The invention describes a method and an arrangement for transmitting an optical transmission signal with reduced polarization-dependent loss. A first transmission signal component and a second orthogonal transmission signal component of the optical transmission signal are transmitted with a time difference between said transmission signal components.

The invention describes a method and an arrangement for transmitting an optical transmission signal with reduced polarization-dependent loss. A first transmission signal component and a second orthogonal transmission signal component of the optical transmission signal are transmitted with a time difference between said transmission signal components.

An optical transmission apparatus for transmitting wavelength-multiplexed light, the optical transmission apparatus includes: an optical transmitter configured to transmit light of a third wavelength to be arranged between a first wavelength and a second wavelength adjacent to the third wavelength in the wavelength-multiplexed light, and a controller configured to control a bandwidth of the light of the third wavelength to be arranged in a first bandwidth narrower than a spacing between the first wavelength and the second wavelength.

An optical transmission apparatus for transmitting wavelength-multiplexed light, the optical transmission apparatus includes: an optical transmitter configured to transmit light of a third wavelength to be arranged between a first wavelength and a second wavelength adjacent to the third wavelength in the wavelength-multiplexed light, and a controller configured to control a bandwidth of the light of the third wavelength to be arranged in a first bandwidth narrower than a spacing between the first wavelength and the second wavelength.

A communications system may include a transmitter node, a receiver node, and an optical communications channel coupling the transmitter node and receiver node. The transmitter node may include a pulse transmitter and a pulse divider downstream therefrom. The receiver node may include a pulse recombiner and a pulse receiver downstream therefrom.

A communications system may include a transmitter node, a receiver node, and an optical communications channel coupling the transmitter node and receiver node. The transmitter node may include a pulse transmitter and a pulse divider downstream therefrom. The receiver node may include a pulse recombiner and a pulse receiver downstream therefrom.

A tap-coefficient control circuit sets the tap coefficient converged by the second tap coefficient updater as an initial value of the tap coefficient in the first digital filter which is to be updated by the first tap coefficient updater, arranges the tap coefficients converged by the second tap coefficient updater in descending order of contribution degree to the convergence operation of tap coefficient update in the first tap coefficient updater, judges the tap coefficient not less than upper specified number to be valid and the tap coefficient less than the specified number to be invalid, and sets the tap coefficient of the first digital filter corresponding to the tap coefficient judged to be invalid to zero not to be used in a calculation of the first tap coefficient updater until a next judgment result is made.

A tap-coefficient control circuit sets the tap coefficient converged by the second tap coefficient updater as an initial value of the tap coefficient in the first digital filter which is to be updated by the first tap coefficient updater, arranges the tap coefficients converged by the second tap coefficient updater in descending order of contribution degree to the convergence operation of tap coefficient update in the first tap coefficient updater, judges the tap coefficient not less than upper specified number to be valid and the tap coefficient less than the specified number to be invalid, and sets the tap coefficient of the first digital filter corresponding to the tap coefficient judged to be invalid to zero not to be used in a calculation of the first tap coefficient updater until a next judgment result is made.

An optical receiver, e.g., for an Optical Supervisory Channel (OSC), whose optical front end comprises a polarization-diversity coherent optical receiver configured to receive a conventional intensity-modulated (e.g., OSC) signal. Four quadrature components of the received OSC signal detected by the polarization-diversity coherent optical receiver are sampled at a relatively high sampling rate and are used to calculate the Stokes parameters of the OSC signal. As a result, the Stokes parameters can be updated at the high sampling rate, which can be suitably selected to enable polarization tracking with a relatively high time resolution and/or at relatively high SOP-rotation speeds. The four detected quadrature components are appropriately combined in the receiver DSP to determine the intensity of the received OSC signal, which is then used in a conventional manner to recover the OSC data encoded therein.

A passive dual polarization unit and coherent transceiver and/or receiver including one or more passive dual polarization units are provided. An example passive dual polarization unit includes a polarization splitter configured to split an input signal into a TE mode and TM mode signals; TE/TM splitters each designed to split the TE/TM mode signals into first TE/TM signals and second TE/TM signals; a first TE signal polarization rotation component for receiving the first TE signal and providing a third TM signal having the same magnitude and time dependence as the first TE signal; a first TM signal polarization rotation component for receiving the first TM signal and providing a third TE signal having the same magnitude and time dependence as the first TM signal; and TE/TM couplers that couple the second TE/TM signals and the third TE/TM signals to generate output TE/TM signals.