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 ultra-fast, short-hop wireless links where large datasets have to be transferred across
hospital campuses or between research facilities on 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
around 100 billion times every second.
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.
The use of acoustic waves to vibrate the quantum wells inside the quantum cascade laser generates the impact of a pulse from
another laser onto an aluminium film. This caused the film to expand and contract, sending a mechanical wave through the quantum
The THz band is a new and vast frequency resource expected to be used for future ultrahigh-speed wireless communications.
Terahertz could offer ultrahigh-speed links to satellites as well, which can only be wireless. That could, in turn, significantly boost in-
flight network connection speeds. Other possible applications include fast download from contents servers to mobile devices and
ultrafast wireless links between base stations. Another, completely new possibility offered by terahertz wireless is high-data-rate
minimum-latency communications. Optical fibers are made of glass and the speed of light slows down in fibers. That makes fiber
optics inadequate for applications requiring real-time responses. Today, you must make a choice between ‘high data rate’ (fiber
optics) and ‘minimum latency’ (microwave links). You can’t have them both. But with terahertz wireless, we could have light-speed
minimum-latency links supporting fiber-optic data rates.
Author: Yash Shah