Tuesday, October 28, 2014

CST interviews Professor Mário G. Silveirinha, University of Coimbra, Portugal


Professor Mário G. Silveirinha is an associate professor in the Electrical Engineering Department at the University of Coimbra in Portugal. His interests include metamaterials, nano-optics and plasmonics. His group won the CST University Publication Award in 2012 for a research paper on ultraconfined interlaced plasmons. We had the opportunity to ask him a few questions about his research and his use of simulation.

CST: Hello Mario, we’re happy you could take the time to speak to us. The paper which won our University Publication Award was for a study of ultraconfined interlaced plasmons. What was the background to this work – was it purely theoretical, or are there applications for these plasmons?

There are indeed many applications!

In general, the diffraction of light prevents us from doing many interesting things. For example, diffraction limits the miniaturization of microwave and optical devices because the confinement of light in a standard waveguide (e.g. an optical fiber) requires that the characteristic size of the cross-section should be of the same order of magnitude as the light wavelength.
In our work, we explored the potentials of a novel artificial material formed by a dense mesh of crossed metallic wires showing that it supports localized charge density oscillations (interlaced plasmons), whose characteristic spatial size is determined by the entanglement of the grids, rather than by the electrical length of the metallic wires.
Interestingly, because of the deeply subwavelength size of the interlaced plasmons, they can serve as the basis for either novel ultra-subwavelength waveguides, or for the design of novel broadband “superlenses” able to restore subwavelength features inaccessible to conventional systems.
For example, in a follow up study (M. G. Silveirinha, C. R. Medeiros, C. A. Fernandes, J. R. Costa, New J. Phys. 13, 053004, 2011) we experimentally verified that the interlaced plasmons enable to resolve objects separated by subwavelength distances over a broad range of frequencies. This can have interesting applications in sensing, microscopy, and in radiofrequency identification systems (RFID).

CST: How did you use simulation in this project, and how did it fit in with the theoretical and experimental work?

We used CST MICROWAVE STUDIO® (CST MWS) to characterize the electromagnetic response of a microwave prototype that served to demonstrate the excitation, ultra-confinement, and the propagation of the interlaced plasmons. The agreement between CST and our experimental results was really good! Moreover, the results obtained with CST compared extremely well with an analytical model developed by us.

CST: Did the award help you or your group in carrying out research?

Absolutely! Most of all, I would like to say that we were really honored that our research work was distinguished by CST. The award gave us additional resources to run our simulations, and this was extremely useful because CST MWS is an invaluable work tool in most of our projects.

CST: Is there any other work you’re involved in that you would like to highlight?

Yes, recently we became interested in the problem of trapping light in a bounded open material cavity. The lifetimes of light oscillations in closed lossless cavities, e.g. a closed metallic box with perfectly conducting walls, can in theory be infinitely large because the photons are unable to escape the system. However, in open systems the light energy continuously leaks away in the form of a radiated wave, and hence the oscillation lifetime is finite. Interestingly, we discovered a way out of this bottleneck (M. G. Silveirinha, Phys. Rev. A, 89, 023813, 2014), and demonstrated that in the limit of no material loss volume plasmons may provide perfect electromagnetic shielding. Our solution allows for free light oscillations with an infinite lifetime in a dielectric core, despite the fact that the cavity is open and transparent to the radiation coming from the outside world. CST MWS was essential to support our ideas, and allowed us to demonstrate how based on nonlinear materials it may be possible to trap quantized amounts of radiation – with a very specific value of the electromagnetic energy – in an open cavity!

CST: Thank you for your time, and for sharing some very interesting results with us!

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