In order to reduce mutual interferences between POLMUX and signals, the signals are transmitted with differed to each other carrying signals, thereby making it possible to obtain the circular polarization of each resulting POLMUX signal. Each second POLMUX signal is transmissible with an opposite circular polarization. In order to reduce also interferences when only one modulated data signal is transmitted through a POLMUX channel, a polarization plane of modulated data signals of each second POLMUX channel is turned at 45°. In a variant, polarization multiplex signals are produces and the resulting polarizations thereof in adjacent channels are perpendicular to each other.