Light propagation in conventional photonic systems is ruled by the Lorentz reciprocity law. According to the reciprocity principle, if the positions of the source and receiver are swapped the transmission level is unchanged. Thus, reciprocal systems are inherently bidirectional, independent of any spatial asymmetry.
“One-way” light flows can be obtained with ferrites or other iron garnets biased with a static magnetic field. Indeed, nonreciprocal devices, such as isolators and circulators, are essential building blocks of communication systems. However, at optical frequencies the standard solutions are bulky and/or challenging to integrate on-chip. Thereby, there is a great interest in novel approaches that can enable the “one-way” functionality in future integrated photonic platforms.
In project One-Way, a research team from IT, coordinated by Mário Silveirinha, studied several unconventional mechanisms to break the Lorentz reciprocity. The main research direction was inspired by the electrodynamics of systems with moving components. Results have shown that in some conditions the relative motion of two uncharged material bodies, such as a metal sphere moving very fast and parallel to a metal sheet, may trigger the emission of coherent light. The emitted energy is due to the spontaneous conversion of the kinetic energy of the moving body into radiation, some sort of a laser pumped by the physical “motion”. However, the effect is significant only when the distance between the two objects is on the order of 10nm and the relative velocity is about one tenth of the speed of light in vacuum.
To overcome this restriction, researchers suggested imitating the translational motion of a uncharged body in vacuum with a drift electric current in a solid state material. Indeed, the electromagnetic response of a material with drifting electrons is to some extent equivalent to that of the corresponding moving structure and with no drifting electrons. Building on this idea, it was showned that a “cavity” formed by a drift-biased graphene sheet and a second graphene sheet with no drift current may spontaneously emit mid-IR radiation due to the conversion of the drifting electrons kinetic energy into light.
Furthermore, the drifting electrons can effectively drag the plasmon waves along the direction of motion, in the same manner as a boat near a water fall is dragged by the stream when the stream velocity exceeds some threshold value. Thus, the drift-current bias can enable a “one-way” propagation. The gain provided by the drift-current biasing may allow for the amplification of the signal, and thereby to boost the propagation length of the plasmons.
These findings may open interesting perspectives in nonreciprocal electromagnetics and offer new opportunities to control the flow of light with one-atom thick nonreciprocal devices and design robust and practical light sources at the nanoscale.
Daniel Dinis, who recently concluded his PhD in Telecommunications at University of Aveiro (UA) hosted by IT, supervised by Arnaldo Oliveira and José Vieira (Both from IT/UA), received an honorable mention in this years´ edition of the IBM Scientific Award.
Since its first edition in 1990, this award is attributed every year by IBM Portugal to a young Portuguese researcher to distinguish works of high merit in the field of Computer Science.
The work that got Daniel the honorable mention is entitled “Real-time Tunable Delta-Sigma Modulators for All-Digital RF Transmitters”, and was developed in collaboration with researchers from Mitsubishi Electric Research Laboratories (Cambridge, MA, USA), namely Dr. Rui Ma, Principal Researcher. Daniel is currently a Radar Front-End Engineer at Thales Nederland B.V., in The Netherlands, which prevented him from attending the event. However through a video presentation played during the ceremony he got to explain the lines that oriented the work developed within his PhD. “The 5G is the next generation of mobile communications. Some of the most innovative features include the use of a massive number of radios in the base stations, peak data transmission rates in the order of Gbps, with low latency and a high density of mobile devices. However, previous generations cannot be ignored by encouraging the design of new flexible and highly integrated radio transceivers. The thesis proposes flexible and software-defined radio architectures capable of supporting high-bandwidth and multi-band signal transmission. Unlike conventional approaches based on digital-to-analog converters and analog conversion systems, the proposed architectures have a fully digital radio datapath from baseband up to the RF stage, which enables the design and development of highly-integrated radio systems”, explained Daniel.
The 28th award ceremony of the IBM Science Award was chaired by President Marcelo Rebelo de Sousa, in Instituto Superior Técnico (IST), Lisbon, this January 16, who handed the diploma to this edition´s winner Marija Vranic from the Instituto de Plasmas e Fusão Nuclear. Maria Vranic thus succeeds to Caroline Conti, the last year´s winner of the €15k award, whose PhD was accomplished at ISCTE-IUL hosted by IT.
Besides President Marcelo Rebelo de Sousa, there were also interventions of other high-profile personalities such as the Minister of Science, Technology and Higher Education, Manuel Heitor, the President of IBM Portugal, António Raposo de Lima, the President of IST, Arlindo de Oliveira and the President of the Jury and also the President of IT, Carlos Salema.
Photo: Daniel during his video presentation