From Opals to Optics: Colloidal Photonic Crystals

Over a decade ago, theorists predicted that photonic crystals active at visible and near-infrared wavelengths would possess a variety of exciting optical properties. Only in the last several years, however, have experimentalists begun to build materials that realize this potential in the laboratory. This lag between experiment and theory is primarily due to the to the challenges associated with fabricating these unique materials. As the term “crystal” suggests, these samples must consist of highly perfect ordered arrays of solids. However, unlike conventional crystals, which exhibit order on the angstrom length scale, photonic crystals must have order on the submicrometer length scale. In addition, many of the most valuable properties of photonic crystals are only realized when samples possess a “full” photonic bandgap. For such systems, large dielectric contrasts and particular crystal symmetries create a range of frequencies over which light cannot propagate. Realizing the nanoscopic architectures required to form such systems is a challenge for experimentalists. As a result, fabrication schemes that rely on lithographic techniques or spontaneous assembly have been a focus in the development of the field.