Non-classical interference in integrated 3D multiports
  We demonstrate three and four input multiports in a three dimensional glass platform, fabricated using the femtosecond laser direct-write technique. Hong-Ou-Mandel (HOM) interference is observed and a full quantum characterisation is performed, obtaining two photon correlation matrices for all combinations of input and output ports. For the three-port case, the quantum visibilities are accurately predicted solely from measurement of the classical coupling ratios. 
Thomas Meany, Michael Delanty, Simon Gross, Graham D. Marshall, M. J.   Steel, and Michael J. Withford
quant-ph physics.optics