Highly Efficient Coupling Between Inner and Surface Fields in Photonic Crystal Waveguides

Connecting inner and surface propagation field in photonic crystal waveguides (PCWs) with an efficient method is critical to achieve flexible designs and applications in photonic integrated circuits. This letter realizes highly efficient coupling between inner and surface PCWs by modifying the structures of waveguides and interface. The aim of the modification is to achieve a good match of modal field profiles between different types of waveguide structures as well as suppress the reflected field at the interface. The numerical results based on finite difference time-domain simulations show that the bandwidth for coupling efficiency larger than 90% can be as broad as over 100 nm.