Orbital angular momentum entanglement via fork-poling nonlinear photonic crystals Lu, L. L. ; Xu, P. ; Zhong, M. L. ; Bai, Y. F. ; Zhu, S. N. Abstract Publication: Optics Express Pub Date: January 2015 DOI: 10.1364/OE.23.001203 Bibcode: 2015OExpr..23.1203L