  Light carrying orbital angular momentum constitutes an important resource for
both classical and quantum information technologies. Its inherently unbounded
nature can be exploited to generate high-dimensional quantum states or for
channel multiplexing in classical and quantum communication in order to
significantly boost the data capacity and the secret key rate, respectively.
While the big potentials of light owning orbital angular momentum have been
widely ascertained, its technological deployment is still limited by the
difficulties deriving from the fabrication of integrated and scalable photonic
devices able to generate and manipulate it. Here, we present a photonic
integrated chip able to excite orbital angular momentum modes in an 800 m long
ring-core fiber, allowing us to perform parallel quantum key distribution using
2 and 3 different modes simultaneously. The experiment sets the first steps
towards quantum orbital angular momentum division multiplexing enabled by a
compact and light-weight silicon chip, and further pushes the development of
integrated scalable devices supporting orbital angular momentum modes.
