Responsible scientist: Assoc. Prof. Dr. Frank Gunzer
Photonic crystals are regular structures with certain defects (e.g. a regular arrangement of air holes in GaAs, defects are locations where air holes have been left out). Such structures allow light of a certain wavelength to propagate in certain areas, and prohibit such a propagation in other areas. This is similar to semiconductor crystals, where electrons with a certain energy can be thought of being able to travel throughout the whole crystal, and electrons with different energy cannot; the energy ranges are called bands if thy allow the electron to travel, and band gap if they do not. For photons in photonic crystals, these energy ranges are correspondingly also called bands and band gaps.
Thus, photonic crystals are good candiates for applications where light has to be guided as in e.g. fibers, but also switches etc. For example, by incorporating materials with strong Kerr-Effect, the guiding behavior can be controlled via the light's intensity. This principle can be used to create optical bi-stability as e.g. in optical flip-flops, and many other applications are possible.
The perferomance of these structures depend strongly on their set up (symmetries, materials, etc.). With help of the FEM method, many different parameters can be tested and thus photonic crystal based devices be developed for certain applications such as e.g. low light power optical switching.