Researchers from École Polytechnique Fédérale de Lausanne (EPFL) have developed a method of reconfiguring microwave photonic filters without the need for an external device. The research may enable more compact, environmentally friendly filters at lower cost. Potential applications include those involving detection and communication systems. By establishing interference between two pulses within a microcomb, the researchers were able to accurately control the pulses in order to reconfigure the outgoing radio frequency. The effort generated different types of microcombs on a silicon nitride chip, to produce high-quality soliton pulse signals. The wavelength of the signal generated can be modified either by varying the light source or by changing the shape or material of the optical channel it passes through. “Using a light source that can combine several wavelengths means that we can keep the filter’s structure quite simple,” said Camille Brès, who leads the Photonic Systems Laboratory. “If we can reconfigure the frequency by altering the light pulse, we don’t need to change the physical support.” Researchers from EPFL's Photonic Systems Laboratory, led by Camille Brès (left), have reconfigured microwave photonic filters without an external device. Potential applications include detection and communications systems. Courtesy of EPFL. For the filters to be used in various applications, they also need to be capable of altering the outgoing radio frequency. “Current filters require programmable pulse shapes to set the outgoing frequency and improve the wave quality, which makes the systems complex and hard to market,” said Jianqi Hu, a Ph.D. student in the Photonic Systems Laboratory and lead author on the study. To overcome this obstacle, the researchers generated on-chip interference between two solitons. By modifying the angle between them, they were able to reconfigure the filter frequency. The development means that the systems can be made fully portable and used with 5G and terahertz waves. The research was published in Nature Communications (www.doi.org/10.1038/s41467-020-18215-z).