Integration of Nanoemitters onto Photonic Structures by Guided Evanescent-Wave Nano-Photopolymerization

In this article, we demonstrate the feasibility of self-positioning nanoemitters onto optical waveguides by visible-light nanoscale photopolymerization. A light-sensitive material containing nanoemitters is photopolymerized at interfaces by using the evanescent field of the light propagating in photonic structures. By exploiting this method, it is possible to pattern polymeric ridges containing CdSe/ ZnS nanocrystals (NCs) directly on top of optical guiding structures. Photopolymerization experiments have been performed in the case of a single ion-exchange glass waveguide (IEx WG) and of a double waveguide made of the IEx WG with a thin titanium dioxide film fabricated on top of it. Atomic force microscopy (AFM) and spectroscopy analyses highlight the reliability and reproducibility of the fabrication technique. Continuous ridges of controlled thickness have been realized on top of a single waveguide interface with thicknesses as small as 18 nm, thus thick enough to contain only a photoluminescent NC monolayer in the vertical direction. In the presence of the double waveguide (TiO2 layer on top of the IEx WG), AFM measurements reveal that the thickness of the photopolymerized ridge has a sinusoidal modulation. This is due to a light beating phenomenon theoretically predicted in the case of light propagating in coupled waveguides. In our case, the light beating can be efficiently exploited to photopolymerize ridges with modulated thickness. Overall, the flexibility of the reported nanoscale fabrication technique paves the way toward the controlled positioning of single nanoemitters in proximity of nanoantennas or other elaborate plasmonic/photonic structures.