Vertical couplers for multi-layer photonic integrated circuits
Similar to microelectronic circuits, future photonic chips will include multiple layers of different materials to integrate functionality in a single circuit. 
One of the key challenges is to couple light between the different layers.
Together with the nanophotonics group at the Centre for Advanced Photonics and Process Analysis, we have now developed an efficient and compact coupler for vertically integrated system. We use a two-level tapered waveguide to efficiently couple light between a silicon and a silicon nitride layer.