Light coupling between nanowire and optical waveguide by microsphere photonic nanojet

Abstract

The invention presents and demonstrates a novel light coupling system and design method for highly efficient coupling of Nanowires or Nanowires with embedded Quantum Dots (NWQDs) to optical waveguides, and is based on an optical arrangement employing an mesoscale optical dielectric microelement, like a dielectric microsphere (or alternatively half-sphere, cylinder, half-cylinder of mesoscale dimensions) placed between the nanowire and the optical waveguide, suitably optimized in terms of: 1) Size (diameter) of the microsphere, 2) Refractive index of microsphere, 3) Distance between the nanowire and the microsphere, 4) Distance between microsphere and waveguide. Upon suitable design of the optical arrangement, the photonic nanojet emitted by the microsphere illuminated by the nanowire, excites efficiently the guided eigenmode(s) of the input waveguide, thus launching optimally light with high coupling efficiency to lossless guided modes. The method is tolerant and robust in terms of displacements, misalignments, and imperfections given also the current state of the art tools, like nano / micro manipulators for accurate handling of such elements (nanowires, microspheres). Application of the method has been successfully demonstrated in the most demanding case of directly laser written waveguides of low refractive index contrast in silica and silica-on-silicon platform. The invention solves a very challenging problem and the solution is expected to have a high impact in Quantum technology due to the interest of developing optical quantum computers based on highly customised and scalable quantum photonic integrated circuits.

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