APPARATUS AND METHOD EMPLOYING POLARIZATION MODULATION TO REDUCE EFFECTS OF POLARIZATION HOLE BURNING AND/OR POLARIZATION DEPENDENT LOSS

摘要

The effects of polarization dependent hole burning and/or polarizationdependent loss are reduced by modulating the state of polarization (SOP) of anarbitrarily polarized optical signal being launched into the transmission pathperiodically through a predetermined sequence of polarization states. The sequenceof polarization states is selected such that on average the launched modulated signalexcites substantially all possible polarization states with substantially equalprobability, independent of the input SOP to the polarization modulator. In oneexemplary embodiment, the SOP is modulated by a combination cascade of arotating half-wave plate followed by a quarter-wave plate, which rotates at adifferent angular speed. In another exemplary embodiment, the SOP is modulatedby a combination cascade of two variable phase retarders oriented at fixed angles of0° and 45°, where the modulation frequencies of the two retarders are substantiallydifferent from each other.