WIRELESS COMMUNICATIONS
❱❱ Optical frequency combs generated in quantum cascade lasers. The discovered harmonic comb regime produces a spectrum with an intermodal spacing that is 10 to 100 times larger than that observed in fundamental frequency combs (below) enabling completely new applications in this platform
other basic issues for such data carrier waves. Terahertz beams transmitted through materials
can be used for material characterisation, layer inspection and as an alternative to X-rays for producing high-resolution images of the interior of solid objects. Today, they play a role in medical and communications technology, but also in materials testing; they were used to inspect the plastic insulation on the space shuttle. “Developing the terahertz bandwidth opens up
new directions,” says Shaghik Atakaramians from the University of New South Wales. “For example, terahertz security screenings at airports are increasingly used to discover hidden items and explosive materials as effectively as X-rays, but without the dangers of X-ray ionisation.” Wireless communications using the terahertz
spectrum could be used to expand the world’s increasingly over-subscribed bandwidth requirements, thanks to new technology allowing for its exploitation. Optical fibres are the frontrunners in fast data transmission, with data encoded as microwave radiation, the limitations of which are increasingly apparent. Terahertz radiation provides a more focused signal that could improve the efficiency of communication stations and reduce power consumption of mobile towers. However, scientists have been unable to develop a
Terahertz: T
bridging the wireless communications gap?
Andy Pye looks at why there is a race to generate terahertz waves more efficiently and cheaply
erahertz radiation lies at the far end of the infrared band, just before the start of the microwave band. The “terahertz gap” is so- called because technology for its generation and manipulation is in its infancy.
Terahertz (THz) radiation has frequencies
higher than 95 gigahertz (GHz) and are thus higher in photon energy than typical wireless carrier waves, such as Bluetooth or standard Wi- Fi. It is outside the range where the US Federal Communications Commission (FCC) has established service rules. Bandwidth in this region of the spectrum could be available for use in future wireless technologies, but little is known about power requirements, architectures, hardware or
terahertz magnetic source, a necessary step to harness the magnetic nature of light for terahertz devices. The problem is that powerful radiation sources, known as emitters, are needed to generate the waves. Most current terahertz generators use large, complex optical systems operating at very low temperatures to produce terahertz frequencies.
SUB-WAVELENGTH FIBRE GENERATOR Electrical and optical engineers in a collaboration of Australian universities have designed a novel platform that could tailor telecommunication and optical transmissions. They have experimentally demonstrated their system using a new transmission wavelength with a higher bandwidth capacity than those currently used in wireless communication. So the Australian researchers investigated how the
pattern of terahertz waves changes on interaction with an object. The idea was that a magnetic terahertz source could theoretically be produced when a point source is directed through a sub- wavelength fibre (a fibre with a smaller diameter than the radiation wavelength). The fibre was made of a glass material that supports a circulating electric field, which is crucial for magnetic induction and enhancement in terahertz radiation. Another advantage of the source-fibre platform, in
this case using a magnetic terahertz source, is the proven ability to alter the enhancement of the terahertz transmissions by tweaking the system. “We could define the type of response we were getting from the system by changing the relative orientation of the source and fibre,” Atakaramians says. This ability to selectively enhance radiation isn’t
limited to terahertz wavelengths. “The conceptual significance here is applicable to the entire
March 2018 /// Environmental Engineering /// 15
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