A technique is provided for an optical multiple input multiple output (MIMO) processing system. The optical (MIMO) processing system includes an interface to a multi-mode fiber at a first end of the optical processing system; M first single-mode waveguides coupled to the interface; wherein the first waveguides are arranged to carry M first optical signals, respectively; N second single-mode waveguides at a second end of the optical processing system, wherein the second waveguides are arranged to carry N second optical signals, respectively, wherein the N second optical signals are associated with N modes carried by the multi-mode fiber; and an optical processing core arranged to transform the first optical signals into the second optical signals such that a correlation between the second optical signals is decreased compared to a correlation between the first optical signals using a plurality of optical couplers for coupling each of the M first optical signals with one another, such that each of the N second optical signals is a linear combination of all of the M first optical signals.