On the system level benefit of optimized four-dimensional optical modulation formats

Abstract:
The optical single mode fiber channel is inherently a four-dimensional channel. With the introduction of the coherent receiver concept to optical systems earlier research results from sphere packing in four dimensions became easily applicable and promised relevant gains over standard antipodal modulation formats like DP-QPSK (dual polarization quadrature phase shift keying). In the paper we compare the improvement of the system performance of different constellations in combination with specific forward error correcting codes with the theoretical Shannon limit for a linear Gaussian channel. We also discuss some selected implementation aspects of optimized four-dimensional modulation formats.