IRG-I Highlight
New photonic crystal structures "freeze" light
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Supercollimation effect over a 0.3 cm sample. (a) Top view of the light guided along the photonic crystal, using an IR camera, for l = 1.5 microns. (b) Intensity maps of scattered light obtained by NSOM at positions labeled (1)-(3) in a (corresponding to 0.02 cm, 0.10 cm and 0.30 cm along device). Beside each image is a beam cross-section of the intensity map and a fit of this data yielding beam widths of 2.49, 2.54 and 2.71 microns for positions (1), (2) and (3) respectively.
Members of IRG-I of the MIT MRSEC have recently succeeded in the design, fabrication and characterization of a photonic crystal system that can enable the phenomenon of supercollimation to occur over macroscopic length scales (Rakich et al, Nature Materials 5, 93-96, 2006). Traditionally, light diffraction forces optical beams to broaden greatly as they propagate through space or through a bulk material system. However, new optical materials called photonic crystals can be nanoengineered to exhibit diffraction-less propagation. This surprising phenomenon, called supercollimation , effectively freezes the spatial evolution of light inside of a bulk photonic crystal even without the need of optical waveguides.
Supercollimation was demonstrated and characterized as shown in the figure on the left. This is a very important advance demonstrating that control of structure at nanoscales can be used to strongly tailor the effective optical properties of materials even over macroscopic length scales. In particular, supercollimation eliminates, for the first time, several fundamental problems associated with optical waveguides in optoelectronic devices including coupling alignment issues and cross-talk issues that arise between parallel and intersecting waveguides.
