When plasmonic resonances interact with sharp modes often the result is a Fano
interference processes. This happens because the plasmonic excitations are usually broader than the others resonances, and the characteristic narrow asymmetric Fano line-shape is obtained. The spectral shaping of plasmon resonances in metal nanostructures via controlled plasmon hybridization and Fano interferences is receiving growing attention, due to the possibility of designing new materials with a controlled response to light at the nanoscale.

We show that considering a plasmonic resonance in the original Fano model a simple and exact analytic relation can be found.