Plasmonic multi-level coupled systems: route to 3D integration

Surface-plasmon-polaritons are surface electromagnetic waves that propagate at a metal-dielectric boundary. They enable the observation of unique optical phenomena in a 2-dimensional evanescent wave system, due to their lower dimensionality and their ability to confine and enhance the optical field. Recent technological advances have seen a lot of effort put in an attempt to achieve 3D routing of optical signals, for example by using 3D photonic crystals, while still attempting to maintain confined wave-guiding with a vertical footprint of several micrometers. To idealize this and allow equally strong and scalable plasmonic integration, 3D plasmonic circuitry should be enabled. This would demand an ideal platform to support the circuits residing at the various layers and also to allow the efficient delivery of plasmonic signals to and from these individual layers. Therefore, a compact and robust technique that can enable this would be highly beneficial.

Tel-Aviv University researchers in Israel, led by professor Ady Arie, developed a novel type of plasmonic solution. They believe that their new coupled plasmonic system, which is based on a stack of metal-dielectric layers, would provide a long lasting, robust and scalable solution to the aforementioned shortcoming. Their work is now published in the research journal, Optics Express

The research team exploited the autonomous principle, that the physical interaction between plasmons supported by a vertical stack of metal/dielectric layers can be described by a coupled multi-level system, where each metal/dielectric interface acts as a single level. These individual levels can couple to each other and thus transfer energy, of the plasmonic signal, between them. Equipped with this, they demonstrate the coupling between two plasmons on two different interface, which is a plasmonic two-level system. Next, the authors extend this concept to a plasmonic four-level system, where four plasmons propagating on different interfaces can be coupled. In such a four level structure, the authors observed that it becomes possible to adiabatically eliminate the plasmonic waves in all the intermediate interfaces (or levels), when the permittivities and thicknesses of the intermediate layers are appropriately selected, thus transferring the plasmonic signal only between the outer layers. In addition, the authors show that it is also possible to shape the wavefront of the propagating plasmons in this system, and this shape will be maintained even when transferring the plasmons energy between the different levels.

The research team, that also included Dr. Itai Epstein, Dr. Haim Suchowski, Dror Weisman and Roei Remez from Tel Aviv University, has provided analytical and experimental demonstrations of propagation dynamics in multi-level coupled plasmonic system. This developed technique is of significant value for plasmonic on-chip circuitry and sensing, and will pave the way to new possibilities for 3D integration technologies. Altogether, this novel system can support multiple wavelengths, making it attractive to multiplexing applications and can be further extended to other well-known concepts for efficient and robust coupling.