Materials have special optical properties if the refractive index is modulated periodically in space on a wavelength scale. They are of great interest with respect to future photonic devices. The propagation properties of light in such materials are strongly depending on the details of the structure. This corresponds to the complex band structure of the respective dispersion relation.
Present investigations aim at a realization of materials with a so called complete photonic band gap. The fabrication of such structures is still a challenge, therefore different technological approaches are being studied. Corresponding model calculations are expected to predict and understand the optical properties.
Several ways to fabricate and to characterize Photonic Crystals are discussed. Holographic lithography and its crystallographic background is described in more detail. This includes the dependence of the lattice type and the basis element inside the Wigner-Seitz-cell on the configuration of the interfering laser beams. Design freedom and restrictions are outlined. Direct laser writing is discussed, too. The combination of both methods is expected to be particularly useful.
For best results a high refractive index contrast is needed calling for infiltration of the photoresist structures which serve as templates.

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