Method for transmitting at least one first and one second data signal in polarization division multiplex in an optical transmission system

#The present invention relates to a method for transmitting at least one first and one second data signal in polarization division multiplex in an optical transmission system which includes a transmitting arrangement and a receiving arrangement which are connected to one another via at least one optical fiber link section.

#In optical transmission systems, the transmission capacity of existing optical transmission systems can be extended by transmitting the optical data signals in polarization division multiplex. To transmit optical data signals in polarization division multiplex, in each case two carrier signals which are respectively modulated with a data signal are generated in at least one transmitting arrangement with the same wavelength. The first and second modulated signals exhibit a mutually orthogonal polarization in this case. The mutually orthogonally polarized modulated signals are combined to form an optical polarization division multiplex signal. The optical polarization division multiplex signal is injected into the optical transmission fiber and transmitted via the optical transmission link to a receiving unit. At the receiving end, the two orthogonally polarized modulated signals are recovered from the polarization division multiplex signal in a wavelength-dependent and polarization-dependent manner.

#One of the essential problems in transmitting optical data signals in polarization division multiplex is separating the two orthogonally polarized modulated signals precisely out of the polarization division multiplex signal. This requires the determination of a control criterion for controlling a polarization control element arranged at the receiving end from the received optical polarization division multiplex signal. The modulated signals transmitted in a mutually orthogonally polarized manner are separated with the aid of the controlled polarization transformer and, for example, a downstream polarization splitter or a polarization filter.

#FIG. 1 shows, by way of example, an optical transmission system for transmitting at least one first and one second data signal in polarization division multiplex.

#FIG. 2 shows, by way of example, the spectrum of the first and second modulated optical signals.

#FIG. 3 shows the amplitude variation of the spectral component determined at the frequency corresponding to the first transmission bit rate in dependence on the angle of polarization.

#FIG. 1 diagrammatically shows, by way of example, an optical transmission system OTS which exhibits a transmitting arrangement SA and a receiving arrangement EA connected via an optical transmission link OF. In the transmitting arrangement SA, a first and second signal generating unit TX1, TX2, a first and second modulator unit MU1, MU2, a delay element D and a polarization multiplexer PM are provided, by way of example. The receiving arrangement EA includes a polarization control element PTF, a polarization splitter PBS, a first and second optoelectrical transducer RX1, RX2, a first and second filter unit FU1, FU2 and a control unit CU.

#The first signal generating unit TX1 of the transmitting arrangement SA is connected via a first connecting line VL1 to the first modulator unit MU1 which is connected to the first input I1 of the polarization multiplexer PM via a second connecting line VL2. The second signal generating unit TX2 is connected via a third connecting line VL3 to the second modulator unit MU2 which is connected via a delay element D to the second input E2 of the polarization multiplexer PM by a fourth connecting line VL4. The delay element D is only provided optionally which is shown by a dashed line in FIG. 1.

#The output E of the polarization multiplexer PM is connected to the input of the optical transmission link OF, the output of which is conducted to the input I of the polarization control element PTF of the receiving arrangement EA. The optical transmission link OF can consist of a number of optical transmission link sections not shown in FIG. 1 (indicated by a dashed line in FIG. 1).