanophotonic slow-light waveguides consisting of long sequences of coupled resonators. Our results show that disorder limits how much light can be slowed, and that localization leads to spatially concentrated and locally trapped light in a quasi-one-dimensional waveguide at wavelengths near the band edge.