MIMO optical wireless at the nanoscale

In recent years, the rise of the field of optical nanoantennas has been largely impacting the way we control and engineer light-matter interactions at the nanoscale, translating and exploiting relevant antenna concepts from radiofrequencies to the optical domain. By efficiently coupling localized, or guided, optical fields to free-space radiation, and vice versa, optical nanoantennas find application in many different scenarios, e.g., sensing, photovoltaics, enhancement of weak non-linearities and quantum effects, local scattering control for wave-shaping metasurfaces, etc. Interestingly, pairs of plasmonic nanoantennas have also been proposed to realize optical wireless broadcasting links, which may allow sending nanoscale optical signals between two points on a chip, with lower attenuation than in conventional plasmonic waveguides (A. Alù and N. Engheta, Phys. Rev. Lett. 104, 213902, 2010). In a different context, it has been shown that subwavelength plasmonic nanostructures and nanoantennas can be designed to maximize the scattering/radiation contributions from several multipolar channels at the same time (dipolar radiation, quadrupolar, etc.), realizing 'superscatterers' with, in principle, unbounded scattering cross section (Z. Ruan and S. Fan, Phys. Rev. Lett., 105, 013901, 2010). Here, by combining these concepts, we will show that it is possible to increase the capacity of optical wireless interconnects by using different multipolar radiation channels (i.e., orthogonal spherical harmonics) to simultaneously carry multiple optical signals (with identical frequency and polarization), effectively realizing a multiple-input multiple-output (MIMO) optical wireless link at the nanoscale.