Photonics: practically there?

Materials that contain a photonic band gap have the potential to manipulate light with remarkable precision. Successful fabrication of such structures, known as photonic crystals, has fueled interest in a whole host of novel optical devices, ranging from miniature lasers and all-optical circuits to smart textiles and biomedical transport systems. Growing confidence that ‘the time is right’ to realize the new technology’s commercial potential has been demonstrated by the emergence of numerous start-up companies, all bidding to bring such innovative products to market. The photonics revolution, proponents say, is just around the corner.Strange things happen to light when it passes through photonic crystals. A significant variation in refractive index between the material’s periodic lattice structure and its substrate traps transmitted photons in either one area or the other, creating distinct ‘allowed’ and ‘forbidden’ energy regions. Light with wavelengths equivalent to the forbidden region, the so-called photonic bandgap, is stopped from passing further. Wavelengths from the rest of the electromagnetic spectrum, on the other hand, are free to continue their passage through the material unhindered. In effect, the material is able to halt the passage of light just as the periodic potential of semiconductors, such as silicon, bars electrons from occupying the forbidden energy bandgap.