Breakthrough in Terahertz Quantum Cascade Lasers

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A research team from the University of Leeds and the University of Nottingham believe they have found a way of delivering ultrafast modulation, by combining the power of acoustic and lightwaves. They published their findings in Nature Communications.

The research involves the control of terahertz quantum cascade lasers, which the team reports could lead to the transmission of data at the rate of 100 gigabits per second, around one thousand times quicker than a fast Ethernet operating at 100 megabits a second.

The lasers are thought to eventually provide ultrafast, short-hop wireless links where large data sets have to be transferred across hospital campuses or between research facilities on universities. To be able to send data at these increased speeds, the lasers need to be modulated rapidly by switching on and off or pulsing around 100 billion times every second.

“This is exciting research,” said John Cunningham, professor of nanoelectronics at Leeds. “Ironically, the same electronics that delivers the modulation usually puts a brake on the speed of the modulation. The mechanism we are developing relies instead on acoustic waves.”

Instead of using external electronics, the researchers at Leeds and Nottingham used acoustic waves to vibrate the quantum wells inside the quantum cascade laser.

The acoustic waves were generated by the impact of a pulse from another laser onto an aluminum film. This caused the film to expand and contract, sending a mechanical wave through the quantum cascade laser.

“Essentially, what we did was use the acoustic wave to shake the intricate electronic states inside the quantum cascade laser,” said Tony Kent, professor of physics at Nottingham. “We could then see that its terahertz light output was being altered by the acoustic wave.”

Cunningham added that his researchers did not reach a situation where they could stop and start the flow completely, but they were able to control the light output by a few percent.

“We believe that with further refinement, we will be able to develop a new mechanism for complete control of the photon emissions from the laser,” Cunningham said, “and perhaps even integrate structures generating sound with the terahertz laser, so that no external sound source is needed.”

Published: February 2020
In general, changes in one oscillation signal caused by another, such as amplitude or frequency modulation in radio which can be done mechanically or intrinsically with another signal. In optics the term generally is used as a synonym for contrast, particularly when applied to a series of parallel lines and spaces imaged by a lens, and is quantified by the equation: Modulation = (Imax – Imin)/ (Imax + Imin) where Imax and Imin are the maximum and minimum intensity levels of the image.
Research & TechnologyUniversity of LeedsUniversity of NottinghamEuropeEnglandterahertz quantum cascade laserEthernetnanoelectronicsacoustic wavesquantum wellsLasersquantum cascade lasersQCLsmodulationTech Pulse

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