Experimental propagation of optical Laguerre-Gauss beams in turbulence

We show the feasibility of free-space orbital angular momentum (OAM)-based laser communication through a laboratory experiment in which three OAM channels -each on an independent Laguerre-Gauss (LG) laser mode- are simultaneously transmitted over 11 m on a common optical axis, using single transmit and receive apertures. Each channel is modulated using on-off keying (OOK) at 80 Mb/s and imposed OAM by a computer-controlled hologram, programmed on a spatial-light modulator (SLM). The OAM modal crosstalk is measured as a function of OAM mode distance between constituent channels. Furthermore, an outdoor experiment of LG beam propagation is carried out over a 400-m horizontal link. The propagated LG beams are analyzed by both direct imaging of the received profile and detection of the OAM using a receiver assembly similar to that of the laboratory experiment. Several OAM states are successfully recorded and evaluated with this link to analyze the effects of OAM crosstalk due to imperfect mode transmission, optical misalignment, aberrations, and turbulence.