Photonic Structures

Yablonovitch and co-workers were amongst the first to suggest constructing artificial three dimensional periodic structures to manipulate the proagation of light. The structure he designed, `Yablonovite' was built on a lengthscale of millimetres and shown to have a complete photonic band gap, that is to prohibit the propagation of microwaves in all directions for certain wavelengths.

`Yablonovite' is made by covering a slab of material with a mask consisting of a triangular array of holes. Then, each hole is drilled through three times at an angle of 35.26 from the normal and spread out 120 degrees on the azimuth. This forms a network of intersecting holes below the surface with an FCC structure. (See the figure above)

In order the produce a crystal which has a band gap at optical wavelengths it is necessary to scale the production process down to a micron length scale. This has, however, proven to be technically challenging. Finding the equivalent of a drill bit with a micron diameter is far from straightforward! This has motivated a search for other structures which are more easily fabricated. One possibility is the Logpile structure, the simple cubic version of which is shown in the second figure. This has proved to be a very useful trial system on which we can test many of our ideas and computational methods.