Controlling Photonic Nanojets: From the Standpoint of Eigenmodes

In this letter, we explain how to quickly engineer and optimize photonic nanojets (PNJs) using eigenmode expansion and a transmission matrix theory. We systematically investigate how to realize an ultra-narrow beam waist and how to steer and shift the PNJ hot spot position using different linear combinations of eigenmodes. The ability to design complex beam shapes makes the technique attractive in numerous applications, including inspecting nanoparticles located deep inside a cell, super-resolution imaging, and optical lithography.