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Tunable crystal has potential to increase bandwidth for telecomms

A team led by researchers at Sandia National Laboratories in the USA has created a plasmonic, or plasma-containing, crystal that is tunable, which could enhance high-speed electronics.

The effect is achieved by adjusting a voltage applied to the plasma, making the crystal agile in transmitting terahertz light at varying frequencies. The crystal could increase the bandwidth of high-speed communication networks as well as enhancing high-speed electronics.

‘Our experiment is more than a curiosity precisely because our plasma resonances are widely tunable,’ said Sandia researcher Greg Dyer, co-primary investigator of the study. ‘Usually, electromagnetically induced transparencies in more widely known systems like atomic gases, photonic crystals and metamaterials require tuning a laser’s frequencies to match a physical system. Here, we tune our system to match the radiation source. It’s inverting the problem, in a sense.’

The plasmonic crystal method could be used to shrink the size of photonic crystals, which are artificially built to allow transmission of specific wavelengths, and to develop tunable metamaterials, which require micron- or nano-sized bumps to tailor interactions between manmade structures and light. The plasmonic crystal, with its ability to direct light like a photonic crystal, along with its sub-wavelength, metamaterial-like size, in effect hybridises the two concepts.

The crystal’s electron plasma forms naturally at the interface of semiconductors with different band gaps. It sloshes between their atomically smooth boundaries that, when properly aligned, form a crystal. Patterned metal electrodes allow its properties to be reconfigured, altering its light transmission range. In addition, defects intentionally mixed into the electron fluid allow light to be transmitted where the crystal is normally opaque.

The crystal transmits in the terahertz spectrum, a frequency range invisible to the human eye. Scientists also must adjust the crystal’s two-dimensional electron gas to electronically vary its output frequencies.

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