  Recent experiments in orbital angular momentum multiplexing have demonstrated
its potential for improving the link capacity in optical interconnection
networks. Meanwhile, compact photonic integrated orbital angular momentum
(de-)multiplexing devices are needed to address requirements such as high
scalability, fast configurability, low cost and low power consumption. Here we
report on a large-scale integrated tunable orbital angular momentum mode
multiplexer, which supports up to 20 multiplexed orbital angular momentum modes
over 16 wavelength channels with 30 GHz channel spacing. A testbed of nine
multiplexed OAM beams encoded with 28 Gbaud 16-quadrature amplitude modulation
signal is demonstrated, achieving a 1.008 Tbit s-1 aggregated rate with low
penalty and sub-microsecond reconfiguration rate of the orbital angular
momentum mode. This device offers an effective solution for replacing bulky
diffractive optical elements, paving the way for orbital angular momentum
multiplexing in optical interconnection networks.
