Researchers have developed a method to control terahertz quantum cascade lasers, which could lead to the transmission of data at the rate of 100 gigabits per second. That ultrafast data transfer would be about 1,000 times quicker than a fast Ethernet operating at 100 megabits a second.
What distinguishes terahertz quantum cascade lasers from other lasers is the fact that they emit light in the terahertz range of the electromagnetic spectrum. They have applications in the field of spectroscopy where they are used in chemical analysis. The lasers could also eventually provide ultrafast, short-hop wireless links where large datasets have to be transferred across hospital campuses, between research facilities in universities, or in satellite communications.
To be able to send data at these increased speeds, the lasers need to be modulated very rapidly, switching on and off or pulsing about 100 billion times every second. Engineers and scientists have so far failed to develop a way of achieving this. The new method delivers ultrafast modulation by combining the power of acoustic and light waves. The same electronics that deliver the modulation usually put a brake on the speed of the modulation. The new mechanism relies instead on acoustic waves.
A quantum cascade laser is very efficient. As an electron passes through the optical component of the laser, it goes through a series of “quantum wells” where the energy level of the electron drops and a photon or pulse of light energy is emitted. One electron is capable of emitting multiple photons. It is this process that is controlled during the modulation.
Instead of using external electronics, the researchers 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.
While the flow could not be stopped and started completely, the light output was controlled by a few percent. With further refinement, a new mechanism can be developed 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.