Magnets tune photonic crystal

Researchers from Fudan University in China have found that it is possible to use a magnetic field to quickly shift or block certain frequencies of electromagnetic signals passing through photonic crystals made from semiconductor material.

Photonic crystals are materials containing regularly spaced tiny rods or holes. The spacing of gaps in the material determines the way that electromagnetic radiation like radio and light waves flows through the material.

Photonic crystals could be used to make chips that control the flow of electromagnetic radiation similar to the way that today's computer chips control the flow of electricity. The researchers' method could be used to make devices that switch and filter different wavelengths in the gigahertz and terahertz ranges used in high-speed radio communications. The method does not work for the visible or infrared light used in optical communications.

Applying a magnetic field to the researchers' crystal changes its dielectric constant, which determines the strength and frequency of electromagnetic waves that can pass through the material. The method changes the crystal's properties more quickly than methods that use temperature or electricity, according to the researchers.

The tunable photonic crystals could be used in practical applications in five years, according to the researchers. The work appeared in the November 5, 2003 issue of Physical Review B.