Fabrication-induced disorder in waveguides can cause strong field localization, severely limiting applications. In photonic crystal waveguides (PhCW's), localization has been observed close to the band edge for intentionally strong disorder. Here, we couple light into a PhCW which has been fabricated without intentional disorder. We find localization close to the band edge due to inherent fabrication defects. With a transmission-type near-field microscope, we probe the near-field above the PhCW. We find that the near-field probe shifts the localization resonances to the blue. From the magnitude of the shift, we measure localization length. Strong localization is reached when the localization length becomes shorter than the waveguide, which is accompanied by a sharp drop in transmission. This work points out a novel method for measuring localization length in a disordered waveguide. It pinpoints the limit of usefulness of PhCW's as waveguides for slow light, but opens up the possibility of using them as large-area sensors.


Seminar, January 21, 2011, 12:00. Seminar Room

Hosted by Prof. Niek van Hulst and Prof. Frank Koppens