Optical connection carries data via orbital angular momentum

Researchers at Tsinghua University (Beijing, China) believe they have come up with a practical way to use optical beams that carry orbital angular momentum (OAM) to increase the data-carrying capacity of wireless optical interconnects. Beams with OAM carry quanta of angular momentum that, for a certain frequency, can be encoded on the beam by electro-optic tuning of the mode order in a ring cavity at that frequency. Decoding is done using gratings and Mach-Zehnder interferometers.

The ring cavity, which is fabricated on an integrated-optics chip, has, in addition to the ring, a bus waveguide and eight download waveguides (each including an arc-shaped section next to the ring and a grating near the ring’s center). Light from the ring is coupled into the download waveguides and is emitted by the eight gratings to form a free-space beam with OAM. At the other end, quaternary (rather than octenary) decoding is done to allow for beam degradation. The decoding is accomplished (on another integrated-optics chip) by coupling the free-space light into waveguides using gratings, and then coherently superposing the results to recover the signal either using an interferometer or arrayed-waveguide gratings. The OAM device could also be used to create vortex beams. Contact Xue Feng at[email protected].