Photons will replace electrons in countless tasks because they move faster and consume less energy. These tiny particles of light have the added benefit of being surprisingly flexible, with their frequencies ranging from 1,000 to 10,000 times that of electrons. Thus, using light rather than electricity to manipulate microwaves provides technicians with a much wider bandwidth. Microwave photons are particularly useful in communication systems, the Internet of Things and beamforming. At present, however, microwave photonics systems are still not capable of generating light pulses on computer chips.
Researchers at the Laboratory of Photonic Systems at the école Polytechnique Fédérale de Lausanne (EPFL) have just made a major breakthrough in this field: they have developed reconfigurable radio-frequency filters that can generate high-quality microwaves without the need for bulky external equipment. By creating interference between two pulses within a microcell, they were able to precisely control the pulses in order to reconfigure the RF.
The microwave photonic filter converts the incoming RF into an optical signal, which is then processed by a photonic device to extract information. A photoreceptor converts the signal back to RF. As recently as April this year, researchers in another lab at the école Polytechnique Fédérale de Lausanne succeeded in generating different types of microcombs on a silicon nitride chip to produce high-quality pulsed signals of solitary waves. All that remains is to show that these pulse signals can be used to reconfigure microwaves and that the system is as flexible, linear, spectrally pure, and noiseless as previous, more cumbersome devices, which is exactly what the researchers at the Laboratoire de la Photonique et des Systèmes (LPS) were aiming to do by optimizing the chip.
The technology used in these chips, which are smaller than a coin, is based on the interaction of light with its surroundings. The wavelength of a signal can be modified by changing the light source or by changing the shape or material of the optical channel through which it passes.
Camille Bresse of the Photonic Systems Laboratory explains, "Using a light source that can combine multiple wavelengths means that we can keep the structure of the filter fairly simple." The researchers were able to replace a laptop-sized light generator with a miniature on-chip optical resonator that uses laser pulses to produce perfect solitary waves.
For these filters to be put to practical use in a variety of applications, they also need to be able to change the outgoing frequency.
Jianqi Hu, a doctoral student in the Photonic Systems Laboratory and lead author of the study, said, "Current filters require programmable pulse shapes to set the outgoing frequency and improve the wave quality, which makes the system complex and difficult to put into use." To overcome this obstacle, the researchers generated on-chip interference between two solitary waves by modifying the angle between them, making it possible to reconfigure the filter frequency. This breakthrough means that these systems can be made fully portable and used with 5G and terahertz waves.
Nature Communications published the research.