It is therefore an object of the disclosure of this document to attain a data transmission system with a simple transmitter implementing polarization multiplexing using either DML or EAM and a receiver with only one PD. A data transmission system 1 which comprises a transmitter 3 and a receiver 5, wherein the transmitter 3 comprises a first signal processor 11 and an optical signal generator 13, the optical signal generator 13 outputs an optical signal which comprises X and Y polarization components, ex(t) and ey(t), and wherein the first signal processor 11 receives a first data stream, Sx, and a second data stream, Sy, and controls the X and Y polarization components to reflect the first and the second data streams, respectively, wherein the receiver 5 comprises only one photodetector 21 and a second signal processor 23.