Orthogonal-polarization heterodyne OSNR monitoring insensitive to polarization-mode dispersion and nonlinear polarization scattering

An in-band optical signal-to-noise-ratio (OSNR) monitoring technique that utilizes the polarization orthogonality and heterodyne mixing is proposed. The technique is not only insensitive to polarization-mode dispersion but also robust to nonlinear polarization scattering induced by interchannel cross-phase modulation. Moreover, the technique places no special requirements on the signal properties, such as modulation format and bit rate. The monitoring technique is demonstrated experimentally in both linear and nonlinear systems.