Orbital angular momentum beams generated by passive dielectric phase masks and their performance in a communication link

We demonstrate the generation of orbital angular momentum (OAM) beams using high-efficient polarization-insensitive phase masks. The OAM beams generated by the phase masks are characterized in terms of their tolerance to misalignment (lateral displacement or tilt) between the incident beam and phase mask. For certain scenarios, our results show that (a) when the tilt angle is within the range of -20 to +20  deg, the crosstalk among modes is less than -15  dB; and (b) lateral displacement of 0.3 mm could cause a large amount of power leaked to adjacent modes. Finally, OAM beams generated by the phase masks are demonstrated over a two-channel OAM-multiplexing link, each channel carrying a 40 Gbit/s data stream. An optical signal-to-noise-ratio (OSNR) penalty of ∼1  dB is measured without crosstalk at the bit error rate (BER) of 3.8×10^-3. With crosstalk, an OSNR penalty of <1.5  dB is observed at the same BER.