Optical Beehive

A team of Italian and German physicists has developed a new, flexible fabrication technique for rewritable photonic crystal devices, which could make it easier to create and modify circuits in which photons process information in the same way that electric currents do in electronics.

Photonic crystals are structures with a periodically varying refractive index that affects the transmission of light inside the crystal; they behave like a mirror by blocking light propagation at some wavelengths and behave like a transparent medium by letting other wavelengths get through. Defects in the periodic structure, arranged in specific geometries, can act as resonant cavities, mirrors, waveguides, or the optical analogue of transistors.

The new technique is based on a two-dimensional lattice of microscopic pores arranged in a beehive pattern. The researchers can then insert defects by injecting different materials into the pores, which are a few hundreds of nanometers wide. In the photonic crystal, light is mostly confined to the two-dimensional structure, but small amounts leak outside of the plane and can be read out with a near-field microscope. Francesca Intonti, of the European Laboratory for Non-linear Spectroscopy, in Florence, says that the technique makes it easier and more flexible to experiment with different materials and configurations, compared with other fabrication techniques such as lithography; using liquids also allows for the circuits to be reconfigured at will. Another possibility, she says, could be to inject liquid crystals, whose refraction index could then be tuned from the outside, or light-emitting materials, which could act as local sources of laser light. So far, the researchers have created photonic components pixel by pixel, but in principle the process could be automatized, Intonti says.

Intonti et al., Applied Physics Letters, 20 November 2006
Contact Francesca Intonti
European Laboratory for Non-linear Spectroscopy
Tel: +39-055-4572499
intonti@lens.unifi.it
Also see: PNU 633