Optical transmission apparatus, optical transmission system, and polarization dependent loss monitor

An optical transmission system comprising:

• a first optical transmission apparatus including
• a first receiver configured to receive information,
• a polarization level controller configured to control power level of light to be transmit, and
• a first transmitter configured to transmit the light;
• and
• a second optical transmission apparatus coupled with the first optical transmission apparatus via an optical transmission path, the second transmission apparatus including
• a second receiver configured to receive light including different polarization components from the first optical transmission path
• a coherent detector configured to perform coherent detection of received light including different polarization components,
• an adaptive equalizer configured to adaptively equalize, by a digital filter, a complex electric signal for each of the polarization components obtained by the coherent detection, a gain value for controlling an amplitude of the complex electric signal being applied to the complex electric signal,
• a polarization dependent loss monitor configured to determine a polarization dependent loss of the optical transmission path, based on a correction filter parameter obtained by correcting a filter parameter of the digital filter according to the gain value, the filter parameter being adaptively updated by an adaptive equalization of the adaptive equalizer, and
• a second transmitter configured to transmit information indicating the polarization dependent loss determined by the polarization dependent loss monitor to the first optical transmission apparatus,
• wherein
• the first receiver receives the information indicating the polarization dependent loss transmitted from the second optical transmission apparatus,
• the polarization level controller controls power level of the light to be transmitted for each of the polarization components, based on the information indicating the polarization dependent loss received by the first receiver so as to reduce a power level difference between the polarization components of the light, and
• the first transmitter transmits the light including the different polarization components to the optical transmission path linked to the second optical transmission apparatus.