Time provides a new window into plasmonic signal analysis

The plasmonic phenomena that occur at the interface of some (typically metallic) materials have fundamental characteristics that are particularly intriguing from the electrical engineering perspective. The oft-optically excited, nonradiative resonances offer potential opportunities to achieve faster communication while also shrinking semiconductor devices beyond the current limits dictated by resistance and thermal effects.

While plasmonic investigations, both theoretical and experimental, typically unfold in the frequency domain, the time domain offers a more practical viewpoint for the propagation of signals. Though time is the more complicated dependency on which to explore propagation behavior, the abrupt starts and stops inherent to information transfer make it necessary. Agrahari et al. address this need in their recent article examining — in the time domain — the propagation of a plasmonic pulse across an air gap.

“The FDTD technique that we used has been known and used from the 1960s,” said co-author Akhlesh Lakhtakia. “The key issue was the formulation of a problem that was both doable and interesting.” For a sufficiently complex signal that was still computable, the problem employed a symmetric geometry for two metallic structures on either side of a dielectric gap, vacuum in this case.

The authors analyzed a pulsed surface plasmon polariton, the propagating form of a plasmonic excitation, as it moved through the computational domain in time. Simulated video of the signal propagation included with the work, initiated by a ∼30 femtosecond pulse, shows the signal traveling from one side of the gap to the other. They also developed time-domain specific methods for verifying the temporal broadening and amplitude effects their numerical simulations revealed. With this new modeling tool in hand, they are also beginning similar investigations using nontrivial dielectric materials.

Source: “Information carried by a surface-plasmon-polariton wave across a gap,” by Rajan Agrahari, Akhlesh Lakhtakia, and Pradip K. Jain, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5037919 .