Generation of orbital-angular-momentum entangled biphotons in twisted nonlinear waveguides

We describe the generation of photon pairs entangled in optical angular momentum (OAM) through spontaneous four-wave mixing (SFWM) in circular arrays of nonlinear waveguides. We show that the incorporation of the array twist along the waveguides can enable robust generation even in presence of defects and inhomogeneities. We present analytical results and numerical simulations based on coupled-mode equations for the classical pump field and a discrete Shrodinger equation for the biphoton wave function. (paper)