doi:10.1038/nindia.2012.28 Published online 27 February 2012
Researchers have gained insight into new aspects of certain crystals that will help design novel devices for fibre-optic communication. They studied Bragg wave coupling in self-assembled nanosized organic photonic crystals under visible and near-infrared light.
Bragg wave coupling is rare phenomenon present in photonic crystals that can be used to tailor light propagation and emission. Such crystals also stop light from propagating over a frequency range known as the photonic stop-gap, similar to electron bands in semiconductors. Within the stop-gap, high reflectivity is accompanied by low light transmission through the crystal structure.
Bragg wave coupling is important because it forms the basis of the photonic stop-gap. However, no studies have so far explored Bragg wave coupling beyond visible wavelengths in photonic crystals.
The researchers synthesized two types of photonic crystals from nanosized beads of polystyrene and poly(methyl methacrylate). They then irradiated the crystals with visible and near-infrared light and studied their various optical properties, including Bragg wave coupling.
The researchers irradiated the crystals at various angles, and found that Bragg wave coupling extended over an angular range of 18°. The incident light penetrated deep inside the crystals and diffracted on various crystal planes. At an incidence angle of 53°, two diffracted Bragg waves of equal intensity were coupled in the crystals at a separation of 100 nm.
"This wave coupling in photonic crystals can lead to many applications such as a threshold-less laser that funnels all its photons into lasing without any waste," says lead researcher Rajesh V. Nair.