Counterpropagating Twin Photons in the Telecom Range: a Narrow-Bandwidth Semiconductor Source

We experimentally demonstrate a counterpropagating twin photons source consisting of an AlGaAs multilayer waveguide. In our geometry, a pump beam impinging on top of a waveguide generates parametrically two counter propagating, orthogonally polarized signal/idler guided modes through a type II nonlinear interaction. Two phase-matched processes occur simultaneously in our scheme: in the first one, the photon copropagating with the z component of the pump beam is TM polarized and the counter propagating one is TE polarized. In the second one, the vice versa occurs. The most attractive application of this device is a narrow-bandwidth fibered source of entangled photon pairs, where signal and idler photons are collected at the opposite waveguide facets with low coupling losses.