Glasses Make Versatile Crystals

Max Glaskin

Photonic quasicrystals with complete bandgaps can be made in glasses that are typically used for fiber optic telecommunications.

Researchers at the University of Southampton have shown that materials with a low refractive index, such as silicon nitride and glass, are suitable hosts.

"These quasicrystalline lattices could be used wherever you need a complete bandgap, such as in rare-earth doped glass lasers. They could also find a home when high isotropy is required, such as in sharp waveguide bends," said Greg Parker, leader of the research team, which has built a quasicrystal with twelve-fold symmetry.

At the entrance face of the photonic quasicrystal, multiple beam-diffracted reflections can be observed.

Photonic crystals inhibit the spontaneous emission of light because their bandgaps prevent the propagation of some electromagnetic waves. They can be created by etching two-dimensional periodic lattices of vertical air holes into dielectric slab waveguides.

The problem is that they can be made only in high-refractive-index materials, such as gallium arsenide. When these are combined with optical fibers, transmission is reduced significantly.

The Southampton team made two-dimensional quasicrystalline lattices, instead of periodic, so they would be more isotropic. "The higher degree of symmetry means you can come in at more different angles and the optical properties look the same," said Parker. The experiments, which were reported in the April 13 issue of Nature, showed that complete bandgaps could be created in materials with a low refractive index.

British Technology Group holds the patents on the work. "Rather than commercializing the devices ourselves, we would prefer that companies interested in utilizing the technology come to an agreement with [British Technology Group] and then work with us to develop commercial systems," said Parker.

However, the researchers are starting a spin-off company to see what commercial opportunities they can exploit themselves.

Meanwhile, they are proceeding with research into three-dimensional modeling so that they can predict more accurately how the planar, or 2-D, devices work.