GaN directional couplers for integrated quantum photonics
  Large cross-section GaN waveguides are proposed as a suitable architecture to achieve integrated quantum photonic circuits. Directional couplers with this geometry have been designed with aid of the beam propagation method and fabricated using inductively coupled plasma etching. Scanning electron microscopy inspection shows high quality facets for end coupling and a well defined gap between rib pairs in the coupling region. Optical characterization at 800 nm shows single-mode operation and coupling-length-dependent splitting ratios. Two photon interference of degenerate photon pairs has been observed in the directional coupler by measurement of the Hong-Ou-Mandel dip with 96% visibility. 
Yanfeng Zhang, Loyd McKnight, Erman Engin, Ian M. Watson, Martin J.   Cryan, Erdan Gu, Mark G. Thompson, Stephane Calvez, Je...
physics.optics cond-mat.mtrl-sci quant-ph