The new terahertz quantum cascade laser could enable high-speed transfer of up to 100 gigabits per second. (Image Credit: University of Leeds)
Researchers from the University of Leeds and the University of Nottingham have developed a new approach that allows them to control terahertz quantum cascade lasers using light and sound. The breakthrough could enable transfer speeds of up to 100 gigabits per second, which is one thousand times quicker than Ethernet speeds of 100 megabits per second. The team published their findings in the Nature Communications journal on February 11, 2020.
Terahertz quantum cascade lasers differ from traditional lasers because they have the capability to emit light in the terahertz range of the electromagnetic spectrum. Additionally, the technology has applications in the field of spectroscopy for chemical analysis. The lasers could also offer ultra-fast, short-hop wireless links where huge datasets need to be transferred across hospital institutes or between research facilities in universities. It could even be used in satellite communications.
To transfer data at high speeds, the lasers will need to be rapidly modulated by switching on and off approximately 100 billion times every second. To achieve this, the research team combined sound and light waves.
"This is exciting research," John Cunningham, professor of nanoelectronics at Leeds, said in a news release. "At the moment, the system for modulating a quantum cascade laser is electrically driven -- but that system has limitations. Ironically, the same electronics that deliver the modulation usually puts a brake on the speed of the modulation. The mechanism we are developing relies instead on acoustic waves."
A quantum cascade laser is highly efficient. As an electron passes through the optical component, it passes through a series of quantum wells where the electrons energy level drops and releases a photon or a pulse of light energy. A single electron has the ability to emit multiple photons. This process is what’s being controlled during modulation.
Instead of relying on external electronics, the team used acoustic waves to vibrate the quantum wells in the terahertz quantum cascade laser. They produced sound waves by projecting a pulse from another laser onto an aluminum film. This resulted in the film’s expanse and contraction, which sent 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."
The laser will need to undergo small modifications before being added in communication technology or used for spectroscopic imaging and analysis.
"We did not reach a situation where we could stop and start the flow completely, but we were able to control the light output by a few percents, which is a great start," Cunningham said. "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, and perhaps even integrate structures generating sound with the terahertz laser so that no external sound source is needed."
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