Researchers working at Brown University in Rhode Island have succeeded in creating novel photonic crystals that can be modified in milliseconds. Usually the properties of photonic crystals - which can control the flow of photons - are fixed after they have been fabricated, but the new photonic crystals can be tuned dynamically in order to respond to different wavelengths of light.
The new tunable photonic crystals are made from materials known as holographic-polymer dispersed liquid crystals (or H-PDLCs). Jun Qi and colleagues expose this material to four laser beams, which create an interference pattern. Coherent interference results in the formation of liquid-crystal droplets, and it is these that form the photonic crystals.
The transmission spectrum of the photonic crystals that are made in this way can be varied by applying an electric field that changes the refractive index of the droplets. A wide spectrum of light can be affected, because the new photonic crystals can be built on a wide range of scales. The crystals can also reproduce the effects of structures such as diamond and anisotropic lattices.
The tunable photonic crystals should be useful as optical filters, and with further development may lead to novel lasers and optical waveguides.