Highly efficient optical filter based on vertically coupled Photonic   crystal cavity and bus waveguide
  We experimentally demonstrate a new optical filter design based on a vertically coupled photonic crystal cavity and a bus waveguide monolithically integrated on the silicon on insulator platform. The use of a vertically coupled waveguide gives flexibility in the choice of the waveguide material and dimensions, dramatically lowering the insertion loss while achieving very high coupling efficiencies to wavelength scale resonators 
Kapil Debnath and Karl Welna and Marcello Ferrera and Kieran Deasy and   David G. Lidzey and Liam O'Faolain
physics.optics