The current Wi-Fi and cellular data traffic is growing exponentially, but unless the wireless link capacity is actually increased, then exponentially increasing traffic is bound to cause many problems. The upcoming 5G network is just a temporary solution.
Researchers are currently investigating sub-millimeter wavelengths in the terahertz frequency-electromagnetic spectrum to develop long-term solutions. Data transmitted at the terahertz frequency can be hundreds of times faster than current wireless speeds.
Researchers at the School of Engineering and Applied Science (SEAS) at Harvard University have discovered that infrared frequency combs in the quantum cascade green laser pointer can provide a new way to generate terahertz frequencies. They also discovered a new phenomenon in quantum cascade laser (QCL) frequency combs that allow these devices to act as integrated transmitters or receivers that effectively encode information.
Federico Capasso, professor of applied physics, said: "This research represents a complete paradigm shift in the way lasers operate. This new phenomenon converts the green laser pointer, a device that operates at optical frequencies, into an advanced modulator of microwave frequency. This is of great technical significance for the efficient use of bandwidth in communication systems."
Frequency comb is a widely used high precision tool for measuring and detecting light at different frequencies. Unlike conventional lasers that emit a single frequency, the frequency comb can simultaneously emit multiple frequencies, evenly spaced to resemble the comb teeth. Optical frequency combs are used to range from measuring specific molecular fingerprints to detecting exoplanets in the distance.
The SEAS study represents a complete paradigm shift in the way green laser pointers operate. However, the researchers are not interested in the light output of the laser.
Marco Piccardo, a post-doctoral researcher at SEAS and the first author of the paper, pointed out: "We have a great interest in the changes in the internal laser and the electronic frame of the laser. We have shown for the first time that lasers with optical wavelengths can operate as microwave devices."
Within the laser, simultaneous operation of light at different frequencies produces microwave radiation. The researchers found that light in the laser cavity causes electrons to oscillate at microwave frequencies, all of which are in the communication spectrum. This oscillation can be modulated externally to encode information onto the carrier signal. Capasso said that if properly operated, QCL is a natural frequency comb. Capasso pointed out: "We call them harmonic combs. They are not very close to each other, but they are far apart. And they are still adjustable, which opens up a whole new perspective for our research. Never before in lasers This function has been demonstrated. We have shown that the green laser pointer can act as a so-called quadrature modulator, allowing two different messages to be transmitted simultaneously over a single frequency channel and successfully retrieving information at the other end of the communication link. ”
The Harvard Technology Development Office has implemented measures for intellectual property related to the project and is exploring opportunities for commercialization.
Capasso said: "At present, due to limited bandwidth, terahertz sources have great limitations. This discovery opens up new applications for frequency combs and may become a source of terahertz wireless communication in the near future."