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 SEM image of a slab of macroporous silicon, representing atwo-dimensinal Photonic Crystal (a). The pore walls are about 100 µm tall and about 25 µm wide in the direction of transmission (b).Omitting some pores yielded a wave guide structure (c). The extremely smooth finish of the structure is clearly visible (d). Courtesy of Dr. R. Wehrspohn, University of Karlsruhe.
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.
Source: AIP
Related Links:
Intonti et al., Applied Physics Letters, 20 November
2006.
European
Laboratory for Non-linear Spectroscopy
Photonic
Crystals Tutorial
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