An optical modulation apparatus comprises first, second, and third optical modulators arranged so as to collectively modulate light coupled into a first optical input in all three dimensions of the three-dimensional Stokes vector space, to produce an optical output signal. The optical modulation apparatus further comprises a modulating circuit having a digital input configured to N generate first, second, and third modulating signals for driving the first, second, and third optical modulators so as to map digital data to an M-point optical constellation in the optical output signal. The points in the M-point optical constellation are distributed in the three-dimensional Stokes vector space such that the constellation figure of merit for the M-point optical constellation equals at least half of the maximum achievable constellation figure of merit for M points in the three-dimensional Stokes vector space.