a modulation method for optical communication comprises the step of generating an optical signal modulated between a plurality of different states of polarization and between different phase states . the plurality of states of polarization comprises first states of polarization . the first states of polarization define a single great circle on the poincaré sphere . the method is characterized in that the plurality of states of polarization further comprise one or more second states of polarization located outside the great circle . such additional second states of polarization increase the symbol alphabet .