Polarization diversified integrated circuits for orbital angular momentum multiplexing

We present a free-space coherent communication link employing orbital angular momentum (OAM) multiplexing using polarization diversified 2D-3D hybrid photonic integrated circuits (PICs). The PICs support multiplexing/demultiplexing of up to 15-OAM states with dual polarizations. We characterize the hybrid device, including phase errors and crosstalk performance. Then, we use two hybrid PICs for a free-space coherent communication link demonstration. We utilize polarization, frequency, quadrature, and space dimensions to achieve a 1.68-Tb/s link bandwidth and a 9.6-b/s/Hz spectral efficiency.