A novel slot waveguide with tunable, two-dimensional electron gas could
form the basis of a room temperature THz modulator, according to
Massachusetts-based Tufts University.
Through lack of THz facilities, the researchers have created a lower
frequency prototype, than can amplitude modulate a 250GHz carrier to 96%
intensity with a 14GHz signal.
“This is a very promising device that can operate at terahertz
frequencies, is miniaturised using mainstream semiconductor foundry, and
is in the same form factor as current communication devices,” said Dr
Sameer Sonkusale of the University’s Nano Lab. “It’s only one building
block, but it could help to start filling the THz gap.”
According to the paper High speed terahertz modulator on the chip based on tunable terahertz slot waveguide
in Scientific Reports, electromagnetic energy is confined in the
waveguide formed in an InGaAs layer sandwiched between two AlGaAs
layers.
The two dimensional electron gas forms in the InGaAs through differences between its bandgap and that of the surrounding AlGaAs.
At the carrier frequency, its carriers make the 2-D gas lossy causing the carrier to decrease as it passes through.
A negative bias reduces the electron density in the gas lowering
attenuation, while a positive bias increases electron density and
increases attenuation. The full mechanism is described in the paper,
which is available free.
The prototype operates at with under 2V drive and consumes little power.
http://www.electronicsweekly.com/news/research-news/low-power-chip-modulator-thz-potential-2017-01/
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