Encoding/decoding using superpositions of spatial modes for image transfer in km-scale few-mode fiber

Space domain is regarded as the only known physical dimension left of lightwave to exploit in optical communications. Recently, lots of research efforts have been devoted to using spatial modes of fibers to increase data transmission capacity in optical fiber communications. In this paper, we propose and demonstrate a different approach to exploiting the space dimension, i.e. transferring image by space dimension encoding/decoding using superpositions of spatial modes in km-scale few-mode fiber. Three grayscale images are successfully transmitted through a 1.1-km few-mode fiber by employing either 4 modes, i.e. three linearly polarized (LP) modes of LP₀₁, LP_11a, LP_11b and one orbital angular momentum (OAM) mode of OAM_-1, or 2 modes (OAM₊₁, OAM_-1). The bit-error rate is evaluated and zero error among all received data is achieved, showing favorable fiber link communication performance using the spatial modes of fiber for encoding/decoding. Moreover, we also demonstrate the 4 modes (LP₀₁, LP_11a, LP_11b and OAM_-1) encoding/decoding for image transfer in a 10-km few-mode fiber in the experiment.