Light control becomes crystal clear

Japanese research paves the way to the control of photons in specialised crystals.

Photonic crystals, which block the propagation of light at particular wavelengths, could represent the future of computing, because light is a much faster and more efficient means of transmitting information than electrons. But first, crystals must be developed that accurately control light not just block it. Researchers at Kyoto University, Japan claim to have succeeded in synthesising just such a crystal.

Photonic crystals block light thanks to photonic band gaps, through which light of specific wavelengths cannot pass. Scientists have developed three-dimensional photonic crystals that block light of varying wavelengths, but in order to produce functional photonic chips the crystals must also emit light in a controlled manner. For this, defects and light emitters must be added to the crystals, which nobody had yet achieved.

The Japanese team built on earlier work where they constructed highly effective photonic crystals by stacking single crystalline GaAs layers on a GaAs substrate using a precise laser-assisted alignment technique. To these GaAs layers, the researchers fused a light-emitting layer comprising an InGaAsP multiple quantum well grown on an InP substrate, and then added an equal number of GaAs layers on top. Crystals of either five or nine layers were constructed, with the nine layer crystal around 200nm thick.

The researchers found that the InGaAsP layer would emit light when excited by a laser and that this is normally suppressed over a broad range of wavelengths by the GaAs layers, with the nine layer crystal most effective. The researchers generated point defects of varying sizes in the light emitting layer, which caused the crystal to emit light, but only at the defects. Furthermore, the light wavelengths emitted by the crystal depended on the size of the defect.

The researchers claim that the development of this crystal is ’an important step towards the complete control of photons in photonic crystals’.

Jon Evans