F.A.Q. - Photonic crystals

Photonic crystals are materials exhibiting a periodic dielectric structure on a microscopic scale. This periodic structure implies a number of unique properties that makes photonic crystals especially attractive for integrated optics use.

Photonic crystals have properties that cannot be realized by conventional integrated optics. A carefully designed photonic crystal, for example, is capable of prohibiting the propagation of light, a phenomenon that can occur either for any direction or just for specific directions. In addition, the reflection and refraction properties are far from conventional. All this gives rise to completely new device concepts and applications that are far more functional than classic solutions.

The main benefits of photonic crystal devices are without doubt their small size and the high integration density. The counterparts of classical waveguide bends, couplers and interferometers are usually one hundred to one thousand times smaller when made of photonic crystal material. In particular the ability to guide light around sharp bends will allow us to design photonic circuits comparable to those in micro-electronics. We have developed concepts for DWDM devices roughly fifty times smaller than AWGs, with channel-spacing which is equivalent or even smaller.

Photeon's photonic crystal devices are designed in such a way, that their fabrication is fully compatible with semiconductor processes. The planar structures can be fabricated in state-of-the-art foundries.

Similar to the energy-gap for electrons in a semiconductor, photonic crystals exhibit an energy-gap for photons. This means that photons, whose energy (and thus frequency) is in a certain region, are not allowed to exist inside the photonic crystal. This region is called a bandgap, because by convention, the allowed energy values with respect to the wave number are expressed in terms of bands in a photonic crystal. So if there are forbidden energies, there are no energy-bands in that region and a bandgap occurs.

Starting with normal waveguides, a huge variety of devices can be realized with photonic crystal technology. These include couplers, interferometers, laser cavities and demultiplexers for both polarization and wavelength, all of which can be integrated very densely.